HomeMy WebLinkAbout20162249.tiffRESOLUTION
RE: APPROVE ADOPTION OF WELD COUNTY PARKWAY DRAINAGE MASTER PLAN
WHEREAS, the Board of County Commissioners of Weld County, 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 has been presented with a proposed Weld County Parkway
Drainage Master Plan, on behalf of the Department of Public Works, and
WHEREAS, after review, the Board deems it advisable to adopt said plan, a copy of which
is attached hereto and incorporated herein by reference.
NOW, THEREFORE, BE IT RESOLVED by the Board of County Commissioners of Weld
County, Colorado, that the Weld County Parkway Drainage Master Plan be, and hereby is,
adopted.
The above and foregoing Resolution was, on motion duly made and seconded, adopted
by the following vote on the 18th day of July, A.D., 2016.
BOARD OF COUNTY COMMISSIONERS
WELD COUNTY, COLORADO
ATTEST: dittev
Weld County Clerk to the Board
Mike Freeman Chair
Sean P. Conway, Pro -Tern
tal
ozad
AP
Kirkmeyer
ty Attorney.�-
Steve Moreno
Date of signature: 7/ /'3O\Co
r?� Pw(a), A6(6e.)
1- rs-Zollo
2016-2249
EG0073
MEMORANDUM
TO: Clerk to the Board
DATE: July 13, 2016
FROM: Elizabeth Relford, Transportation Manager
SUBJECT: Adoption of Weld County Parkway Drainage
Master Plan
In July of 2015 Weld County received a Tier 1 ($200,000) Energy and Mineral Impact Assistance
grant from the Colorado Department of Local Affairs to evaluate the opportunities to develop a
regional drainage master plan for the Weld County Parkway, which extended along WCR 49 to
WCR 50. As stated in the grant application: "This project involved developing a master storm
drainage plan for an area where growth is expected in unincorporated Weld County at the
confluence of the South Platte and Cache la Poudre Rivers." As you know, this area incurred
severe damage from the September 2013 Flood and was inadequately protected from future
storm events.
While the project area consisted of 11.5 square miles, the study area involved 37 square miles.
In May of this year, the Commissioners were provided an electronic copy of the draft Drainage
Master Plan. The draft report was also posted on the Public Works website (currently on the
Engineering page) and on May 11th Public Works hosted a public open house that land owners
in the area were invited to attend and comment. The Planning Department provided referral
comments, which were incorporated into the plan along with comments of Public Works staff.
The drainage master plan provides a project list for the County to implement storm drainage
improvements to reduce peak flows, mitigate flooding, and protect people and property. While
the plan identifies many potential detention ponds, the recommended near -term improvements
include installing culverts under driveways on the south side of WCR 60.5 east of WCR 49 and
replacing culverts under WCR 49 at WCR 60.5, and under WCR 52 just west of WCR 47. These
facilities are low -impact, in existing right-of-way, and will alleviate existing issues.
Existing drainage issues affecting the Project area will be exacerbated as development progresses
upstream and in the areas of the Parkway and WCR 49. By appropriately planning and
implementing improvements prior to and concurrently with development, existing and potential
drainage issues can be remedied. Therefore, Public Works recommends adoption of the Weld
County Parkway and WCR 49 Corridor Master Drainage Plan. I am available to answer any
questions you may have.
2016-2249
Farnsworth
Master Drainage
Plan for the Area
surrounding Weld
County Parkway
June 2016
Table of Contents
ail apter '1 introduction 3
1.1 Authorization ... 3
1.2 Purpose and Need ,,...,...*.
1.3 Baseline Information .,..,rrr .
1A Design Procedures .-5
1.5 Previous Studies 6
Chapter 2 Acknowledgements 11
Chapter 3 Project Area Description t12
3.1 Location 12
3.2 History .....12
3.3 Rivers and Creeks .....16
Chapter 4 Hydrologic Modeling ..19
4.1 General 19
4.2 Watershed Description af.,,r.r .19
4.3 Design Rainfall 22
4A Subcatchment Characteristics 24
4.5 Hydraulic Parameters 29
4.6 Irrigation Ditches t.29
4.7 Culverts .._ 30
4.8 Detention Ponds --.35
4.9 Summary of Historical Conditions •• • • 35
4.10 Summary of Existing Conditions 35
411 Summary of Proposed Conditions ,..... f. r, + 51
4.12 Near -Term Improvements 90
Chapter 5 Analysis of Improvement Alternatives 92
5.1 General ..92
5.2 Summary of Drainage Improvement Alternatives 92
5.3 Criteria for Drainage improvement Alternatives a.. , 92
5.4 Cost Estimates..92
5.5 Alternatives Considered,95
5.6 Cost -Benefit Analysis a. , ., r r 95
Chapter 6 Summary and Recommendations ......103
Appendices:
Appendix A - Study Area Soils Information
Appendix B - Info WMM Schematic Drawings
Appendix C - Relevant CFI FPM Sheets
Appendix D - Existing and Proposed Reference Drawings
Appendix E - HY-8 Results and Culvert Designs
Appendix F - Floodplain Report
Appendix G - Model Results
Appendix H - Estimated Construction Cost Summaries
Appendix I - Miscellaneous Weld County Maps
Appendix J - Survey Photographs
Appendix K-- Public Meeting Information
Q
Chapter 1 Introduction
41 A Authorization
Weld County (County) has contracted Farnsworth Group, Inc. (Farnsworth Group) to complete a
regional drainage master study (study) for the area surrounding the newly constructed Weld
County Parkway (Parkway) and the future widening of Weld County Road (WCR) 49 south of
the Parkway. The Parkway is an extension of the WCR 49 Corridor, which extends from U.S.
Highway 34 south to Interstate 76. The Parkway significantly improves traffic flow through the
County and provides an additional crossing over the Cache La Poudre (Poudre) and South
Platte Rivers. The Parkway was completed and opened to the public in November of 2015; the
WCR 49 Corridor improvements are not anticipated to be complete until 2017.
This Study addresses and provides regional solutions to existing drainage issues, as well as
solutions to mitigate potential future issues in this area of the County. The Project area,
including the Parkway and WCR 49, is shown below in Figure 1.
Weld County Parkway and WCR 49 Regional Master Drainage Plan Project Area
Figure 1 Project Area, Parkway, and WCR 49
Page 3 of 103
1.2 Purpose and Need
The purpose of this Study is to provide the County with the information need ea to make
stormwater management decisions, especially concerning the Parkway and the WCR 49
Corridor. This information includes a list of stormwater management and drainage
improvements recommended to reduce peak flows, mitigate flooding, and protect people and
property. Specifically, the study includes the following:
1) Identification of existing irrigation facilities
2) Review of existing data/previous studies
3) Review of existing survey and topography
4) Ground survey
5) Baseline modeling, including:
a. Stormwater modeling -- InfoWMM
b. Floodplain modeling — HEC-RAS
c. Localized culvert modeling — HY-8
6) Identification of significant flooding and drainage issues
7) Capital improvement plan (ClP)/Stormwater management alternatives
8) Estimated construction costs
9) Water quality features
10) Hydraulic analysis and conceptual designs
In this area of the county, staff have observed or been notified of areas of localized flooding.
The design of the Parkway did not include an overall drainage master plan for the entire Project
area; the design only considered local drainage. Therefore, drainage facilities were designed
based on limited data. The lack of available data has brought attention to the existing drainage
patterns and problems within the Project area.
This Study focuses on an area of approximately 11.5 square miles (Project area). The Project
area includes the immediate and surrounding area of the Parkway, as well as WCR 49
extending south from U.S. Highway 34 to WCR 50. In order to determine the extent of offsite
drainage impacting the Project area, a broader 37 square mile Study area was evaluated. With
the exception of the entire Lone Tree Creek Watershed, the Study area encompasses the
Project area, as well as surrounding areas that drain to the Project area.
Existing drainage issues affecting the Project area will be exacerbated as development
progresses upstream and in the areas of the Parkway and WCR 49. By appropriately planning
and implementing improvements prior to and concurrently with development, existing and
potential drainage issues can be remedied.
1.3 Baseline Information
information used for this Study included:
• Mapping and survey information
• Natural Resources and Conservation Service (FRCS) soils map for Weld County
• Flood Insurance Studies (FIS) and Digital Flood Insurance Rate Maps (DFIRM), updated
in 2016.
• Various drainage reports within the Study area provided by Weld County.
Page 4 of 103
1.3.1 Mapping and Survey
Mapping information utilized for this Study included:
• Aerial images using the most recent imagery from Google Earth (Google, 2014);
• Post -flood aerial topographic LIDAR was performed by Photo Science under contract
to the United States Geological Survey (USGS) for the area within the South Platte
watershed in Colorado. From the LIDAR, a raster DEM M with 5 -foot cells was developed
for watershed modeling purposes.
o The accuracy of the topographic mapping was evaluated by an independent
survey of ground points (Compass Data).
o Survey Project Specifications:
• Accuracy: 3 cm RMSEz (6 cm 1195)
• Coordinate System: NAD 83 (2011)
• Vertical Datum: NAVD 88 (Geoid 12A)
• Projection: UTM and Colorado State Plane
• Zone: 13 North
• Source: Photo Science, 2014, Report of Survey — Ground and Quality
Control Points, South Platte River, Colorado Flood LFDAR, prepared for
USGS, January 31, 2014.
O Additionally, Farnsworth Group's in-house surveying team surveyed structures
and other important features within the Project area. Farnsworth Group's
survey team was not able to collect survey data for all structures due to
unwilling or unresponsive property owners. The Civil 3D files of surface data
used for design of the new Parkway were provided by the county's consultant
on the Parkway design. All survey and design data was incorporated into one
raster which served as the base for watershed modeling. As the widening of
WCR 49 south of the Parkway is still in the design phase, this surface data
could not be incorporated into the raster. Therefore, County staff directed that
existing conditions of the road be utilized to complete the Study.
Farnsworth Group's survey group took photos of a l l surveyed structures and
completed a visual analysis of the structures' general condition. These
photographs are provided in Appendix J.
• Weld County is currently completing a design for replacement of the WCR 53 bridge
that crosses the South Platte River. The project is in the early stages of design and is
not ready to be incorporated into the HEC-RAS river model.
1.4 Design Procedures
Design procedures and parameters used in the Study follow those recommended by Weld
County in the RFP. Computer models and design guidelines include the following:
• I nfoSWrv1M (Version 14.0)
• HE -1 (Version 4.1)
• HY-8 (Version 7.30)
• Civil3D (2015)
• Arcview GIS (Version 10.3)
Page 5 of 103
• Flowfvlaster (Bentley — Version v8i)
• Weld County Public Works, April 2012. Weld County Engineering and Construction
Criteria.
• Weld County, Colorado. Charter and County Code Chapter 23, Article 12.
• Colorado Department of Transportation, 2004. CDOT Drainage Design Manual.
* Urban Drainage and Flood Control District, 2016. Urban Storm Drainage Criteria
Manuals (1— 3).
• USGS, 2014. USGS — Regional Regression Equations for Estimation of Natural
Streamflow Statistics in Colorado.
• USGS PeakFQ (Version 7.1)
• Colorado Water Conservation Board (CWCB), September 2008. Colorado Ploodplain
and Stormwater Criteria Manuals, Volume di & 2.
• City of Greeley, January 2008. Design Criteria and Construction Specifications — Section
,11— Stormwater Drainage.
• Urban Drainage and Flood Control District, December 2010. User Manual for Cost
Estimator for Master Planning (UD-MP Cost), Version 1.1.
• Shannon & Wilson, Inc., November 19, 2013. + eotechnical Report — Weld County Road
49 Extension Project, Weld County, Colorado.
1.5 Previous Studies
Previous studies related to stormwater management within our Project area, along with
floodplain studies include:
• The County's design consultant for the Parkway performed a drainage design and
prepared a drainage report for the Parkway area. The drainage design was only for the
area directly adjacent to the Parkway.
O Atkins and Bohannan Huston. 2013. Weld County Road 49 Extension, Roadway
Improvements Project, Final Drainage Report.
O Atkins. 2013. Weld County Road 49 Extension, Roadway Improvements Project,
Design.
• The County's design consultant for the Parkway performed two floodplain studies for the
project. They are as follows:
O Cache La Poudre River Bridge — See Figure 2 below:
• We received the digital HEC-RAS model for the design of the Poudre
River Bridge, but did not receive acopy of any writtenreport to reference.
The design was completed by Atkins.
O South Platte River Bridge — See Figures 2 and 3 below:
• Atkins. 2014. Weld County Road 49 Extension (South Platte River)
Conditional Letter of Map Revision (CL OR) Application.
• Colorado Department of Transportation (COOT) had a CLOMR submitted for the
permanent flood repairs performed following the 2013 flood. This Study was performed
only for a section of the South Platte River. See Figure 4 below:
Tsiouvaras Simmons Holderness Consulting Engineers. 2014. Conditional Letter
of Map Revision US -34 and US -34D Permanent Flood Repairs.
• Weld County Public Works. 2015. Weld County Road 49, Parkway Drainage — Retention
Ponds (At Intersection of Highway 34 and WCR 49). See Figure 5 for Pond Design.
Page 6 of 103
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Figure 2: Image from Atkins 2014 South Platte CLOMP Application - Showing General Areas of Poudre
and South Platte River Bridges
Page 7 of 103
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Page 8 of 103
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Figure 5: Plan Views of Parkway Retention Form's,
Page 10 of 103
Chapter 2 Acknowledgements
Farnsworth Group wishes to acknowledge the various individuals who assisted in the preparation
of this Master Drainage Study. The following Weld County staff provided extensive guidance and
knowledge that made this Study possible:
• Mike Bedell, PE — Senior Engineer
• Don Dunker, PE — Weld County Engineer
• Clay Kimmi, PE — Senior Engineer
• Elizabeth Relford — Transportation Manager
In addition, residents of Weld County provided insight concerning specific problem areas following
storm events. A public meeting was held on May "I 1, 2016 at 6:30 PM at the Weld County
Administration Building (1150 O Street, Greeley, CO 80631) to present the findings and results of
the Study. A summary of those in attendance at the meeting is presented in Appendix K.
The following members of the Farnsworth Group project team have contributed in the preparation
of this Study.
S
*
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Cundall, PE — Engineering Manager
Brian Zick, PE — Senior Engineering Manager
Scott Turner, El — Project Engineer
Austin Snow, El — Project Engineer
Rob Lauer — Project Designer
Jack Lowery — Senior Designer
Dave Berglund, PLS — Senior Land Surveyor and Team Leader
Xuehua Bai, PE — Bai Engineers
Page 11 of 103
Chapter 3 Project Area Description
3.1 Location
he Project area is iocated east of the City of Greeley and west of the Town of Kersey, in
unincorporated Weld County. The Parkway roughly bisects the project, and crosses both the
Poudre and South Platte Rivers. Figure 6, on the following page, identifies the Project area in
relationship to these rivers,
The Project area begins at the intersection of WCR 60.5 (formerly SH 263) and Fern Avenue,
then heads south to US 4. It then turns east past the Peterbilt Truck Center and neighboring
storage yard, and then heads south until WCR 50. From there, the boundary runs approximately
one-half (1 /) mile east of the WCR 49 and WCR 50 intersection, then turns north until WCR 58.
The boundary runs along WCR 58 until it intersects WCR 53, where it turns north until reaching
WCR 60 5. From here the boundary runs along WCR 605 until it reaches the starting point at
WCR 60.5 and Fern Avenue.
3.2 History
The Project area has historically been utilized for agricultural purposes, primarily cuhivatea
farmland. There are also several large feedlots and dairies in the vicinity. The County as a
whole has experienced a substantial increase in oil and gas production in recent years. The
confluence of the South Platte and Poudre rivers is also located within the Project area.
There are also six irrigation ditches located in the Project area, as follows:
• Ogilvy
• Plumb and Dailey
• Patterson
• Latham
• Gilmore
• East Neres Canal
The Study area is mostly "flat", which can inhibit proper flow of drainage due to low velocities
and local depressions. Because the watershed is rural, sto rmwz to r infrastructure is lacking.
Farm fields generally drain to roadside ditcieE w; county roads and railroads act as per ms that
channel runoff to field corners or low spots. Culverts are commonly used in these locations to
drain across roadways. Any ponded water eventually evaporates or infiltrates.
