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WELD COUNTY
CODE ORDINANCE 2006-7
IN THE MATTER OF REPEALING AND REENACTING, WITH AMENDMENTS, CHAPTER 8
PUBLIC WORKS, OF THE WELD COUNTY CODE
BE IT ORDAINED BY THE BOARD OF COUNTY COMMISSIONERS OF THE COUNTY OF
WELD, STATE OF COLORADO:
WHEREAS,the Board of County Commissioners of the County of Weld,State of Colorado,
pursuant to Colorado statute and the Weld County Home Rule Charter, is vested with the authority
of administering the affairs of Weld County, Colorado, and
WHEREAS, the Board of County Commissioners, on December 28, 2000, adopted Weld
County Code Ordinance 2000-1,enacting a comprehensive Code for the County of Weld, including
the codification of all previously adopted ordinances of a general and permanent nature enacted
on or before said date of adoption, and
WHEREAS, the Weld County Code is in need of revision and clarification with regard to
procedures, terms, and requirements therein.
NOW, THEREFORE, BE IT ORDAINED by the Board of County Commissioners of the
County of Weld, State of Colorado,that certain existing Chapters of the Weld County Code be,and
hereby are, repealed and re-enacted, with amendments, and the various Chapters are revised to
add the following to read as follows.
CHAPTER 8
PUBLIC WORKS
ARTICLE XI
Weld County Storm Drainage Criteria
Division 1
General Provisions
Section 8-11-10. Purpose and authority.
This Weld County Storm Drainage Criteria is adopted in order to provide minimum
standards to preserve and protect the public health, safety, and general welfare in the
unincorporated lands of Weld County, pursuant to authority granted by Part 4 of Article 15 of Title
30, and Article 35 of Title 30, C.R.S.
Section 8-11-20. Adoption of storm drainage standards - short title.
The Denver, Colorado, Urban Drainage and Flood Control District's"Urban Storm Drainage
Criteria Manual," consisting of Volume 1 (June 2001), Volume 2(June 2001), and Volume 3, Best
Management Practices(September 1999), is hereby adopted by reference, with the amendments
which are set forth herein. The provisions of this Article XI shall be known as the "Weld County
Storm Drainage Criteria." All facilities for storm drainage on properties located within the
unincorporated lands of Weld County,whether public or private,shall be designed and constructed
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in accordance with such criteria, unless required otherwise by an applicable master drainage plan
approved by Weld County. A copy of the "Urban Storm Drainage Criteria Manual" shall be kept
on file in the office of the Weld County Clerk to the Board of County Commissioners for inspection
during regular business hours. It may be downloaded by visiting the Urban Drainage and Flood
Control District web site at www.udfcd.org,or ordered by contacting the Urban Drainage and Flood
Control District at 303-455-6277.
Section 8-11-30. Weld County Addendum to the Text of the Urban Storm Drainage Criteria-
Volume 1
A. Chapter 1 - Drainage Policy
1. Amend Section 1.4 Planning to read:
"Storm drainage is a part of the total urban environmental system.
Therefore, storm drainage planning and design must be compatible with
comprehensive regional plans. A master plan for storm drainage should be
developed and maintained in an up-to-date fashion at all times for each
urbanizing drainage watershed in the Denver regionwatersheds in Weld
County. The planning for drainage facilities should be coordinated with
planning for open space and transportation. By coordinating these efforts,
new opportunities may be identified that can assist in the solution of
drainage problems. Natural drainageways should be used for storm runoff
waterways wherever feasible. Major consideration must be given to the
floodplains and open space requirements of the area (White 1945).
Planning and design of stormwater drainage systems should not be based
on the premise that problems can be transferred from one location to
another. Stormwater runoff can be stored in detention and retention
reservoirs. Such storage can reduce the drainage conveyance capacity
required immediately downstream. Acquisition of open space having a
relationship to drainageways will provide areas where storm runoff can
spread out and be stored for slower delivery downstream."
2. Amend Section 1.5 Technical Issues to read:
"Storm drainage planning and design should follow the criteria developed
and presented in this Urban Storm Drainage Criteria Manual (Manual).
Every urban area has two separate and distinct drainage systems, whether
or not they are actually planned and designed. One is the initial system,and
the other is the major system. To provide for orderly urban growth, reduce
costs to future generations and avoid loss of life and major property
damage, both systems must be planned, properly engineered and
maintained. The determination of runoff magnitude should be by the
Rational Formula, the Colorado Urban Hydrograph Procedure (CUHP),
HEC-1, HEC-HMS, or statistical analyses based on an adequate record of
actual measured flood occurrences as set forth in the RUNOFF chapter of
this Manual. Use of streets for urban drainage should fully recognize that
the primary use of streets is for traffic. Streets should not be used as
floodways for initial storm runoff. Urban drainage design should have as an
objective reduction of street repair and maintenance costs to the public.
Irrigation ditches should not be used as outfall points for initial or major
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drainage systems, unless such use is shown to be without unreasonable
hazard, as substantiated by thorough hydraulic engineering analysis, and
written approval of the ditch owner(s) is obtained. In addition, irrigation
ditches cannot be relied on for mitigating upstream runoff. Proper design
and construction of stormwater detention and basins are
necessary to minimize future maintenance and operating costs and to avoid
public nuisances and health hazards. This is particularly important, given
the many detention and retention facilities in the Doi ive. ey;‘,.(Weld County.
The various governmental agencies within the Denver region have Weld
County has adopted and needs to maintain theirits floodplain management
programs. Floodplain management must encompass comprehensive
criteria designed to encourage,where necessary,the adoption of permanent
measures which will lessen the exposure of life, property and facilities to
flood losses, improve the long-range land management and use of flood-
prone areas, and inhibit, to the maximum extent feasible, unplanned and
economically unjustifiable future development in such areas."
3. Amend Section 1.6 Flood Insurance to read:
"Flood insurance is an integral part of the strategy to manage flood losses.
The Det wee reg;rn rbhuuld e.n,ourage an rto'uet}pa. r Weld County
continues to participate in the National Flood Insurance Program, set forth
in the National Flood Insurance Act (NFIA) of 1968, as amended."
4. Add the following to Section 2.1 Drainage is a Regional Phenomenon That
Does Not Respect the Boundaries Between Government Jurisdictions or
Between Properties: "Weld County may from time to time enter into
Agreements with adjacent counties to cooperate on regional planning. The
Policy of Weld County shall be to pursue a jurisdictionally unified drainage
effort to assure an integrated drainage system, and to cooperate with other
regional and local planning agencies on drainage matters."
5. Amend Section 3.1.2 Rainfall-Runoff Relationships to read:
"A program should be maintained to collect and analyze rainfall-runoff
relationships in urban areas of the Dcrncr .ey;u.Weld County."
6. Amend Section 3.1.4 Library to read:
"The D;st ;1/4.tWeld County should acquire and actively maintain a library,
which should be available for use by all governmental agencies, practicing
planners, and engineers. The public should be encouraged to use the
library as part of the Dishict'aWeld County's educational and outreach
programs."
7. Amend Section 3.1.5 Runoff Magnitudes to read:
"Where practical, the magnitude of computed and measured runoff peaks
should be tabulated for Denver regionWeld County streams and gulches so
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that comparisons may be readily made between watersheds and erroneous
values may be more easily identified."
8. Amend Section 3.2 Floodplain Data to read:
"The program to delineate flood hazard areas along all waterways in the
region should be maintained. This program should make full use of such
sources as the District's flood I lazard Area Delineation studies, the FEMA
Flood Insurance Studies, data from the Natural Resources Conservation
Service, the USGS, and floodplain studies by private consulting engineers.
This information should be regularly reviewed and updated to reflect
changes due to urbanization, changed channel conditions, and the
occurrence of extraordinary hydrologic events."
9. Amend Section 3.2.2 Data Inventory to read:
"The information collected should be stored in a contra) Dist,l..t
depositoryWeld County Department of Public Works file available to all
planners, developers, and engineers."
10. Amend the first sentence of Section 3.2.4 Priority for Data Acquisition to
read:
"The Di0t,i.tWeld County will establish priorities for acquisition of data
because it is recognized that not all of the data can be collected at one
time."
11. Amend Section 3.3.1 Master Plan to read:
"Drainage design does not lend itself to a piece-meal approach; therefore,
master plans for drainage should be prepared on a priority basis. Such
plans already cover most of the developed major drainageways in the
DistrictWeld County. Additional plans will be developed for areas yet
unplanned. In addition, existing master plans will be updated as needed to
reflect changed conditions that take place over time."
12. Amend Section 4.1 Total Urban System to read:
"Storm drainage is a part of the total urban environmental system.
Therefore, storm drainage planning and design should be compatible with
comprehensive regional plans. Master plans for storm drainage have been
developed and maintained in an up-to-date fashion for most of tl1.,
watersheds in the Denver regianWeld County. An effort to complete the
coverage of drainage master plans for yet unplanned areas of the
ashit.tWeld County should be continued until full coverage is achieved."
13. Amend Section 4.1.2 Master Plan to read:
"Each-municipality and county in the Denver legion is responsible for master
planning—for urban storm drainage facilities within its boundaries and
environs- The District can help to coordinate efforts. Cooperation between
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governmental agencies is needed to solve drainage problei i is and joint city,
county--and District efforts are encouraged. Carrying forward master
planning-is-best-accomplished on a priority phased basis so that the most
demanding problems, such as areas of rapid urbanization, may be
add,csocd at art early date.Early work includes the planning of major
drainageways from the point of outfall, proceeding in an upstream direction.
The major drainageways are generally well defined and often dictate the
design of the initial drainage system, including storm sewers, detention
facilities, and water quality systems. The D;stI;b'tWeld County has
established a suitable format for master plan reports and drawings so that
a uniform planning approach and coordination of efforts can more easily be
made. Master planning should be done in enough detail and with adequate
thoroughness to provide a ready drainage development guide for the future
in a particular watershed. Generalized concepts based on rule-of-thumb
hydrological analyses should not be used as master plans; a more rigorous
analysis is necessary. The Policy of Weld County shall be to enforce and
implement adopted Master Drainage Plans. These Master Drainage Plans
may be amended from time to time in the future."
14. Amend Section 4.1.3, paragraph#2, Planning Process Ingredients to read:
"2. Initial Drainage System Planning. All local and regional planning
must take into consideration the initial drainage system to transport
the runoff from storms expected to occur once every 2 to 10 years.
The planner of an initial system must strive to minimize future
drainage complaints."
15. Amend the second paragraph of Section 4.1.6 Water Quality to read:
"Sanitary sewerage systems that overflow or bypass untreated sewage into
surface streams should not be permitted in the Denvl., cg;a,rWeld County.
Existing systems that discharge sewage should be adjusted by their owners
to eliminate this problem."
16. Add the following to Section 4.5 Detention and Retention Storage:
"The Policy of Weld County shall be to require regional and/or on-site
detention for all future developments. Temporary or interim detention/
retention may be required if the downstream regional facilities have not yet
been constructed per the applicable Master Plan. Stormwater retention
facilities are normally not allowed in Weld County, but will be considered for
special circumstances. It is Weld County policy to require detention of
runoff from the 100-year storm falling on the developed site and release of
the detained water at the rate of the runoff of the 5-year storm falling on the
undeveloped site. Detention releases based on soil types are not approved
for Weld County. Proposed developments must provide for safe
conveyance of off-site flows through the proposed development site. Off-
site flows may be routed through or around the proposed detention facilities.
Positive drainage must be provided."
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17. Amend Section 4.5.4 Reliance on Non-Flood-Control Reservoirs to read:
"Privately owned non-flood control reservoirs cannot be used for flood
mitigation purposes in master planning because their per petuity cannot be
reasonablyguaranteed. Publicly owned water storage reservoirs(city,state,
water district, irrigation company,etc.)should be assumed to be full for flood
planning purposes and, therefore, only the detention storage above the
spillway crest can be utilized in regard to the determination of downstream
fluod peak flaws.Jurisdictional dams are classified by the State Engineer as
either low, moderate, or high hazard structures depending on conditions
downstream. Dams are classified as high hazard structures when, in the
event of failure, there is a potential loss of life. Dams presently rated as low
or moderate hazard structures may be changed to high hazard rating if
development occurs within the potential path of flooding due to a dam
breach. In this case, the reservoir owners would be liable for the cost of
upgrading the structure to meet the higher hazard classification.
The Policy of the Weld County shall be to:
1. Restrict upstream development to areas outside of the jurisdictional
dam water surface elevation created by a 100-year storm plus
freeboard.
2. Restrict downstream development to areas outside of the
jurisdictional dam 100-year floodplain. The jurisdictional dam
100-year floodplain is defined as either:
a. The 100-year floodplain downstream of the emergency
spillway assuming the dam is full to the elevation of the
emergency spillway at the beginning of the 100-year storm
and the 100-year storm is routed through the dam and out
the emergency spillway,
OR
b. The path that the basin's 100-year floodplain would form
through the downstream development if the dam were
removed by the owner."
18. Amend Section 4.5.5 Reliance on Embankments to read:
"The detention of floodwaters behind embankments created by railroads,
highways or roadways resulting from hydraulically undersized culverts or
bridges should not be utilized by the drainage engineer for flood peak
mitigation when determining the downstream flood peaks for channel
capacity purposes unless such detention has been covered by a binding
agreement approved by Hie Diotr;utWeld County."
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19. Amend Section 5.1 Design Criteria to read:
"Storm drainage planning and design should adhere to the criteria
developed and presented in this Manual maintained by the D;st,;ctWeld
County."
20. Amend Section 5.1.1 Design Criteria to read:
"The design criteria presented herein represent current good engineering
practice, and their use in flit Dci.vcn Ic9kiWeld County is recommended.
The criteria are not intended to be an ironclad set of rules that the planner
and designer must follow; they are intended to establish guidelines,
standards and methods for sound planning and design. The Weld County
Department of Public Works may grant variances from the design criteria of
this Manual by acceptance of the Final Drainage Report in which the
variance request is well documented."
21. Delete the second paragraph of Section 5.2.1 Design Storm Return Periods:
"There are mart' developed areas within the Denver urban region that do
not fully conform to the drainage standards projected in this Manual. The
multitude of problei ns associated with these areas historically provided the
cniphaao ickiuii..J to N; J vvah dcvcluNmcut of tins Manual. It ;o
recognized that upgrading these developed areas to conform to all of the
policies, criteria, and standards contained in this Manual will be difficult, if
not impractical, to obtain, short of complete redevelopment or renewal.
I lowever, flood-proofing techniques can be applied to these areas."
22. Amend Section 5.2.2 Initial Storm Provisions to read:
"The initial storm drainage system, capable of safely handling 2-to 10-year
floods deli&,d;ng ai i local ci;t014, is necessary to reduce the frequency of
street flooding and maintenance costs, to provide protection against
regularly recurring damage from storm runoff, to help create an orderly
urban system,and to provide convenience to urban residents. Normally,the
initial drainage system cannot economically carry major runoffs, though the
major drainage system can provide for the initial runoff. A well-planned
major drainage system will reduce or eliminate the need for storm sewer
systems (Jones 1967). Storm sewer systems consisting of underground
pipes are a part of initial storm drainage systems."
23. Amend Section 5.4.1 Use of Streets to read:
"Streets are significant and important in urban drainage, and full use should
be made of streets for storm runoff up to reasonable limits, recognizing that
the primary purpose of streets is for traffic. Reasonable limits of the use of
streets for transportation of storm runoff should be governed by reasonable
design criteria as summarized in Table DP-1 and in the Streets/Inlets/Storm
Sewers chapter of this Manual. Urban drainage design should have as
objectives reduction of street repair, maintenance costs, nuisance to the
public, and disruption of traffic flow.
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When maximum allowed encroachment is present, the storm sewer system
design based on the initial storm should commence. Development of a
major drainage system that can often drain the initial runoff from the streets
is encouraged, thus making the point at which the storm sewer system
should commence further downstream. Initial and major drainage planning
should go hand-in-hand.
While it is the intent of this policy to have major storm runoff removed from
public streets at frequent and regular intervals and routed into major
drainageways, it is recognized that water will often tend to follow streets and
roadways and that streets and roadways often may be aligned so they will
provide a specific runoff conveyance function. Planning and design
objectives for the major drainage system with regard to public streets should
be based upon following the limiting criteria summarized in Table DP-2 and
in the Streets/Inlets/Storm Sewers chapter of this Manual.
The allowable flow across a street should be within the criteria presented in
Table DP-3 and in the Streets/Inlets/Storm Sewers chapter of this Manual.
An arterial street crossing will generally require that a storm sewer system
be commenced, unless the topography is such that day-lighted inlet culverts
or other suitable means can transport the initial storm runoff under the
arterial street or water can be routed to a major drainage facility. Bubblers
(inverted siphons which convey flows beneath roadways) are not
encouraged in the Denve„cgiu,Weld County because of possible plugging
with sediment and difficulty in maintaining them. Collector streets should
have cross pans only at infrequent locations as specified by the governing
agency and in accordance with good traffic engineering practices. The local
street criteria for overtopping also apply to any private access road that
serves commercial areas or more than one residence, for emergency
access and safety reasons."
24. Add the following to Section 5.5 Irrigation Ditches: "It is the policy of Weld
County to prohibit the discharge of stormwater runoff from developed areas
into irrigation ditches and facilities, except as required by water rights or
where such discharges are in conformance with approved Master Drainage
plans. Further, wherever new development will alter patterns of drainage
into irrigation ditches by increasing flow rates or volumes, or will change the
historic concentration points of runoff, the County shall require each new
development to obtain written consent of the appropriate ditch company
before approving the drainage design and development."
