HomeMy WebLinkAbout20042138 PRELIMINARY DRAINAGE REPORT
GLORALOMA ESTATES, PUD
WELD COUNTY, COLORADO
General Location and Description
A. General Location
The site is part of the Southeast Quarter of Section 9, Township 2 North, Range 67
West of the 6th Principal Meridian, Weld County, Colorado. The site is bordered
on the north by agriculture, on the east by Weld County Road (WCR) 19, on the
south by WCR 22, and on the west by agriculture.
B. General Description
The existing site contains 105 acres +1-, and its land use is currently agricultural.
Although the existing site is recorded as one lot, it is physically divided into two
tracts of land by the combination of the Coal Ridge Ditch Alignment and a 30-foot
wide strip of land that is part of a Recorded Exemption filed in 1962 (see the
Preliminary Plat included with the Change of Zone submittal for further details).
As indicated on the plat, Tract A is to remain open space with agricultural uses and
facilities for the existing Gloraloma Ranch hone farm. As Tract A is to remain
undeveloped, its historical drainage patterns will not be impacted by the proposed
development. Because Tract A does not contribute runoff to the proposed
development, it is not part of this drainage analysis.
The portion of the site to be developed(hereafter referred to as "the site") contains
approximately 69 acres and is currently open space used by the Gloraloma Ranch
horse farm. The topography of the site drains toward the northwest corner with
slopes ranging from 1% to 4%. Currently the site's soil consists of an overlay of
topsoil, silty sand, silty clayey sand, and sandy lean clay. Various boring locations
indicated the soils are underlain by claystone and siltstone bedrock at depths of 6'/2
to 25 feet. There are no major storm drainageways in place to control the current
storm runoff from the site. The Coal Ridge Ditch irrigation lateral crosses the site
at the northwest corner. Community Panel No. 080266-0867 C—that would have
illustrated the site—was not printed since the area is located in Zone C, according
to the Flood Insurance Rate Map (FIRM) for Weld County, Colorado, Map Index
for Community Panel Numbers 080266 0001-1075, dated September 27, 1991.
Accordingly, the site is not located in the 100-year floodplain.
2004-2138
C. Proposed Subdivision
The proposed development will have 20 residential lots with an average lot size of
2.3 acres, while the remainder of the site shall remain open space with equestrian
trails, landscaped buffers, and stormwater management facilities. This will result
in a gross density of one lot per 3.5 acres. There will be three access points to the
site: two access points will be off WCR 19, and the third will be at northwest
corner providing access to the oil/gas wells and the equestrian facilities located on
Tract A. Paved roads and soft-surface trails throughout the site will provide
connectivity between the lots.
II. Drainage Basins and Sub-basins
A. Major Drainage Basin Description
Due to the existing topography and drainage basins of the properties adjacent to
Gloraloma, off-site flows will not impact the site adversely. Along the eastern
boundary of this site, WCR 19 forms the equivalent of a ridgeline. The property
east of WCR 19 drains east to northeast and the Gloraloma site historically drains
west or northwest. The 45-acre parcel of land west of the proposed development is
graded away from the site and towards two lakes located within that parcel. The
lakes also receive the discharge from the adjacent property south of WCR 22. This
off-site discharge from the adjacent property to the south is captured by the Bull
Canal located immediately north of WCR 22 and is conveyed west and then north
to the lakes. The small parcel of land (owned by others) located at the southeast
corner of the site drains towards WCR 22 and its runoff is captured by the Bull
Canal. The adjacent property north of Gloraloma has an area of approximately 15
acres consisting of row crops that drain south to southwest. Historically, as this
off-site drainage reaches Gloraloma's northern boundary, it turns west and then
flows towards the Coal Ridge Ditch at the northwest corner of the proposed
Gloraloma development. The off-site flow from the north does not enter Coal
Ridge Ditch but rather continues flowing west along the toe of the ditch's built-up,
southern bank.