....1 WCR 49 Corridor
In 2014, Weld County began construction on the WC Parkway as part of the larger WCR 49
Corridor project. The intent of the project is to provide improved connectivity from the
middle/north portions of the county south to 1-76. The Parkway portion of the project, which
extends from WCR 49 and Highway 34, north and west to WCR 47 and WCR 60.5, was
completed in November, 2015. The portion of WCR 49 between Highway 34 and 1-76 is
currently under construction.
Page 12 of 103
3.2.2 Recent Flooding
In 2013, during the second week of September, Weld County and other areas along the
Colorado Front Range experienced a major flooding event following several days of heavy rain.
A large number of agricultural parcels, roads, and bridges were damaged andlor mined as a
result of flooding in the South Platte. Figures 7-9 display damage to WCR 53, which is the
eastern edge of the Project area. Figure 10 displays a breach of Highway 34.
The 2013 flood was of a greater magnitude than what is commonly experienced in this area.
However, this area has experienced smaller flooding events many times in the past. Because of
the flow paths of the South Platte and Poudre Rivers within the area, flooding has historically
and consistently occurred near the confluence of the rivers during spring runoff and rainy
months.
The Project area is located across FE MA Weld County DFIRM I R M Panels with Map Number —
0812 C and the following Community Numbers — 154 E, 1561 E, 1565E, 1575E, 1544E, 1563E,
1735C, and 1775E. The relevant OF I RMs are located in Appendix Ci
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Figure 7: Extent of 2013 Flood in area of WCR 53 (photo from Weld County Facebook site)
Page 14 of 103
Figure 8: Extent of 2013 Flood in area of WCR 53 Bridge (photo from Weld County Facebook site)
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Y.p'•A s, ilsts'l t .-" '^ •�' L+! 2•• .rt _+. I v 1. r'. y,
• r T,.'4711.i. y Lic:• •'•ti..r• a.: .. • t �•r, l: , • r , �:
1. :
• AO
1
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•
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,1444•♦ 7• •
,S
'1-1"'„4114, .
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♦r'
Figure 9: W R 53 Bridge after 2013 Flood, (photo from Weld County Facebook site)
Page 15 of 103
Figure 10: Area of Highway 34 that breached as a result of 2013 South Platte River flooding. (photo from
Weld County Facebook site)
33 Rivers and Creeks
In addition to the Poudre and South Platte Rivers, Sand Creek and Lone Tree Creek are also
present in the Study area. Limited information is available regarding the properties and flow
rates of these creeks. Based on aerial imagery, Sand Creek originates from water diverted out
of the Greeley Canal No. 3.
floodplain analysis for each of the two rivers was completed as part of this Study using H B -
1 ; however, the Study's intended use focuses on storm events affecting the Project area as
opposed to flooding related to the river floodplains. See Appendix F for the full Floodplain
Report.
3.3.1 Lone Tree Creek
Lone Tree Creek is a tributary of the South Platte River whose headwaters originate in
Wyoming. It joins the South Platte downstream of its confluence with the Poudre River. No
published flow rates or hydraulic models were identified for Lone Tree Creek. As a detailed
hydrologic and hyd raul no analysis for the creek is outside the scope of this Study, regression
equations from the LISGS -- Regional Regression Equations for Estimation of Natural
, treamfow Statistics in Colorado, 2014 were used to determine peak flow rates for different
Page 16 of 103
storm recurrence intervals. The Study area is located in the "Plains Hydrologic Region" in the
aforementioned USGS publication. The regression equations for this region are provided in
Figure 11.
Peak Streainflow Equations for Plains Hydrologic Region
Generalized rsquaacs i tSp regress ion_ 69 swims
Approximate range of prafider variables
A: 05-2:930 square miles ancl 6.P1OO: 2.4-5A inches
1s =
=
1v'regx,#n
106% it 5? .
1FIS #59 gir
10(I' 444ice 64,11:1)
ion St 143 ti
x.00 .41.
1`' An"
SEP= 183.
SEP= 142.
EP = 136.
,SEP 137_
SEP 139.
SEP= 141_
SEP= 160.
SEA= 141_
ps ok = 40,
p:i
FelidOR2 = 58,
pseud ` = 62,
pseudi = 64,
pseuds _ 65
pseudoR2 = 65
pseudoR2 = 70.
5atE = 174,
SWE = 134,
air = 128,
= 128,
= 129,
SAE = 1.31.
ATE =14, and
128.
Figure 11: U - Plains Hydrologic Region -Regression Equations for Estimation of Natural Streamflow
Statistics in Colorado, 2014.
Using this method, the storm event and subsequent flow rates in Lone Tree Creek were
calculated and are provided in Table 1.
Table 1: Lone Tree Creek Calculated Flow Rates Utilizing 018GS Regional Regression Equations
Storm
Return
Period
,
Peak Flow Rate (cis)
2 -year
280
5 -year
827
10year
33.'I
..........
•... •. ..
25 -year
. __ .._ _._.._ •......... _
.1_, • ..... _.......... _.
2A80
i
50 year
I
3,483
•
1OO-year j
4,936
L
500 -year jj
9,347
These storm events were compared to USGS peak flows recorded at USGS Station No.
06753990 — Lone Tree Creek near Greeley, CO. However, only seven years of data is
available, and as such, a true comparison is impossible. Reviewing the station data, the largest
peak flow recorded was only 477 cfs, The 100 -year flow rate calculated with the regression
equations was 4,936 cis. This presents a substantial difference, but is the best result achievable
with the available information. The locations of stream gages are shown in Figure 12, below.
Page 17 of 103
1
l
WELD COUNTY PARKWAY - MASTER DRAINAGE PLAN
DRAINAGE PLAN AREA %MTH AREA USGS STREAM GAGES
u i31CCU . S
V?ALN CREEK. AT
�OUT I NEAR
P ATTEVILLE, OD
Figure 12: USGS — Gaging Stations
Chapter 4 Hydrologic Modeling
4.1 General
Hydrologic modeling was performed using Innovyze InfoSWMIW software. This software is a
comprehensive hydrologic, hydraulic, and water quality simulator that is fully integrated with
Arcl* The computational engine utilized in the case of this product is the U.S. Environmental
Protection Agency Storm Water Management Model (EPA SWMM). In this manner, models
developed using I nfoSW MMt can be exported to, and processed in, EPA SWMM.
The EPA SWMM engine generates storm hydrographs for each subcatchment and routes them
through various conveyance elements. Of the three routing methods available (steady -flow,
Kinematic Wave, and Dynamic Wave), Dynamic Wave routing was utilized. This routing method
solves the one-dimensional saint -'tenant equation, which includes flow continuity in conduits
and at junctions, as well as momentum within channels. As a result, Dynamic Wave routing
includes the effects of channel storage, surcharged conduits, backwater, flow reversal, and
entrance/exit losses; greatly increasing model accuracy. It comes at the expense of having to
use shorter time -steps (a one minute time step was used) to reduce continuity error, resulting in
increased model run time. As this is a relatively small study and limited to the analysis of three
storm events, the benefits of Dynamic Wave routing far outweigh the slightly diminished run
speed.
For this study, the 10-, 50-, and 100 -year storm events were considered. Three models,
including the Historical Conditions, Existing Conditions, and Proposed Conditions, were
developed.
nfo W M® contains a flexible set of hydraulic modeling capabilities used to route runoff
through a network of pipes, channels, storage/treatment units and diversion structures. These
include the ability to:
• Use a wide variety of standard and open conduit shapes, as well as natural channels
• Model special elements such as storage/treatment units, flow dividers, pumps, weirs,
and orifices
• Apply external flows and water quality inputs from surface runoff, groundwater interflow,
infiltration/inflow, and user defined inflows
• Choose between unifier flow, kinematic wave, or full dynamic wave flow routing methods
• Model various flow regimes, such as backwater, surcharging, reverse flow, and ponding
4.2 Watershed Description
As discussed in Section 1.2, for the development of this Study, a watershed larger than the
Project area was analyzed to account for off -site drainage (study area). The Study area was
divided into ten major basins and designated as follows:
• Railroad
• Kersey
• South Platte
• Parkway
Page 19 of 103
• Poudre
• Eaton
• Sand Creek
• Lone Tree Creek
• Airport
• WCR 53
The major basin delineation is shown in Figure 14; model schematics are provided in Appendix
B. Generally, runoff generated north of the Poudre River will drain southeast until ifs intercepted
by the river. The northeast region of the study area will drain southeast until intercepted by Lone
Tree Creek or the Poudre River. Between the Poudre and South Platte Rivers, roughly half of
the subcatchments drain north to the Poudre, and the other half east to the Platte. The
southern -most portion of the Study area primarily drains north into a Union Pacific Railroad
track. The tracks cause this runoff to channelize and flow east towards Kersey. Figure 13
provides a general depiction of the railroad tacks.
Figure 13: Union Pacific Railroad Tracks Extending East
Page 20 of 103
rAt •J -"OS r'
As the Project area is located in a rural region, there is little stormwater infrastructure. Borrow
ditches and cultivated fields are the primary conveyances for runoff. However, these facilities
cannot accommodate large flow rates generated by major storms. Given that many of the fields
slope at less than 1%, an elevation difference between a roadway crest and surrounding field of
a few feet can cause many acres to become inundated and retain water* While water ponding
against roadways is not ideal, it does serve to detain water and attenuate flows within basins. In
many of these locations, the storage effect provided by an elevated roadway is insufficient to
detain all runoff. Additionally, some locations were void of outlets (it roadway culvert) or
contained inadequate outlets to drain water from the fields. As such, there are several locations
where runoff will pond and eventually overtop the roadway (these locations are discussed in
section 4.10).
4.3 Design Rainfall
The Study area is rural and located outside of the Urban Drainage and Flood Control District
(UDFCD) boundary. Therefore, the Colorado Urban Hydrograph Procedure (CUHP) method
cannot be utilized for developing a rainfall distribution. Furthermore, an in-depth hydrological
statistical analysis for determining a design rainfall distribution is outside the scope of this Study.
Given the Project area proximity to the City of Greeley, Farnsworth Group utilized the design
storm distributions published in the City of Greeley Storm Drainage Criteria and Construction
Specification Volume II (Figure 15).
According to the Weld County Engineering & Construction Criteria, Section 5.4.3:
"Where development is proposed in larger watersheds, design hydrology should use longer
storm durations appropriate for the size and time of concentration of the entire watershed,," For
watersheds between 10 and 20 square miles, a 3 -hour design storm distribution is
recommended. As the Project area is 11.b square miles, a -hour distribution was utilized.
Page 22 of 103
1
DESIGN STORMS FOR GREELEY
INOREME TAI. RA 11/41FALi DEPTH/RETURN PERIOD
TI l E
(MIN) !
BASINS LESS S THAN ISO. . MILES
BASINS BETWEEN 5 AND 10 SO. MILES
ASINS BETWEEN 10 AND 20 SO. MILES
r 2-YR
(irti
15- T Ri i
(in) I
10- i rr'i
(in)
I -'Y`fl
(in)
10 i_ YR i
in) I
2.=w [R
fin)
I, = YR I
(in) I
10- I R
fn)
I S- i R
On)I
I WO- YR
(in )
2-YA 1 5-Y R
' 10- R 1
5- R 1
;MVKV -Y R
On) I (in)
On) 1 (in) i
(in) I
5
0.02 'x,03
0.04
40.0'1 0.03
0.02
0.103 0.04 U.UO
0.03
,x.02 0.03
0.'C4 0.63
0.{
0.04
0.09
0,15
0.06
0.13
0..21
0.07 0.09
0,14 0,13
0.24 0.20
0,08
0.13
0.22
0.04 € 0.06
0.07
0.09 0.08
0,04
0.06 (107 0.09
0.08
10
0.09 { 0.13
0.14
0.13. 0.13
0.09
0.13 0.14 0.13
0.13
15
-
0,171 0.23
0.20
0.20 0.22
20
25
0,16
0,22 0,25 0,20•
0,22
0.26: 0.37
044
0.38 0.39
0.25
0.36 0.42 0.36
0.37
0.23 ,
0.34
0.40 0.34
035
0.14
007`
0,05
0.19 0.20 0.50
0.09 0.01 0.29•
0,07 0.08 0.20
0.67
0.37
0.22
0.15 0.19
0.21
0.83 0.70
0.13
0.17
0.19 0.57;
0.63
30
0.07
0.05
0.09
0.07
0.10 0.27
0.08 0,20:
0.35
0.22
35
40
45
50
55 ..
0,07! 0.09
' 0,05' 0,07
0,10
0.08
0,30 0.39
020 0.22
0.03
0.03
0.03
0.05
0,05
0,05
0.07 0.13
0.06. 0.08:
0.06 0.08:
i
0.17
0.14
0.11
1 0.03 0.05
0.07
0.13 0.17
0.03
0.03
0.03
0.05 0.07 0.13
0,05 0,0$ 0.08
0.05 0.06 0.06{
0.17
0.14
0.11
0.03: 0.05
0.03 0p05:
'
0.0€:
0.06
0.08 0.14
0.08 0.11
0.03
0.03
0.05
0,05
0.06 0.08
0.06 0.06'
0.11
0.11
0.03" 0.05
0.0€ .
0.08 0.11
' 0.03
0.05 0.06 0.08
0.11
85
70
0.Oi3. 6.05
• 0.02 0.05
0.06
0.06.
0.06: 0.11
0.06 0.06.
0.03
0.05 0.06 0,06
0.11
0.02E
0.05
0.06 0.06
0.06
0.02
0.05 0.06 0.06;
0.06
0.02'
0.04
0.06 0.05
0,06
75
0.02 0.04
0.06
0.05 0.06:
0.02
0.04 0.06 0.05.
0.06
80
85
0.02;
0.03
0.04
0.05 0.03-
0.02{
• 0.02
0.03 0.04 0.01
0.03 0.03 0.04
0.03
0.03
0:02
0.03
0.04 0.05
0.03
0.02:+
0.03
0.03 0.04
0.03
0.02
003 0,03
0.€34 0.03
0.02
0.03 0.03 0.04
0.03
0:021
0.03
0,03 0.04
0,03
90
D, 0i
O.Q 0.03.
0.04 0.03.
0.02'
0.02.
0.03
0.02
0.03 0.04:
0.03 0.04:
0.03
0.03
0.02
; 0.02
0.02
I
- 0.022
0,01
0.03 0.03 0.04
0.02 0.03 0.04
0.02 0.03 0.04
0.02 0.03 0.04
002 0.03 0.014
0.03
0.03
0.03
0.03
O03
0.02E
0.02
0, 03
0.02
0,03
0.03
0.041 0.03.
0.04 0.03
95
100
105
0.02
0.02
0.03 0.04,
0.03
0.02,
0.02
0.03
0.04 0.031
0.02.
0101
0,02
0.02
0,03 0.04
0.03 0,04
0.03
0.03
110
115
12t
1 6, 0 12
0.02
0.03.
46,63
0,04 0.03
0,01
0,02
0.04' 0.031
0.01
0.02
0,02 0.04
0.03
0.01
0.02 0.02 0.04 0.03
! 0.01
0.02 0.02 0.04
0.03
0.{11
0.01
0.02 0.02'
0.02
i
125
130
135
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0; 02!
0.01
0.01
0.02
0. 02
0.01
140
0.01
0.01
0.01
0.01
0.01 0.01
0.01 0.01
0.01
0,01
145
150
0.01
0.01
0.01 0.01
0.01
155
0.01
0.01
0.01 0.01
0.01
160
165
0.01
0.01
0.01 0.01
0.01
0.00. 000
0.01 0.0o
01.01
170
175
180
0.{ 0 - 0.00E 0.00 0, 00
0401
0.010• 6.001 0.00 0.00
0.01
TOTAL4
1,2u. 1.72 2.04 2.81 3.21
1.18.
1.69 2.00 2.76 3.15
1.24 1.73 2.05 2.79 3.22
P Iaren^a
'aid Tracey, RI
-
Precipitation-Freque y Analysis. of the Western United States
(I AA Atlas) Volume I!I - Colorado 1973
G -reel cey
Great. ham the Ground Up.
PUBLIC WORKS DEPARTMENT
SORMWATER MANAGEMENT DIVISION
ism OW MIR" COMM IIOU1
STORM DRAINAGE DESIGN AND
TECHNICAL CRITERIA
TABLE 3-1
SCALE: NTS
REVISED MARCH 2007
Figure 15: City of Greeley Storm Drainage and Technical Criteria, Section 3.0 — Table 3-1: Design Storms
for Greeley.