25. Amend Section 5.5.1 Use of Ditches to read:
"The irrigation ditches coursing through urban areas are laid out on flat
slopes and with limited carrying capacity. Based on experience and
hydraulic calculations, irrigation ditches cannot, as a general rule, be used
as an outfall point for the initial storm drainage system because of physical
limitations. Exceptions to the rule can occur when the capacity of the
irrigation ditch is adequate to carry the normal ditch flow plus the initial storm
runoff with adequate freeboard to avoid creating a hazard to those below the
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ditch. Written approval must be obtained from the ditch owner stating that
the owner understands the physical and legal (i.e., liability) consequences
of accepting said runoff. If there is a question about the use of irrigation
ditches as outfalls for initial storm runoff, there is no question about their
unsuitability as an outfall for the major storm runoff. Without major
reworking of irrigation ditches to provide major carrying capacity without
undue hazard to those downstream or below the ditch, the ditches are
almost always totally inadequate for such a use and should not be used as
an outfall. Moreover, because ditches are normally privately owned, one
cannot assume the perpetual existence or function of a ditch. Land
planners and engineers with a proposed development downhill from a ditch
should shall plan for pre-ditch drainage conditions as well as continued ditch
seepage. For new development, it shall be the policy of Weld County to
prohibit undetained discharges to roadside ditches located in the County
right-of-way. In the event a proposed development wishes to design
stormwater discharge to a County right-of-way,the developer,at the request
of the County, shall have the requirement to design and construct drainage
improvements to the right-of-way at the developers' own expense. Such
improvements shall include, but not be limited to: detention ponds, armored
channels, culverts, and other drainage facilities. Cost-sharing of such
needed improvements may be borne by adjacent developments, such cost
sharing to be negotiated by the developer. Weld County may require written
agreements and construction bonding of such offsite drainage
improvements."
26. Amend Section 5.5.3 Conformance With Master Plan to read:
"Use of irrigation ditches for collection and transport of either initial or major
storm runoff should be prohibited unless specifically provided in a Distribt'0
raster planthe Weld County master plans, or approved by tl io Drat,k,tWeld
County and the ditch owner."
27. Amend Section 5.6 Detention and Retention Facilities Maintenance to read:
"The significant cost of handling stormwater runoff, coupled with the social
benefits to be derived from proper storm drainage facilities, points towards
the use of detention and retention basins for storage of stormwater runoff
in the Denvel ieviuutWeld County. Maintenance provisions must be
arranged. Maintenance of detention or retention facilities includes the
removal of debris, excessive vegetation from the embankment, and
sediment. Without maintenance, a detention/retention facility will become
an unsightly social liability and eventually become ineffective."
28. Amend Section 6.1 Purpose to read:
"Various governmental agencies within the Denver region should initiate
fleodplai,, management pio jrat,1s. Floodplain management includes
comprehensive criteria designed to encourage, where necessary, the
adoption of permanent state or local measures which will lessen exposure
of property and facilities to flood losses, improve long-range land
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management and use of flood-prone areas, and inhibit, to the maximum
extent feasible, unplanned future development in such areas."
29. Amend first sentence of Section 6.2 Goals to read:
"There are two goals in regard to floodplain management: •To reduce the
vulnerability of Denver regionWeld County residents to the danger and
damage of floods."
30. Amend Section 6.3.2 New Development to add the following: "The Policy of
Weld County shall be to outsource engineering review of all CLOMR and
LOMR submittals received with a development application. The developers
shall reimburse the Weld County Department of Public Works for all
outsourced engineering review costs. Upon FEMA approval of a CLOMR
or LOMR, payment of all outsourced engineering review costs is due and
payable to Weld County. Developers are welcome to contract directly with
our outsourced consultant(s)for the preparation of CLOMR's and LOMR's,
if they so desire."
31. Amend Section 7.1 Adoption of Drainage Master Plans to read:
"This Manual and master plans should be adopted and used by all
governmental agencies operating within tl Glattl,.tWeld County."
32. Amend Section 7.3 Amendments to read:
"Problems in urban drainage administration encountered by any
governmental agencyanyone should be reviewed by the D;st,;utWeld County
to determine if equity or public interests indicate a need for drainage policy,
practice, or procedural amendments. The DistrictWeld County should
continually review the needs of the Denver regioncommunity in regard to
urban runoff criteria and should recommend changes as necessary to this
Manual."
33. Add Section 7.5 Drainage Improvements to read:
"Weld County Master Drainage Plans set forth improvements required for
existing and future growth areas. There are areas of Weld County for which
no Master Drainage plans yet exist. Weld County may require a Master
Drainage study in support of proposed development. The policy of Weld
County regarding the design and construction of improvements within the
Master Drainage Plan areas shall be as set forth below, subject to Weld
County budget and appropriation approvals.
1. Weld County shall identify needed design and construction of
improvements as set forth in adopted Master Drainage Plans for
existing and future growth areas.
2. The drainage systems for future development and redevelopment
shall be designed and constructed by the developer(s).
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3. The developers shall be responsible for design and construction of
temporary or interim storm drainage systems required due to the
lack of adequate storm drainage facilities downstream of new
development.
4. The developers may be responsible for design and construction of
permanent storm drainage systems required due to the lack of
adequate storm drainage facilities downstream of new
development."
B. Chapter 3 - Planning
1. Amend first paragraph of Section 7.1 Initial Drainage to read:
"Planning and design for urban storm runoff must be considered from the
viewpoint of the regularly expected storm occurrence, which includes the
initial storm and the major storm. The initial(minor)storm has been defined
fv ll le-al 0a acnred by tl D;0L it:thy Weld County to have a return frequency
,ai, g f om mice ;. 2 years to-once-in 10 years of once in tem (10)years
(the 10-year storm)for all uses. The major storm has been defined to have
a return period of 100 years. The objective of major storm runoff planning
and design is to reduce the potential for major damage and loss of life. The
initial drainage system is necessary to reduce inconvenience, frequently
recurring damages, and high street maintenance and to help create an
orderly urban system with significant sociological benefits."
2. Amend second paragraph of Section 9.1 Storm Sewers to read:
"The initial drainage system, including storm sewers, is that portion of the
total drainage system that often receives the most attention from engineers.
It is what the average citizen considers to be the urban drainage system.
It is what directly contributes to the orderly growth of a community by
handling the storm runoff expected to occur once every two to ten years ten
(10)years (the 10-year storm)for all uses."
3. Amend Section 9.4 System Sizing to read:
"The suggested design return periods to be used by local jurisdictions in the
Denver region for storm sewer design for all land uses is 2-to 10-years The
design return period to be used for storm sewer design in Weld County is
the 10-year storm for all land uses. Storm sewers passing flow under
County roads shall have a minimum design capacity for the 10-year storm
and a minimum diameter of 15 inches or equivalent open area. System
sizing design shall adhere to Weld County street inundation criteria of six(6)
inches for the minor storm, and 18 inches for the major storm event. This
is a departure from the policy of recommending different return periods for
different land uses. Experience has shown that it is not practical to vary
storm sewer design by land use because a single system often serves
multiple land uses. Instead, greater attention is necessary to ensure that
the major system is adequate to protect the public and property within all
areas, regardless of land use."
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C. Chapter 4 - Rainfall
1. Add the following to Section 1.0 Rainfall: "For proposed Weld County
development drainage design,the Rainfall Depth-Duration-Frequency maps
presented in the USDCM may be utilized only for those areas of Weld
County shown on the Figures in that manual(Figures RA-1 through RA-12).
Drainage designs proposed for locations outside of the areas of Weld
County covered by Figures RA-1 through RA-12 should utilize the
depth-duration-frequency information provided in the
Precipitation-Frequency Atlas of the Western United States, Volume II -
Colorado published by the National Oceanic and Atmospheric Administration
(NOAA). The NOAA Atlas may be accessed at:
http://www.nws.noaa.gov/oh/hdsc/noaaatlas2.htm. Where development is
proposed in larger watersheds,design hydrology should utilize longer storm
durations appropriate for the size of the entire watershed. See Tables RA-1
and RA-3 in the USDCM for storm duration and area adjustments."
D. Chapter 5 - Runoff
1. Add the following to Section 3.3.1 Rainfall: "See Tables RA-1 and RA-2
within the USDCM Rainfall Chapter for 1-hour and 2-hour rainfall area
adjustments and distributions. For locations outside of Weld County,
covered by USDCM Figures RA-1 through RA-12, utilize the
depth-duration-frequency information provided in the
Precipitation-Frequency Atlas of the Western United States, Volume II."
2. Amend Section 5.1 Published Hydrologic Information to read:
"The Disti 1Weld County has prepared hydrologic studies for the ,Majority
of the major drainageways within D;st.iutWeld County boundaries. These
studies contain information regarding peak flow and runoff volume from the
2-year through 100-year storm events for numerous design points within the
watershed. They also contain information regarding watershed and sub-
watershed boundaries, soil types, percentage imperviousness, and rainfall.
The studies are available at the District libraryWeld County Department of
Public Works. When published flow values are available from the
DistrictWeld County for any waterway of interest, these values should be
used for design unless there are compelling reasons to modify the published
values."
E. Chapter 6 - Streets/Inlets/Storm Sewers
1. Amend Section 1.3 Components of Urban Stormwater Collection and
Conveyance Systems to read:
"Urban stormwater collection and conveyance systems within the Dist.i,,t
Weld County are comprised of three primary components: (1)street gutters
and roadside swales, (2) stormwater inlets, and (3) storm sewers (and
appurtenances like manholes,junctions, etc.). Street gutters and roadside
swales collect runoff from the street (and adjacent areas) and convey the
runoff to a stormwater inlet while maintaining the street's level-of-service."
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2. Amend first two paragraphs of Section 2.2 Design Considerations to read:
"Certain design considerations must be taken into account in order to meet
street drainage objectives. The primary design objective is to keep the
spread (encroachment) of stormwater on the street below an acceptable
value for a given return period of flooding. As mentioned previously, when
stormwater collects on the street and flows down the gutter,the top width(or
spread) of the water widens as more stormwater is collected. If left
unchecked, the spread of water would eventually hinder traffic flow and
possibly become hazardous (i.e., reduced skid resistance, hydroplaning,
splash, etc.). Based on these considerations, the Diat,idWeld County has
established encroachment (spread) standards for the minor storm event.
These standards w.,c give] the POLICY J apto, and are 1cpcated ;it
Table ST-2 for eonvenienceare provided in Chapter 3, Planning, Section 9.4
of the Weld County Storm Drainage Criteria.
Standards for the major storm and street cross flows are also required. The
major storm needs to be assessed to determine the potential for flooding
and public safety. Cross flows also need to be regulated for traffic flow and
public safety reasons. The Distik,tWeld County has established street
inundation standards during the major storm event and allowable cross-
street flow standards. These standards were givort in thy POLICY cliaptcl
and are repeated in Table ST-3 and Table ST-4 for eanvenienceare
provided in Chapter 3, Planning, Section 9.4 of the Weld County Storm
Drainage Criteria. Allowable flow depth is measured vertically from the
gutter flowline at the curb face."
3. Amend second paragraph Section 2.3.1.3 Allowable Gutter Hydraulic
Capacity Weld County to read:
"There are two sets of reduction factors developed for Denver metropolitan
areas (Guo 2000b)and they shall also be utilized for Weld County. One is
for the minor event, and another is for the major event. Figure ST-2 shows
that the reduction factor remains unity (1.0) for a street slope <1.5%, and
then decreases as the street slope increases."
4. Add the following to Section 3.1 Inlet Functions, Types and Appropriate
Applications: "The standard inlets permitted for use in Weld County streets
are:
INLET TYPE PERMITTED USE
Curb Opening Inlet Type R All street types with 6" vertical curb
Grated Inlet Type C All streets with a roadside ditch or swale
Grated Inlet Type 13 Alleys or private drives with a valley
gutter
Combination Inlet Type 13 All street types with 6" vertical curb
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PAGE 13 ORD2006-7
5. Add the following to Section 3.3.6 Inlet Clogging: "To account for effects
which decrease the capacity of the various types of inlets, such as debris
plugging, pavement overlaying, and variations in design assumptions, the
theoretical capacity calculated for the inlets is to be reduced by the factors
presented below for the standard inlets permitted for use in Weld County.
WELD COUNTY
ALLOWABLE INLET CAPACITY
CONDITION INLET TYPE PERCENT OF
THEORETICAL
CAPACITY ALLOWED
Sump or CDOT Type R
Continuous Grade
5' length 88
10' length 92
15' length 95
Continuous Grade Combination Type 13 66
Sump Grated Type C 50
Grated Type 13 50
Sump Combination Type 13 65
6. Amend the first paragraph of Section 3.4.2 Design Considerations to read:
"The primary design consideration for the location and spacing of inlets on
continuous grades is the spread limitation. This was addressed in Section
2.2. Table ST-2 lists pavement encroachment standards for minor storms
in the Denver metropolitan area."
7. Amend the third paragraph Section 4.2 Design Process, Considerations,
and Constraints to read:
"Once a final layout is chosen, storm sewers are sized using hydrologic
techniques (to determine peak flows)and hydraulic analysis (to determine
pipe capacities). This is accomplished by designing the upstream pipes first
and moving downstream. ripes sizes smaller than 15 inches are not
is , 111,1 ndud fu, 0tu,.,, J...sou.sThe minimum size storm sewer pipe within
a Public Right-of-Way or Public Drainage Easement shall be 15 inches in
diameter or equivalent open area. Refer to the"Weld County Development
Standards and Specifications Governing the Construction of Public
Improvements", latest edition, for allowable storm sewer pipe materials.
Pipes generally increase in size moving downstream since the drainage
area is increasing. It is not good design practice to decrease the pipe size
moving downstream,even if a steeper slope is encountered that will provide
2006-2538
PAGE 14 ORD2006-7
sufficient capacity with a smaller pipe. The potential for clogging is always
a concern."
8. Add the following to Section 4.4.1 Flow Equations and Storm Sewer Sizing:
"The Manning's roughness coefficient "n"for all storm sewer pipe capacity
Weld County calculations shall be 0.013 regardless of pipe material (ie.
Concrete, PVC, or HDPE) with the exception of corrugated metal pipes
which shall have a coefficient of 0.025."
9. Add the following to Section 4.5 Hydraulic and Energy Grade Line
Calculations: "The hydraulic grade line and energy grade line shall be
calculated for each storm sewer system and included in the Final Drainage
Report. Each storm sewer system shall be profiled on the Final
Construction Drawings and shall include the design flow hydraulic grade line
(HGL). The energy grade line (EGL) for the design flow shall be at least 6
inches below the final finished elevation of the manhole rims and inlet
flowlines."
F. Chapter 7 - Major Drainage
1. Add the following to the first Paragraph of Section 3.2.3.2 Side Slopes: "For
constructed or natural channels with sideslopes steeper than 2:1,
appropriate construction setbacks from the channel edge may be required
to allow potential future channel meandering. Access for maintenance may
require easement."
2. Amend Section 3.2.7 Summary of Preliminary Design Guidance to add the
following note to Table MD-2: "Grass lined open channels conveying < 50
cfs may reduce the minimum 1.0 foot freeboard requirement to the
freeboard required to conveying 1.33 times the 100-year design flow. The
reduced freeboard may only occur if a 1.0-foot minimum freeboard is not
physically or reasonably possible and a variance request is submitted."
3. Delete the first paragraph of Section 3.2.8 Maintenance Eligibility and
replace with the following:
"The iequirementa below must be satisfied as of June 2001 for a major
drainage channel to be eligible for District maintenance. Note that the
District's "Maintenance Eligibility Guidelines" may change with time. The
reader is directed to look up the latest full maintenance eligibility criteria at
the District's Web site (www.UDFCD.org). Maintenance Eligibility
Guidelines as of June 2001 are also provided on the Cdversion of this
Mar,ual.Weld County will only maintain eligible major drainage ways by
special agreement. The requirements below must be satisfied as of
(adoption date)for a major drainage channel to be eligible for Weld County
maintenance. Note that the Weld County "Maintenance Eligibility
Guidelines" may change with time."
2006-2538
PAGE 15 ORD2006-7
4. Amend the first sentence of Section 3.2.8.3 Grass-Lined Channel Design to
read:
"The design for a grass-lined channel must meet the following criteria to be
eligible for DistrictWeld County maintenance:"
5. Amend Section 3.3.4 Maintenance to read:
"A maintenance access road with a minimum passage width of 12 feet shall
be provided along the entire length of all major drainageways. The local
lUvcu i.inc.It Way Iaqui.e the rued to be 0u,faced with C inches of Class 2
roadbase or a 5-inch-thick concrete slab.Weld County and the design
engineer shall work together to provide access to all major drainageways as
determined appropriate at the time of preliminary and final design. Weld
County encourages volunteers to assist Weld County in performing routine
maintenance of all the drainage ways within the County through an Adoption
program and will assist these groups in a variety of ways."
6. Amend the fourth paragraph of Section 3.5 Choice of Channel Lining to
read:
"Manufactured channel linings such as gabions,interlocked concrete blocks,
synthetic linings,etcetera,are not recommended for new developments, but
will be considered by Weld County on a case-by-case basis. As with
concrete- and riprap-lined channels, all of these types are best considered
for helping to solve existing urban flooding problems where right-of-way is
very limited. Manufactured channel linings should be used with caution,and
each type of channel lining must be scrutinized for its merits, applicability,
ability to meet other community needs, long term integrity,and maintenance
needs and costs."