The majority of the discharge from Gloraloma (Basins El, E2, and E3) currently
flows north to northwest toward the northern boundary. Upon reaching this
boundary, it joins the flow from the property to the north and follows the historical
flow path to the west. The remainder of the discharge from the site (Basins E4 and
E5) flows towards the lakes located in the adjacent property on the west. The
proposed development will provide detention ponds at the historical outfalls of
Basins El, E2 and E3. These ponds are sized to detain the developed 100-year
storm event (see Table 4) and will release at the historic 5-year release rate (see
Table 1). In order to prevent the developed flow from traveling along the
historical flow paths of Basins E4 and E5 and entering the adjacent 45-acre parcel
to the west, a retention pond will be constructed according to the retention pond
design criteria specified in the Urban Storm Drainage Criteria Manual.
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B. Sub-Basin Description
Sub-basins for the proposed development were determined from the grading plan,
layout of the roads, and other factors that determine basin size and shape. The
sub-basins are shown on the Preliminary Drainage Plan (Appendix 2) along with
the proposed detention and retention ponds.
III. Drainage Design Criteria
A. Regulations/Development Criteria
The criteria for the site are to detain the developed 100-year stormwater runoff and
release it at a 5-year historic discharge rate. The Urban Storm Drainage Criteria
Manual, (USDCM, published by the Urban Drainage and Flood Control District—
Denver, Colorado), as well as good engineering practices, have been used to
calculate the stormwater runoff and design the stormwater facilities for this site.
B. Hydrological Criteria
The design storms used were the 5-year for historic discharge and the 100-year for
developed discharge. Since the sub-basins are less than 90 acres, the Rational
Method was used to calculate historic and developed stormwater runoff.
Intensity/duration/frequency curves were developed using the procedure described
in Volume I of the USDCM to obtain the rainfall data used for each storm
specified. A composite runoff coefficient (C) value was calculated based on the
average lot size and assumptions of how each lot would be developed (see Table
2). The retention and detention ponds were sized using the Modified FAA Method
as described in the USDCM,Volume I.
C. Waivers/Variance from Criteria
No waivers or variances are requested at this time.
IV. Wetland Preservation and Mitigation
There are no jurisdictional wetlands located on this property.
V. Drainage Facility Design
A. General Concept
Proposed drainage patterns for the site will be similar to the historic flow paths.
The stormwater from the site will be routed to detention ponds throughout the site
by the proposed ditches and storm culverts. From the detention ponds, the
stormwater will be discharged to a historic flow path at an attenuated rate.
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B. Specific Details
The 5-year historic and 100-year developed discharges were calculated and are
summarized in the tables in Appendix 1. Since the developed discharge is greater
than the historic discharge, detention ponds will be constructed with a release rate
equal to or less than the 5-year historic rate. Pond spillways will be designed to
provide a point for controlled release in the event the outlet structures become
plugged. The retention pond was sized in accordance with Volume 2 of the
USDCM's specifications for retention facilities. Table 4 summarizes pond
volumes required for the routed sub-basins.
C. Conclusions
When developed, the site's runoff will be increased. Detention ponds throughout
the site will control the increased runoff from the site. The detention ponds will
detain the 100-year flow from the developed condition and discharge it at the 5-
year historic rate. The design of the proposed drainage facilities will not adversely
affect adjacent sites and is consistent with the historic flow patterns of the site.
VI. Stormwater Quality Considerations
A. General Concept
,r.
The stormwater management plan (SWMP) will be in accordance with good
engineering, hydrologic, and pollution control practices. The main objective of the
plan is to identify the best management practices (BMP) that, when implemented,
will meet the terms and conditions set by federal, state, and local agencies. The
plan will identify potential sources of pollution that may reasonably be expected to
affect the quality of stormwater discharges associated with the construction
activity from this site. In addition, the plan will describe the implementation of
BMP that will be used to reduce pollutants in stormwater discharges associated
with the construction activity.
B. Specific Details
1. Overlot clearing of the areas to be disturbed will consist of topsoil stripping
and sub-grade preparation for fill or cut, as required by the grading plans.
2. Installation of erosion-control devices will include silt fencing, diversion dikes,
temporary seeding, and outlet-control protection in the stormwater
management areas.
3. Rough sub-grade will be obtained for building foundations, roads, ponds and
landscaped areas.
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4. The utilities, the paving operations, and finally, the permanent ]materials
handling completed for the site.
5. The contractor will be responsible for identifying and specifying materials
handling and spill-prevention control, including, but not limited to, exposed
materials such as fertilizers, chemicals, waste piles, and equipment
maintenance and fueling areas.