Page 23 of 103
4.4 Subcatchment Characteristics
4.4.1 Subcatchment Delineation
The InfoSWMNIsSubcatchment Manager Tool was used to automatically delineate
subcatchment boundaries and determine subcatchment area based on the Digital Elevation
Model (DEM) generated from the post 2013 flood LiDAR. The subcatchments delineated by
Info WMl ' were then reshaped, merged, or split using Info W AM® and ArcGIS tools, until an
appropriate watershed delineation was achieved. In addition to basin delineation, the
Subcatchment Manager was used to calculate subcatchment slope and width (subcatchment
area divided by overland flow length) by extracting information from the DEM.
The ten major basins discussed in Section 4.2 were further split into a total of 106
subcatchments, ranging in size from less than 1 acre, to over 900 acres, with an average area
of 221 acres, Subcatchments were delineated to provide discharges at points such as: existing
drainage facilities, natural channels, roadways (WCR 49 and the Parkway in particular), and
potential areas of flooding. Figure 16 displays the subcatchment delineation within the major
basins.
Page 24 of 103
I
INS
EAT
fp tic
'OLDIE BASE
osl
CREEK BASIN
Figure 16: ubcetchrn of Delineation Within Major Basins
—RAILROAD OAD EAE. I Ir
LEGEND
a.
. o
1
i
r
i
I
Page 25 of 103
4.4.2 Imperviousness
ubcatchment imperviousness is based on land use, and was determined from the most recent
aerial photography (Google Earth, 2014). Table 6-3 of the UDFCD manual, Volume I, Runoff
chapter (UDFCD, 2016) provides percent imperviousness values based on land use, see Table
. For agricultural land use, a 2% imperviousness is recommended. As agriculture is the
predominant land use, most subcatchments in the existing conditions model were assigned a
3% imperviousness. The increase from 2 to 3% is to account for roads, homesteads, oil and gas
pads, eta, that are scattered throughout the subcatchments. A thorough area -weighted average
imperviousness was calculated for those subcatchments containing larger developments and
more diverse land uses (industrial and commercial developments, airports, etc.).
For the Historical Conditions model, a 2% imperviousness was applied to all subcatchments, ents, To
account for potential development in the vicinity of the Parkway and WCR 49, a 60%
imperviousness was assumed for 1,000 feet on both sides of WCR 49, extending north through
the Parkway and along WCR 47. These imperviousness values were used in the Proposed
Conditions model.
Page 26 of 103
Table 2: UDFCO Manual Volume 1, Chapter 6.0 Runoff — Table 8-3: Recommended Percentage
Imperviousness Values,
Land
Surface Characteristics
Use or
Percentage
Imperviousness (%)
Business:
Downtown Areas
95
Suburban Areas
75
Residential:
Single-family
1
15 acres or larger
12
0.75
2.5
20
acres
. ` - . aurae
30
0.25 acres or less
45
Apartments
75
Industrial:
Light areas
80
Heavy areas
90
Parks, cemeteries
10
Playgrounds
25
Schools
55
Railroad yard areas
50
Undeveloped
Areas:
Historic flow analysis
2
Greenbelts, agricultural
Off -site flo ► analysis (when land
I use not defined)
4
Streets:
Paved
100
Gravel (packed)
40
Drive and walks
90
Roofs
90
Lawns,
sandy soil
2
Lawns, clayey soil
Page 27 of 103
4.4.3Infiltration and Depression Storage
Soil information for each subcatchment was obtained from the Natural Resource Conservation
Service (NRCS) Web Soil Survey, and is provided in Appendix A. For infiltration calculations,
soils are designated as belonging to either hydrologic group A, B, C, or D. Type A soils exhibit
the highest infiltration rates, while Type D exhibit the lowest infiltration rates. For subcatchments
bcatch me nts
containing more than one soil hydrologic group classification, an area -weighted average was
calculated. Within Arc l , the "intersect" tool was utilized to split the NRCS soil shapefile pefile along
subcatchment boundaries. This allowed the total area of a particular soil hydrologic group within
a subcatchment to be calculated exactly. All hydrologic groups are found in the Study area, with
Types A and B dominating.
For this Study, Horton's infiltration model was implemented. Table 6-7 of the UDFCD manual,
Volume I, Runoff chapter (UDFCD, 2016) provides parameters for use with this equation based
on the soil hydrologic group, and are shown in Table 3, below. The parameters consist of initial
and final infiltration rates, as we l l as a decay coefficient.
Table 3: UDF O Manual, Volume 1, Chapter 640 Runoff Table 6-7: Recommended Horton rs Equation
Parameters
NRCS Hydrologic
Soil Group
Infiltration (inches per hour) I
Decay
Initial—fj
Find —f,
Coefficient —,a
A
5.0
1.0
011007
B
4.5
0.6
0.0018
C
3.0
0.5
0.0018
D
3.0
03
0.0018
Depression losses include the combined effect of vegetation and small, scattered surface
depressions that ca ptu re water and prevent it from running off. Recommended depression
losses for pervious and impervious areas were taken from Table 6-6 of the UDFCD manual,
Volume I, Runoff Chapter, shown below in Table 4. Within each subcatchment, impervious
areas were assigned depression losses of 0A inches; pervious areas were assigned depression
losses of 0.4 inches.
Page 28 of 103
Table 4: UDFCD Manual, Volume 1, Chapter 6,0 Runoff — Table 6-6, Typical Depression Losses for
Var'rt'.ue Land Covvre.
Land Cover
Range in Depression (Retention)
Recommended (in)
impervious:
Large paved areas
0.0 - 015
OA
Roofs -flat
OA - 0.3
0.1
Roofs -sloped
0.05 - 0.1
0.05
Pervious:
Lawn grass
0 - 0.5
0.35
Wooded areas and open fields
0.2 0.6
0.4
4.5 Hydraulic Parameters
I-nfo WMM utiiizies a network of links and nodes to convey flow through the model. Links
consist of conduits and weirs; relevant nodes include junctions and storages units. Conduits are
used to model flow in natural and manmade channels, as well as through storm sewers and
culverts. Input criteria for conduits includes length, shape, dimensions (or channel width and
maximum depth), and Manning's roughness. Conduit slope is based on the upstream and
downstream junction elevations. Weirs were utilized to model overtopping at roadways and
spillways for several storage units. Input criteria for weirs includes type (transverse, sideflow, ' -
notch, or trapezoidal) crest elevation, spillway height, length, discharge coefficient, and side
slope (if any).
Storage units were utilized extensively to model the effects of water backing up at roadways,
water ponding at culverts, and as retention/detention ponds for flow attenuation. Input
parameters for a storage unit includes invert elevation, maximum depth, infiltration rate, and a
depth -area curve.
4.6 Irrigation Ditches
i here are a number of active, semi -active, or abandoned irrigation ditches and canals Within
Weld County. These irrigation facilities were originally designed with flat slopes and lirni.te'd flow
conveyance capacities to convey irrigation water to farmers, settlers, and other users. Because
the canals and ditches were usually designed to traverse watersheds, many of these facilities
have historically intercepted storm runoff from the upstream rural and agricultural type basins.
As discussed in the Colorado Water Conservation Board (CWCB), Colorado Floodplaln and
Stormwater Criteria Manuals, Volume #' & 2, September 2008: "Since irrigation facilities are not
designed and constructed to safely convey storm runoff flows, they should not be used as outfall
points for storm drainage systems, unless it can be proven safe through appropriate detailed
engineering analysis and the facility owner's written consent can be secured, since the owner%
liability from ditch failure increases with the acceptance of storm runoff, the responsibility should
be clearly defined before a combined system is approved,"
Page 29 of 103
Further, "In evaluating the interaction of irrigation ditches with a major drainage way for the
purpose of basin delineation, the ditch should not be utilized as a basin boundary due to the
limited flow capacity of the ditch. Also, the ditches will generally be flowing full or near full during
major storms and, therefore, the tributary basin runoff would flow across the ditch. Drainage
analysis should assume that an irrigation ditch does not intercept the storm runoff from the
upper basin and that the upper basin is tributary to the basin area downstream of the ditch.,,
Therefore, irrigation ditches were largely ignored in the hydrologic models.
4.7 Culverts
Culverts are used in a variety of ways in a drainage system, including but not limited to:
• Limit the discharge from a specific area
Convey a natural drainage way under a newly constructed roadway
• As outfalls for detention ponds
When sizing and deciding upon placement of a culvert, the following must be considered:
• Allowable headwater depth to diameter ratio. County Criteria establishes H*W/D=2.
• The upstream and downstream effects of restricting ONE any) discharge.
• The extent of roadway overtopping during design storms. According to Weld County
Engineering and Construction Criteria:
O► 6 -Inches of overtopping is allowed for the 10 -year storm
O 18 -Inches of overtopping is allowed for the 100 -year storm
o Weld County staff stated that overtopping of the Parkway and WCR 49 was
designed not to occur in a 100 -year storm event.
• Minimum velocity requirement of 3 ftls (as noted in UDFCD CD Manual Chapter 11) to
prevent sedimentation in the culvert, The flat topography in the Project area makes this
a difficult criteria to meet. In some instances, the minimum velocity► will not be achieved
and the County wi l l have to perform scheduled maintenance to remove sediment and
debris.
• Most suitable pipe material for culvert application. Typical materials are as follows:
o Corrugated Metal Pipe (CMP)
O Coated CMP
o Reinforced Concrete Pipe (RCP)
Typically C M P or RCP are used when placed under a roadway. For the purposes of this study,
conceptual designs and cost estimates were completed based on the use of RCP.
Concentrated discharge and turbulence at culvert inlets and outlets present a challenge to
erosion and scour control; generally, outlet velocities greater than 5 ft/sec require downstream
outlet protection. The following are common methods used to protect the culvert and channel at
inlets and ou#falls:
• Flared end section
• Toe wa l l
• Headwall
Page 30 of 103
• Wingwall
• Riprap apron
Low tailwater basin
• Grouted boulders
Impact basin
Typically a riprap apron or grouted boulders are used in conjunction with some combination of
the first four (4) of the above list to control scour. Figure 17 shows a culvert that was
constructed as part of the Parkway project and displays some of these features. For the
purposes of this Study, riprap aprons are planned and included in the conceptual designs and
cost estimates.
Culverts, both existing and proposed, were included in the hydrologic models. Additionally, each
of the culverts in the model was analyzed using HY-8, a Federal Highway Administration
(FHWA) Culvert Analysis Program (FHWA 2009). Existing culverts were analyzed for Existing
Conditions flow rates; proposed culverts were analyzed based on the attenuated developed flow
rates from the Proposed Conditions model, Existing culverts not proposed to be replaced by
detention ponds were also analyzed based on the developed condition flow rates; only culvert
C-2 showed overtopping during the 50 -year and 100 -year storm events, at depths of 0.17 and
0,20 feet, respectively — both within the criteria for acceptable overtopping depth, Table
provides a summary of existing culverts, and Tables 6-7 provides a summary of HY-8 results.
Full results are provided in Appendix E.
Figure 17: Example Culvert with Riprap Apron and Flared End Section
Page 31 of 103
Table 5: Existing Culvert Datat
Culvert
ID
LengthInlet
(ft)
Elevation
Invert
-
(ft)
Outlet
Invert
Elevation
. ft)
Slope
(ft/ft)
Type
. Shape
Dimensions .
Width
Y
Height
Otel
125.0
4633,7
4631.4
0,018
RCP2
Elliptical
6.3
4
C-2
100.0
4630.6
4630.0
0.006
RCP
Circular
2.5
--
--3
45.0
4631.9
4631.8
0.003
RCP
Circular
1.5
--
C-4
6O.O
4612,6
4612.5
0.002
CM P3
Circular
1.5
--
C-5
88.7
4604.4
4604.2
0.003
RCB4
Box
20
9
C-6
120.1
4619.6
4619.2
0.004
RCP
Circular
2
--
C-7
221.1
4621.0
4615.8
0,024
RCP
Circular
1.5
--
C-8
57.0
4621.0
4620.8
11002
RCP
Circular
2
--
C-9
145,0
4621.5
4621.2
04 001
RCP
Circular
2
--
C-10
125.0
4627.0
4626.5
0.004
RCP
Circular
2
....
4628.2
4627.8
0.003
RCP
Circular
2.5
--
1.15.1
4625.7
46251
0.004
RCP
Circular
2
--
-1
C-13
444.0
4618.3
4617.5
0.00.
RCB
Box
10.5
6.3
-14
x.80.8
4634.6
4634.3
0,002
CMP
Elliptical
4,45
248
-15
195.9
4637.4
4637.3
0.0001
CMP
Elliptical
4.45
2.8
16
1'351
463445
4634.5
0.0001
RCB
Box
8
4
4642.0
4641.5
0.009
RCP
Circular
2
--
C-1
50.0
4642.0
4641.5
0.016
RCP
Circular
2
--
C-19
65, 0
4638.5
4629.5
0.138
C
M P
Circular
2
--
C-
0
65,0
4634.5
4633.5
0.015
RCP
Elliptical'
3.8
2.2
-
1
45.0
4631.8
4631.4
0.009
RCP
Elliptical
2.2
1.6
67.0
4760.0
4758.9
0.017
CMP
Circular
4
--
&23
90.0
4633.3
4633.2
0.001
RCP
Circular
1.5
--
C-24
75.0
4676.7
4675.9
0.011
RCP
Circular
2.5
--
C-25
1 47.0
4658.3
4668.0
0.007
CMP
Elliptical
2
1.5
C-26
1 110.0
_-_ 4628.5
4627.0
0.014
RCP
Elliptical
3.8
2.2
Notes:
'Not All Culverts Analyzed Were Used in SWMM M Model
2Reinforced Concrete Pipe
3Corrugated Metal Pipe
4Reinforced Concrete Box
'Culvert C-20 consists of 4 barrels
Page 32 of 103
Table 6: Existing Conditions H Y-8 # esu/ts
Culvert
ID
SWMM
Input
10 -year
Event
50 -year Event
100 -year
Event
(CFS)
Input
Flow
Outlet
Velocity
(ft/s)
Outlet
Depth
(ft)
Overtopping?
Overtc
in
?
Overtopping
Depth
eft
Input
(CFS)
Flow
Outlet
Velocity
(mss)
Outlet
Depth
(ft)
P
Overtopping?
pP 9
Overtopping
Depth n
Input
(CFS)
Flow
Outlet
Velocity
(Ws)
Outlet
Depth
(ft)
Overtopping?
?
Overtopping
Depth
(ft)
C-1
JCT-131
92.10
13.13
1.48
--
--
157.58
14.93
2.05
--
--
177.41
15.37
2.21
--
--
0-2
JCT-211
4.17
8.92
0.37
--
--
14.86
11.90
0.75
--
--
21.25
12.93
0.92
--
--
C-3
JCT-172
1.06
3.01
0.38
--
--
6.06
5.16
0.95
.
--
8.27
5.90
1,11
--
--
C-4
CDT
-59
4.39
2.69
0.16
Yes
0.05
30.11
2.90
0.17
Yes
0.21
52.69
2.93
0.18
Yes
0.31
C-5
JCT-209
51.66
4.40
0.59
--
--
93.77
5,34
0.88
--
107.36
5.57
0.96
--
--
C-7
CDT
203
4.49
7.92
0.54
--
Air Me
8.86
9.36
0,79
-
12.56
10.10
0.99
--
--
C-8
CDT
-161
4.40
4.21
0.73
--
--
838
5.18
1.04
--
--
12.41
5.93
1.26
--
--
C-9
CDT
-160
3.07
2.54
0.82
--
--
6.43
3.72
1.08
• --
--
9.33
4.56
1.24
--
--
C-10
JCT-203
0.81
2.69
0.30
--
--
1.34
3.03
0.40
--
--
1.86
3.30
0.47
--
--
C-11
JCT-201
3.17
3.65
0.58
--
--
5.14
4.18
0.74
--
--
5.86
4.33
0.79
--
--
C-12
CDT
-200
19.08
7.21
1.57
--
--
19.92
7.39
1.60
--
--
20.04
7.41
1.61
--
--
C-17
CDT
-229
7.91
5.64
0.63
--
--
26.28
7.32
1.11
Yes
0.03
32.34
7.67
1.25
Yes
0.08
C-18
C-19
JCT-165
0.89
5.28
0.15
--
--
5.21
15.61
0.32
-
--
7.81
15.30
0.44
--
--
C-20
CDT
-230
5.98
3.64
0.17
--
--
23.20
6.31
0.42
--
--
44.06
7.69
0.59
--
--
C-21
CDT
-154
5.44
5.56
0.54
--
--
17.38
7.65
1.06
--
--
23.59
7.90
1.14
Yes
0.06
C-22
CDT -232
3.47
3.55
0.52
--
9.37
4.96
0.82
13.81
5.55
1.00
--
--
-23
CDT -78B
18.16
6.56
1.22
Yes
• 0.09
40.35
6.69
1.24
Yes
0.22
57.18
6.77
1.25
Yes
0.29
C-24
CDT -71
7.15
6.31
0.70
--
--
22.31
8.52
1.32
-l-
--
27.57
8.98
1.50
--
--
C-25
JCT-76
7.14
5.51
1.03
--
--
22.30
6.43
1.21
Yes
0.16
27.57
6.45
1.21
Yes
0.19
C-26
SUB
-25
4.44
6.14
0.36
--
--
7.80
7.09
0.48
Yes
0.16
8.90
7.14
0.53
Yes
0.19
Notes:
Culverts C-6, -13, -14, -15, -16 were not included in the SWMM Model and therefore were not modeled in HY-8
Page 33 of 103
10 -year
Event
50
-year
Event
100_yer, Event
Culvert
ID
SWMM
Input
Input
(CFS)
Flog
Outlet
Velocity
(ft/s)
Outlet
Depth
(ft)
PDepth
'
Overtopping?