7. Add the following to Section 4.1.5 Trickle and Low-Flow Channels: "Under
drain pipes shall not be used in lieu of trickle channels within Weld County
but will be considered by Weld County on a case-by-case basis."
8. Amend the first paragraph of Section 4.1.7 Water Surface Profile to read:
"Water surface profiles should be computed for all channels,typ;callyfo. tl ,
10-year a..d 100 yea. eve,.taconveying > 50 cfs within Weld County.
Computation of the water surface profile should include standard backwater
methods, taking into consideration all losses due to changes in velocity,
drops, bridge openings,and other obstructions. Computations should begin
at a known point and extend in an upstream direction for subcritical flow. It
is for this reason that the channel should be designed from a downstream
direction to an upstream direction. It is necessary to show the energy
gradient on all preliminary drawings to help ensure against errors. Whether
or not the energy grade line is shown on the final drawings is an option of
the reviewing agency, although the District encourages this."
9. Add the following as the third paragraph of Section 4.1.7 Water Surface
Profile: "Hydraulic grade lines shall be shown on the Final Construction
2006-2538
PAGE 16 ORD2006-7
Drawing profiles of open channels conveying > 50 cfs within Weld County.
It is not necessary to show energy grade lines on Final Construction
Drawing profiles, but it is encouraged. The energy grade line for the design
flow shall be at, or below, the final finished top of channel bank elevation.
Hydraulic grade lines on Final Construction Drawings are encouraged and
will ease assessment and review of compliance with street inundation
criteria."
10. Amend Section 4.1.8 Maintenance to read:
"Grass-lined channels must be designed with maintainability in mind. See
Section 3.2.8 for the District's Maintenance Eligibility Guidelines,which also
provide guidance for elements of design that permit good maintenance of
these installations. A stable maintenance access road with a minimum
passage width of 12 feet shall be provided along the entire length of all
t I law. J.an IayovJaya. The Iwal ywt,I",', ,i It II IUy1Vl{UIIV tI Mr read to L,
surfaced with 6 inches of Class 2 roadbase or a 5-inch-thick concrete
slabWeld County and the design engineer shall work together to provide
access to all major drainageways as determined appropriate at the time of
preliminary and final design."
11. Amend the fifth paragraph of Section 4.2.2 Design Procedure to read:
"Water surface profiles ,Iluatshall be computed, typically for the 10 01N1
100-year enc.Itafor all open channels conveying > 50 cfs within Weld
County. Computation of the water surface profile should utilize standard
backwater methods, taking into consideration all losses due to changes in
velocity, drops, bridge openings, and other obstructions. Computations
begin at a known point and extend in an upstream direction for subcritical
flow. It is for this reason that the channel should be designed from a
downstream direction to an upstream direction. It is necessary to show the
energy gradient on all preliminary drawings to help prevent errors. Whether
or not the energy gradient line is shown on the final drawings is the option
of the reviewing agency but is encouraged by the District."
12. Add the following to the last paragraph of Section 4.2.2 Design Procedure:
"Hydraulic grade lines shall be shown on the final drawing profiles of open
channels conveying>50 cfs within the Weld County. Energy grade lines on
final drawing profiles are encouraged. Hydraulic grade lines on Final
Construction Drawings are encouraged to ease assessment and review of
compliance with street inundation criteria."
13. Amend second paragraph of Section 4.2.3 Life Expectancy and
Maintenance to read:
"A.IIa6,Li Ia,IcL,ac,,cas ruad-vvIH I a-minii nun i passage width of 12 fact shall
be provided along the entire length of all major drainageways. The local
government may require the road to be surfaced with 6 inches of Class 2
Ioadbase or a 5-inch-thick concrete slab.Weld County and the design
engineer shall work together to provide access to all major drainageways as
determined appropriate at the time of preliminary and final design.
2006-2538
PAGE 17 ORD2006-7
14. Amend the second paragraph of Section 4.3 Concrete-Lined Channels to
read:
"Concrete-lined channels can be used for conveyance of both subcritical
and supercritical flows. In general, however, other types of channels such
as grass-lined channels or channels with wetland bottoms are preferred for
subcritical flows. The use of a concrete-lined channel for subcritical flows
should not be used except in unusual circumstances where a narrow right-
of-way exists. Vegetated channels are normally preferable in Lb. Donva,
regionWeld County because available thalweg slopes are generally steep
enough.
15. Amend the fourth paragraph of Section 4.3 Concrete-Lined Channels to
read:
"In th0 Daiwa, ; .rWeld County, all channels carrying supercritical flow
shall be lined with continuously reinforced concrete linings, both
longitudinally and laterally. There shall be no diminution of wetted area
cross sections at bridges or culverts. Adequate freeboard shall be provided
to have a suitable safety margin. Bridges or other structures crossing the
channel must be anchored satisfactorily to withstand the full dynamic load
that might be imposed upon the structure in the event of major trash
plugging."
16. Amend Section 4.3.6 Maintenance to read:
"Concrete channels require periodic maintenance including debris and
sediment removal, patching, joint repair, and other such activities. Their
condition should be periodically monitored, especially to assure that flows
cannot infiltrate beneath the concrete lining. A mail,tc,,'atlea acbeoa IJSU
with a minimum passage width of 12 feet shall be provided along the entire
length of all major drainageways. The local government may require the
road to be surfaced with 6 inches of Class 2 roadbase or a 5-inch-thick
u ,i icte olaUWeld County and the design engineer shall work together to
provide access to all major drainageways as determined appropriate at the
time of preliminary and final design."
17. Amend Section 4.4.1.3 Wire-Enclosed Rock (Gabions) to read:
"Wire-enclosed rock, or gabions, refers to rocks that are bound together in
a wire basket so that they act as a single unit. The durability of wire-
enclosed rock is generally limited by the life of the galvanized binding wire
that has been found to vary considerably under conditions along waterways.
Water carrying sand or gravel will reduce the service life of the wire
dramatically. Water that rolls or otherwise moves cobbles and large stones
breaks the wire with a hammer-and-anvil action,considerably shortening the
life of the wire. The wire has been found to be susceptible to corrosion by
various chemical agents and is particularly affected by high-sulfate soils.
Wire-enclosed rock installations have been found to attract vandalism, and
flat mattress surfaces seem to be particularly susceptible to having wires cut
and stones removed. For these reasons, thy Dist,k.tWeld County
2006-2538
PAGE 18 ORD2006-7
discourages the use of wire-enclosed rock. If the designer chooses to utilize
gabions, they should be placed above the low-flow channel or 2-year water
surface elevation. All flat mattresses must be filled with topsoil and then
covered with a 6-inch layer of topsoil."
18. Amend Section 4.4.7 Maintenance to read:
"A maintenance accose road with a minimum passage widtl t of 12 fcet shall
be pi.v;Jed alvny-LI IC cnti,c Ici1ylli of all maws di ale iayaway°. TI is Iva,at
government play require the road to be surfaced with 6 inches of Class 2
roadiase or a 5-inch-thick concrete slabWeld County and the design
engineer shall work together to provide access to all major drainageways as
determined appropriate at the time of preliminary and final design.
Requirements for District maintenance eligibility are reviewed in Section
3.2.8 of this chapter. Of particular concern is long-term loss of riprap,
particularly due to the public moving the rock(for smaller sizes). Grout can
deteriorate with time, and this should be monitored, as well. Improper grout
installation creates long-term maintenance problems."
19. Amend Section 4.5 Bioengineered Channels to read:
"Bioengineered channels(see Photographs MD-10 and MD-11)emphasize
the use of vegetative components in combination with structural measures
to stabilize and protect stream banks from erosion. The aa6;ctWeldCounty
advocates the integration of bioengineering techniques into drainage
planning, design, and construction when the use of such channels is
consistent with the Dist,;cfeWeld County's policies concerning flow carrying
capacity,stability,maintenance,and enhancement of the urban environment
and wildlife habitat. The following discussion on bioengineered channels
interfaces closely with Section 4.2, Wetland Bottom Channels, and Section
4.6, Natural Channels; designers are encouraged to read Sections 4.2, 4.5
and 4.6, concurrently. In addition, because bioengineered channels require
some structural assistance to maintain stability in urban settings, the
designer is referred to guidance on drop structures in the HYDRAULIC
STRUCTURES chapter."
20. Amend Section 4.5.3 Bioengineering Resources to read:
"The purpose of this section is to provide the designer with an overview of
bioengineering and basic guidelines for the use of bioengineered channels
on major drainage projects within tie Diet,;ctWeld County. There are many
sources of information on bioengineering that the designer should consult
for additional information when planning and designing a bioengineered
channel (Watson, Biedenharn, and Scott 1999; USFISRWG 1998; Riley
1998; and Biedenharn, Elliot, and Watson 1997)."
21. Amend the first two paragraphs of Section 4.5.4 Characteristics of
Bioengineered Channels to read:
"The following characteristics are generally associated with bioengineered
channels:
2006-2538
PAGE 19 ORD2006-7
1. Their design must address the hydrologic changes associated with
urbanization (increased peak discharges, increased runoff volume,
increased base flow, and increased bank-full frequency). These
changes typically necessitate the use of grade control structures. In
the absence of grade control structures, especially in the semi-arid
climate of the EX.'Eve, at .aWeld County, purely bioengineered
channels will normally be subject to bed and bank erosion, channel
instability, and degradation.
2. In addition to grade controls, most bioengineered channels may
require some structural methods to assist the vegetation with
maintaining channel stability. Examples include buried riprap on
toes and outer channel banks(see Figures MD-16, MD-17 and MD-
18)."
22. Add the following to the last paragraph of Section 4.5.4 Characteristics of
Bioengineered Channels: "Weld County is open to review and accept
alternate bioengineering methods that provide protection to toe of bank
slopes (i.e. jacks and lunkers, etcetera)."
23. Amend the first paragraph of Section 4.5.5 Advantages of Bioengineered
Channels to read:
"Public reaction to bioengineered channels is generally favorable, not only
inflict]upulaa, IVO,northern Colorado,but also regionally and nationally.
In contrast to major drainageway stabilization projects that focus on
structural measures, such as concrete-lined or riprap-lined channels,
bioengineered channels:"
24. Amend subparagraph 6 of Section 4.5.5 Advantages of Bioengineered
Channels to read:
"6. Create a living system that maywill strengthen over time."
25. Add the following to Section 4.5.5 Advantages of Bioengineered Channels:
"8. Are less costly to maintain."
26. Amend the first paragraph of Section 4.5.6 Technical Constraints to read:
"The following constraints aremay be associated with bioengineered
channels:
1. There is only limited experience to rely on for successful design of
urban channels. The majority of the experience with bioengineering
techniques relates to channels in nonurban settings.
2. The semi-arid conditions that characterize DenverWeld County can
be at odds with the need for an adequate water supply for
maintaining the vegetation. Careful species selection that reflects
the site's soils and water availability characteristics is essential.
3. A basic design criterion within thy Dioti.tWeld County is to
demonstrate channel stability during the major(100-year)storm,due
2006-2538
PAGE 20 ORD2006-7
to public safety and property protection concerns within urban areas.
There is little evidence (locally, regionally, or nationally) as to
whether purely bioengineered channels can withstand 100-year(or
lesser) flood forces.
No Change to remainder of paragraph.
27. Amend the second paragraph of Section 4.5.6 Technical Constraints to
delete the sixth bulleted item: "Large trees can threaten the integrity of
structural protection by root invasion, by toppling and damaging the
protection works,by toppling and directing flow into an adjacent unprotected
Lank, or by leaving voids in ernbanknients due to decomposition."
28. Amend the second paragraph of Section 4.5.6 Technical Constraints to
amend the last bulleted item to read:
"Many of these problems may be avoided through selection of the
appropriate type and species of vegetation. Such selections and expert
advice must be obtained from qualified individuals in revegetation and
bioengineering. Invasion by other species is quite likely over the years the
MEI.y...0a.0J i,l.an lel is arupa.(Atli C"
29. Amend the first two paragraphs of Section 4.6 Natural Channels to read:
"Natural waterways in ti.0 Dui .cy;o.MWeld County are sometimes in the
form of steep-banked gulches,which have eroding banks and bottoms. On
the other hand, many natural waterways exist in urbanized and to-
beurbanized areas, which have mild slopes, are reasonably stable, and are
not currently degrading. If the channel will be used to carry storm runoff
from an urbanized area, it can be assumed that the changes in the runoff
regime will increase channel erosion and instability. Careful hydraulic
analysis is needed to address this projected erosion. In most cases,
stabilization of the channel will be required. Stabilization using
bioengineering techniques, described in Section 4.5 of this chapter, has the
advantage of preserving and even enhancing the natural character and
functions of the channel. Some structural stabilization measures will also
be required in combination with the bioengineered stabilization measures.
In thy Dui Ivor a.caWeld County, most natural waterways will need drops
and/or erosion cutoff check structures to maintain a mild channel slope and
to control channel erosion. Typically, these grade control structures are
spaced to limit channel degradation to what is expected to be the final stable
longitudinal slope after full urbanization of the tributary watershed. In the
Denver area, this slope, depending on watershed size and channel soils,
has been observed to range from 0.2 to 0.6%, with the South Platte River
itself approaching a slope of 0.1%. Whenever feasible, natural channels
should be kept in as near a natural condition as possible by limiting
modifications to those necessary to protect against the destabilizing
hydrologic forces caused by urbanization."
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PAGE 21 ORD2006-7
30. Amend the fifth paragraph of Section 4.6 Natural Channels to read:
"The following design criteria are recommended when evaluating natural
channels:
1. The channel and overbank floodplain should have adequate capacity
for the 100-year flood.
2. A water surface profile should be defined in order to identify the 100-
year floodplain, to control earthwork, and to build structures in a
manner consistent with the DiatrIct's and IuaalWeld County's
floodplain regulations and ordinances."
No change to remainder of section.
Section 8-11-40. Weld County Addendum to the Text of the Urban Storm Drainage Criteria-
Volume 2
A. Chapter 8 - Hydraulic Structures.
1. Add the following to Section 4.1.2 Bridge Opening Freeboard: "The bridge
low chord elevation shall be a minimum of 1-foot above the 100-year water
course energy grade line."
B. Chapter 9 - Culverts
1. Amend the third paragraph of Section 1.1.2 Headwater to read:
"The headwater elevation for the design disci large should be consistent with
the freeboard and overtopping criteria in the POLICY chapter of this Manual
(Tables DP1 through DP-3). The designer should verify that the watershed
divides are higher than tl le design headwater elevations. In flat terrain,
drainage divides are often r undefined or nonexistent and culverts should be
located and designed for the least disruption of the existing flow distribution.
The maximum culvert headwater to diameter ratios are:
STORM FREQUENCY HEADWATER TO DIAMETER
10-Year HW/D < 1.0
100-Year HW/D < 1.5
The minimum culvert capacities are:
STREET MINIMUM CAPACITY
CLASSIFICATION (RECURRENCE INTERVAL)
Local 10-Year
Collector 10-Year
Arterial 10-Year
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PAGE 22 ORD2006-7
When the flow in a roadside ditch exceeds the capacity of the culvert and
overtops the cross street,the flow over the street crown shall not exceed the
minor storm and major storm depth limits presented in Chapter 3, Planning,
Section 9.4 of the Weld County Storm Drainage Criteria manual. Weld
County may require additional culvert capacity in order to prevent flooding
of adjacent properties."
2. Add the following to Section 2.1.1 Energy and Hydraulic Grade Lines: "The
hydraulic grade line and energy grade line shall be determined for each
culvert system and included in the Final Drainage Report. Each culvert
system shall be profiled on the Final Construction Drawings and shall
include the design flow hydraulic grade line."
3. Amend Section 3.5.3 Culvert Diameter to read: "It is the policy of Weld
County to require a minimum culvert diameter of 15 inches. Weld County
may require additional culvert capacity in order to prevent flooding of
adjacent properties. After the invert elevations have been assumed and
using the design computation forms(e.g., Figure CU-8), the capacity charts
(e.g., Figure CU-7),and the nomographs,the diameter of pipe that will meet
the headwater requirements should be determined. Since small diameter
pipes are often plugged by sediment and debris, it is recommended that
pipe smaller than 18 inches not be used for any drainage where this Manual
applies. Since the pipe roughness influences the culvert diameter, both
concrete and corrugated metal pipe should be considered in design, if both
will satisfy the headwater requirements. Refer to the"Weld County Design
and Construction Standards and Specifications",latest edition,for allowable
culvert pipe materials. The Manning's roughness coefficient "n" for all
culvert pipe sizing calculations shall be 0.013 regardless of pipe material
(Concrete, PVC, or HDPE) with the exception of corrugated metal pipes
which shall have a coefficient of 0.025."
4. Add the following to the last paragraph of Section 4.1 Projecting Inlets: "At
a minimum, a culvert entrance and outlet shall include a flared end section.
Erosion protection (riprap, etcetera) may be required."
5. Amend the fifth paragraph of Section 8.0 Trash/Safety Racks to read:
"Tho Dist,ictWeld County strongly recommends against the installation of
trash racks at culvert outlets, because debris or a person carried into the
culvert will impinge against the rack, thus leading to pressurized conditions
within the culvert,virtually destroying its flow capacity and creating a greater
hazard to the public or a person trapped in the culvert than not having one."