C. Conclusions
During construction, non-stormwater components of discharge are not expected.
The project will irrigate some common open areas and common landscaping
elements of the project. We expect that small amounts of irrigation discharge will
occur during the end of construction and following construction activities. Final
stabilization will be achieved by the contractor's final vegetative cover installation
following fmal grading procedures. The contractor will be responsible for
establishing a healthy stand of grass or vegetative cover where specified.
VII. References
The Urban Storm Drainage Criteria Manual, published by the Urban Drainage and
Flood Control District,Denver, Colorado, June 2001.
VIII. Appendix 1
A. Vicinity Map Page 7
B. Table 1—Historic Runoff Page 8
C. Table 2—Developed Basin Characteristics Page 9
D. Table 3—Developed Runoff Page 10
E. Table 4—Storm Water Pond Sizing for 100-year Event Page 11
IX. Appendix 2
A. Existing Drainage Map (24x36) Pocket 1
B. Preliminary Drainage Plan (24x36) Pocket 2
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APPENDIX 1
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PICKETT ENGINEERING, INC. VICINITY MAP
808 8TH STREET
GREELEY, COLORADO 80631
PH: 970.356.6362 FAX: 970.356.6486
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Table 1
Historic Runoff 1
5x OYeAeim , CMnneitM ', 4:w �" IntmaRY% nalb 4r SYar.. 100 YMr; )
BMMI M.('cm). '. CS 0100 - 'Length(11) Sine 1%) Ta(min) -tenni on stogie I%), . '4(min) ' '1.(mhI P11 Pt,,, .= Maui (IMO Mane Ws) Runoff His)
El. 16.28 0.08 0.35 500 1.54 35.71 1309.00 1.42 28.15 82 1.35 2.55 1.31 2.56 1.7 14.7
18.09 0.06935 275 3.02 21.21 1500.00 1.45 29.88 51 1.35 2.65 1.50 2.94 2.2 18.6
280 3,13 2115 1495.00 190 25.82 47 1.35 2.65 1.56 3.10 1.7 14.7
E4 '' 14.88 0.08935 265 1.46 2646 870.00 1.23 18.88 45 1,35 265 1.62 3.18 19 18.8
E8 5.58 0.08 0.35 350 1.59 29.56 43000 0.98 10.45 40 135 265 1.75 3.43 as 8.7
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CO
TABLE 2
Developed Basin Characteristics
Total Lot Acreage= 69ac
Number of Lots = 20
Avg.Lot Size = 2.3ac
Approx.Open Space= 15 ac
imperviousness 6 Year"C" 100 Year it"
Residential Lot Areas Size(Acts) (%) Ccetikbnt .CoeMckart
pasture 1.000 0 0.08a35
llerrt 0.030 90 0.73 0.81
Raise and Driveway 0.070 90 0.73 0.81
.`,,Paved Road. 0.044 100 0.90 0.96
Graveithoufrre ts 0.015 40 0.30 0.50
Uirdevebped. 1.141 2 0.09 0.36
Total B Weighted Average 2.300 7 0.13 0.39
`.Ynparviousness 6 Year 7C" .100 Year"C"
Open Space Areas size(Acres) ' (%) Coellicient CaeRcient
Undeveloped 14.560 2 0.09 0.36
Paved Road 0.330 90 0.73 0.81
Gravel Shoulders 0.110 40 0.30 0.50
.^ Total 8 Weighted Average 15.000 4 0.11 0.37
Calculated "C" 5-year. C5= 0.13
100-year. C100= 0.39
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Table 3
Developed Runoff
' - „•lengthFlWs) Flow%
Main. -Mae ° Ce _ Cl®"' 08', 'Len91h`QQ 1%)? 1}mf) •'kngBC(8) ,. `9kpa(%)` "Ti(mln)' ;(mle)' �. P1y.; -P1wo (�hr), ;"(Inbr) -(em) (eh).