Overtopping
(It)
(CFS)
Input
Flow
Outlet
Velocity
(Ws)
Outlet
Depth
(ft)
P-
Overtopping?
Overtopping
Depth (ft)R
Input
Flow
(CFS)
Outlet
Velocity
(ft/s)
Outlet
Depth
(ft)
Overtopping?
Overtopping
Depth
(ft)
C-1
JCT
131
22.4
9.19
0.67
-_
--
92.8
13.56
1.45
--
-.-
148.1
15.15
1.92
--
--
m
C-2
JCT-,211
35.8
14.5
1.3
--
--
61.9
14.9
1.4
Yes
0.17
68.4
14.9
1.4
Yes
0.20
C-3
JCT-172
1.9
5.5
1.0
--
6.4
5.8
1.1
--
9.0
6.2
1.2
--
_-
C-4
CDT -59
3.6
3.7
0.6
--
--
37.5
5.9
1.1
Yes
0.17
65.7
6.0
1.2
Yes
0.30
C-5
JCT-209
51.7
4.4
0.6
--
--
93.8
5.3
0.9
--
--
107.4
5.6
1.0
--
--
C-19
JCT-165
1.11
7.7
0.11
--
--
5.57
13.41
0.37
-_
MI 4S
8.19
16.23
0.43
--
__
C-25
JCT-76
14.9
0.4
1.4
Yes
0.01
27.0
6.4
1A
Yes
009
30.8
6.4 I
1.4
Yes
0.16
C-26
SUB
-25
± 4.44
6.14
0.36
--
--
7.80
7.09
0.48
Yes
0.16
8.90
7.14
0.53
Yes
0.19
Notes:
For Proposed Conditions, only culvert locations without proposed storage ponds were modeled in HY-8
Culverts C-6, -13, -14, -15, -16 were not included in the SWMM Model and therefore were not modeled in HY-8
Culverts C-4 and C-25 were modeled using the proposed improvement designs
Table 7: Proposed Conditions HY 8 Results
Page 34 of 103
4.8 Detention Ponds
Detention storage facilities are used to manage siormwater quantity by attenuating peak flows
during flood events. They can also be designed to enhance stormwater quality by incorporating
design components to promote sedimentation, infiltration, and biological uptake. Regional
detention ponds serve multiple property owners in watershed areas typically ranging from about
130 acres to one square mile. In some cases, regional detention has been proven effective for
watershed areas larger than one square mile, as well as for multiple interconnected facilities
arranged in series. However, due to the complexities associated with how they function within a
watershed, these configurations must be modeled and approved in the context of a formal
master planning process, which is what was completed for the Proposed Conditions.
Regional detention facilities may be constructed by a public entity such as a municipality,
special district, county, or property owner, but should always be based on a master plan or a
detailed hydrologic model approved by the local jurisdiction that accounts for future
development upstream and impacts downstream of the facility. For this Study, detention pond
release rates were restricted to the 10 -year historical peak runoff. If future development in the
Project area occurs within the boundaries of the City of Greeley or Town of Kersey, a lower
release rate may be required. In this instance, developers wi l l need to consult with these
agencies during design.
As a geotechnical ica I investigation was not completed for this Study, soil infiltration on rates for
detention facilities are based on the hydrologic group of the topsoil. Therefore, it is likely that a
pond five feet deep could experience much higher infiltration rates than what was actually
modeled. Additionally, no evaporation loss was considered in the models.
4.9 Summary of Historical Conditions
he goal of historical conditions modeling is to d eierm ine ware rs n ed runoii r pho r'to any lorm Ur
development or other impact by humans. For this Study, peak historical runoff was determined
for the 10 -year storm. These 10 -year flows were subsequently used to limit the peak outflow
from proposed ponds, in accordance with Weld County Drainage Criteria. The 10 -year peak
historical runoff for each subcatchment bcatch rent can be found in Appendix a
4.10 Summa of Existing Conditions
Listing conditions modeling analyzes drainage palterns 'oases on eAisttiny aav 1uprnaL lLb auo
infrastructure. It is useful for identifying inadequate infrastructure or where flooding presently
occurs. The following sections reference specific locations within major basins. For clarity, basin
maps with the referenced locations are provided in Figures 18-21 and 23-28. Full size reference
maps are provided in Appendix [ . Model results are provided in Appendix Ga
4.1 O. Summary of Existing Basins
Railroad Bas i n
~cifh i n this basin, water currently collects at storage units TOR), 200, 400, 500, 600, 900,
1100, 1200, 1300, and 2000. Except for STOR-500, 200, and 400, all of these locations feature
Page 35 of 103
existing culverts, and with the exception of TOR -2000, these culverts have adequate capacity
to prevent any overtopping of roadways during the 100 -year storm.
At STOR-1100, runoff from SUB -98 collects against WCR 49. An existing 48" CMP culvert (C-
22) conveys this flow west under the road into a natural channel. This channel flows northwest,
overtopping the Gilmore Ditch, and into TOR -1 Soo, along WCR 47. Both the channel and
location of BTOR-1300 are considered freshwater emergent wetlands by the U.S. Fish and
Wildlife Service. A 30" RCP culvert (C-24) drains BTOR-1300 under WCR 47. The 100 -year
flow will surcharge the culvert, but water will not encroach on the road. Downstream of TO R-
1300, the natural channel conveys flow to a 24" x 18" culvert (C-25) crossing at WCR 52. This
culvert has inadequate capacity to convey flows in excess of and including the 0-y€ear storm.
Additionally, there is little area for water to pond at this location until capacity becomes
available. Based on the topography, water will flow west on top of WCR 52, as well as in the
adjacent fields for approximately a quarter mile until it turns north.
North of 0625, a natural channel is less defined. Eventually, however, all water exiting C-25 or
spilling over WCR 52 makes its way north to TOR -1200, a homestead at the intersection of
WCR 47 and the Union Pacific tracks. Water ponds here, but two 24" RCP culverts (-17 and
!18) can sufficiently discharge the 100 -year flow before overtopping of WCR 47 occurs,
After discharging from BTO R-12001, water channels against the Union Pacific tracks and flows
east to TO RR9O0. As part of the WCR 54 reconstruction, four 29" x 46" elliptical RCP culverts
(C-20) were placed under the road. These culverts allow water to pass from TOR -900 into
STOR-500, and are more than adequate. At STOR-500, water ponds in a depression formed by
WCR 49, WCR 54, and the Union Pacific Railroad tracks. Eventually, the water reaches an
elevation where it will spill over the railroad tracks. As TOR -500 fills, water will back up into 20 and pond at TOR -900.
At STOR-400 water floods the field west of WCR 47, but does not overtop. These ponding
areas contain no drainage outfalls and will retain water until it evaporates and/or infiltrates.
At TO 8-2000 (east of WCR 49, just south of W R 54), an existing 15 -inch culvert (C-23) is
inadequate to drain water east underneath WCR 54 into STOR-600. Here, water will pond
against WCR 54 until it overtops at an approximate depth of 3" during the 100 -year storm.
Water that is conveyed through the 15 -inch culvert into STOR-600 will drain through an existing
.2' x 1.6' RCP elliptical pipe (C-21). Basin 94B drains to an 18 -inch CMP (C-3) that prevents
water from overtopping WCR 54.5 (WCR 54 becomes WCR 54.5 east of WCR 49 because it
heads northeast). This 18 -inch CMP and the elliptical RCP at TOR -boo outfall north of MR
54. 5, and south of the Latham ditch. If the Latham ditch is flowing full (the assumed condition for
this Study), the water will spill over the ditch until it channels against the Union Pacific tracks; it
will then flow east towards WCR 51.
Page 36 of 103
At STOR-200, (north of railroad, west of WCR 49) water is retained between WCR 54 and the
railroad tracks, and will eventually overtop WCR 54 at an approximate depth of 2 -inches,
Remaining water will be retained until it evaporates and/or infiltrates.
Water that overtops at TOR -200 and 500, as well as runoff from subcatchment (SUB) 81A will
pond against WCR 49 at the Latham Ditch crossing. It was assumed that a temporary, artificial
channel would be created between the top of the Latham Ditch and the bottom chord of the
WCR 49 bridge crossing the ditch. An artificial channel with rectangular of dimensions V x 20'
was created in the model to drain this water under the bridge, and atop the ditch.
Page 37 of 103
'RUNOFF CU RENII,'V
PONCA N THESE AREAS
STOR-:Ua!
STOR-1 2U,
kafr
RUNOFF CURRENTLY
PONDS 04 Mile AREAS
STOR-LIDD
i-i$1110
Figure 18: Railroad Basin Existing Conditions
' I'
S
O
0
K RUNOFF 'CURRENTLY
PONDS IN THESE AREAS
5TOR.4O0
StOgt2Ogo
STORE
P
XPTP a CULA9k1 trail
arm's SS)
PRAJLCT k e4Za4t=
Inallagimar
bta.t Pt tvition
114
Page 38 of 103
Kersey Basin
No culverts or other existing storm titer infrastructure were found during the Kersey Basin
ground survey or identified otherwise. Runoff from SUB -80 and 81 flows east until it is retained
by WCR 49 at TOR -300 and TOR -1000. This water floods the fields west of WCR 49, but
does not achieve an elevation high enough to overtop the road (4633 ft. at STOR-300; 4635 ft.
at TOR -1000). From aerial photographs it is apparent that some runoff from SUB -82 (east of
WCR 49) drains northeast and ponds at an agriculture supply company. The remaining portion
of SUB -82 flows northeast and collects against Highway 34.Again from aerial photographs, this
water seems to pond at a homestead. A Major storm event could significantly inundate the
aforementioned business and residence.
ce
Figure 19: Kersey Basin Existing Conditions
Page 39 of 103
P_oudre Basin
Approximately half of this basin is located outside of the Project area; the other half within the
100- and 500 -year Poudre and South Platte floodplains. Only ditch related infrastructure was
identified during the survey. Therefore, water is likely to pond along WCR 45 and WCR 58.
Figure 20: Poudre Basin Existing Conditions
Page 40 of 103
co
South Platte Basin
Similar to the Poudre re Basin, a large portion of this basin is located within the South Platte 100 -
and 500 -year floodplains. Development has been mostly limited to cultivated fields and private
access roads. During the 2013 flood, a section of Highway 34 between WCR 45 and WCR 6
was washed out. This has since been replaced with a bridge to allow passage of water.
There are numerous RCP culverts (C-5 through -10) that convey runoff under the Parkway.
Culvert -S is located within the South Platte 100 -year floodplain. No issues were found with
Culvert C-6, as it drains an insignificant amount of area. Culverts C-7, CsES, and C-9 form an
interconnected loop that eventually outfalls into the South Platte. No significant issues were
identified with these culverts. Culvert G-10 likewise does not experience any problems, but
discharges openly into a field east of the Parkway.
Further west, water will pond against the Highway 34 and WCR 47 intersection (STOR-I 700).
The field southwest of the intersection will flood, but water will not encroach on either roadway.
Three ditch culverts (O-14, -15, and -16) carry irrigation water north under Highway 34. As is
the case with ail ditches in this Study, these were assumed to be running full during peak runoff.
As capacity becomes available, however, this field will partially drain through the ditch culverts.
Approximately one foot of water will remain as it cannot overtop the ditches.
Page 41 of 103
2*e
Figure 21: South Platte Basin Existing Conditions
Page 42 of 103
ParkwayBali n
All of the identified drainage infrastructure in this basin was constructed as part of the Parkway
project. There are two RCP culverts (C -I I and Col2) that drain runoff under the Parkway.
Discharge from C-4141 flows east towards WCR 49 5. A small, raised, irrigation ditch causes this
water to pond on top of the roadway at TOR 1500. If it breaches or overtops the ditch it will
flow northeast through fields, and overtop several other roads (WCR 51, and WCR 58) before
joining the South Platte.
To prevent runoff from the Parkway spilling onto surrounding fields, the County constructed a
small detention pond (TOR -1600) north of Highway 34 and on both sides of the Parkway.
(Figure 22). This pond was only designed with enough capacity to handle roadway runoff from
the Parkway, however. During the 100 -year storm, the pond fills and the adjacent field will flood,
which will in turn surcharge the 24" RCP (C-12) draining the pond. Discharge from C-12 will flow
east and overtop WCR 49.5, approximately 1/7 mile north of Highway 34. It continues east joining
with runoff from adjacent subcatchments until overtopping WCR 58 at the intersection of WCR
58 and WCR 53, and joins the South Platte.
Nip
. .� ,)
;71r
isI.g i.'�.«!Fr'ta ...if. �aa': r,t'k :', `�bj. ' e;� ;•.. i i __
4
S
Figure 22: Western Portion of Existing WC Parkway Detention Pond (Locking South)
Wit"
.t
Page 43 of 103
•
II
Figure 23.' Parkway Basin Existing Conditions
I30n RCP ) -
4 4....UNOMPCURRENTIL
:ON0'S D IN THIS RE
STO 1600
s
1.•
ar
1 p`�
; r -R' i N O F F C U R R E N T
. -PONDS I �`r- , ,► SiTOR-270000
RUNOFF CU _ ENTLy
--PONDS I'_.' HIS AREA
STOP -3200
_
t
rr
RUNGEWEURRENTLY
IN This AREA
STOR1.1 00 t
aaistijimidlin7
E340 ( . V ST Cott
ire PROJECT WA.20114:44W
500 ;DOG
MIR 711, ..M.+
90.1,1 I. fieof
11
Im w
r
ft
ri
M
Page 44 of 103
Eaton Basin
This basin was a part of the larger Study area to determine the extent, if any, its impact has on
the Project area. As it does not have any impact, it is outside the scope of this Study and was
not evaluated.
EMS 3143, CULVERT {G4$}
E.X* BMW (p4)
PROJECT AREA SOMI ARY
6 M*J 1000 Sty
SCALE: 11'■ low
Figure 24: Eaton Basin Existing Conditions
Page 45 of 103
Sand Creek Basin
This basin was delineated to determine flows in Sand Creek, which runs under WCR 60,5 to join
the Poudre River. No problem areas were identified in this basin.
Figure 25 Sand Creek Basin Existing Conditions
Page 46 of 103
Lone Tree Creek Basin
As the Lone Tree Creek watershed extends into Wyoming, only relevant portions of the
watershed were evaluated for this Study, A total of 11 subcatchments drain south and collect at
the intersection of WCR 49 and WCR 60.5. An existing CMP culvert (C-4) that conveys flow
east under WCR 49 is almost completely buried. Therefore, water ponds at this location (STOR-
1400) until it overtops WCR 49 and continues east towards Lone Tree Creek.
Figure 26: Lone Tree Creek Basin Existing Conditions
Page 47 of 103
Airport Basin
Two newly constructed culverts for the Parkway as well as one existing culvert were identified
along the Project area boundary. Runoff entering these culverts comes from subcatch rnents
north of WCR 60. 5, which include a majority of the Greeley -Weld County airport. All three
convey flow south under WCR 60. 5, where it eventually joins the Poudre River. A 4' x 6231
elliptical culvert (-1) was placed northwest of the WCR 47, WCR 60.5 intersection; a 30" RCP
culvert (C-2) to the northeast of the intersection. Surcharging occurs at -1, which drains south
into the Ogilvy Ditch, but no overtopping of WCR 60.5 occurs. If the ditch is running full (which
was assumed) water will back up until it exits via the newly constructed spillway just west of the
Parkway. After spilling, the water will flow south into the Poudre. Culvert C-2 does not surcharge
and drains into TOR - 00, a large pond that was constructed southeast of the WCR 47, WCR
60.5 intersection. A 24" pipe underneath the Ogilvy Ditch drains TOR -boo, which only reaches
approximately 5% of its capacity during the 100 -year storm, south to the Poudre.