6. Amend Section 8.1 Collapsible Gratings to read:
"The Diat,iiWeld County does not recommend the use of collapsible
gratings. On larger culverts where a collapsible grating is deemed
necessary by a local jurisdiction or an engineer, such gratings must be
carefully designed from the structural standpoint so that collapse is achieved
with a hydrostatic load of perhaps one-half of the maximum backwater head
allowable. Collapse of the trash rack should be such that it clears the
2006-2538
PAGE 23 ORD2006-7
waterway opening adequately to permit the inlet to function properly without
itself contributing to potential plugging of the culvert."
C. Chapter 10 - Storage
1. Add the following subparagraph to the sixth paragraph of Section 2.0
Application Of Different Types Of Storage: "6. Above ground parking lot
detention ponds may be utilized when land area for a grassed lined
detention pond is not available. To prevent damage to and floatation of
automobiles, parking lot detention ponds shall not exceed 12 inches in depth
at any point. Parking lot detention ponds shall have signage to inform the
general public about the potential for flooding. The 100-year water surface
elevation of a parking lot detention pond shall not encroach into a public
street."
2. Amend Section 3.1.2 Use of Regional (i.e., Hydrograph Routing) Detention
Sizing Procedure to read:
"For tributary catchments larger than 90 acres in size, the D1st,k.tWeld
County recommends or may require the use of hydrograph flood routing
procedures(i.e., using CUHP-generated hydrographs and reservoir routing
calculations, see Section 3.4). In addition, if there are upstream detention
facilities in the watershed,hydrograph routing methods should be employed.
If off-site tributary areas contribute runoff to an on-site detention facility, the
total tributary area, assuming fully developed off-site land uses, must be
included in the sizing of the on-site storage volumes in order to account for
the total runoff volume in the watershed. Sizing of detention storage
volumes shall utilize outflow hydrographs that have been properly calculated
to account for variable head discharge rates."
3. Add the following to Section 3.1.3 Water Quality Capture Volume in Sizing
Detention Storage: "Within Weld County, the water quality capture volume
shall be considered a portion of the total 100-year detention pond volume."
4. Amend first paragraph of Section 3.2.1 Maximum Allowable Unit Release
Rates for On-Site Facilities to read:
"The maximum allowable unit release rates per acre for on-site detention
facilities for a number of design return periods are listed in Table SO-1.
These rates apply unless other rates are recommended in a District-
avpuuvI UWeld County-approved master plan."
5. Amend Section 3.2.2 Empirical Equations for the Sizing of On-Site Detention
Storage Volumes to read:
"Urbonas and Glidden (1983), as part of the District's ongoing hydrologic
research, conducted studies that evaluated peak storm runoff flows along
major drainageways. The following set of empirical equations provided
preliminary estimates of on-site detention facility sizing for areas within the
Dist,I,,tWeld County. They are not intended for use when off-site inflows are
2006-2538
PAGE 24 ORD2006-7
present or when multi-stage controls are to be used(e.g., 10-and 100-year
peak control) at the storage facility. In addition, these equations are not
intended to replace detailed hydrologic and flood routing analysis, or even
the analysis using the Rational Formula-based FAA method for the sizing
of detention storage volumes. The District does not promote the use of
these empirical equations. It does not object, however, to their use by local
governments who have adopted them or want to adopt them as minimum
requirements for the sizing of on-site detention for small catchments within
their jurisdiction. If the Dist,,dWhere Weld County has a master drainage
plan that contains specific guidance for detention storage or sizing of on-site
detention facilities, those guidelines should be followed instead. The
empirical equations are as follows:..."
Remainder of Section - No Change.
6. Amend Section 3.2.4 Multi-Level Control to read:
"The Dist,,t,tWeld County recommends that no more than two levels of
controls, in addition to the WQCV controls, be used for on-site detention
facilities. These levels should be the 100-year storm, in combination with
thy 5-or the 10-year storm. More levels of control may appear to provide
increased protection, but the added complexity of design and the
questionable accuracy of the extended precision for such requirements
rarely justify their use. Design Example 6.1 shows calculations of allowable
release rate and storage requirement using empirical equations."
7. Add the following to Section 3.3 Design Storms for Sizing Storage Volumes:
"The 10-year and 100-year storms shall be the design storms for all water
quality and detention pond designs, respectively, within Weld County."
8. Amend Section 3.3.2 Drainage and Flood Control to read:
"Sizing of storage facilities and outlet works for flood control purposes is
generally based on whether the facility is on-site or regional. For an
individual development site, local municipalities will often dictate the on-site
detention design storms that need to be addressed by the new
development. On a watershed level,full system master planning studies are
needed to identify the appropriate release rates for various design storms.
Thus, whenever a District-approvedWeld-County approved master plan
recommends detention sites and release rates or on-site detention/retention
storage and release rates, those rates should be used in final design of
detention/retention facilities. Other considerations that have to be taken into
account include downstream system stability, the stream's capacity to
convey discharges from the detention/retention facility in combination with
the downstream runoff contributions to the drainage system, potential for
flood damages to downstream properties, and other factors that may be
specific to each situation at hand."
9. Add the following to Section 3.3.3 Spillway Sizing: "Each detention pond
shall contain an emergency spillway capable of conveying the peak
100-year storm discharge draining into the detention pond. The invert of the
2006-2538
PAGE 25 ORD2006-7
emergency spillway shall be set equal to or above the 100-year water
surface elevation. The depth of flow out the emergency spillway shall be<6
inches and the spillway shall have effective erosion protection."
10. Amend Section 3.3.4 Retention Facilities to read:
"When a retention basin is proposed as a temporary solution to an evolving
drainage problem, tiro Dist.i,.tWeld County recommends that it be sized to
capture, as a minimum, the runoff equal to 1.5 times the 24-hour, 100-year
storm plus 1-foot freeboard. The facility also has to be situated and
designed so that when it overtops, no human-occupied or critical structures
(e.g., electrical vaults) will be flooded, and no catastrophic failure at the
facility(e.g., loss of dam embankment)will occur. It is also recommended
that retention facilities be as shallow as feasible to encourage infiltration and
other losses of the captured urban runoff. When a trickle outflow can be
accepted downstream, one shall be provided and sized in accordance with
the locally approved release rates, preferably capable of emptying the full
volume in 10 to 14 days."
11. Amend subparagraph #2 of Section 3.4 Reservoir Routing of Storm
Hydrographs for Sizing of Storage Volumes to read:
"2. Determine Hydrology: Determine the inflow hydrograph to the
storage basin and the allowable peak discharge from the basin for
the design storm events. The hydrograph may be available in
pubfo6ed &at,ket outfall plan.,6ig or a n[ajar dia; ..g0way
,t,aotci plan IcpuutWeld County Master Drainage Plans or Updates.
The allowable peak discharge is limited by the local criteria or by the
requirements spelled out in a District-appio edWeld County-
approved master plan."
12. Amend subparagraph #3 of Section 3.4.1 Initial Sizing to read:
" The outflow rate Qo (cfs) calculated as:
0) - * QA, (SO-10)
in which Qpo is the peak outflow rate. The allowable peak outflow rate is
determined from a DistrictWeld County master plan, local ordinance, or
other considerations described in Section 3.3.2."
13. Amend Section 3.4.2 Initial Shaping to read:
"The initial shaping of the storage basin provides a starting point for defining
the stage-storage relationship. The stage-storage relationship will be
refined during preliminary and final design phases of the project. The initial
shaping is easiest when regular geometry(such as a triangle or rectangle)
is used for approximation. The detention volume needed for any specific
design storm is combined with site constraints (e.g., size or depth
2006-2538
PAGE 26 ORD2006-7
limitations, number of control stages, etc.) and the simplified formulas
describing the basin geometry in order to develop an initial depth, length,
and width for the basin. Design spreadsheets can be used to assist in
preliminary shaping of the storage facility. The DistrictWeld County does
not encourage the use of storage facilities with uniform, geometric
properties. To the contrary, ti.y Di0L i :Weld County encourages designers
to collaborate with landscape architects to develop storage facilities that are
attractive visually, fit into the fabric of the landscape, and enhance the
overall character of an area. However, using regular geometry can
approximate initial shaping of a non-uniformly shaped facility."
14. Amend Section 4.0 Final Design Considerations to read:
"Final design of a storage facility should recognize the kinds of
considerations described in this section. It is beyond the scope of this
Manual to provide detailed dam design guidance. There are many excellent
references in this regard such as Design of Small Dams (U.S. Bureau of
Reclamation 1987). Thy Dlst1i,,tWeld County urges all designers to review
and adhere to the guidance in such references because the failure of even
small embankments can have serious consequences for the public. General
guidelines for the final design phase of detention or retention facilities
follows."
15. Amend Section 4.3 Geometry of Storage Facilities to read:
"The geometry of a storage facility depends on specific site conditions such
as adjoining land uses, topography, geology, preserving/creating wildlife
habitat, volume requirements, etc. Several key features should be
incorporated in all storage facilities located within the DistrictWeld County
(see Figure SO-6). These include(a)4:1 or flatter side slopes of all banks,
(b)low-flow or trickle-flow channel unless a permanent pool takes its place,
(c) forebay, (d) pond bottom sloped at least 1 percent to drain toward the
low-flow or trickle-flow channel or the outlet, and (e)emergency spillway or
fin tl.c embankment to N.cvcu it i.atastg up'ik. fa;lui c vvl ic.r
overtoppedwith erosion protection designed to safely convey the 100-year
overtopping flows."
16. Amend subparagraph #2 of Section 4.4 Embankments and Cut Slopes to
read:
"2. Freeboard—The elevation of the top of the embankment shall be a
minimum of 1 foot above the water surface elevation when the
emergency spillway is conveying the r naximum design or emergency
flow100-year water surface elevation in the detention pond. When
relevant, all SEO dam safety criteria must be carefully considered
when determining the freeboard capacity of an impoundment."
17. Add the following two subparagraphs to Section 4.4 Embankments and Cut
Slopes:
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PAGE 27 ORD2006-7
"5. Emergency Spillway Downstream Protection-In order to protect the
emergency spillway from catastrophic erosion failure, buried riprap
shall be placed from the emergency spillway downhill to the
embankment toe of slope and covered with 6 inches of topsoil. The
riprap shall be sized at the time of final engineering design.
Grouting of the riprap may be required.
6. Concrete Cutoff Wall - A concrete cutoff wall, 8 inches thick, 3 foot
deep, extending 5 feet into the embankment beyond the emergency
spillway opening, is encouraged on all private detention ponds and
required on all publicly-owned regional detention ponds. A concrete
cutoff wall will permanently define the emergency spillway opening.
The emergency spillway elevation shall be tied back into the top of
embankment using a maximum slope of 4:1."
18. Add the following to Section 4.7 Outlet Works: "The outlet pipe of regional
detention ponds shall contain a minimum of two (2) concrete cutoff walls
embedded a minimum of 18 inches into undisturbed earthen soil. The cutoff
walls shall be a minimum of 8 inches thick. The outlet pipe bedding
material shall consist of native earthen soil and not granular bedding
material to at least the first downstream manhole or daylight point."
19. Add the following to Section 4.8 Trash Racks: "For safety reasons, trash
rack angles are to be 3 horizontal to 1 vertical (3:1) or flatter per Urban
Drainage research (Nelson & Kroeger, 2005)."
20. Add the following subparagraph to Section 4.10 Operation and
Maintenance: "15. An operations maintenance manual for each water
quality pond, detention pond, and outlet structure
facility shall be developed and provided to the Weld
County Department of Public Works and the
development Homeowners'Association at the time of
final submittal."
21. Add the following to Section 4.11 Access: "Drivable access applies only to
Regional Detention facilities within Weld County. Each regional detention
pond will be considered on a case-by-case basis at the time of final design."
22. Add the following as the third paragraph of Section 5.0 Criteria For District
Maintenance Eligibility: "Regional Master Planned detention ponds,
designed and constructed by or on behalf of Weld County, shall be owned
and maintained by County as specified in the applicable Development
Agreement(s). All other detention ponds shall be considered privately
owned and privately maintained."
D. Chapter 11 - Flood Proofing
1. Amend the second paragraph of Section 1.2.1 Classification of Flood
Proofing to read:
2006-2538
PAGE 28 ORD2006-7
"In th°Dcmc, int.trupol;I
.CII I Cal L.aWeld County,flood-proofing efforts should
focus on permanent measures due to the rapid response of most of the
Front Range stream systems. Contingent measures are more effective
when combined with an early flood warning system or in areas not
immediately adjacent to a stream channel."
2. Amend Section 4.1.1 Determine Flood Hazards to read:
"Information about flooding in the area is available from th.ast,ictal id-kn.af
uff;..;al.Weld County officials or directly from FEMA at:
http://www.msc.fema.gov/hardcopy.shtml. Local officials, design
professionals, and contractors can use this information,along with the flood
hazard information developed by FEMA and other agencies and
organizations, to provide advice about retrofitting options."
3. Amend the first paragraph of Section 4.1.3 Contact Local Officials to read:
"Thy D;sti;ct and 1. afWeld County officials have copies of the FIS and
FIRM published for the community by FEMA. D;striket or cuni.iiiunityWeld
County officials can determine whether a building is in the regulatory
floodplain and, if so, the FPE at the location of the building."
E. Chapter 12 - Revegetation
1. Amend Section 1.0 Introduction to read:
"This chapter provides information on methods and plant materials needed
for revegetation of drainage facilities within the Urban Drainage and Flood
Centel Dist1;ct(District)Weld County. Establishment of a robust cover of
vegetation is critical to the proper functioning of drainage structures such as
grass-lined channels, detention basins, retention ponds, and wetlands.
Vegetation serves multiple purposes, including stabilization of structures to
prevent excessive erosion and removal of pollutants in stormwater. The
semi-arid nature of the climate,prevalence of introduced weeds,and variety
of soil types encountered in the DistrictWeld County virtually mandate
prompt implementation of a revegetation plan to achieve revegetation
success."
2. Add the following to the last paragraph of Section 2.0 Scope of This Chapter
and Relation to Other Relevant Documents: "See revisions to RV tables
included in this chapter for Weld County-specific seed mix
recommendations."
3. Add the following as a bulleted item of Section 3.2 Site Preparation: "•
Before revegetation work is started, an inventory of vegetation should be
taken. If noxious weeds, as listed in Weld County Code, Chapter 15, exist
on-site, appropriate steps need to be taken before, during, and after work
is completed, to control their spread. Contact the Weld County Department
of Public Works Weed Division Supervisor at 970-304-6496 for additional
information if needed."
2006-2538
PAGE 29 ORD2006-7
4. Add the following as a bulleted item of Section 3.3 Seeding and Planting:
• Seed mixtures should be coated with Mycorrhiza at the rate of 2
pounds per acre at the time of seeding. If mulching with straw, be
sure the straw is seed free and weed free."
5. Amend the second and third bulleted items of Section 3.4 Maintenance to
read:
• Access to and grazing on recently revegetated areas should be
limited with temporary fencing and signage while plants are
becoming established (,lye,iially thy fi1ot ycarfor 1 to 2 years at
least).
• Weed infestations should be managed using appropriate physical or
chemical, or-biolugh..01 methods as soon as possible. (Sec the otlm,
documents referenced for details on weed management options.)"
6. Add the following as the last bulleted item of 3.4 Maintenance:
• The project owner/developer, not Weld County, will be responsible
for site maintenance until vegetative establishment."
7. Amend the first paragraph of Section 4.2 Soil Amendments to read:
"Native topsoil should be stripped and saved for revegetation. If this is not
appropriate due to poor soil quality or for some other reason, then subsoil
can be made conducive for plant growth through the use of amendments.
Since soil pH is typically suitable within thy Dist,iL:tWeld County,
amendments are usually needed for increasing organic matter content or
providing nutrients in the form of fertilizers. Consideration should be given
to importing topsoil, from the vicinity, instead of amending poor quality
subsoil, as this may be less expensive."
8. Amend the third paragraph of Section 4.2 Soil Amendments to read:
"Detailed information on the types and amounts of soil amendments and
fertilizers needed is beyond the scope of this document and can be found
in the documents previously referenced. However, information is provided
on the use of humate soil conditioner and biosol fertilizer. Both of these
materials are relatively new and show promise as soil conditioners and
sources of slow-release fertilizers for revegetation work in the Dial �tWeld
County."
9. Amend the second paragraph of Section 4.3 Recommended Seed Mixes to
read:
"Recommended seed mixes for the bottom (wet soils) and side slopes of
drainage facilities within t3 Dist iktWeld County are included in Tables RV-
1 and RV-2. Mixes for different soil conditions in upland areas are provided
in Tables RV-3 to RV-6. The seeding rates in these mixes are
recommended minimum rates that should be used for drill seeding. These
2006-2538
PAGE 30 ORD2006-7
rates should be doubled for broadcast seeding and increased by 50% if a
Brillion drill or hydro-seeding is used."
10. Add the following as the fourth paragraph of Section 4.3 Recommended
Seed Mixes: "The inclusion of wild flowers in the seed mix is optional in
Weld County. Areas seeded along Weld County roads may be spot sprayed
by the county to control the spread of noxious weeds. This spraying may
affect some wild flower species. Do not plant trees or shrubs in the County
right-of-way."