81. 9.41 0.13 0.39 420 1.0 38 1359 1.7 12 47 135 2.65 1.8 3.1 1.9 11.3 l
,.:.82.,... 972 0.13 0.39 350 1.2 31 935 1.7 B 39 1.35 285 1.8 3.5 2.3 13.3 l
83{ 3.00 0.13 0.39 320 3.4 21 430 2.8 3 24 1.35 2.65 2.4 4.7 0.9 5.5
3.88 0.13 0.39 350 2.9 23 810 2.5 4 27 1.35 2.65 2.2 4.3 1.1 6.2
85 10.42 0.13 039 250 3.8 18 1420 19 12 29 1.35 265 2.1 4.1 2,9 18.9
",`84' 9.09 0.13 0.39 310 2.9 22 560 1.3 5 27 1.35 265 2.2 4.3 2.8 15.4
'87 10.82 0.13 0.39 410 2.0 28 610 1.4 8 34 1.35 2.65 19 38 2.7 15.8
1.47 0.13 0.39 25 2.0 7 510 1.2 5 12 1.35 2.85 33 6.5 08 3.7
89 ' 4.55 0.13 0.39 340 1.5 28 575 0.8 7 35 1.35 2.65 1.9 3.7 1.1 8.8
810, 2.43 0.13 0.39 390 1.0 35 0 0.1 0 35 1.35 2.65 1.9 38 06 3.6
811 2.89 0.13 0.39 350 1.0 33 0 0.1 0 33 1.35 2.85 20 39 0.7 4.1
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Table 4 )
Storm Water Pond Sizing for 100-year Storm Event based on Modified FAA Method from USDCM Volume 2
,,, :� o .a t t at01ag!
i Contributing .,_, �'1 Routed,4 r yWm 100 Year VRequlnd yL .
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Pond `:Basins_ -TotalArea(acre) -` , 0100 t_`", (min). , P1e,' _ `P14; ,, pnlhr)'t Runolft(ofs) :Away- 'Description .�
':1 B1a 22.13 0.39 47 1.35 2.65 3.10 26.7 6.16 Retention Pond
-- -2 `° 84,86,&810 15.20 0.39 36 1.35 2.65 3.67 21.7 1.64 Detention Pond
*3 BB&B11 13.11 0.39 33 1.35 2.65 3.87 19.8 1.33 Detention Pond
-,_,`4. S7&BB 12.09 0.39 34 1.35 2.65 3.80 17.9 1.23 Detention Pond
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APPENDIX 2
Wetland and Rare Species Evaluation
Gloraloma Subdivision rn�
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Prepared For:
Pickett Engineering, Inc.
808 8th Street
Greeley, CO 80631
Prepared By:
Wildland Consultants,Inc.
1001 Jefferson Drive
Berthoud, CO 80513
March 2003
1.0 Introduction
The proposed Gloraloma Subdivision is located in Weld County in Section 9, Township 2
North, Range 67 West. The site is bordered by Weld County Road 22 on the south,
Weld County Road 19 on the east, and agricultural land on the north and west. Figure 1
shows an aerial view of the project area. Attachment A includes site photographs. The
site has been farmed in the past. It is currently being used for horse pasture.
Wildland Consultants, Inc. completed a field reconnaissance of the site on March 14,
2003 to evaluate the potential for wetlands and threatened and endangered species.
2.0 Vegetation and Wetlands
The vegetation on the site is dominated by weeds and seeded grass. Common species
include Russian thistle(Salsola kali), kochia(Kochia scoparia), mustard(Descurania
spp.), and seeded grasses (brome grass, wheatgrass). There are no areas of native
grassland on the site.
A drainage swale runs across the northwest corner of the site. This area supports a
riparian-like grove of plain's cottonwood (Populus deltoides)trees.
Based on our field reconnaissance there are no jurisdictional or non jurisdictional
wetlands within the development boundaries. The drainage swale does not have wetland
hydrology or wetland soils. The drainage swale is not considered a wetland as defined by
the Army Corps of Engineers wetland delineation manual (Army Corps of Engineers
1987).
ZUSGS 4rTh N of Denver, Colorado United States UYSS:, 1999
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Figure 1. Aerial View,Gloraloma Development
3.0 Threatened,Endangered, and Special Status Species
There are no known locations of rare plants on or near the development site (System for
Conservation Planning 2003).
There are no wetland or riparian zones on the site that provide potential habitat to the
federally listed Ute ladies' tresses orchid (Spiranihes dilivualis). This rare orchid occurs
along streams and associated wetlands that flow into the South Platte River(U.S. Fish
and Wildlife Service 1992). The pond adjacent to the site and the drainage swale are not
directly connected to the South Platte River system.