A half mile west of the WCR 47, WCR 60.5 intersection, at C-19, water drains through a grate
inlet connected to a 24" CMP culvert. Water ponds over the inlet but does not overtop WCR
60, 5.
Page 48 of 103
0
Figure 27: Airport Basin Existing Conditions
Page 49 of 103
WCR 53 Basin
Two subcatchments north of WCR 60.5 drain south towards the road. Existing culverts convey
this water under the road without any overtopping during the 100 -year storm. South of WCR
60.5, runoff drains towards the South Platte. Water will channel against WCR-53 as it flows
south but will not overtop the roadway.
n
tgiep
5a
Figure 28: R 53 Basin Existing Conditions
�I
fISTPCGILV ' F' IP4
FX?8TPIf i SUMS IN•64
�■rrr se CT mrAPeSe CT mu, roochapv
0 *Xi 1040
grid
! PIP MS
Page 50 of 103
4.11 Summary of Proposed Conditions
As previously stated, the County is evaluating the impacts of possible development along WCK
49 and the Parkway. To address future issues associated with development, as well as existing
problems identified in the previous section, the Proposed Conditions model was developed. This
model was developed by using the Existing Conditions model as a base, and then updating the
network to reflect future conditions and proposed improvements. Future development was
incorporated into the model by assuming an imperviousness of 60% extending to 1,000' on
either side of the corridor, extending from ,just south of WCR 50 and WCR 49, all the way north
to WCR 66 and WCR 47. Model results are provided in Appendix G.
As major drainage channels and storm sewers are not present in the Project area, detention
facilities were extensively used to capture and attenuate runoff from subcatchments. bcatch ments . However,
due to the low sloping topography, pond outfalls were difficult to place. As such, many ponds
utilize flat or near flat pipes to drain them.
4.11.1 Proposed Improvements
The locations of proposed drainage improvements are approximate. When and if the County
decides to construct any of the proposed improvements, a detailed design will be completed
which will include an exact location.
Proposed improvements were organized based on the major basin within which they are
located. For clarity, basin maps showing the locations of proposed improvements are provided
in Figures 29-33. Full size reference maps are provided in Appendix a Additionally, detention
pond exhibits (Exhibits 1-23) displaying the configuration and volume calculations are provided
at the end of each major basin section. Following the exhibits are summary tables containing
the proposed improvements and their associated cost. See Chapter 5 for more information on
cost calculations.
It should be noted some of the ponds shown in the exhibits provide a surplus of volume when
compared to the model results. This is partly due to grading requirements needed to fit the
ponds at the proposed locations, as well as an effort to utilize existing topography and reduce
the amount of land disturbance. The primary benefit of oversized ponds is the flexibility it
provides in terms of storage volume and release rate. A summary table (Table 13) at the end of
Section 4.1111 is provided to highlight the difference between model results and what is
provided in the pond exhibits. The pond volumes identified in the following sections refer to
those that were actually graded and shown in the exhibits.
Railroad Basin
STOR-1100
Construct a 6.63 acre-feet detention pond and replace the existing 48" CMP with an 18" RCP
that is restricted to release at the historic 10 -year rate of 9.89 cfs. This will control water ponding
ing
against WCR 49 and attenuate discharge.
Page 51 of 103
BYOB -1300
Construct a 1340 acre-feet detention pond and restrict the existing 30" RCP to release at 11 cfs.
This is well under the 10 -year historic rate of 41.5 cfs, but is necessary to prevent flooding
downstream at TOR -1 00. Because STOP -1300 is located in a freshwater emergent wetland
area, a detailed wetland inventory and survey will need to be submitted to the United States Army
Corps of Engineers (USAGE). As the proposed detention pond will disturb more than 0.1 acres,
an Individual Permit will required. This is more expensive than a Nationwide Permit, and takes
longer to receive. An estimated expense of $20,000 has been incorporated into the overall project
cost to account for obtaining an Individual Permit.
0-25
Replace the existing 18" x 24" DAP culvert with a 19" x 30" RCP culvert to facilitate flow under
WCR 52.
TQ R3300
Construct a 8.81 acre-feet detention pond between WCR 45 and WCR 47, Construct
approximately 2,400 feet of 18" storm sewer to drain TOR -3300 into TOR -1 Zoo. The release
rate from this pond is self -restricting to approximately 1.8 cfs due to the low sloping outlet pipe.
The purpose of this pond is to attenuate runoff from SUB -89 and 90 prior to reaching TOR -1200.
STOR-1200
Construct a 5.16 acre-feet detention pond and remove the southernmost 24" RCP. Restrict the
remaining 24" RCP to release at the historic 10 -year rate of 12.6 cfs,
STOR-900
No improvement is required, as the four existing culverts (C-20) are more than capable of draining
this area.
STOR-200
Construct a 7.81 acre-feet detention pond. A 15" flat RCP wilt need to be installed through the
U nion Pacific ROW to drain the pond into STOR-900.
S TOR -50
Expand the existing depression to 22.80 acre-feet. Install a flat 24" RC equalizer pipe underneath
the expanded WCR 49 to connect to STOR-600.
0.
• TOR -20
Construct a 43.19 acre-feet detention pond as well as three 18" RCP culverts that drain from
STOP -2000 to STOP -600 The culverts discharge at a maximum rate of 48.86 cfs, which is less
than the 10 -year historic rate of 59 cfs from subcatchment anent 94A.
S TOR-600
Expand the existing depression to 9.79 acre-feet. Utilize the existing 1,62x .2' RCP culvert to
drain this pond unrestricted. The peak discharge in this culvert is approximately 20.98 cfs.
Page 52 of 103
STOP -2900
Construct a 53.13 acre-feet pond in-between the Union Pacific tracks and the Latham Ditch that
collects runoff from SUB -81A, as well as discharge from TOR -600 and C-3. Construct two 18"
storm sewer outfalls I s that extends east approximately 850 feet, These pipes will be nearly flat
and discharge at approximately 6.4 cfs,
Uri
SED POND
.4STOR I200)
P IMPT
POND
4300) . '
-4
PROPOS ED POND
I TOR -600f
PROPOSED 'PON
7 (STORM: -9001
.4
Figure 29: Railroad Basin Proposed Improvements
moposeo PON°.
(ST'OR-2000
fit 00050) COS CRT
ORINKAGD MIND frIn
"%CUE CT Mirk liatiPilkA
itAL!: Iset Mi '
1
Page 53 of 103
rn
a
1
C
et
WI JO pc ° Bed
-i _
Outkin Sunny
Spa
C
Surface
Area
(e)
Inc en1
Skean
(
"iclai
snag.
tc4t)
4700
1034
tost322-
2.43
2A3 i
__duel
113024
4-1f2
2.55
4.9
..
767
4763
AI MO
Zee
47,84 ,
4765
124441
10.47
. 2,00
130
2.93 -
13.40
c fact=■ an r at Arra
4
Met
i
SCALAUM'
Totals
al.977.0D €h_ Id
4_, ri Cu- 282 .,Q az.
c_$3 tom. rd. 213972.5.1. Q . Yd. spa
C)
Prujed No:
BOOk No;
Drawn by
v4owe .i
01.1255 00
9L
04/22.:'°6
WELD COUNTY' MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
TOR -1100
Farnsworth
GROUP
1612 SPECHT POINT ROW, SUS 105
FORT COLLINS, COLORADO 80525
(9 70) 484.7477 / Fnitew..
e
es
Exhibit 2: STOR-1300
COL 10 SS e68d
dininSamm-
I
Cut. -Fill Sumary
lie
ate.
eacta
Stage
(t)
Surface
Area
(ft2)
hcrementat
S garage
(ac -1t}
TTota
S torage
� (ar_- ,,
4677.5
62965
4675 5
67513
150
150
4679
69828
0:79
:2,
4
74540
1 65
:3.17
4661
79359
1.77 ....
'5.71
4681.5 , 81810
0.at
:15,63
.Z 4.it3
att
Net -
N
i
TS
SCMr c i-urica
#00 :-ArC
1.0 i_004
Sq. Et.
717S . 70 Cu- _ci..
L'_ .14 3a. Id.. 71E7.5€ Cu. Yaii. --
r. aLa
S2726.20 Sq. !'t .
7179.7D Cu. Id.
32.14 Zu_ Id,. 7161.5€ tea. id.C_rruu,
Pro r i No: 0151255
book No:
Drawn yti':
�ieviewe
JC
04,/2
f _
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, Co
PROPOSED STORAGE
POND EXHIBIT
STOP -1300
Fnrncwnrfh
ate■ ■■V vw a�
GROUP
1612 SPECHT POINT ROAD, SUITE 105
-FORT GOWNS, S, COLORADO €8 325
Q70) 4847477 1r fc4-ve_corrr
p _
Exhibit 3: TOR -3300
Mr JO 99 O6 d
airirP511 Sassy
get
Stage
fit)
`
h;nmen#al
Storage -
a .4), :
Sftoe
Area
Or,
Total
Storage
( 4)
:
283529
•
M
4644..0
!
3 28
3428
4844_5
283145
LT 42760
3.33
8.61
Cut Fact== rail taint Warta
Cut
PILL
Nee
I
ereditE ?say
Szei -wao 'tots— 1.030 laCCIO 291114.20 r $R. I t. 75.20.6E Cu. Ai.
27 2.76 Cu.. 'Id.. ?li7.9L ut. Id.‹Cut)
2511 162.5O !$q. Pt. 7520.66 Cu. 11d.
asta.eye Cu. 'sad. 7147.41 Cu. 74L<Catr>
Pv i t No;
Cook No;
Drawn by:
Re
0151255 :
-L ti
4/22 `6
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, Co
PROPOSED STORAGE
POND EXHIRFI
STOR-3300
Farnsworth
GROUP
1612 SPECHT POKT ROAD. SUITE 105
FORT COLLINS, COLORADO 80325
(970) 434-7477 / U i .com
0
ii
Exhibit 4: TOR -1200
£01 40 4.9 efied
C,
Proloct Na
Ito:
Drawn tai*
Dale;
01 51 25.
Je:
04 22P6
Std-: CO Vain
Stage ,
1*)
Sorbs*
Ate
)
hctehtar'ttai
Slaws
Walt)
Tole
Storage
(EA)
4639,5
4640
' 83996
86329
9$
0. 93
1
a ......__....._..._.Q
911071
95t220
..
2.04
2.15
3.0,
4642
5.18
9€450 r'S . rp. w'1tmt Cat- fd. 95 -'ft Ca- 2t 6535.13 . idi.'
WELD COUNT'S MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
ST R-1200
C9/0_ _ Id. Q5_6:1%c Xd_ 6525.12 u. id_ <Nut+
Farnsworth
GROUP
1612 SPECHT +INT ROAD. SUITE 105
FORT Cwt$, COLORADO 80525
'M) 4$4-7477 If itr$ - am
rrl
{.l
0
COI 4° es 062d
CPC, istiee,smiat4.0%V., 41141.114.414-Kiissims,...
..
Y
uy,..,..,.,,vv IrYC1,.�1
sr'DR-2o9
Stage
ot)
Ana
t)
Storage
Eat -t)
......_...
SlicaPI
Cac-ft
. 4633
v__
$3
a J.„...._______,_..
•4634
87968
1 ge
i is
434 5
130
"( 25
3 21
4635,0
193260
1.85
51
4835.50
259 I ZI
2.75
`x.81
Cut
Dram Coo raccor rul ran 24 arra
Cat
ran
N
asimnimrst
9c4LE-1' ! •
34,111-2 DI Vain i_i9i0 t
11-1 03 2S5411.14 5q_ rt _
CO ea_ 'd.
Totals
Sq. rb.
LAO- cc a z. ted.
209.172 Ca- Yot 'I 3 i 29 Car 'al_ cnits>
9
Project No; 51255
Book No;
Drown b►�►: 9L
rcir;
Data; 04
:•
WELD COUNTY MASTER DRAINAGE TUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-200
Farnsworth
GROUP
1612 SPECHT PONT ROAD, SUITE 105
FORT COLLINS, COLORADO 80525
(970) 464-7477 / irwF f-w.crr
D
r
Exhibit 6: TOR -50G
talc) 6S eBed
.t
Clithnn
On racist= tin Thaw IS Iris
1
Std
(1)
Syriac*
Ares
(fe)
Inc rernintal
SACCO
(ac -t)
Total
Std
(ac -01
4631
284596
4631 Y5
209299
3 C6
3,C6
4632.6
270791
8.29
9.3
X3.5
ZI0394
-
0.51
15.57
40300
218106
4.7"4
4,10
OaS
Net
N
..n.- - an
SCALE. lloscr
tfR-ODO Vats i-000
1..020
.S_04 Rs_
?44.46 On_ Tv& otos ca.,
rt00,1,1Ctio rtri, <Cucto.
Totals
7021.54_O4 Sc- F
__4T -3f Cu_ Tel.
1.7-os Ca.. Id..
Project No:
Book No;
Drawn by:.
Reviewed:
Date;
01:51255
RL
Jt
44/22
WELD COUNTY MASTER R DRAINAGE STUDY
WELD COUNTY,
PROPOSED STORAGE
POND EXHIBIT
STOR-500
roa-W1 Cu- ?,.<
WAS
Farnsworth
GROUP
1612 SPEOt4T POINT ROAD, SUITE 105
FORT COLLINS, COLORADO 80525
(97t') 464-7477 of irrfe@f-wirevit
Exhibit 7: STOR-2000
000
tin JO 09 o6ed
id
.110
nis
_tea
x'
a1"
Cut.frill Suanary
btan
d i
r
law rrc aw fU i
- =tom-=
- r ti;
Stage
ODD
Surface
Ares
(W)
bcrornnka
Storage
(s.1't)
Total
Stony
(ac4)
. 257590
2.93..
2.93
2
- 46133
268292
9.04 •
8.95 ...
279151
4.
15,25
41334
l-- 21,78
290169
6,53
4534 '. --
-3013
tre •
2,57
4637 _
-4938.
_.. 318 ! G
7,12
',50T. - .,
3518
4319
Net
Sat re
y
-1008 Vats LOCO
1.000
392266. 65 Lac. fli. 1131=9. 55 Cu,. Yd.
10.15 Cu. Yd. 104066. 39 Ca. Id. Cat,:,
rote
MB . 65 Bei. As. 10029. Cis. Yd.
1,1£3.18 c Yd. 104561 _ * cu . Yd. <Con
0
Pruje i FIB: ' 51255 DO
Book No:
Drawn ter:
Revue
Dote; 04/22
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-2000
Farnsworth
GROUP
1612 S1EGHT POINT ROW. SUFI -105
FORT GAS* COLORADO 50525
{970) 484-7477 f in1 -w_cam
Exhibit 8: TOE' -5`00
£01 to 4a 068d
STOR-5110
11
Project No:
Book No:
Cktnitin ter:
Red:
pato:
141
Y..� ..vs.T .fa..
-avow
aPairiered
ran
skk,
STOROX)
9.1111ary
Cat Factor fill ram= 14
„rveit'
Stage
C111
Surface
Ama
d")
luirerneelal
Storage
tac4)
Tom
Storage
( 4)
4531-0
133017_
2
130029
3 12
3.12
4633
145092
E 3.M
6.38
4634
151259
3.4C
SIP
STC14-6X Vella
1.900 1 'x+5.9t Sq. r,
a a MY
152-17 Td- 46:17-14 Cu, Yd. %.- s,
Tettala .155 3q. rt.
414!0.01. PCs. W.
52w11 Cu, 'ed. '+_e4 'Yd-Cra►t
0151255 00
04/22
F�
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-600
Farnsworth
GROUP
1612 SPEC -IT POtNT ROAD SLATE 105
FORT COLLINS, COLORADO 80525
O1 484.7477 f info@fw_cnn
006e -801S =6 EtiPPG
COL Jo Z9 aGed
STORM0D
It
Age
(t)
Surface
Area
0")
hcrame a1 ;
Storage
(nit
TolaP
Storer
otemiti
4C7,5
oxi
462$
550 353
e21 I
616
4629
569109
12 4
19,11
. 4430 1
588015
13:23
32,39
1
607071
13.72 1:
46 1
31.5
616555
7.02
53.13
enjerill Mint?