11. Amend Table RV-1 as follows:
Table RV-1—Recommended Send Mix for High Water Table Conditions'
Growth Growth Lbs
Common Name(Variety) Scientific Name Season Form Seeds/Lb PLS/Acre
Redtop' Agrostis alba Warm Sod 5,000,000 0.1
Switrhgrass(Pathfinder) Panicum virgatum Warm Sod/bunch 389.000 2.2
Western wheatgrass(Arriba) Pascopynrrn smifht Cool Sod 110.000 7 9
Inland saltgrass Distich/is spicata Warm Sod 520.000 1.0
Wooly sedge Carex lanuginose Cool Sod 400,000 0.1
Baltic rush Juncus balticus Cool Sod 109,300.000 0.1
Prairie cordgrass Sporting pectinate Coll Sod 110.000 1.0
12.4
wildflowers
Nuttall's sunflower He//anthus nuaallii -- --- 250.000 0.10
Wild bergamot Monarda fisfuksa ... --- 1.450,000 0.12
Yarrow Achilles milletolium -- --- 2,770.000 0.06
Blue vervain Verbena hastata -- -- 0.12
0.40
'For areas of facilities located near or on the bottom or where wet soil conditions occur. Planting of
potted nursery stock wetland plants 2-foot on-center is recommended for sites with wetland hydrology.
Nonnative.
a. Delete the row containing Redtop (Agrostis alba).
b. Delete the row containing Nuttall's sunflower(Holianthus nuttallii).
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PAGE 31 ORD2006-7
12. Amend Table RV-2 as follows:
Table RV-2—Recommended Seed Mix for Transition Areas'
Growth Growth Lbs
Common Name(Variety) Scientific Name Season Form Seeds/Lb PLS/Acre
Sheep fescue(Ducar) Festuca ovina Cool Bunch 680O00 1.3
Western wheatgrass Pascopyrum smdhu Cool Sod 110.000 7.9
(Anibal
Alkali sacaton Saotobolus aircldes Warm Bunch 1,758,000 0.5
Slender wheatgrass Elymus trachycaulus Cool Bunch 159.000 5.5
Canadian bluegrass Poa compress° Cool Sod 2.500,000 0.3
(Ruebensy'
Switch grass(Pathfinder) Panicum virgatum Warm Sod/bunch 389.000 1.3
16.8
Nfildfiowers
Blanket flower Gas/ardla anstata -- --. 132.000 0.25
Prairie coneflower Ratibida columnans --- --- 1230,000 0.20
Purple prairie clover Petalostemum purpurea ..- --- 210,000 0.20
Gayfeather Liatnspunctata --- -- 138.000 0.06
Flax Linum lowish -- -- 293.000 0.20
Penstemon Penstemon sMctus -.- - 592.000 0.20
Yarrow Achilles rnifleb //um --- - 2,770,000 0.03
1.14
'For side slopes or between wet and dry areas.
2 Substitute 1.7 lbs PLS/acre of inland salt grass(Distichlis spicata)in salty soils.
'Nonnative.
a. Delete the row containing Canadian bluegrass (Ruebens) (Poa
compressa).
b. Delete the row containing Flax* (Linum lewisii).
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PAGE 32 ORD2006-7
13. Amend Table RV-3 as follows:
Table RV-3—Recommended Seed Mix for Alkali Soils
Growth Growth Lbs
Common Name(Variety) Scientific Name Season Form Seeds/Lb PLS/Acre
Alkali sacaton Sporobolus airoides Cool Bunch 1.750,000 0.5
Streambank wheatgrass Agropyron npanum Cool Sod 156,000 5.6
(Sodar)
Inland salt grass Dishshlis stncta Warm Sod 520.000 1.7
Westem wheatgrass(Arriba) Pascopywm smithii Cool Sod 110,000 7.9
Blue grama(Hachita) Chondnuum gracile Warm Sod 825.000 4.0
Buffalograss Duchies dactyloides Warm Sod 56.000 2.0
21.7
Wildflowers
Blanket flower Gad6vdia aristata --- -- 132,000 0.25
Prairie coneflower Ranbida co/umnans .-- --- 1,230,000 0.20
Purple prairie clover Peta/ostemum purpurea --- --- 210.000 0.20
Gayfeather Liatns punctata -.- -- 138.000 0.06
Blue Flax Latium fewest! -- --- 293.000 0.20
Rocky Mountain penstemon Penstemon stnctus --- --- 592.000 0.20
Yarrow Achillea millefolium -- -- 2,770,000 0.03
1.14
a. Delete the row containing Blue Flax (Linum lewisii).
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PAGE 33 ORD2006-7
14. Amend Table RV-4 as follows:
Table RV-4—Recommended Seed Mlx for Loamy Soils
Growth Growth Lbs
Common Name(Variety) Scientific Name Season Form Seeds/Lb PLS/Acre
Sheep fescue(Durar) Festuca ovine Cool Bunch 680,000 0.6
Canby bluegrass Poe cenbyi Cool Bunch 926,000 0.5
Thickspike wheatgrass Elymus lanceolatus Cool Sod 154.000 5.7
(Critana)
Western wheatgrass Pascopyrum smithy Cool Sod 110.000 7.9
(Arriba)
Blue grama(Hahita) Chondrosum gracile Warm Sod/bunch 825.000 1.1
Switchgrass(Pathfinder) Pamcum vlrgatum Warm Sod/bunch 389.000 1.0
Sideoats grama(Butte) Routelou curtipendula Warm Sod 191,000 2.0
18.8
Wildflowers
Blanket flower Gaillardia ensteta -.. -- 132.000 0.25
Prairie coneflower Ratibida columnaris ..- --. 1.230,000 0.20
Purple prairie clover Petebstemum putpurea -- --. 210.000 0.20
Gayfeather baths punctata --- -- 138.000 0.06
Flax Linum/ewisii --- --- 293,000 0.20
Penstemon Penstemon strictus --- --- 592.000 0.20
Yarrow Achilles mit/elollum -. -- 2.770.000 0.03
1.14
a. Delete the row containing Canby bluegrass (Poa canbyi).
b. Delete the row containing Flax(Linum lewisii).
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PAGE 34 ORD2006-7
15. Amend Table RV-5 as follows:
Table RV-5—Recommandsd Said Mix for Sandy Solls
Growth Growth Lbs
Common Name(Variety) Scientific Name Season Form Seeds/Lb PLS/Acre
Blue grama(Machita) Chondrosum gracile Warm Sod/bunch 825,000 21
Little bluestem(Camper) Schizachyrium Warm Bunch 260.000 3.0
scoparum
Prairie sandreed Calamovilfa bng/folia Warm Sod 274,000 3.0
Sand dropseed Sporobolus cryptandn/s Warm Bunch 5,298.000 0.3
Sideoats grama(Vaughn) Boutebua cunipendula Warm Sod/bunch 191.000 5.6
Western wheatgrass Pascopymm smithii Cool Sod 110.000 8.0
(Arriba)
22.0
Wildflowers
Blanket flower Gaillardia anstata -- --- 132.000 0.25
Prairie coneflower Ratibida column)him ..- -- 1.230,000 0.20
Purple prairie clover Petalostemum purp/ma -- .-- 210.000 0.20
Gayfeather Liatris punctata -.- -- 138.000 0.06
Flax Linum Jewish -- --- 293,000 0.20
Penstemon Penstemon strictus -- --- 592.000 0.20
Yarrow Achilles mN/ofa/ium --- --- 2.770.000 0.03
1.14
a. Change 2.1 to 0.3 in Table RV-5.
b. Change 0.3 to 2.1 in Table RV-5.
c. Delete the row containing Flax (Linum lewisii).
2006-2538
PAGE 35 ORD2006-7
16. Amend Table RV-7 as follows:
Table RV-7—Wlldllower Mix(to b,seeded with grass sand mix)'
Common Name(Variety) Scientific Name Flower Color Seeds/Lb Lbs PLS/Acre
Scarlet globemallow Sphaeralcea coccinea Red/orange 500.000 0.6
Blue flax Linum lewisii Blue 293.000 0.6
Purple prairie clover Petalostenwm purpureum Red-purple 210.000 0.7
White praise clover Peta%ostemum candidum White 354,000 0.6
California poppy Eschschokzia californica Orange 293,000 0.3
Blanket flower Gaillardia anstata Yellow/red 132.000 1.0
Prairie aster Aster tanacetddius Violet 496.000 0.3
Blackeyed Susan Rudbeckia hirta Yellow 1.710.000 0.3
Purple coneflower Echinacea purpurea Purple 117.000 0.9
Yarrow Achilleamllefokum White 2.770.000 0.1
Gayfeather Liafns punctata Rose/purple 138.000 0.6
Total 6.0
'This is a general mix for the District that stresses native perennials that do well in a range of soil types in
sunny locations.
a. Delete the row containing Blue Flax(Linum lewisii).
b. Delete the row containing California poppy (Eschscholtzia
californica).
c. Delete the row containing Blackeyed Susan (Rudbeckia hirta).
2006-2538
PAGE 36 ORD2006-7
17. Amend Table RV-8 as follows:
Table RV-S--Reconwnended Shrubs and Treea'
Planting
Common Name Scientific Name Height(ft) Sun/Shade Zone Notes
Shrubs
Saskatoon Amelanchier alnifolia 3-15 Sun Upland Good for wildlife
serviceberry
Lead plant Amorpha fiuticosa 3-8 Sun Upland Drought tolerant
Rubber Chrysothamnus 2-3 Sun Upland Drought tolerant
rabbitbrush nauseosus
Wild plum Prunus Americana 5-20 Sun/shade Transition Forms thickets
Chokecherry Prunus virginiana 5-20 Sun/shade Transition Forms thickets
Smooth sumac Rhus glabre 4-7 Sun/shade i Upland Good for wildlife
Oakbrush sumac Rhus trilobata 2-6 Sun/shade Upland Drought tolerant
Wax currant Ribes cereum 3-5 Sun/shade Transition Good for wildlife
Redosier dogwood Comus stolonifera 3-9 Shade Wetland Drought tolerant
Sandbar willow Sakx exigua 6-10 Sun Transition Requires more
or wetland water
Snowberry Symphoncarpos 2-5 Sun/shade Transition Prefers moist area
oreophilus
Spanish bayonet Yucca glance 1 -2 Sun Upland Drought tolerant
Woods rose Rosa woodsii 2-3 Sun Upland Establishes quickly
Silver buffaloberry Shepherdia argentea 6-13 Sun Upland Drought tolerant
Trees
Narrow leaf Populus angusufoha 10-30 Sun Transition Requires more
cottonwood or wetland water
Plains cottonwood Populus de/toldes 50 Sun Transition Requires more
water
Rocky Mountain Juniperus 5-15 Sun Upland Drought tolerant
juniper scopukxum
Colorado blue Picea pungens 60-100 Sun Transition Requires more
spruce water
Ponderosa pine Pinus ponderosa 75-100 Sun Upland Drought tolerant
Peach leaf willow Sakx amygdelotdes 15-30 Sun Wetland Requires more
water
'Trees and shrubs should not be planted in the bottoms of drainage channels or where they could
impede flow and decrease channel capacity. II is recommended that containerized stock(e.g..2-gallon.
5-gallon)be used for trees and shrubs.
a. Delete..the row containing Rubber rabbitbrush (Chrysothamnus
nauseosus).
b. Delete the row containing Spanish bayonet (Yucca glauca).
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PAGE 37 ORD2006-7
18. Amend Table RV-9 as follows:
Table RV-a--Recommended Plants for Constructed Wetlands and Retention Pond SMIf1
Depth of Water(ft) Common Name Scientific Name Notes
0- 1.5 Soft stem bulrush Sarpus validus • Planted plants should
Hard stem bulrush Scupus acutus extend above water
Arrowhead Sagiarada latifotia • Plants will invade
Alkali bulrush Scirpus mantimus deeper water with time
Smart weed Polygonum persicana
0.25-0.5 Three-square Scmpus americans • Planted plants should
Spike rush Eleocbens palustrls extend above wafer
0-0.25 Rice cut grass Leersla oryzotdes • Species will adjust to
Nebraska sedge Carex nebrascensis moisture conditions
Soft rush Juncus effuses with time
Baltic rush Juncus balticus
Torrey's rush Juncus torreyi
Foxtail barley Hordeumjubalum
Height above water
0-1 Milkweed Asclepius incarnate
0-3 Switchgrass Panicum virgatum • Best to plant near
Prairie cordgrass Spartlna peainata water where soil is wet
Beebalm Monania fistulosa • Colorful wildflower
I It is recommended that containerized stock be used for wetland plantings. It is not recommended that
cattails be planted since they will invade naturally.
a. Delete the row containing Smart weed (Polygonum persicaria).
b. Delete the row containing Foxtail barley (Hordeum jubatum).
19. Add the following to Section 4.4 Trees, Shrubs and Wetland Plantings:
"GRASS SEEDING RECOMMENDATIONS FOR WELD COUNTY
GENERAL INFORMATION
1. If a species is listed as "15% to 30%" in mixture, please use a
percentage within the given parameters to arrive at the amount used
in the seed mix.
2. The numbers listed in the "Seeding Rate- Dryland" column is to be
used for most dryland sites in this area. The amounts listed in
"Seeding Rate- Irrigated"are to be used for those areas that will be
irrigated, or sites that are highly erodible.
3. A seed mix is complete when a combination of the species chosen
totals 100%.
4. The recommended varieties column lists the preferred varieties that
are known to do well in this area. If this column is blank, refer to a
local seed dealer for recommendations on varieties.
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PAGE 38 ORD2006-7
TO OBTAIN DESIRED SEED MIX
1. Refer to the appropriate range site, defined in the local soil survey.
2. Chose the species within each range site. Names in bold italics
represent the preferred species for each site.
3. If the range of percentage in the mix column lists "up to 45%" then
chose an amount of the species to use in the mix that correlates
within this range.
4. Take the percentage of each species used in the mix and multiple
by the seeding rate.
a. Example:
1) Site is a dryland site.
2) Sand bluestem at 8.0 pounds of PLS/Acre is used at
25% in the seed mix.
3) Take 25% x 8.0 = 2.0 pounds of Sand bluestem to
use in the mix per acre.
4) Multiple the 2.0 pounds by the number of acres to get
the total amount of pounds of the species to use for
the mix.
b. NOTE: The seeding rates are listed in Pounds of Pure Live
Seed (PLS) per acre, and not in bulk pounds.
Refer to the following tables for grass seeding recommendations.