The area around the drainage swale and another low area just east of the drainage swale
provide marginal potential habitat to the federally listed New Mexico butterfly plant
(Gaura neomexicana). This annual plant occurs in sub-irrigated, alluvial soils of
drainage bottoms in Weld County (Spackman et. al 1997).
The site supports 2 small black-tailed prairie dog colonies. The approximate location of
the colonies is shown in Figure 1. The exact colony boundaries have not been
determined. Black-tailed prairie dogs are not currently under federal protection but have
been petitioned to be listed as a threatened of endangered species.
The prairie dog colonies provide potential nesting sites for the burrowing owl. The
burrowing owl is not federally listed but is protected under the Migratory Bird Treaty
Act. The owl nests in prairie dog colonies in Weld County.
The prairie dog colonies and overgrazed pasture also provides potential nesting habitat to
the mountain plover. Known locations for the mountain plover in Weld County are
associated with or near areas that support native shortgrass prairie. However, according
to current guidelines the development site provides potential habitat for this species (U.S.
Fish and Wildlife Service 1999). The mountain plover is proposed to be listed as a
threatened or endangered species.
There cottonwood grove on the site is isolated from other drainages and tributaries to
local streams. Because of this the grove does not provide good potential habitat to the
federally listed Preble's meadow jumping mouse.
The site is mapped as part of winter range for bald eagles (System for Conservation
Planning 2003). The large cottonwood trees around the adjacent reservoir and along the
drainage swale may provide occasional day roosting areas for wintering bald eagles.
There are no mapped or known bald eagle night roosts on the site. The small prairie dog
colonies provide potential foraging areas for wintering bald eagles. There are no bald
eagle nests near the project site.
The cottonwood grove associated with the drainage swale in the northwest corner of the
site provides potential nesting habitat to several species of raptors. One nesting pair of
great horned owls was observed within this cottonwood grove during the field
reconnaissance.
4.0 Conclusions, Recommendations
Project development will result in no impacts to jurisdictional or non jurisdictional
wetlands. No permits from the Army Corps of Engineers should be required for project
construction. Permit
Surveys of the site for the Ute ladies' tresses orchid should not be required, the site does
not provide potential habitat to this rare plant. Surveys of the site for the Colorado
butterfly plant should be completed during the summer blooming period. However, the
likelihood of the plant occurring on the site appears to be low.
Surveys for burrowing owls in the prairie dog colonies should be completed prior to any
ground disturbance or removal efforts if these activities occur between March 1 and
October 31 (burrowing owl activity period)(Colorado Division of Wildlife 1999).
Surveys for nesting mountain plover should be completed on the site according to U.S.
Fish and Wildlife Service guidelines. Surveys should be completed during the spring-
early summer breeding and nesting period.
The cottonwood grove on the site provides quality wildlife habitat, including nest sites
for raptors and a variety of passerine birds. If possible the development design should
avoid disturbance of the cottonwood grove.
5.0 References
Colorado Division of Wildlife. 1999. Survey Guidelines for Burrowing Owls.
Spackman, S., B. Jennings, J. Coles, C. Dawson, M. Minton, A. ICratz, and C. Spurrier.
1997. Colorado Rare Plant Field Guide. Colorado Natural Heritage Program.
System for Conservation Planning. 2003. Data Search for Gloraloma Site. Colorado
Natural Heritage Program.
U.S. Army Corps of Engineers. 1987. Corps of Engineers Wetlands Delineation Manual.
U.S. Fish and Wildlife Service (USFWS). 1992. Interim Survey Requirements for
Spiranthes diluvialis. 8 pp.
U.S. Fish and Wildlife Service. 1999a. Interim Survey Recommendations and Guidelines
for Surveys for Preble's Meadow Jumping Mice. Colorado Field Office. Denver, CO.
U.S. Fish and Wildlife Service. 1999. Mountain Plover Survey Guidelines. Colorado
Field Office.
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e••••••.
attarhment A —Site Photogrcodiraphs
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Photo 1. View of Cottonwood Grove to North.
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Photo 2. View of Prairie Doe Colony to North.
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