Name Cut Fa ctc r Flit FSc tc,t 2d Aral*
Cut
Net
i
&CALE5462W
SIVR-2900 Vui+..1m* L000
1.000 €23125.84 sq, rt. 49833.83 cu. Yd.
1970.24 Cu, Yd.. 46043.59 Cu. Xd ,<cut>
Totals
&2312E.84 sq. r . 48833.81 Cu. Id.
$910.24 Cu. Yd. 4696a., 5& Cu. Yd. ':ut>
C
Project No: 0151255 .
nook No:
D+ulnn twi
Rawskock
Dote:
04/221?
WELD COUNTY Y MASTER DRAINAGE STUDY
WELD COUNTY, Co
PROPOSED STORAGE
POND EXHIBIT
STOR-2900
Farnsworth
GROUP
1612 5PECHT POINT ROAD, SUITE 105
FORT COLLINS, COLORADO 60525
1 484-7477 / fsn.cnrm
Table 8: Railroad Basin Proposed l n rovements and Associated Costs Summar
Improvement
ID
Easement/
ROW
Engineering
Contract
Admin/CMMI
Contingency
Total
Capital Cost
Annual
0 & M Cost
50 -Year
0 & M Cost
Capital
Legal/
Administrative
$178,200
$1812,132
$364,2(55
$546,397
STOR-2900
$910,662
$5,824,304
$37,398
$1,869,900
$3,642,648
STOR-0600
$816,200
$54,450
$122,430
$40,810
$81,620
$204,050
$1,319,560
$11,251
$562,550
STOR-2000
$2,'981,191
$134,650
$447,170
$149,060
$298,119
$745,298
$4,754•497
$27,179
$1,358,950
STOR-0500
$1,631,446
$89,100
$244,717
$81,572
$163,145
$407,862
$2,617,842
$18,069
$903,450
STCIR-0200
$628,825
$111,375
$94,324
$31,
4.
$52,883
$157,206
$1,088,054
$22,499
$1,124,950
STOR-1200
$432,636
$29,700
$64,895
$21,632
$43,264
$108,159
$700,286
$6,028
$301,400
STOR-3300
$706,774
$116,325
$106,016
$35,339
$70,677
$176,694
$1,211,825
�reev
$25,794
• . •. . •
$1,289,700::
STOR-1300
$527,080
$34,650
$79,062
$26,354
$5.2,708
$131,770
$851,624
$7,044
w
$352,200
STOR-1.100
$1,012,825
$66,825
$151,924
$50,641 T
$
$101,283
$253,206
$1,636,704
$13,589
$679,450
C-25
$16,186
$0
T $2,428
$809
$1,619
$4,047
$25,089
$5
$2,500
$12,395,811
$814,275
$1,859,372
$619,790 t$1,239,583
TOTALS:
$3,098,954
$20,027,785
$168,901
$8,445,050
Page 63 of 103
Kersey Basin
STOP -1000
Construct a 12.90 acre-feet detention pond to collect runoff from SUB -81 B. A15" RCP cutfall
was utilized for this pond to allow adequate pipe cover. Based on current topography, this pipe
will be flat and discharge east of WCR 49 at a rate of 1.08 cfs.
STOR-300
Construct a 29.73 acre-feet detention pond to collect runoff from SUB -80. Install three 18" RCP
culverts to a l l o the pond to drain in 72 hours. Based on current topography, these culverts can
slope at approximately 0.3% and discharge at a combined rate of 17.65 cfs, far less than the 10 -
year historic rate of 37.4 cfs.
Figure 30: Kersey Basin Proposed improvements
Page 64 of 103
Exhibit 10: STOP -1000
CU 40 S9 a6ed
Stage
(t)
Surface
Area
0')
heremenlad
Storage
(ac -It)
Tea
S
*A)
4833.5
8
•
MA
1
1 :,.
.
435 ,
niita ,
10 95
1290
oat/nil amt
Throe ractor flit ratan 2d Ara
tat
nu
N
Valve 1.000
1.DOID 7217215. c b fl,. rt.
amt.= Qs. mis. 1716.19 Cu. U. 2010.67 Ca. ld. 'll3.,b
Totals
720245-C4 Sig_ f.
2.476_32 Qo,.. Yid_ 4'?1.6,13D Ca. a
S SO_ CY Ca_ Yd.4a.].
C)
Project tic: 5125.5
ea* :
Drawn by
rE
qL
JC
04/22 '
WELD COUNTY MASTER DRAINAGE STUDY
DY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOW -1 COO
Farnsworth
GROUP
1612 SPECHT POKT ROAD, SUITE 105
FORT COt.t.WNS, COLORADO 90525
{970 484-7477 / infaWf-vp,coirsti
tr
I
CO
O
t
O
EU 40 99 ebecl
ett t mSkanaitty
Kee
cut rgets3Ct
Spa
(N)
r
Surface
A.R. 1
(V)
hcoemenual '
y
MONOStorageSto�
(ac -4)
a
Total
l *
4831 5
4632
869753
9.63
t I as
4632.5
837038
9,91
19.74
3_Q
674348
_
9,19
29.73
nu Patton on 2d Area
rill
I
N
U
riraiinumman
WILE 11451,
Tiblune 1.000
1.4X1O t90'761_2C i. rt.
#I72, u ita _ ' d.. 3320.07 ts. Kt52 45 OA- ?d.* ►a
Tarsals
290761.20 ,j_ Tit_
. n.= 4N7L.. tea.
0.07 Ca.. 1d.. 5CGZ. $,5 Cu_ Yd. Qut..-
rkojec# No: 51255 )C
Book No:
Dintrmork by: RI
Reviewo
Dote:
04/2 2 ..
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT'
STOR-300
GROUP
1612 zPECHT POINT r ROADJ. sun 105
FORT O0€1.94S). COLORADO 60525
(970)484-7477 f info f'w_
Table 9: Kersey Basin Proposed Improvements and Associated Costs Summary
Improvement
ID
,
Capital
Easement/
ROW
Engineering
Legaif
Administrative
Contract
Admin/CM
Contingency
Total
Capital Cost
Annual
O & M Cost
4
SO -Year
O & M Cost
$2,101,361
$316,800
$315,204 _
$210436
i $3,573,909
$64,162
i $3,208,1+00
STOR-0300
$105,068
$525,340
STOR-1000
$932,022
$217,800
$139)803
$46,601
$93,202
$233,006
$1,662,434
$43,902
$2,915,100
TOTALS:
$3,033,383
$534,600
$303,338
$753,346
i
$6,123,200
$108,064
$455,007
$151,669
$5,236,343
Page 67 of 103
South Platte Basin
STOR-2100, 2200, and 2300
Construct 5. 5, 2.16, and 0.26 acre-feet detention ponds at these locations. The existing
culverts can be utilized (C-7, -8, C-9) but should be restricted to the 10 -year historic release
rate. Given the proximity of these ponds to each other, the combined release rate from SUB -62
and SUB -61 was used for culvert -7. Therefore, C-7 releases at 6.2 cfs, C-8 at 681 cis, and C-
9 at 4.8 oft
STOR-3000
Construct a 1.05 acre-feet detention pond to capture runoff from SUB -63. The existing 24" RCP
(C -IC) can be restricted to release at the 10 -year historic rate of 0.6 cis. As this represents a
minimal discharge, no channel was created in the receiving field.
Page 68 of 103
0
Figure 31: South Platte Basin Proposed improvements
Page 69 01103
Exhibit 12: T Rat 100
co 4 jO 0L 96ed
Ftrl•c.' No: '51255
Book No:
Drawn :
Rennewuck
Dale:
L
C
(04/22 "a
4.17
STOP -21W
Stage
(it)
Surface
Area
(P1
ltrerrstatal
Storage
(ac -at)
_ Total
Storage
(ab"t$
4621:5
"
95519
:.
4822
: r
1oal.
.1. .
X2-5
4623
92663
. .�,1,01r ., „�.....
i 05 is_307
202 ,.
4823.5
4824
95095
.l'aY .
97554
1. L18i
swe.'NM4N. #.4 wn 'i,w en,4a. w t nL
1.11
4.14
. CT r r *TfR. rr. TrrMrIA�'IVT'Iww.'MNNY�
5.2$
art/rill SIIIIMILry
Now Cot racy= ra=at as area
51C11-2100 Volumw LOCO
1-tegt 9160-Dt Sq. Etr
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
ST R-21 00
Cc
N917.20 at. 'Idt-
5017-X+ Ca- Yt
nu
Mit
I
N
arn
2 Ca, Yd. Etal.eG cu. id.Ct>
2--a O'- 'bL 5DL4. Cm. td.
Farnsworth
GROUP
1612 SPECK'. PCHNT ROAD, SUITE 105
FORT c 1.r$, COLORADO 80525
{gm 464-7477 / inool@f-w.wm
o Lois :ct - ITI4x3
C13110 e6ed
Pm't No:
Book Ho:
Drawn by;
Reviewed;
Orris:
. 51255:
RL
04-0122: f
STOR,2300
STOR22110
STOR-2169
Catkin Summary
_ •.t.r_c la a
Stage
I $or1
Am*
Wren" entail
Stange
Total
Stange
(1)
t12)
(ac t)
{ac�#t)
4621.0
c 43702
45387
c.,5t
0 51
4022
L 4?
0,53
1 04
X2.5
541`m
_ C.55
1.;58
482
5 1
..._. C.57
2-113
Ira crap racier nat tactar 2d Area
•7LLf4-2200 Main
totals
i_Gag
=Oar fed 3q.. e
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-2200
c.se• cu., Yid.
4t9.D6 C.. %d..
Fin
Vet
intimme
scolti resort
C.0 Cu_ Yd. 24e+. Si Oa_ YomcraWr
CI- IX Ca- IS- Mkt_ del Oa- ? .<t
Farnsworth
GROUP
1612 S T -f POINT ROAD, SUITE 105
FORT COWKS0 COLORADO 80525
N70) 484-7477 if i f-w.com
I
Exhibit 14: TOR -2300
£Ol 40 U. aned
Project No:
book It
t crwn by:
Reviewed:
Doh):
.51255
04/22P
Slags
(t)
5 ct
Area
(f)
'
bcrermental
Stonge
(ac -t)
IS
Storage
tat4)
4520,5
1091
1
1489
0.01
0.04
0..01
0.06
4422
2314
4C2
9145
. 0.06
0.12
4623
1+128
_ 0.14
023
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-2300
Farnsworth
GROUP
1612 SPECHT ANT ROAD, SUITE 105
FORT COMM, COIDRADO 80525
11 4847477 / 3nfoef-w_com
000c-eioi :gip 11
£01 4° CL 060d
Ass
snot -moo
atk/rYl1 Sunny
Nagar
Surface
Incremental
Total
8ttgt
Ares
Stingy
ape
4821,0
15585
CAS
• \ .
[t_12
48227,55
v
11,756
71.�i.
4425 bSI ^YYwf,l\.+-4410
1JL4M'.J-lY�r._V'
I , .. .liv.'1r
Yv1 Md,W
4. '- - .i
ifa,,,,..
4429 44420
.4WiR TH
1.05
C
Cut Fact rut Farr 2d Area
Out
N
flt-3000 War
3._SOO 1.0430
47844 434 'Sq.. ft.
5113,0.1 Lam.. Yd_ 35_52 Oa_ YAL 114.21 Cu. rd. t .
Total.
45d44-34 Wit. r -
012_0R Cu. Yd. 35 -ea cat. d. 't'#_21 Cu_ 3 i_ >
Book Nar�:
rte ti
Rovievpsict
Imo;
0151255-
9L
04/27
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
TOR -
Farnsworth
GROUP
1612 SPECHT POINT ROAD, SUITE 105
FORT COLLINS, COLORADO 80525
t970) 484-7477 / irrio@f-w. m
Table 10: South Platte Basin Proposed Improvements and Associated Costs Summary
ID
Capital
Engineering
Legal/
Administrative
Improvement
Easement/
ROW
Contract
A.dmin/CIVI
Contingency
Total
Capital Cost
Annual
0 & IttA Cost
50 -Year
0 & Isii Cost
$58,554
$19,518
$331,050
STOP- 100
$390,360
32175
$39,036
$97,590
$637,233
$6,621
5TOR-
2200
$22,275
$8,432
$16,865
$42,161
$283,675
$4,545
$168,645
$25,297
$227,250
...s....
-2300
$37,622
$9,900
$5,,643
$2,201
$110,050
STOP
$1,8841
$3,762
$9,406
$68,214
STOR-3000 000
$93,652
$24,750
$14,048
$9,365
5,23,413
$169,9115/128
$256,400
$4,683
$690,279
$103,542
$34,514
$18,495 I $924,750
TOTALS:
$89400
$69,028
$172,570
$1,159,033 I
Page 74 of 103
Parkway Basin
STOR-1600
Construct a 21.68 acre-feet detention pond that ties into the existing detention pond. This pond
can utilize the existing 24" RCP that was constructed with the Parkway, but should be restricted
to discharge at the 10 -year historic rate of 15.1 cfs. Additionally, a 2,350 feet trapezoidal
channel should be constructed to safely convey this water east to TOR -3 OO. This channel
should have a bottom width of eight feet, 4:1 side slopes, and a maximum depth of two feet. In
reality, due to the relatively flat slope of this channel, it will act like an extension of the proposed
STOR-3200. However, it wilt still achieve the task of safely conveying TOR -1600 discharge in
a controlled manner.
TOR -3200
Construct a 21.58 acre-feet detention pond along WCR 49.5 to detain runoff from SUB -74 as
well as discharge from TOR -1 bog. Two 23" x 14" elliptical RCP culverts restricted to a
combined discharge of g cfs (the 10 -year historic rate) would be the most economical outfa l l
configuration. To achieve 6" of fall, they will need to cross the road diagonally and run for
approximately 260 feet. In order to construct the proposed outfall, ll, the roadway will likely need to
be raised to provide adequate cover.
STOR-3100
Construct a 2.42 acre-feet detention pond along WCR 49.5 to intercept runoff from SUB -75. A
15" RCP restricted to the 10 -year historic rate of 2.9 cfs should be installed to drain TOR -3100
into TOR -3200. The pipe will be approximately 240 feet in length but can slope at close to
1.5%.
Proposed Storm Sewer
Given the quantity and density of proposed detention ponds TOR -2500, STOR-2700, 700, TO R-
1Boo, and TOR -2800, as well as the difficulty of constructing outfalls, a storm sewer is being
proposed to collect water from the afore named ponds. Furthermore, given the depth of these
ponds, the most convenient method to drain them is via storm sewer.
Beginning at STOR-2500, a flat, 15" RCP pipe will drain into STOR-2700. To achieve adequate
cover without creating a mound in useable farmland, as well as to surcharge the pipe without
deepening the pond further, a drop manhole is proposed. The 15" RCP will then drain TOR -
700 into TOR -1800. An 18" RCP storm sewer is proposed in WCR 49.5 to carry water from
STOR-1800 north to WCR 58. Here, a 15" lateral from TOR -2800 will connect to the 18" storm
sewer. The storm sewer then turns east under WCR 58 until discharging in a cultivated field
north of WCR 58 and west of 'SCR 51.
S T R- 600 and TOR -2500
Construct a 2.44 acre-feet detention pond at STOR-2600 and a 2.87 acre-feet detention pond at
ST R-2500. The existing 30" culvert (C-$11) crossing the Parkway drains STOR-2600 600 into
STOR-2500. The Co u nth► Staff recommended placing a pond at STOR-2500, 00, as it is a small
strip of non -utilized farmland between the Parkway and an oil and gas well. To decrease the
Page 75 oof 103
r
required pond size at STOR-2600, the release rate was restricted to cfs, which is
substantially more than the 10 -year historic release rate of 23 cfs. However, once discharged
into TOR -2 Soo, water is detained and slowly released at 2.3 cfs. There is some flexibility in the
release rates of these ponds, but will depend on future conditions.
STOR72700
Construct 6.46 acre-feet detention pond in a cultivated field east of the parkway to collect runoff
from SUB -66B and TOR -too. Discharge into the proposed sewer at the historic rate of 7.1
cfs. Given the low slope of the proposed storm sewer, the maximum discharge currently only
reaches 3.18 cfs.