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Table RV-10 GRASS SEEDING TABLES BASED ON RANGE SITES
Species indicated in bold italics indicates the preferred species
RANGE SITE: Deed Sands, Choppy Sands, Sandy Bottomland, Sandy Meadow, Sandy
Foothills, Sandy Divide
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Sand Bluestem Elida, Woodward, Garden 20 to 35 8.0 16.0
Yellow Indiangrass Llano, Holt, Cheyenne, Oto 10 to 30 5.0 10.0
Switchgrass Grenville, Nebraska 28, 10 to 30 2.5 4.5
Blackwell, Pathfinder
Prairie sandreed Goshen 10 to 30 3.5 6.5
Sideoats grama Vaughn, Butte, Niner, up to 15 4.5 9.0
El Reno, Haskell
Little Bluestem Pastura, Cimmarron up to 10 3.5 7.0
Blue grama Hachital, Lovington up to 10 1.5 3.0
Western wheatgrass Arriba, Barton, Rosana up to 10 8.0 16.0
Needleandthread up to 15 7.5 15.0
Thickspike Critana up to 10 5.5 11.0
wheatgrass
Indian ricegrass Paloma up to 10 6.0 12.5
RANGE SITE: Sandy Plains
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Sand Bluestem Elida, Woodward, Garden 15 to 30 8.0 16.0
Prairie sandreed Goshen 10 to 25 3.5 6.5
Switchgrass Grenville, Nebraska 28, 10 to 30 2.5 4.5
Blackwell, Pathfinder
Sideoats grama Vaughn, Butte, Niner, 5 to 20 4.5 9.0
El Reno, Haskell
Yellow Indiangrass Llano, Holt, Cheyenne, Oto 5 to 20 5.0 10.0
Western wheatgrass Arriba, Barton, Rosana up to 20 8.0 16.0
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Blue grama Hachital, Lovington up to 15 1.5 3.0
Little bluestem Pastura, Cimmarron up to 10 3.5 7.0
Needleandthread up to 15 7.5 15.0
Thickspike Critana up to 10 5.5 11.0
wheatgrass
Indian ricegrass Paloma up to 10 6.0 12.5
RANGE SITE: Loamy Plains Clayey Plains, Loamy Slopes
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Western wheatgrass Arriba, Barton, Rosana 20 to 45 8.0 16.0
Sideoats grama Vaughn, Butte, Niner, 20 to 40 4.5 9.0
El Reno, Haskell
Blue grama Hachital, Lovington 10 to 25 1.5 3.0
Green Needlegrass up to 30 5.0 10.0
Needleandthread up to 15 7.5 15.0
Switchgrass Grenville, Nebraska 28, up to 20 2.5 4.5
Blackwell, Pathfinder
Big bluestem Kaw up to 10 5.5 11.0
Little bluestem Pastura, Cimmarron up to 10 3.5 7.0
Buffalograss Texoka, Sharps Improved up to 10 Bur: 8.0 Bur: 16.5
Floret: 3.0 Floret: 6.0
Yellow Indiangrass Llano, Holt, Cheyenne, Oto up to 10 5.0 10.0
RANGE SITE: Gravel Breaks, Loess Breaks, Sandstone Breaks
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Sideoats grama Vaughn, Butte, Niner, 20 to 45 4.5 9.0
El Reno, Haskell
Little bluestem Pastura, Cimmarron 10 to 35 3.5 7.0
Western wheatgrass Arriba, Barton, Rosana 10 to 20 8.0 16.0
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Blue grama Hachital, Lovington 5 to 15 1.5 3.0
Switchgrass Grenville, Nebraska 28, up to 20 2.5 4.5
Blackwell, Pathfinder
Prairie sandreed Goshen up to 20 3.5 6.5
Yellow Indiangrass Llano, Holt, Cheyenne, Oto up to 20 5.0 10.0
Big bluestem Kaw up to 20 5.5 11.0
Needleandthread up to 15 7.5 15.0
Indian ricegrass Paloma up to 10 6.0 12.5
RANGE SITE: Shaly Plains, Alkaline Plains, Salt Flat, Salt Meadow, Saline Overflow
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Western wheatgrass Arriba, Barton, Rosana 30 to 45 8.0 16.0
Sideoats grama Vaughn, Butte, Niner, 20 to 40 4.5 9.0
El Reno, Haskell
Alkali sacaton Salado 10 to 35 1.0 1.5
Switchgrass Grenville, Nebraska 28, up to 20 2.5 4.5
Blackwell, Pathfinder
Blue grama Hachital, Lovington up to 15 1.5 3.0
Yellow Indiangrass Llano, Holt, Cheyenne, Oto up to 10 5.0 10.0
Big bluestem Kaw up to 10 5.5 11.0
RANGE SITE: Overflow
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Western wheatgrass Arriba, Barton, Rosana 30 to 45 8.0 16.0
Green Needlegrass Vaughn, Butte, Niner, 10 to 30 5.0 10.0
El Reno, Haskell
Switchgrass Grenville, Nebraska 28, 10 to 20 2.5 4.5
Blackwell, Pathfinder
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Big bluestem Kaw 5 to 20 5.5 11.0
Yellow Indiangrass Llano, Holt, Cheyenne, Oto 5 to 20 5.0 10.0
Blue grama Hachital, Lovington up to 10 1.5 3.0
RANGE SITE: Wet Meadow
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Switchgrass Grenville, Nebraska 28, 15 to 30 2.5 4.5
Blackwell, Pathfinder
Yellow Indiangrass Llano, Holt, Cheyenne, Oto 15 to 30 5.0 10.0
Big bluestem Kaw 15 to 30 5.5 11.0
Prairie Cordgrass 15 to 30
Little Bluestem Pastura, Cimmarron up to 10 3.5 7.0
Western wheatgrass Arriba, Barton, Rosana 10 to 20 8.0 16.0
Slender wheatgrass San Luis up to 10 5.5 11.0
RANGE SITE: North of Highway 14
COMMON NAME RECOMMENDED % IN SEEDING RATE
VARIETIES MIX
DRYLAND IRRIGATE
D
Western wheatgrass Arriba, Barton, Rosana 30 8.0 16.0
Blue grama Hachital, Lovington 30 1.5 3.0
Sideoats grama Vaughn, Butte, Niner, 30 4.5 9.0
El Reno, Haskell
Buffalograss Texoka, Sharps Improved 10 Bur: 8.0 Bur: 16.5
Floret: 3.0 Floret: 6.0
20. Add the following as the last two bulleted items of Section 4.5 Mulching:
"• At least 70 percent (%) of the mulch by weight shall be ten (10)
inches or more in length.
• The appropriate use of fabric blankets under trees and shrubs is
suggested."
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21. Amend Section 5.0 Post-Construction Monitoring to read:
"Monitoring is necessary to check the status of revegetation work and to
implement any follow-up measures needed, such as mowing,weed control,
watering, overseeding, etc. This is especially important for establishing
native species since it may take several yoaiothree to five years for
vegetation to become adequately established. Sites should be observed
several times during their first two to three growing seasons and at least
oncetwice a year thereafter. The guidelines in Section 3.4 should be
followed.
Design Examples - Weld County does not have specific values to use for
the C1, C2, and C3 coefficients within the "Detention Volume by Modified
FAA Method" spreadsheet. Please use the Urban Drainage and Flood
Control District (Denver area) values."
Section 8-11-50. Weld County Addendum to the Text of the Urban Storm Drainage Criteria-
Volume 3
A. Chapter 2 - New Development Planning
1. Amend Section 1.2 Four-Step Process, portion titled "Step 3", second
paragraph to read:
"Constructed Grass, Riprap, or Concrete-Lined Channel. This method of
channel stabilization has been in practice for some time; it is described in
Volume 2 of the Manual. The water quality benefit associated with these
channels is the reduction of severe bed and bank erosion that can occur in
the absence of a stabilized channel. On the other hand, the hardlined low
flow channels that are often used do not offer much in the way of water
quality enhancement or wetland habitat. Thy Urban. Drainage anJ tread
Canto' D;0t,ktWeld County does not recommend the use of riprap or
concrete lined flood conveyance channels, but does recommend the use of
low-flow channels lined with soil-riprap."
2. Add the following to the last paragraph of Section 1.3 Other BMPs: "Weld
County will consider and allow use of new, innovative BMP technologies
upon review of the proposed BMP(s) on a case by case basis."
3. Amend second paragraph of Section 1.5.4 Guidance for Selecting and
locating WQCV Facilities to read:
"Laying out WQCV facilities within a development site and watershed
requires thought and planning. Often, this decision-making occurs during
a master planning process undertaken by local jurisdictions and the
DistrictWeld County. Outfall system plans and other reports may depict a
recommended approach for implementing WQCV on a watershed basis.
Such reports may call for a few large regional WQCV facilities, smaller sub-
regional facilities, or alternatively an on-site approach. It is always a good
idea to find out if a master planning study has been completed that
2006-2538
PAGE 44 ORD2006-7
addresses water quality and to attempt to follow the plan's
recommendations."
4. Add the following to the last paragraph of Section 1.5.5 Incorporating
WQCV into Stormwater Quantity Detention Basins: "Weld County requires
that the 100-year detention volume be provided for a given site and allows
the WQCV to be incorporated within the 100-year volume."
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B. Chapter 3 - Structural BMP'S
1. Amend third paragraph of Section 6.4 Design Considerations to read:
"Perforated outlet and trash rack configurations are illustrated in the
TYPICAL STRUCTURAL BMP DETAINS AND SPECIFICATIONS chapter.
Figure EDB-3 equates the WQCV that needs to be emptied over 40 hours,
to the total required area of perforations per row for the standard
configurations shown in that section. The chart is based on the rows being
equally spaced vertically at 4-inch centers. This total area of perforations
per row is then used to determine the number of uniformly sized holes per
row (see detail in the TYPICAL STRUCTURAL BMP DETAINS AND
SPECIFICATIONS chapter). One or more perforated columns on a
perforated orifice plate integrated into the front of the outlet can be used;
however, the fewer the number of columns, the better, maximizing the size
of the orifice. Using least number of columns and the largest possible
orifice, reduces clogging possibilities. Other types of outlets may also be
used, provided they control the release of the WQCV in a manner consistent
with the drain time requirements and are°ppuvcddccepted in advance by
tl a Dist1;t,tWeld County."
2. Add the following to Section 9.0 Retention Pond (RP) - Sedimentation
Facility: "Retention facilities are normally not allowed in Weld County, but
will be considered by Weld County for special circumstances. Retention
facilities shall be sized to contain a volume equal to twice the 100-year
storm runoff volume plus one foot of freeboard. Water within a retention
facility shall be mechanically removed and disposed of off-site by the
property owner within 48 hours after a storm event."
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C. Chapter 4- Typical Structural BMP Details
1. Amend Table 1 as follows:
Table 1—Typical Notes For RIM,RP and CWB Outlet Structures
1. The details shown herein are conceptual design in nature. Preparation of final design plans that
address details of structural adequacy,excavation.foundation preparation.concrete work.
reinforcing steel,backfill,metalwork,and appurtenances, including preparation of technical
specifications,are the responsibility of the design engineer in charge of the project.
2. Alternate designs to the typical outlet structures shown here'may he considered:however,
alternate designs must address the hydraulic and trash handling functional futures and inert for
the structures shown in this Manual.
3. Wingwalls shown herein are designed to have the structure to be backfilled to be flush with the
side slopes of the basin. The use of this geometry is recommended and permits the structure to
blend into the landscape most aesthetically.Other geometries may be considered.however they
need to be developed with full consideration of public safety,aesthetics,maihtainabily.and
function. The superiority of these design should be demonstrated to be equal to or better than the
design concepts shown in this Manual.
4. Permanent Water Surface refers to the water surface of the micro-pool for Extended Detertbn
Basins and the permanent pod for Constructed Wetland Basins and Retention Ponds.
5. Perforated orifice plate shown herein is used to provide the specified the drain time of the WQCV.
To reduce clogging potential, t is recommended that the largest possible circular opening be
selected to minimize the number of columns. The intent is to have an outlet that empties the
WOCV in the time specified(e.g.. 12-.24-or 40-hours),and being within-3%to 5%of this time is
considered acceptable, See Figure 4 for orifice design information.
6. Vertical Trash Rack option is preferred:however,an Adverse-Slope Trash Rack is also
acceptable.Both help to shed the accumulated trash as the water level after the storm recedes.
The use of a Continuous-Slope Trash Rack for WQCV outlets is not recommedded.See Figure 6
for trash rack design information.
7. Drainage or flood control detention above the WQCV may be sized for any storm event specified
by local srormwater criteria and not only to the 2-or 10-year events shown herein.
8. Underdrains along the perimeter of the permanent pool.including a shutoff valve,are
recommended for Constructed Wetland Basins and a Retention Ponds to help dewater the pool for
rehabilitative maintenance.
9. When the outlet designs differ from those shown herein:
a) Provide needed orifices that are dstributed over the vertical height of the WQCV.with the invert
of the lowest orifice located at 2'-6",or more above the bottom of the micro-pool and above the
bottom of Retention Ponds and Constructed Wetland Basins.
bt Provide loll hydraulic calculationsdemonstrating that the outlet will provide the minimum
required drain time of the Water Quality Capture Volume for the BMP type being used.
c) Outlet openings(orifices)shall be protected by trash racks having a minimum net open area
specified in Fig 7. All opening dimensions shall be less than any dimension of outlet openings.
d) Trash racks shall be manufactured from stainless steel or aluminum aloy structurally designed
to not fail under a full hydrostatic load on the upstream side and assuring zero backwater
depth on the downstream side.
Urban Drainage and Typical Outlet Structure General Notes
Flood Control District for Extended Detention Basin,
Drainage Criteria Manual(V.3) Retention Pond and Constructed Wetland Basin Outlets
a. "8. Underdrains alongaccessible from the perimeter of the
permanent pool,including a shutoff valve,are recommended
for Constructed Wetland Basins and a Retention Ponds to
help dewater the pool for rehabilitative maintenance."
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PAGE 47 ORD2006-7
2. Delete, in its entirety, Figure 1 - Typical WQCV Outlet Structure Profile,
Including 100-year Detention.
Note; Sze 2- though 100-year merger
trash reds with the aid of figure 7.
Overtopping
Protection
Emergency gpl y
Overflow Outlet tenter Fl
w/ Trash Roan
100-YR or targer.Flood Water SurracjZ
_ WQCV Water Surfoc�i Fllehed ,(rode
N'ltaty (See
S Orifice Plate,
4)
r.y ....i (
Permanent Nate i■1
Surface 3ar4 T . 1W-VR Orifice
�h Control Outlet
1l (See lg Roth 6) Mt Pipe m 120X, of 100-yR Capacity
UndeNain °round
Micro-Pool (Optional)
prow Box Outlet Dotlon
Overtopping
Overlie. and Emergency Protection
Spglwoy
100-YR ce Larger Fleed Water Surface
CCV Water Srfac.�_
Or-We a Plat eer's
Neap. (See Figure 4
Permanent Water 4 central Outfit
SurPoasr 1 6
Trash U. - —
See r urn a r' 'Outlet Pipe 1200 of 10-YR Capacity
• .. _ ._._. . Undrdroln lyourd
Niw-Pod (Optional)
Overtopping Spillway Option
Urban Drainage and figure I
Flood Control Ofitrrat Twice *ICU Outlet Structure Profiles
Dothan Criteto Manuel (V.3) Including 100-Year Detention
RPM ereew nisei
Figure 1—Typical WOCV Outlet Structure Profile.Including 100.year Detention.
2006-2538
PAGE 48 ORD2006-7
3. Amend Figure 2 as follows:
Mete Slzs 2- through 100-year endow
trot melts with the aid of figra 7. Overtopping
IoM
la
100-YR or Larger Flood Mention
E rgene` FIoaA �d�
Overflow with Trash Rork
2- to 10-YR Detention
Overflew With Trash Rack
100-YR a Lags Mod Water Sakes
Zr to12YR Mater 1pf�oe Finished Crods
"COY Meter Surface —Z .+...
•
HM Per manent Water If i 1 ▪ 1100-YR OrificeSurface= o>h e/' ▪ Control Outlet
F wa ' ��.` ,r 'anis Pips - UDC of 106-M Capacity
- Orifice Plats
(See figure 4
2- to 10-YR Orifice
Undedrels Around Control Outlet
Micro-Pool (Options)
Droo Bois Outlet Option
100-YR or Larger Overtopping
Flood Spillway Protection
2- to 10-YR Oetentice Outlet with Trash Rock
100-1R or Larger Flood Water Dolan =
2- to 10-YR Water Surfs s—
Ilsmv Perngront Water 13Cr4
Suffices 2- to 10-YR Orifles
rooh M Control Outlet
Soar.ung�+'S Outle P
- 10 _- Capacity
Orifice Rate
(Soo Figaro 4] ur yy ►rp mylf
Micrror Pool '( O1ti ns)
Overtopping Spillway Option
Urban Droroge and Figure 2
flood Control District
Typical CV Outlet Structure Profile
Orafnage Criteria Monual (V.3) Inoludng 2— to 10—Year and 100—Yea Detention
Floe%HS eeeey
Figure 2—Typical WMCV Outlet Structure Profile.Including 2-to 10-year and 100-year Detention.
a. Delete the Overtopping Spillway Option from Figure 2.
b. Change "Outlet Pipe = 120% of 100-YR Capacity" within the Drop
Box Outlet Option to"Outlet Pipe= 100%of 100-YR Capacity"within
the Drop Box Outlet Option.
2006-2538
PAGE 49 ORD2006-7
4. Amend Figure 2-a as follows:
Rata Size 2- through 100-„or overarm
trash meta with the old of figure 7. OvOlbD'►ing
100-`YR or larger Flood Detention E gonoy Soinoy Protection
Overflow with Trash Rock Fleoi
2- to IO-YR Detention
Overflow with Trash Rack
100-YR or Larger Flood Meta Surface
3=ta_1QYR Wotar lalica_g. —
Finished Crude
W✓aCV Mister 9rfou ��. •
n..
New Pr ant Water 1P—r4 .� 100-YR Orifice
Sus_11 s roil, R•ck Control Outlet
See re sere, ' OWet Pb. - um of 10a-M1 Cmadty
Orifice Not
(See Figure 4)
2- to 10-YR Orifice
r
Uiledre roun Conbd Outlet
Mkron-Pod tiOptlAond'
Urea Box Outlet Option
Ix—MI or Larger Overtopping
Flood Spick Preteetton
2- to Mit er Lager Detention d Wt with hash Root
ID0.YR ar Larger need Water Surface s
2-fig t5B WetLSwface s_
WQCV Water Surface _s
a......v
F.uov Perna mint Water 1 r4 t
Surface= 2- to 10-YR OrificeTrash n R Central outlet
CutNt PIPe = 120X of 1. apacfty
Wire Rate
(See Figure 4J ;gm
gd�rain ggrround
uJt- cal (OptlondJ
Overtopping Spillway Option
Urban Dreinoge and Figure 2-e
Flood Control District Alternate
Drainage Criteria Manual (v.3) Typical WGCV Outlet Structure Profiles
roe le-rem edamIncluding 2— to 1D—Yearand 100—Year Detention
Figure 2-a—Typical WOCV Outlet Structure Profile,Including 2-to 10-year and 100-year Detention.
a. Delete the Overtopping Spillway Option.
b. Change "Outlet Pipe = 120% of 100-YR Capacity' within the
Drop Box Outlet Option to "Outlet Pipe = 100% of 100-YR
Capacity" within the Drop Box Outlet Option".
2006-2538
PAGE 50 ORD2006-7
D. Chapter 5 - Maintenance Recommendations
1. Add the following introductory paragraph prior to Section 1 Grass Buffer:
"Weld County will require that all submittals include an Operations and
Maintenance manual for all water quality and detention pond facilities. The
operations and maintenance manuals shall also be distributed to the
applicable Homeowners' Association and/or business park association (or
equivalent). The operations manuals will include instructions on safe and
correct operations, repair, and maintenance of all installed equipment and
facilities and recommended inspection schedules."
E. Chapter 6 - Industrial and Commercial Best Management Practices
1. Add the following introductory paragraph under Section 1.0 Introduction:
"Weld County will require that all submittals include an Operations and
Maintenance manual for all industrial and commercial water quality and
detention pond facilities. The operations and maintenance manuals shall
also be distributed to the applicable business park association (or
equivalent). The operations manuals will include instructions on safe and
correct procedures for the operation,repair,and maintenance of all installed
equipment and facilities. The manuals shall provide recommended
inspection schedules."