STOR-1800
Construct a 5.5 feet deep, 2.93 acre-feet detention pond to collect runoff from SUB -66C and
discharge from TOR -27001 Given the proximity of SUB -66B and SUB -66C, the allowable
discharge from STOR-1800 0 was set at the combined historic rates of the basins. Therefore,
discharge into the proposed storm sewer was limited to 11,9 cfs, but only achieves a discharge
of 6.78cfs.
TOR -2800
Construct a 2.04 acre-feet detention pond to capture runoff from SUB -66A and protect the
existing residence. Discharge into the proposed 15" storm sewer lateral was limited to the 10 -
year historic release of 3.7 cfs.
Page a 76 of 103
1v0
Figure 32: Parkway Basin Proposed Improvements
i ants
r
..411ra1l
POND
sE (STOR42VO)
SIORtit SEWER
PEED POW
, { it
.. _o t a nj
n Alt 1
MIND CrillinlIng
o a a -
*gla
Page 77 of 103
Exhibit 16: `TOR -1600
E U JO 9L abed
Stags
&t1
Su
Area :
t
ttai 4 g!
Stour
(ac-*)
'rota i
Stange 1
) it
4a2eAci
6
4627
7257 i.
(LOS _
aw 0,05 .w...ga_mi
4628
677454 '
5.76
5_
,
4529
700233 =
15.0.0
21.7,4
otlitf Snarl
Na Cum E'er
rill twists Da Ames
Curt
-
f
i
cia .t
I
ea -pleat, vas tow S.9 729102. 02, 99 Sq. Ft.
tern._ 99 r' t. Yd. 9b1-34 Cu. Yd.
total*
non..99 Yl. 951?4_59 Cu_ We
9C1._34 Cite Yd-.
-4!213.615 Ca. 7 d.c }
,k3 - 6S Ca - Irtuierove,
Ps
Projed No:
Lawn
Reviovicd:
51255
9L
Jc
(14/22/16
WELD COUNTY MASTER
-�DRAINAGE STUDY
WELD COUN 1D , CO
PROPOSED STORAGE
POND EXHIBIT
STOR-1600
Farnsworth
GROUP
1612 SPECHT PONT ROAD, SUS 108
FORT COLLWIS, COLORADO 80525
(970) 484-747 / inbiggoor}oom
rn
via
pvg
1
tta
EW.°GL368d
catatu suanary
0
Cot Tartarflu is 24kara
Stage
t)
Surface
Area
Ott i
Incrementat
Storage
(ac -4)
vat
Storage
(ac* )
4423.5
507708
4624.0
504
6.90
6.90
4625
2S2
14_6B
21,58
Olt
T).
I
U Lei
wax inlay
=If Volute
1. ICC 1 MOO
C20,51. 97 &j_ Ft_ 12$51x..9f Ca. ?db,
1641B.44 ! 1 t1 SI.S) Cu. Td{ >
TotaLs
1 _ r �+c - rt..
12451.94 '. rd.
105,44 Ca,. rJ, 1O12,50 Cu.. Yd.cCut>
Project Mx 01;1255 ao
Bit No
Reviewed:
Dots:
X
04/22/46
WELD COUNTY MASTER DRAINAGE SLIMY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-3200
Farnsworth
GROUP
1612 SPECHT POINT ROAD,,. sunrif 105
FORT GOWNS, COLORADO €10325
(9701484.7477 / 1tilbo@F-v1r_£orn
Exhibit 18: TOR -3100
cot 40 09 °bed
IIMOMIZa _
ti
_ "
Stage :
(t)
Surfice
Area
tin
Picrenen$al
Stage
Cart
TAE
Storage
`ac" )--.—ii,
_
+ 7..0
9914
�.
444....
$5164
0 77 •
0.,'x7
......
.....7918 .......
2`42
... 1 65
bare
Cut INctur noctur .dd &rs
Os
i
N
d I
ret
SCALE 116,W
-3L D Value 1.CAQ
1-000
wraoara5 5q- rt.
;5=.4a Cu- Ida 2-l$ eU. T&
2207.20 en_ YOL<Cimc*
Totals
9029-0_35 rsq. .,
.i 0a'_2I0 en_ is
Project NO:
Book tt
Dunn by:
Re+
WSW
151255
13L
4/72t
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-3100
Farnsworth
GROUP
1612 SPECK POINT ROAD, SUITE 105
FORT CC LRC, COLORADO 80525
(970) 454-7477 / i -w-curn
Exhibit 19: 'TOR 2600
co' 40 Le abed
VIAIY -"V*II "I
I
VI
I •"V"•'% .*WWII"'•"MAA AV IJI7-.
Cut/ .l Suntory
Kam
Darr r
Stage
Surface
Area
incremental
Storage
Total
Storage
4629.5
41368
9.0
4112
Man
4630
1382$1
n9
Factor fl .a._.i
u
S
SuR '�r13Q
1-000 1.091
,laic- ::_:l Su_ rt.
IMP MI
a :
Z7,?:: --;.D5 Cu- 'Yd. -cc n.:
3.to. q- rt
�.- .. . Cu.
.: 5 emu._ '1d. c'3t i
PiQjus::t No:
Look No:
Drown by:
Rovewed
d
R)0;
-25f:is GO
04/72/'
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, , CO
PROPOSED STORAGE
POND EXHIBIT
TOR -2
!I Farncwnrfh
GROUP
1612 SPECFr POINT ROAD.. SUITE 105
FORT GOWNS, COLORADO 50525
(970) 484-7477 ict€ -w'.Corn+
Exhibit 20: STOR-2500
R -25O0
€ o i Jo Z8 a6ed
i
STl t -26W
cataJri sue.
blame
Stage
urface
Area
'
Incremental
Storage
.. _ .._ .. ,
.,....s.........
Storage
..
Total
,.......... - ........,..,.....
_....- - - -..IM .......................
.... ......... ..n a . . ..:1
c... x.
i
464+5
27416
625
29746
0.33
0.33 /
4626
34514
014
1.06
..�.. ..J..,
....................(iy,�j'} ............
47R`2 7
............ 39413.......
..........
.............. ........... yf7, .....
br "� 4.
��
..
1,91
4628
_
44440
0.96
_
2.87
il3t racter nu. Factor 24 Mn
Cs
'
o
Witis-Ort
SICEL-a4X1 Vulvae
c 1.060
1 -dam *7M_26 S4_ it_
5969_27 cn. Yd_
I-24 Cu. d . 5.46S.02 Liar YoL CINC).
764als 47660.25 IN,.
5969.17 Cats_ Yd.
1-24 OA. a stet _02 4a. Tot >
C,
Prat i No:
ikieic No;
Dawn by;
REMowed
15 255
RL
04122/ 6
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-2500
Farnsworth
GROUP
1672 SPECK PONT ROAD, SUITE 105
FORT CO S, COLORADO 80525
(970) 484-7477 / ir�f+a r !-w.com
£01 JO £9 e68d
Project No:
Book No:
[]tots; bit;
Reviewed:
255 1 �_u
04/27 f' E
atage
(I
Sur e ;
Area •
01r)
hcret';ental f Total
Storage Storage
40c -t) r (ac4)
4623.0
83190
4824
90147
1 I s tiQ
V342
215
4.14
4628 104775 _
2.32 : 6.46
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY. Co
PROPOSED STORAGE
POND EXHIBIT
STOR 2700
Farnsworth
GROUP
1612 sPEOfi` POlicr ROAD, SUITE T05
PORT CO NS, COLORADO 80525
(970) 484-7477 ( in#o+@fw w.cOm
Exhibit 22: TOR -1800
CO 40 179 e6ecl
PiqNo: . "51255
Book No:
Dawn ty;
Few;
Oulu; D4/22
L
Surface iiwrem+mtal
Stage I Area Stoma.
(t) M.Y (ac-# )
Total
Sung.
Ca-li
4616.5 ; 15330
4019 .
10660
0.18
0,13
2
19413
0.41
0.60
4621 I 22
040
1.Oa
25291 .. ....
..... 0155 .. ..
1.62
4023 17 0.52 2.214
4024 31066 0.09 2.03
WELD COUNTY MASTER DRAINAGE STUDY
WELL COUNTY, CO
PROPOSED STORAGE
POND EXHIBIT
STOR-1800
Farnsworth
GROUP
1612 SPECK!' PONT ROAD, SUITE 105
FORT COMM COLORADO 80525
1970) 484-74 / info@f-w-torft
tot, 1O 98 062,E
met -dais tZ P17N 3
Outitrillasigary
att raCtoilt
nal Fa 211
Stage
(I)
Sege.
: Area
Incremental ;
Storage
Total
Storage
+4$2....5.......
14310
_
017
, _......4022.._....a...-1
.......
_._...........01 ...._._..
044
- --
4624
20316
a99
4625
22969,
0.50
1.49
4626
25578
0.56
2.04
3T -O300 Volume
1.000 1.000
CUt
Z559S.14 Sc. e . 1;c .4e .. Yu. 0.01 V . _*r1. 2sfC _if , '_d, <
i
N
pct
*CALE "��
Tota2r
25,55.B.14 5cf. rt.
: cRC_4 Cu.
G T .m . ri _ _ c �'t' :�; (.471,02t.
t
Pr ojeci No:
BookNo:
Damen by:
Revbewlix:1:
Oak:
C1512-55 LA)
RL
JO
04/72 f
WELD COUNTY MASTER DRAINAGE STUDY
WELD COUNTY, Co
PROPOSED STORAGE
POND EXHIBIT
STOR-2800
IN Farncwnrth
im
GROUP
1612 SPECHT POINT ROAD, SUITE 145
FORT COLLINS; COLCRADO 60525
1970494-7477 d antfo i-vrccorr
Table 11: Parkway Basin Proposed improvements and Associated Costs Summary
Improvement
ID
Capital
Easement/
ROW
Engineering
Legal/
Administrative
Contract
Admin/CM in/CM
Contingency
Total
Capital Cost
Annual
0 & M Cost
50 -Year
0 & M Cost
STOR-2600
$104,890
$54,450
$15,734
$5,245
$10,489
' $26;223
$217,031
$11,076
553,800
STOR-25OO
$384,187
$29,700
$57,628
$19)209
$ 38,419
$96,047
$625,190
$7,473
$160,536.
STOR-2700
$567,691
$69,300
$85,154
$28,385
$56,769
$141,923
$949,222
$15,465
$773,250
STOR-1800
$342,722
$29,700
$51,408
$17,136
$34,272
$85,681
$560,919
$6,901
$345,050
STOR-2800
$469,083
$54,450
$70,362
$23,454
$46,908 I..
$117,271...........
$781,528
$14,207
$710,350
STOR-1600
$1,6169,336
$331,650
$242,900
$80,967
$161,934
$404,834
$2,841,621
$73,874
$3,693,700
5T0R-3100
$283,613
$49,500
$42,542
$14,181
$28,361
$70,903
$489,100
$10,195
$509,750
STOR-3200
i $1,546,087
$247,500
$231,913
$77,304
$154,609
$386,522
$2,643,935
$50,295
$2,514,750
TOTALS:
$5,317,609
$866,250
$797,641
$265,881
$531,761
$1,329,404
$9,108,546
$189,486
$9,261,186
Page 86 of 103
Lone Tree Creek Basin
C-4
i Replace the existing buried CMP culvert with two 18" RCP culverts. This will eliminate
overtopping of R 49.
WCR 60.5
Driveway culverts are recommended along the south side of WCR 60.5 to prevent localized
ponding by facilitating the flow of drainage towards Lone Tree Creek.
Figure 33: Lone Tree Creek Basin Proposed Improvements
Page 87 of 103
0
Table 12: Lone Tree Creek Basin Proposed Improvements and Associated Costs Summary
Capital
Easement/
ROW
Administrative
Contract
Admin/CM
Improvement
ID
Engineering
Legal/
Contingency
Total
Capital Cost
Annual
0 & M Cost
50 -Year
0 & M Cost
$2,50
$0
$31493
C-4
$34,93
$5,240
1,747
$8,734
$54448
$120
C 86015 Driveways
$0
$ 3,141
$1,047
$ 2,O94
$210
$6,000
$16,386
$4,097
$ 26,765
$51,320
$0
$12,831
TOTALS:
$8,381
$2,794
$5,587
$80,913
$330
$8,500
Page 88 of 103
Airport savita I
-I
In the developed condition, the 100 -year discharge at the 41 x 6.33' elliptical RCP pipe will
overtop WCR 60.5 an approximate depth of 5.75". This is in compliance with County criteria,
and therefore, no improvement is proposed.
O-2
Similarly, the 100 -year developed flow at the 30" RCP will overtop WCR 60.5 at an approximate
depth of 2.4}". Again, no improvements are proposed.
Poudre Basin
No improvements proposed.
' 53 Basin
No improvements proposed.
Table 13: Comparison of Proposed Pond Storage Volume and Hydrologic Model Maximum Storage
Volume (100 -year Event)
STOR
Model Results
Pond Volume
Maximum
Acre-feet,
Proposed
Volume
Pond
Acre-feet
Difference
Acre-feet
ID
200
5.52
7.81
2.29
300
27.83
2913
1.90
500
19.43
22:80
3.17
600
8.46
9.79
1.33
1000
4.00
12.90
8.90
1100
1O57
13.40
2.83
1200
4.59
.16
0.57
1300
5.54
6.63
1.09
1600
16.62
21.68
5.06
1800
2.52
2.93
V.1
2000
32.55
43.19
10.64
2100
5.06
.
0.19
2200
1.94
2.16
0.22
2300
0.07
0.26
0.19
2500
2.19
2.87
0.68
2600
1.78
2.44
0.66
2700
...
6.13
6.46
0,33
2800
1.89
2.04
0.15
2900
45.09
53.13
8.04
3000
0.77
1.05
0.28
3100
1.34
2.42
1.08
3200
14.40
21.58
7.18
3300
6,28
6.61
0.33
Page 89 of 103
4A 2 Near -Term Improvements
Prior to any development occurring along the Corridor, it is recommended the County proceed
with replacing/adding the culverts identified in the previous section. These facilities are low -
impact and will alleviate existing issues. To recap, these improvements include replacing
culverts at Cri25 (Railroad Basin) and C-4 (Lone Tree Creek Basin), and installing new driveway
culverts south of WCR 60.5 and east of the Parkway (Lone Tree Creek Basin). The associated
project costs for these improvements are provided in Table 14. Designs for these culverts are
provided in Appendix E.
Page 90 of 103
Table 14: Summar of Constniction Costs for ea -Term Improvements
Capital
Easement/
ROW
Legal/
Administrative
Total
Cost
Improvement
ID
Engineering
Contract
_ Admin/CM
Contingency .
Capital
Annual
0 & M Cost
6th -Year
0 & M Cost
$0
$2,428
$809
$25,089
C-25
$16,186
$1,619
$4,047
$50
$2,500
Ce4
148
$8+4,934
so
$5,240
$1,747 ....._
$3,493
$8,734 I
$126
$6,000
$10,500
CR60*5 Driveways
$16,386
$0
$0
$3,141
$1,047
$2,094
$4,097
$261765
210
$16,878
$106,002
TOTALS:
$87,506
$10,809 I $3,603
$7,206
$380 c
$19,000
Page 91 of 103
Chapter 5 Analysis of Improvement Alternatives
51 General
The alternative phase begins ins with a brief consideration of a number of possible solutions to the
drainage concerns in the Project area. The objective of this investigation was to approach the
identification of potential alternatives in a broad and conceptual manner and to ensure that all
feasible/common sense types of solutions were considered. Solutions were evaluated for the
Minor 10-, 50-, and Major 100 -year storm events. These include the Minor (10 -year) and Major
(100 -year) events recognized by the County. Urbanized areas, including the Town of Kersey
and City of Greeley, designate the 5 -year storm as the Minor event. Howevert no improvements
proposed in this Study lie within urbanized area boundaries. Sheet 5 in Appendix I displays the
urbanized boundary where a 5 -year release rate would be required. Protection of the Weld
County Parkway and WCR 49 widening was the primary goal of this Study.
5.2 Summary of Drainage Improvement Alternatives
Following completion of the Proposed Condition hydrologic analysis, numerous drainage
improvements were evaluated to determine their potential effectiveness in mitigating drainage
problems in flood -prone areas. The following improvements were identified as potential
solutions:
• Construction of storm sewer and channels
• Addition/replacement of culverts
• Construction of detention ponds
5.3 Criteria for Drainage Improvement Alternatives
Drainage improvements were designed in accordance with Chapter 235 Article XII, of the Weld
County Code. Additionally, the following details were assumed in the analysis of potential
improvements at the direction of County staff:
• Future development will include necessary conveyance elements to reach proposed
improvements
• Low sloping, or even flat pipe is acceptable to the County.
• The location and design of proposed improvements is merely approximate
• An operation and maintenance plan will be adopted with the intent that, amongst others,
culverts remain clear, and ponds do not fill with sediment.
5.4 Cost Estimates
The costs for the proposed improvements are based on construction unit costs for recently
completed drainage projects near the project area (including the Denver metro area), costs
published in the UDFCD bid database, and engineering judgment. The costs are summarized in
a spreadsheet provided by UDFCD. The cost basis of the spreadsheet is drawn from Quarter 'I
of 2012. However, the spreadsheet allows the Colorado Construction Cost Index from COOT to
Page 92 of 103
be used to increase the 2012 costs to reflect current conditions. A cumulative increase of 28.5%
was used to adjust the unit costs from Quarter 1, 2012, to Quarter 4, 2015.
The UDFCD spreadsheet provides two methods for estimating the costs associated with
detention ponds. The first method prices each "item" of the detention pond separately, such as
excavation, outlet structure, etc., and sums them. The second method estimates costs entirely
on the size (in acre-feet) of each pond. UDFCD has established a cost per acre-foot of typical
detention ponds, which includes all excavation and appurtenance costs related to the pond.
Also, the following additional costs were accounted for
• Easement to construct within the railroad Right -Of -Way (ROW): Used $50000 for
each recommended improvement project adjacent to the railroad tracks.
• ROW or Easement Purchase: If "Land Acquisition" is required. For ROW/Easement
purchase, a price of $6,600 per acre was utilized. This price was provided by Weld
county staff. For "Temporary Easements" Farnsworth Group assumed 50% of the
purchase price was appropriate.
• Dewatering: ng: Based on the location of the proposed improvement.
• Mobilization: UDFCD uses a 5% cost for this item.
• Traffic Control: For most recommended improvements, a 5% cost was used, however,
if it is adjacent to a larger County Road, it was increased, or if it is in the middle of a field,
the cost was lowered.
• Utility Coordination/Relocation: Estimated costs were contingent on location to WCR
49. These recommended improvements received a higher cost for utility relocation.
Other recommended improvements received a lower cost.
• Contingency: UDFCDUDFCID uses a 25% contingency.
Operation and Maintenance Cost Summary is also included in the UDFCD spreadsheet. All
items required the input of how many times per year that the maintenance item will occur. One
time per year was used on all items. Items used in some or all of the recommended
improvements are as follows:
• Culvert Maintenance: $1.00 per linear foot of culvert.
• Detention Maintenance (sediment removal, mucking out, tree & weed removal,
structural repairs): $1,927 per acre of disturbance.
• Mowing (channels? ponds, etc.): $64.00 per acre of disturbance.
In summary, the "Capital Cost" for recommended improvements is $21,492,956, while the "Total
Capital cost" with ROW/easement purchase, engineering, legal/administration, contract
administration, and contingency included is $35,618,312.
Estimated cost spreadsheets for all recommended improvements are in Appendix H. Below is a
summary table (Table 15) for reference.
Page 93 of 103
Table 15: Summary of Construction Costs for Proposed improvements
Ca. • ital
Easement/
ROW
Engineering
Legal/
Administrative
Continency
Total
Capital Cost
Annual
0 & M Cost
50 -Year
O & M Cost
Contract
Major
Basin
Improvement
ID 1
Ad rn in/CM
STOR-2100
$390,360
i
$58,554
$19,518
$97590
$637,233
$6,621
$331,050
$32,175
South Platte
$39,036
South Platte
STOR-2200
$168,645
$22,275
$1
, 65
$42,161
$283,675
$4,545
$227,250
$25,297
$8,432
9,
$9,406
$68,214
$2 01
$110,050
$5 643
51,
8
,
$ ` '
South
Platte
STOR-2300
$37,622
South Platte
STOR-3000
$93,65►2
$ 24,750
$14,048
$4,683
$9,365
$23A13
$169,911
$5,128
$ 256,400
$104,890
$54,450 •
$15,734
$5,245
Parkwa
ST0 R:2600
STOR-2500
$29,700
$57,628
$19,209
$38,419
57,473
$160,536
Parkway
$96,047
$•625,190
$384,187
.
$69,300
$85,1.5,4
$28,385
$141,923
$949 222
$15,465
$773,250
Parkway .......__FOR
-2700
$567 691
$56,769
$342,722
$29,700
$34,272
Parkway
STOR-1800
t $85,681
$560,919
$6,901
$345,050
$51,408
$17,136
Parkwa
$469 083
$54A50
$117,271
I $781,528
$14,207
,$7103
70,362
$23,454
STOR-2800
$46,908
Parkway
STOR-1600
$1,619,336
$331,650
$242,900
$80,967
$161,934
$4(J4,834
$2,8441,621
$73,874
$3,693,700
'81613
$49 I 0
$42,542
$14,181
" $ 8,361
S 1ORe.3100
$ f 0,903
$489,100
$10,195
$509,750
Parkway
Parkway
STOR-3200
$1,546,087
$247,500
$231,913
$77,304
$154,609
$386,522
$2,643,935
$50,295
$2,514,750
Kersey
_.$* 01.361 1
$316.:• *1
$315L204
$105,068
$525 MO :_
573 909
$64 262
$3,208 100
51 -01,.. -P00............_._.
$210436
SI0R-1000
$932,022
$217,800
$93,202
$233,006
$1,662,434
543,902
$2,915,100
$139,803
$46,601
Kersey
$919,6041....
-..$5,824,304
$37,398
$1,869,900
$546,397
$182432
$364,265
Railroad
5T0R»2900 ..............$3,642,648
Railroad
STOR-0600
$816,200
...$178,200
$204,050
$1,319,560
p$4
$11,251
$562,55.0
-1
$54,450
$122,430
$40,810
$81,620
Railroad
$133,650
$447 179
$149 060
$298 119
$745,298
7541497
$27,179
$1,358,950
ST0 R-2000
$2,981,191
Railroad
STOR-0500
$1,631,446
$89,100
$244,717
$81,572
$163,145
$407,862
$2,617,842
$18,069
$903,450
STOR-0200
$62825
$111,375
$94,324
$31,441
$62,883
$157,206 :
$1,086,054
$22,499
$1,124,950
Railroad
Railroad
STOR-1200
$432,636
$29,700
$64,895
$21,632
$43,264
$108459
$700,286
$6,028
$301,400
Railroad
...$706„774
$114325
$176,694
1,211„
$25,794
��yy
$1,289,700 r
ST0R-3300 .
#
$106,016
$35,339
$70,677
Railroad
ST0R-1300
$527,080
$34,650
$79,062
$26,354
$52,70$
$131,77{
$851,624
$7,044
$352,200
Railroad
$1,0825
$66,825
$253,206
$1,636,704
$13,589
$679,450
5T0R4100
$151,924
$50,641
$101,283
Railroad
C-25
$16,186
$0
$2,428
$809
$4,047
$25,089
$50
$2,500
$1,619
Lone Tree Creek
$34,934
$0
$8,734
$54448
$120
$6,000
$3,493
C-4
$5,240
$1,747
Lone Tree Creek
CR60.5 Driveways
$16,386
0
$3,141
$1,047
$2,094
$4,097
$26,765
$210
$10,500
$2,304,225
$3,223,943
$1,074,648 I
$2,149,297
TOTALS:
$21,488,402
$5,372,105
$35,612,620
$485,276
$24,770,686
Page 94 of 103
5.5 Alternatives Considered
In a large project area such as this, there are many alternatives to evaluate. Additionally, an
area this large lends itself to many locations in which improvements could be constructed.
Farnsworth Group selected the locations of proposed improvements based on historical flow
patterns, and in areas where issues currently exist. The proposed improvements were based
solely on hydrologic/hydraulic conditions and not based on Parcel boundaries. This method
assured that the "most effective" location was selected and utilized.
All proposed drainage improvements are "approximately" located. Their locations and/or sizes
are not set in stone. When and if the county decides to construct any of the proposed
improvements, a detailed design will be completed at that time. During the detailed design
process, the final location of the proposed improvement will be evaluated in detail.
5.6 Cost -Benefit Analysis
Cost -Benefit analysis is a tool for comparing the relative value of alternative public investments.
If the value of significant benefits and costs can be expressed in monetary terms, the net value,
which is benefits minus costs of the alternatives under consideration can be computed.
Fundamentally, drainage and flood management regulations and infrastructure improvements
are geared towards substantially reducing the risk of future flood related damage, hardship,
loss, and suffering.
Cost -Benefit analysis is the method by which the future benefits of a mitigation project are
estimated and compared to its cost. The end result is a cost -benefit ratio,which is derived from
a project's total net benefits divided by its total project cost. The Cost -Benefit Ratio is a
numerical expression of the cost effectiveness of a project.
The cost -benefit analysis considered two conditions:
1. Existing Condition — Current land use, with no new development.
2. Proposed Condition — Developed area extending 1,000 feet on either side of WCR 49
and Weld County Parkway (as detailed in Chapter 4 -- Hydrologic Modeling).
Both conditions were incorporated into the UDFCD FCD Benefit Cost Analysis spreadsheet which
calculates Total Benefits and the Cost -Benefit Ratio. The results can be used to determine if a
project will produce net positive (or negative) benefits, and the relative cost of those benefits.
"Total Benefits" is calculated using the following equation:
Total Benefits = (Existing Damages - Future Damages) +
CExisting Annual O&M Costs — Proposed SO year O&M 'os ts)
If the Total Benefits result is positive, the proposed project may have a positive financial benefit.
If the result is negative, the proposed project may not have a positive financial benefit with
relation to the cost of the project.
Page 95 of 103
I
Existing Damages are costs associated with damages caused by existing drainage issues.
These values are estimated usi nt the methods described in sections 5.6.1 (Existing Conditions)
and 5.6.2 (Developed Conditions).
No monies were allocated to Future Damages as the proposed improvements are designed to
detain the 100 -year storm event. Storm events larger than the 100 -year event may cause
damage, but are infrequent and outside the scope of this Study.
Existing O&M Costs were determined by estimating the annual O&M costs for each of the
project areas if no improvements are constructed. This was calculated using costs obtained
from UDFCD for the following activities:
• Culvert Maintenance: $1.00 per linear foot of culvert.
• Mowing: $64.00 per acre.
Proposed O&M Costs for each proposed improvement project were calculated in the UDFCD
Cost Spreadsheet and include costs for culvert maintenance and mowing (mentioned above)
and the additional following activities:
• Manhole and Inlet Maintenance: $64.00 per manhole/inlet.
• Detention Maintenance: $1,927.00 per acre.
Existing and Proposed O&M Costs were projected over a 50 -year period to calculate the Cost -
Benefit Ratio,
"Cost -Benefit Ratio" is calculated by the following equation:
Total Benefits
Cost Benefit Ratio
Total Cost
While the positive or negative aspect of the total benefits was determined using the Total
Benefits equation above, the Cost -Benefit Ratio establishes the relative strength (or weakness)
of the proposed project relative to its cost and proposed financial benefits. If the result is
positive, then the proposed improvement will have a positive financial benefit. If the result is
negative, then the proposed project may not have a positive financial benefit.
5.6.1 Existing Condition Damages and Cost -Benefit Analysis
The Existing Condition damages that may occur during 100 -year flood events are as follows:
# Agricultural Damage: Dollars lost due to flooded crops.
O Utilizing current USDA (United States Department of Agriculture) records for the
State of Colorado, the maximum crop prices per unit were determined.
O These prices were then multiplied by the County Production Historical Track
Records from USDA to determine the most expensive crop per acre.
o This method allows the damages to be conservative.
Page 96 of 103
locating and potholing all existing utilities within the area of the improvement. The
average amount of damage to existing utilities is estimated at $50,000.
a This amount was not modified for the Proposed Conditions, as there are no
development plans identifying the needs of the developed properties. Therefore,
no utility damage cost can be accurately calculated.
• Road Damage: Same as Existing Conditions.
The Cost -Benefit analysis for the Proposed Conditions is presented in Table 17.
Table 17 — Cost -Benefit details for Pro pposed Conditions
Developed
Project
Conditions
Proposed
Pro'ect
Conditions
si
Total
Benefits
Berg.{
Cost
Ratio
Project
Annual
O&M
Cost
50-YR
O&M
Cost
Developed
Damages
Total
Capital
Cost
50-YR
s
Cost
Total host
$306,779.00
$174,O44.
$327,730.00
$
0.60
048
0.77
022
$283,675
$88414
$1691911
$227,250
tiliot050
$256,400
)
$510,925
$118,264
$4261311
I
itino
209
$10,450
$533,820.00
$274
$310
$15,500
7
$24820,00
$583,820,00
el s
:..
3000
.850 I
it1838zaoo
$217031
$525,190
$653‘1300
$373,650
11701831
$908,840
i
-$2817234.22
$862Aia.00
-$233,334.22
45t9C),621901
$3,0027389.00
4413,4
-$2,371,278.50
$3,290,216400
$21310,228.00
Ste16,632.00
$621,922.00
I $142&O34OO
. $981,096.00
I $1r209,690.00
I -$210,429.22
,497.00
70
-0.28
2500
$1,6 2
$84,600
$90,723.78
0.38
$049,222
$550,019
$781,528
$2,'841,521
I
I
$173,250
$345,050
$710,3
$3,803,700
I $1.14e412
$905,969
Staten
$6,535,321
enn
g
1
,.....
$10848
tia,
1,433
-0.26
s.O.40
0A7
441
- 1800
$992
$49,500
$110,723.78
$161,8
,
*416.
1600
$2,269
$113,450
$£,783,820.00
$2,643$35
1
9,75
$2,5141750
-*
$998,850
$5,158,085
4
3100 .-...._
SM
1$28,000
105.326030
-046
3200
$2, 120
$106,000
$141,351.50
0*49
0.60
0024
$3.573,909i1
$1,662.434
$2,195,100
$3,857,534
11
i
VN
$1,508
/1240900s$4,60020s0
$75,400
$4,5031820.00
1000
$5,824,4
$14•690900
M94 I
{ �
1?
$136,0
I$3,68,420t00
0.33
$1,3197560
$562,550
$1,882,110
0600
$652
$32,600
$1,183,820.00
0.23
$4j54
4V7
$1.368,960
,i
13.4+7
1164
.
.$513,200
t $2,783b+QO
. _
'0.21
0.28
0,55
$2,617,842
$1•086,054
$700,286
$903,450
$1,1241950
$301,400
$3,52�1,292
$2,2115004
$17001,688
0500
$726
$36,300
$1,883:820.00
0. •
$820
141410
8 S203034620000
1200
$247
$12?350
$90,723.78
449
41225168820
i52
$1570600
; $04159,81
1,
$851,824
0,825
Sla700
$352,200
$Z501,526
$1203,824
I
-0.22
-$260,026.59
$154,952400
$2,550.00
1300
$299
$14,950
$91,874.41
0.33
$1,836,704
$25,089
$540148
1479,450
$2,500
$6,000.00 `,
$Z318,154
$27,589
148
O 00
.. 1,433,x,00
k:
0.09
C-25
$50
$2, 500
$5,000.00
-0.01
4880.00
-$5,290.00
$120
apoo1
$5.x.41
$26,765
$10,500.(.70 j
p7,265
-0.14
0.60.5
$210
$10,500
$5,000.00
P MG.
477,913.90
0.18
While the Cost -Benefit ratio for many of the improvements is positive, some of them still show a
negative ratio. However, many of these improvements are interlinked i n lied as they were designed as
a system of regional detention ponds. They work together to attenuate peak flows. If the Total
Benefit column is averaged, it calculates to $477,913.90 and the Cost -Benefit Ratio calculates
to 0.18. Since both are positive, it is indicative that overall, the improvements are beneficial.
Additionally, it is difficult to predict the value of future development and the associated damages
should they flood. As such, developed damages could potentially be higher than the estimates
provided depending on the type of development that occurs. This scenario would increase the
Cost -Benefit Ratio for each project.
From Figure 34 below, it is apparent that detention ponds at BT R-1200, 3300, and 1300 are
not within the 41,000 -foot developed area, and therefore, do not have a large Cost -Benefit Ratio.
Page 99 of 103
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