2. Amend Section 5.0 Structural Controls, Table IC-1 as follows:
Table IC-1--Suggntsd Structural Controls
Control Sources Applicability
Grass Buller Parking Areas Applicable to Industrial and
Commercial Operations
Grass Swale Parking Areas Applicable to Industrial and
Commercial Operations
Modular Block Parsons Parking Areas Applicable to Industrial and
Pavement Commercial Operations
Pavement Micro-Detention Parking Areas Applicable to Industrial and
Commercial Operations
Landscape Micro-Detention Parking Areas Applicable to Industrial and
Commercial Operations
Extended Detention Basin Parking Areas Applicable to Industrial and
Commercial Operations
Constructed Wetlands Parking Areas Applicable to Industrial and
Commercial Operations
Retention Pond All Sources Associated with Industrial or
commercial operations with storage of
large quantities of toxic pollutants.
Constructed Wetlands Parking Areas Applicable to Industrial and
Channel Commercial operations
Spill Containment and Liquid Storage,Washing. Applicability to all Industrial and
Control(Containment Manufacture,Outside Storage, Commercial operations
Diking.Curbing.Installation Waste Management.Fueling
of spill and overflow Areas.Loading and Unloading
protection)
Covering of Storage/ Fueling Areas.Loading and Applicability to all Indushial and
Handling Facilities Unloading,Liquid Storage, Commercial operations
Material Storage,Outside
Manufacturing.Waste
Management
a. Delete"Retention Pond"and replace with "Spill Containment Area."
2006-2538
PAGE 51 ORD2006-7
F. Chapter 8 - Construction Best Management Practices
1. Amend the second paragraph of Section 1.1 General to read:
"An Erosion and Sediment Control Plan must be developed and submitted
to the local jurisdiction to obtaii i a construction or site grading permitWeld
County to obtain a grading permit or a building permit. Site planning and
drainage planning should, whenever possible, occur concurrently with site
grading and erosion control planning. When site grading precedes final
development, an erosion and sediment control plan for site grading must be
submitted. This plan may have to be modified at the time a final site
development plan is prepared. This modified plan must be submitted for
review and approval prior to final development."
2. Amend Section 1.3 Erosion and Sediment Control Plan to read:
"An Erosion and Sediment Control Plan consisting of a written narrative
report and a site plan map must be submitted to the ap1r update Iva,ai
governmentWeld County for review and Opp UV alacceptance. Figures C-1
and C-1A provide standard symbols that can be used on such plans. An
example plan is given in APPENDIX B. The written narrative report can be
a subsection within the drainage report. The erosion and sediment control
plan must include specific inspection and repair/maintenance requirements.
3. Amend paragraph #16 of Section 1.3.1 Narrative Report to read:
"16. The following note - "This Erosion and Sediment Control Plan has
been placed in the(insert name of local jurisdiction)Weld County file
for this project. The plan appears to fulfill the Urbai, Dral,'aye a,RI
flood Control Distrk.l's teL. ik,a+Weld County criteria 011J tl ;t01;
for erosion control and requirements of (insert name of local
ju,;0J;1,tiv1 r). I understand that additional erosion control measures
may be needed if unforeseen erosion problems occur or if the
submitted plan does not function as intended. The requirements of
this plan shall run with the land and be the obligation of the land
owner until such time as the plan is properly completed, modified or
voided."
4. Amend paragraph 3.m of Section 1.3.2 Site Plan to read:
"m. The following note: "This Erosion and Sediment Control Plan has
been placed in the(insert name of local jurisdiction)Weld County file
for this project and appears to fulfill applicable erosion control
criteria. I understand that additional erosion control measures may
be required of the owner and his or her agents due to unforeseen
erosion problems or if the submitted plan does not function as
intended. The requirements of this plan shall run with the land and
be the obligation of the land owner until such time as the plan is
properly completed, modified or voided."
2006-2538
PAGE 52 ORD2006-7
5. Replace the current text of Section 1.3.3 Approval of Erosion and Sediment
Control Plan with the following:"An Erosion and Sediment Control Plan must
be approved prior to issuance of an Over lot Grading or Site Disturbance
Permit by the city or county. The final Erosion and Sediment Control Plan
,I just be cons;stellt grab a Dranl..gc Report considered acceptable to the
approving jurisdiction. Approval of the Erosion and Sediment Control Plan
clues IIVt ill!ply at.i.CNta1n.C ur approval of Drainage Plans, Utility Plans,
Street or Road Plans, Design of Retaining Walls, or any other aspect of site
dtvelupnle, t."An Erosion and Sediment Control Plan must be accepted
prior to issuance of a grading permit or a building permit. The final Erosion
and Sediment Control Plan must be consistent with the Drainage Report.
Approval of the Erosion and Sediment Control Plan does not imply
acceptance or approval of Drainage Plans, Utility Plans, Street or Road
Plans, or any other aspect of site development."
6. Amend Section 1.3.4 Exemptions and Variances to read:
"A provision for exemptions and variances may be provided by a city or
countyWeld County. These are generally processed according to the
applicable subdivision regulations and reviewed on a case-by-case basis."
7. Amend paragraph 1.b of Section 1.3.4 Exemptions and Variances to read:
"b. Grading or an excavation below finished grade for basements,
footings, retaining walls, or other structures Li., plots zoi,ed R1 - R3
of less than five(5)acres in sizewhere the disturbed area will be less
than one (1) acre in size unless required otherwise."
8. Amend paragraph 1.d of Section 1.3.4 Exemptions and Variances to read:
"d. Land-disturbing activities involving less than five (5) ac-resvne (1)
acre of disturbed area. Individual lots involving less than fie (5)
acresone (1) acre of disturbed area in a larger subdivision project
shall not be considered separate development projects, but rather
as a part of the subdivision development as a whole. It will be the
responsibility of the homeowner or homebuilder to conform to all
requirements of the lut.ally-app.uvcdlocally-accepted Erosion and
Sediment Control Plan for the subdivision. As part of any Building
Permit for which a specific erosion control plan is not required, the
following statement must be included: "We have reviewed the
Erosion and Sediment Control Plan for (subdivision name) and
agree to conform to all requirements contained therein and all
erosion control requirements of the(insert name of local jurisdiction).
We further agree to construct and maintain all erosion and sediment
control measures required on the individual lot(s) subject to this
Building Permit and/or in accordance with the provisions of the
Erosion Control section of the Manual of the Urban Drainage and
Flood Control District."
2006-2538
PAGE 53 ORD2006-7
9. Amend paragraph 1.h of Section 1.3.4 Exemptions and Variances to read:
"h. Where the owner certifies in writing to h,cal ju,iadictiu,Weld County
and the Iucal ju,isJik.i 1tWeld County agrees, in writing, that the
planned work and the final structures or topographical changes will
not result in or contribute to soil erosion or sedimentation and will not
interfere with any existing drainage course in such a manner as to
cause damage to any adjacent property or result in the deposition of
debris or sediment on any public way, will not present any hazard to
any persons or property,and will have no detrimental influence upon
the public welfare or upon the total development of the watershed."
10. Amend paragraph 2 of Section 1.3.4 Exemptions and Variances to read:
"2. Variances - Cities and counties may consider waiving or modifying
any of the a iteria which are deemed inappropriate or too restrictive
fu, site conditions by granting a variance. Variances may be granted
at ti,c time of via, suhnnoo,un ur ,cy uest for plan ,evisiwr
Variances must be requested in accordance with the subdivision
regulations and must define:The Weld County Engineer may grant
variances from the criteria of the Construction Best Management
Practices chapter by his/her acceptance of the Final Drainage
Report in which the variance request is well documented."
11. Amend the fourth bulleted item under Section 2.2 Summary of Criteria to
read:
• Revegetation. A viable vegetative cover should be established
within one year on all disturbed areas and soil stockpiles not
otherwise permanently stabilized. Vegetation is not considered
established until a ground cover is achieved which, in the opinion of
th0 city o, county ofju,isJikiGv,rWeld County, is sufficiently mature
to control soil erosion and can survive severe weather conditions.
(Section 3.3)."
12. Amend the 22nd bulleted item under Section 2.2 Summary of Criteria to
read:
• Disposition of Temporary Measures. All temporary erosion and
sediment control measures shall be removed within 30 days after
final stabilization is achieved, or after the temporary measures are
no longer needed,whichever occurs earliest,or as authorized by the
city vi wu,,ty of Iucal ju,iaJk,,Eu,rWeld County. (Section 8)."
13. Amend the second paragraph of Section 2.4.2 Stormwater Quality Plans to
read:
"Where local regulations have not been developed, sStormwater quality
plans should be developed consistent with the guidelines in the
STORMWATER QUALITY MANAGEMENT and BMP PLANNING FOR
2006-2538
PAGE 54 ORD2006-7
NEW DEVELOPMENT AND REDEVELOPMENT chapters of Volume 3 of
the Manual."
14. Amend the second paragraph of Section 3.3.2 Temporary Revegetation to
read:
"To provide temporary vegetative cover on disturbed areas which will not be
paved,built upon,or fully landscaped within 12 months but will be completed
within 24 months, plant an annual grass appropriate for the time of planting
and mulch the planted areas. The annual grasses generally suitable for the
Denve.-nu trupolltan a.L,JWeld County are listed in Table C-2. These are to
be considered only as a general recommendation whenever specific design
guidance for a particular site is not available."
15. Amend the second paragraph of Section 4.1 Vehicle Tracking to read:
"For sites greater than two (2) acres, a stabilized vehicle tracking control
must be constructed(see Figure C-8).Whenever deemed necessary by the
tit/ vi �ouwdly of jai aJk,tuuMWeld County, wash racks shall be installed to
remove mud and dirt from the vehicle and its tires before it enters onto
public roads (see Figure C-8A)."
16. Amend the first paragraph of Section 4.3.3 Sediment Basins to read:
"Areas draining more than 1 acre must be routed through a sediment basin
similar to one shown in Figures C-15, C-15A, and C-16. Sediment basins in
ti is Doi ova, is k,,Meld County shall be designed to a minimum 1,800 cubic
feet of volume per tributary acre and shall be cleaned out prior to becoming
half full."
17. Amend the last paragraph of item #2 under Section 5.1 Working Within or
Crossing a Waterway to read:
"A permit is required for placement of fill in a waterway under Section 404
of the Clean Water Act. The U.S. Army Corps of Engineers has issued
nationwide general permit Number 14 for Minor Road Crossing Fills. This
is defined as placement of less than 200 cubic yards of fill material below
the plane of ordinary high water. The local office of the Corps should be
contacted about the requirements for obtaining a 404 permit. The city o'
t.uunty ufju,;Od;btiv,Weld County should also be consulted and can provide
assistance. A further discussion on the need for 404 permits is included in
Section 2.1, MAJOR DRAINAGE, of the Manual."
18. Amend the first paragraph of Section 5.3 Outlet Protection to read:
"To protect adjacent downstream properties from erosion due to
concentrated flows, a stable outlet or channel is necessary. If there is no
stable outlet, one may have to be constructed. In lieu of constructing a
temporary or permanent outlet to the storm drainageway system,temporary
total retention of the runoff from a 24-hour, 100 year storm may be provided.
Written-approval by the local city or county must be obtained for total
2006-2538
PAGE 55 ORD2006-7
tatc..tlur. Of atu....vvato'may be considered on a case-by-case basis upon
acceptance from Weld County."
19. Amend Section 8.0 Disposition of Temporary Measures to read:
"All temporary erosion and sediment control measures shall be removed and
disposed within 30 days after final site stabilization is achieved, or after the
temporary measures are no longer needed,whichever occurs earliest,or as
authorized by the c;ty or county of kcal jut;sdk4k,.rWeld County and
applicable coordinating agencies (CDOT, CDPHE). For example, a site
containing only one building will have temporary erosion control measures
removed after building construction is complete and final landscaping is in
place. Temporary erosion control measures may be removed from a
commercial construction site or residential subdivision only after streets are
paved and all areas have achieved final stabilization. Trapped sediment and
disturbed soil areas resulting from the disposal of temporary measures must
be returned to final plan grades and permanently stabilized to prevent
further soil erosion. The Professional Engineer preparing the erosion and
sediment control plan shall submit, as part of the narrative report, a
Su iedulc of,o, oval Jatea fu. to'.upu.sty ....t.ul measu1k,.,. TI auln,Jula.
al.uulJ be-w,.siste.tt Witl. kcy-c. ,tsttu..t{u.. phases soul. as street Naa„.y,
final stabilization of disturbed areas, or installation of structural stormwater
controls. The Professional Engineer preparing the construction phase
erosion and sediment control plan shall obtain the approval of Weld County
before removal of any temporary measures."
20. Amend the second paragraph of Section 9.0 Maintenance to read:
"The Professional Engineer preparing the erosion and sediment control plan
,Lull ,t, ao putt of the t.attatwL. ruputt, a aa.hcdule of F,lannell
t..ai..tenance activ t,oa fu, tc...po.aty al.d r,c.tttatte..t o.ua,on and s0J...totft
control measures. The schedule should be consistent with the level of
,..a6.to.la'.uc required fu. tLc uuntrol tt.caaures r,.upuact n tl.c pla.r.The
Professional Engineer preparing the permanent erosion and sediment
control plan shall submit a schedule of planned inspection and instructions
for operations and maintenance for all installed permanent erosion and
sediment control measures. The plan shall include identification and
specifications (size, materials, etcetera)of parts and equipment potentially
needing repair or replacement over the life of the installed measures. A
copy of the inspection schedule and instructions for operations and
maintenance shall be provided to the applicable Homeowners'Association
or Business Park management(or equivalent)."
21. Add Section 10.0 Erosion and Sediment Control Warranty to read: "Prior to
acceptance and approval of all installed permanent erosion and sediment
control measures, Weld County will require that the owner shall warrant the
measures shown on the approved erosion and sediment control plan are
properly constructed, installed, and are free from defective materials and/or
defective workmanship."
Section 8-11-60. Enforcement responsibility.
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It shall be the duty of the Weld County Department of Public Works to interpret and enforce
the provisions of the Weld County Storm Drainage Criteria using the following guidelines:
A. In the interpretation and application, the provisions of the Weld County Storm
Drainage Criteria shall be held as the minimum requirements for promotion of the
health, safety, and general welfare of the community.
B. The Weld County Storm Drainage Criteria is not intended to interfere with,
abrogate, or annul any other regulation, statute, or other provision of law.
C. Where any provision of the Weld County Storm Drainage Criteria imposes
restrictions different from those imposed by any other provisions of the Weld County
Storm Drainage Criteria, or any other regulation or provision of law, that provision
which is more restrictive or imposes higher standards shall govern.
D. The Weld County Storm Drainage Criteria is not intended to abrogate any
easement, covenant, or any other private agreement or restriction, provided that
where the provisions of the Weld County Storm Drainage Criteria are more
restrictive or impose higher standards or requirements than such easement,
covenant, or other private agreement or restriction, the provisions of these
regulations shall govern.
Division 2
Drainage Planning Submittal Requirements
Section 8-11-100. Review process.
All new developments and subdivisions within the jurisdiction of the Weld County Storm
Drainage Criteria shall submit drainage reports, construction drawings, and existing condition and
as-built information in accordance with the requirements of this Article.
Section 8-11-110. Sketch Plan Drainage Report.
The purpose of the Sketch Plan Drainage Report, submitted at the Sketch Plan Review
stage of the Planning Review process, is to identify and define conceptual solutions to storm
drainage problems which may occur on-site and off-site as a result of the proposed development.
In addition, those problems that exist on-site prior to development must be addressed during the
conceptual phase. For proposed projects that will have rural levels of development, the
Department of Public Works will review the site, surroundings, and proposed improvements and
advise the applicant as to what additional information, and/or engineering design may be required
for Change of Zone and Final Plat approvals.
A. All reports shall be typed on 8.5-inch by 11-inch paper and bound. Drawings
measuring 24 inches by 36 inches may be included,as needed. The drawings shall
be bound within the report or included within a pocket attached inside the back
cover of the report. The report needs to stand-alone, therefore, all important
reference material and supporting documents and calculations should be copied
and included within the report appendix. The report shall include a cover letter
presenting the conceptual design for review and shall be prepared or supervised by
2006-2538
PAGE 57 ORD2006-7
an engineer licensed in Colorado. Only original documents sealed in ink will be
accepted. The sealed report shall contain a certification sheet as follows:
1. "I hereby certify that this report for the conceptual drainage design of(Name
of Development) was prepared by me (or under my direct supervision) in
accordance with the provisions of the Weld County storm drainage criteria
for the owners thereof."
Registered Professional Engineer
State of Colorado No.
(Affix Seal)
B. Sketch Plan Drainage Report Contents. Sketch Plan Drainage Reports shall be
prepared in accordance with the following outline and contain the applicable
information listed:
1. General Location and Description.
a. Location.
1) Township, Range, Section, Quarter Section.
2) Local streets within, and adjacent to, the development.
3) Major open channels, lakes, streams, irrigation and other
water resource facilities within and adjacent to the proposed
development.
4) Names of surrounding developments including jurisdictions
(municipalities).
b. Description of Property
1) Area in acres.
2) Ground cover.
3) Major open channels and ownership.
4) General project description.
5) Irrigation facilities and ownership information.
6) Groundwater characteristics (where applicable).
2. Drainage Basins and Sub-Basins.
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a. Major Basin Description.
1) Reference to applicable Weld County or adjacent county
Master Drainage Plan(s).
2) Major basin drainage characteristics.
3) Identification of all irrigation facilities within 200 feet of the
property boundary.
4) Identification of all FEMA-defined 100-year floodplains and
floodways affecting the property.
b. Sub-Basin Description.
1) Historic drainage patterns on the subject property and
adjacent properties.
2) Off-site drainage flow patterns and impacts on the subject
property.
3. Drainage Facility Design.
a. General Proposed Concept.
1) Proposed concept and typical drainage patterns.
2) Compliance with off-site runoff considerations and
constraints.
3) Anticipated and proposed drainage patterns.
4) Identify all requests for variance from Weld County Storm
Drainage Criteria.
b. Specific Details.
1) Describe design storms and source of design storm depth
information (NOAANational Oceanic and Atmospheric
Administration Atlas, Urban Drainage and Flood Control
District maps, etcetera).
2) Drainage problems encountered and proposed solutions at
specific locations.
3) Maintenance access and aspects of the proposed design.
C. Sketch Plan Drainage Report Drawing Contents.
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1. A General Location (vicinity) Map shall be provided at a scale of 1" =2000'
or larger in sufficient detail to identify upstream off-site drainage areas
flowing into the proposed development and general drainage patterns.
2. A Drainage Plan of the proposed development shall be provided at a scale
from 1" = 100'or 1" = 200' on a 24"x 36" drawing. The plan shall show the
following information:
a. Existing contours at 2-foot maximum intervals, contours should
extend at least 200 feet from all project boundaries, or further if
necessary, to show upstream and downstream drainage
relationships impacting the proposed development.
b. Property lines, existing and proposed lot lines, and existing and
proposed easements.
c. Streets with names.
d. Existing drainage facilities, pipes, structures, irrigation facilities, and
sizes.
e. Overall drainage area boundary and sub-area boundaries.
f. Proposed flow directions using arrows.
g. Conceptual location of storm sewers, swales, open channels,
culverts, detention ponds, and other appurtenances.
h. Identification of outfall locations and receiving waters.
Location of all defined 100-year floodplains affecting the property.
j. Any other items so noted within the Drainage Report.
Section 8-11-120. Change of Zone Drainage Report.
The purpose of the Change of Zone Drainage Report is to identify and define preliminary
solutions to problems which may occur on-site and off-site as a result of the proposed
development. In addition, those problems that exist on-site prior to development must be
addressed during the preliminary phase.
A. All reports shall be typed on 8.5-inch by 11-inch paper and bound. Drawings
measuring 24 inches by 36 inches shall be included,as needed. The drawings shall
be bound within the report or included within a pocket attached inside the back
cover of the report. The Change of Zone Drainage Report needs to stand-alone,
therefore,all important reference material should be copied and included within the
report appendix. The report shall include a cover letter presenting the preliminary
design for review and shall be prepared or supervised by an engineer licensed in
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Colorado. Only original documents sealed in ink will be accepted. The sealed report
shall contain a certification sheet as follows:
1. "I hereby certify that this report for the preliminary drainage design of(Name
of Development) was prepared by me (or under my direct supervision) in
accordance with the provisions of the Weld County storm drainage criteria
for the owners thereof."
Registered Professional Engineer
State of Colorado No.
(Affix Seal)
B. Change of Zone Drainage Report Contents. The Change of Zone Drainage Report
shall be in accordance with the following outline and contain the applicable
information listed:
1. General Location and Description.
a. Location.
1) Township, Range, Section, Quarter Section.
2) Local streets within, and adjacent to, the development.
3) Major open channels, lakes, streams, irrigation and other
water resource facilities within,and adjacent to,the proposed
development.
4) Names of surrounding developments including jurisdiction
(municipalities).
b. Description of Property.
1) Area in acres.
2) Ground cover.
3) Major open channels and ownership.
4) General project description.
5) Existing irrigation facilities and utilities and ownership
information.
6) Groundwater characteristics (where applicable).
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2. Drainage Basins and Sub-Basins.
a. Major Basin Description.
1) Reference to Weld County Master Drainage Plan(s) where
applicable.
2) Major basin drainage characteristics.
3) Identification of all irrigation facilities and utilities within
200 feet of the property boundary.
b. Sub-Basin Description.
1) Historic drainage patterns on the subject property.
2) Off-site drainage flow patterns and impacts on the subject
development.
3. Drainage Design Criteria.
a. Regulations: Discussion of the optional criteria selected or the
deviation from the Weld County Storm Drainage Criteria, if any.
b. Development Criteria Reference and Constraints.
1) Discussion of previous drainage studies(i.e., project master
plans) for the subject property that influence, or are
influenced by, the proposed drainage design and how the
studies and plans will affect drainage design for the site.
2) Discussion of site constraints such as slopes, streets,
utilities, existing structures, and the proposed development
or site plan impacts on the proposed drainage plan.
c. Hydrological Criteria.
1) Identify design rainfall (source of design storm depth
information NOAANational Oceanic and Atmospheric
Administration Atlas, Urban Drainage and Flood Control
District maps, etcetera).
2) Identify design storm recurrence intervals.
3) Identify runoff calculation method(s) and any computer
models.
4) Identify detention discharge and storage calculation
method(s) and computer models.
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5) Discussion and justification of other criteria or calculation
methods used that are not presented in, or referenced by,
the Weld County Storm Drainage Criteria.
d. Hydraulic Criteria.
1) Identify capacity references and any computer models.
2) Identify detention outlet type.
3) Identify check/drop structure criteria used.
4) Discussion of other drainage facility design criteria used that
are presented in the Weld County Storm Drainage Criteria.
4. Drainage Facility Design.
a. General Concept.
1) Discussion of concept and typical drainage patterns for
historical conditions.
2) Discussion of compliance with off-site runoff considerations
and constraints.
3) Discussion of the content of all tables, charts, figures, or
drawings presented in the report.
4) Discussion of anticipated and proposed drainage patterns.
b. Specific Details.
1) Discussion of compliance with drainage criteria(street, inlet,
and pipe capacities, etcetera).
2) Discussion of drainage problems encountered and solutions
at specific design points.
3) Discussion of detention storage and outlet design.
4) Discussion of maintenance access and aspects of the
design.
5) Provide copies of Draft Colorado Department of Public
Health and Environment or State Engineer's permit
applications (where applicable).
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5. Conclusions.
a. Compliance with the Weld County Storm Drainage Criteria.
b. Drainage Concept.
1) Effectiveness of drainage design to control damage from
storm runoff.
2) Influence of proposed development on any applicable Weld
County Master Drainage Plan recommendations.
3) Identification and written approval of affected irrigation
company or other property owner(s). Weld County may
require that the applicant provide evidence that off-site
impacted jurisdictions have been notified of the proposed
drainage plans and potential impacts.
6. References.
a. Reference all criteria and technical information used.
7. Appendices.
a. Hydrology Computations.
1) Land use assumptions regarding adjacent properties.
2) Initial and major storm runoff computations at specific design
points.
3) Historic and fully developed runoff computations at specific
design points.
4) Computer model input and output.
b. Hydraulic Computations.
1) Culvert sizing.
2) Storm sewer sizing.
3) Street capacity evaluation.
4) Storm inlet sizing.
5) Swale sizing.
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6) Open channel sizing.
7) Check dam and/or drop structure sizing.
8) Detention pond area/volume capacity and outlet sizing.
9) Changes to Calculation Methods - If applicant/design
engineer modifies any portion of the Urban Drainage and
Flood Control District spreadsheets used for hydrologic or
hydraulic calculations, the applicant/design engineer shall
identify all changes to calculation assumptions or computer
programs as to type of change and specific factors that were
modified.
10) Computer model input and output.
C. Change of Zone Drainage Report Drawing Contents.
1. A General Location (vicinity) Map shall be provided at a scale of 1" =2000'
or larger in sufficient detail to identify upstream off-site drainage areas
flowing into the development, downstream areas receiving site flows, and
general drainage patterns in the project area.
2. A Drainage Plan of the proposed development shall be provided at a scale
from 1" = 100' or 1" = 200'on a 24" x 36"drawing. The plan shall show the
following information:
a. Existing contours at 2-foot maximum intervals, contours should
extend at least 200 feet from all project boundaries or further if
necessary to show upstream and downstream drainage relationships
impacting the development.
b. Property lines, lot lines, utility crossings, and easements.
c. Streets with names.
d. Existing drainage facilities, pipes, structures, irrigation facilities,and
sizes.
e. Overall drainage area boundary and sub-area boundaries.
f. Proposed contours and flow directions indicated with arrows.
g. Location of proposed storm sewers, swales, open channels,
culverts, cross-pans, and other appurtenances.
h. Proposed outfall point(s)for runoff from the development area and
facilities to convey flows to the final outfall point without damage to
downstream properties.
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Location and elevations of all defined 100-year floodplains and
floodways affecting the property.
j. Location and types of proposed permanent erosion control features.
Section 8-11-130. Final Drainage Plan Report.
The purpose of the Final Drainage Report is to update the preliminary design concepts,and
to present the design details for the drainage facilities discussed in the Change of Zone Drainage
Report. Also, any change to the preliminary concept shall be presented. The Final Drainage
Report shall identify all approved requests for variance from Weld County Storm Drainage Criteria.
A. All Final Reports shall be typed on 8.5-inch by 11-inch paper and bound. Drawings
measuring 24 inches by 36 inches shall be included. The Final Drawings shall be
bound within the report or included within a pocket attached inside the back cover
of the report. The Final Report needs to stand-alone, therefore, all calculations,
computer outputs, plans, supporting documents and important reference material
should be copied and included within the report appendix. The report shall include
a cover letter presenting the final design for review and shall be prepared or
supervised by an engineer licensed in Colorado. Only original documents sealed
in ink will be accepted. The sealed report shall contain a certification sheet as
follows:
1. "I hereby certify that this report for the final drainage design of (Name of
Development) was prepared by me (or under my direct supervision) in
accordance with the provisions of the Weld County storm drainage criteria
for the owners thereof."
Registered Professional Engineer
State of Colorado No.
(Affix Seal)
B. Final Drainage Plan Report Contents. The Final Drainage Report shall be prepared
in accordance with the outline shown above under Change of Zone Drainage
Report. In addition to including all of the items required for the report and plans
submitted with the Change of Zone described above under Change of Zone
Drainage Report and Drawings, the Final Drainage Report and Drawings should
include:
1. Proposed location and sizing of all storm sewers, swales, open channels,
culverts, cross-pans, and other appurtenances, including cross-sections of
swales and open channels.
2. Routing and accumulation of flows at various critical points for the minor
storm runoff.
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3. Routing and accumulation of flows at various critical points for the major
storm runoff.
4. Detention storage facilities and outlet works, including proposed 100-year
water surface elevations.
5. Location of all existing and proposed utilities.
6. Routing of off-site drainage flows through the development.
7. Minimum lowest opening elevations of residential and commercial buildings
above the 100-year water surface in streets, open channels, ditches,
swales, or other drainage facilities, as illustrated by the preliminary grading
plans.
8. Proposed on-site private and public drainage easements.
9. Proposed off-site private and public drainage easements.
10. Elevations of manhole and inlet inverts in relation to project datum.
11. Proposed water surface elevations for street encroachments for the minor
and major storm.
12. Critical hydraulic structure dimensions.
13. Orifice plate sizes.
14. Detention pond volumes.
15. All other critical hydraulic elevations.
16. Operations and Maintenance instructions for the proposed stormwater
drainage facilities.
17. Construction-Phase Erosion and Sediment control calculations.
18. Permanent Erosion and Sediment control calculations.
C. The Final Drainage Report design hydraulic calculations shall be provided for each
of the proposed elements of the final drainage design.
Section 8-11-140. Construction Drawings and Specifications.
A. Where drainage improvements are to be constructed in accordance with the
accepted Final Drainage Report, the signed and sealed construction plans (on 24"
x 36"mylar)and specifications shall be submitted in conformance with the Final Plat
for review and acceptance prior to construction. The sealed plans and
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specifications for the drainage improvements shall include all drainage components
designed within the Final Drainage Report.
B. The information required for the drawings and specifications shall be in accordance
with sound engineering principles, the Weld County Storm Drainage Criteria, and
the Weld County requirements for development and subdivision design.
Construction documents shall include geometric, dimensional, structural,
foundation, bedding, hydraulic, landscaping, erosion control, and other details as
needed to construct the storm drainage facilities. The accepted Final Drainage Plan
shall be included as part of the construction documents for all facilities affected by
the drainage plan. Submittal of digital format final plans and as-built drawings may
also be required by the Weld County Department of Public Works. Weld County
requires a minimum of three sets of paper construction plans for use by Weld
County inspectors.
C. Where erosion control and sediment control improvements are to be constructed
in accordance with the accepted Final Drainage Report, the erosion control and
sediment control construction plans(on 24"x 36"mylar)and specifications shall be
submitted in conformance with the Final Plat for review and acceptance prior to
construction. The plans and specifications for the erosion control and sediment
control improvements shall include all erosion control and sediment control
components designed within the Final Drainage Report.
D. Both construction-phase and post-construction (permanent) erosion control and
sediment control construction drawings shall be submitted. The construction-phase
erosion control and sediment control construction drawings shall be submitted
separately from post-construction(permanent)erosion control and sediment control
drawings. The construction-phase and post-construction phase erosion control and
sediment control construction drawings shall be the basis of compliance evaluations
by Weld County inspectors.
Section 8-11-150. As-built drawings.
A. Recording of Drawings.
1. The project record drawings shall be submitted to, and accepted by, Weld
County. Drawings will be submitted in appropriate digital form when
requested by the County.
2. Each drawing shall be labeled "DRAWINGS OF RECORD" in neat large
printed letters.
3. Construction information shall be recorded concurrently with construction
progress by the contractor.
4. Project Record Drawings shall be marked legibly and with an indelible pen.
5. Project Record Drawings shall record actual construction and contain, but
are not limited to, the following:
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a. Field dimensions, elevations, and details.
b. Field changes which are made by minor deviations to the design
drawings.
c. Details, which are not on the original Construction Drawings.
d. Elevations of manhole and inlet inverts in relation to project datum.
e. Critical hydraulic structure dimensions.
f. Orifice plate sizes.
g. Detention pond volumes.
h. All other critical hydraulic elevations.
g. Floodplain and floodway delineations and Base Flood Elevations
(BFEs)where applicable.
h. Dimensions of erosion control installations.
6. Payment of permit fees must precede final acceptance.
B. Submission.
1. The project record drawings shall be submitted to, and accepted by, the
Weld County inspectors with a transmittal letter containing the following:
a. Date.
b. Project Title.
c. Design Engineer's name, address, and telephone number.
d. Title and number of each Record Document.
e. The signature of the Design Engineer and their Professional
Engineering stamp.
2. The initial acceptance of the storm drainage improvements will not be made
until all Weld County installation requirements are satisfied and the Project
Record Drawings are received and accepted by Weld County.
3. Acceptance of storm drainage improvements will not be made until all on-
site drainage easements have been recorded. Acceptance of storm
drainage improvements will not be made until all off-site drainage easement
agreements have been signed and notarized.
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4. The final drawings of the storm drainage improvements will not be made
until the Project Record Drawings are received and accepted by Weld
County.
5. Weld County requires that the Project Record Drawings first be submitted
in blueline form for preliminary acceptance before final mylars are
submitted. Submittal of digital format final plans and digital format as-built
drawings may also be required by the Weld County Department of Public
Works.
BE IT FURTHER ORDAINED by the Board that the Clerk to the Board be, and hereby is,
directed to arrange for Colorado Code Publishing to supplement the Weld County Code with the
amendments contained herein, to coincide with chapters, articles, divisions, sections, and
sub sections as they currently exist within said Code; and to resolve any inconsistencies regarding
capitalization,grammar,and numbering or placement of chapters,articles,divisions,sections,and
sub-sections in said Code.
BE IT FURTHER ORDAINED by the Board if any section,subsection,paragraph,sentence,
clause, or phrase of this Ordinance is for any reason held or decided to be unconstitutional, such
decision shall not affect the validity of the remaining portions hereof. The Board of County
Commissioners hereby declares that it would have enacted this Ordinance in each and every
section, subsection, paragraph, sentence, clause, and phrase thereof irrespective of the fact that
any one or more sections, subsections, paragraphs, sentences, clauses, or phrases might be
declared to be unconstitutional or invalid.
The above and foregoing Ordinance Number 2006-7 was, on motion duly made and
seconded, adopted by the following vote on the 23rd day of October, A.D., 2006.
BOARD OF COUNTY COMMISSIONERS
WELD COUNTY, COLORADO
ATTEST:
M. J. Geile, Chair
Weld County Clerk to the Board
David E. Long, Pro-Tem
BY:
Deputy Clerk to the Board
William H. Jerke
APPROVED AS TO FORM:
Robert D. Masden
County Attorney
Glenn Vaad
2006-2538
PAGE 70 ORD2006-7
First Reading: September 11, 2006
Publication: September 20, 2006, in the Fort Lupton Press
Second Reading: October 2, 2006
Publication: October 11, 2006, in the Fort Lupton Press
Final Reading: October 23, 2006
Publication: November 1, 2006, in the Fort Lupton Press
Effective: November 6, 2006
2006-2538
PAGE 71 ORD2006-7
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