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VICINITY MAP
N.T.S.
7. REFERENCES
1. City of Fort Collins, "Storm Drainage Design Criteria and Construction Standards"
(SDDCCS), May 1984.
2. "Floodplain and Floodway map, Cache La Poudre River Floodway Analysis", August
16, 2000, Ayres Associates.
3. Soil Survey of Larimer County Area, Colorado. United States Department of
Agriculture Soil Conservation Service and Forest Service, 1980.
4. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1 and 2, dated March 1969, and Volume 3, dated September
1992.
Final Drainage and Erosion Control Report Page 8
Nix Farm February 6, 2001
5.5 Permanent Stabilization
A vegetative cover shall be established within one and one-half years on disturbed areas and
soil stockpiles not otherwise permanently stabilized. Vegetation shall not be considered
established until a ground cover is achieved which is demonstrated to be mature enough to
control soil erosion to the satisfaction of the City Inspector and to survive severe weather
conditions.
Final Drainage and Erosion Control Report Page 7
Nix Farm February 6, 2001
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proposed swales. Erosion control effectiveness, rainfall performance calculations and a
construction schedule will be provided with the final report.
5.2 Dust Abatement
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the
contractor shall furnish all labor, equipment, materials, and means required. The Contractor
shall carry out proper efficient measures wherever and as necessary to reduce dust nuisance,
and to prevent dust nuisance that has originated from his operations from damaging crops,
orchards, cultivated fields, and dwellings, or causing nuisance to persons. The Contractor
will be held liable for any damage resulting from dust originating from his operations under
these specifications on right-of-way or elsewhere.
5.3 Tracking Mud on City Streets
It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights -of -
way unless so approved by the Director of Engineering in writing. Wherever construction
vehicles access routes or intersect paved public roads, provisions must be made to minimize
the transport of sediment (mud) by runoff or vehicles tracking onto the paved surface.
Stabilized construction entrances are required per the detail shown on Sheet 7 of the
improvement plans, with base material consisting of 6" coarse aggregate. The contractor will
be responsible for clearing mud tracked onto city streets on a daily basis.
5.4 Maintenance
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Straw bale
dikes or silt fences will require periodic replacement. Sediment traps (behind straw bale
barriers) shall be cleaned when accumulated sediments equal approximately one-half of trap
storage capacity. Maintenance is the responsibility of the developer.
Final Drainage and Erosion Control Report Page 6
Nix Farm February 6, 2001
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Table 3.1 Drainage Summary
Design
Point
Tributary
Sub -basin
Area
(aq
C (2)
C (100)
tc (2)
(min)
tc (100)
(min)
Q(2)tot
ids)
Q(100)tot
(ds)
1
101
0.85
0.95
1.00
5.0
5.0
2.3
8.4
2
102
0.38
0.25
0.31
11.6
11.6
0.2
0.9
3
103
0.83
0.27
0.34
12.7
12.7
0.5
2.0
4
1 104
0.71
0.36
0.44
11.3
8.4
0.5
2.6
105
3.36
0.12
0.15
15.7
15.7
0.8
3.3
106
1.23
0.28
0.36
12.5
12.5
0.7
3.1
7
107
2.18
0.20
0.26
19.3
19.3
0.7
3.2
5
101-103,105
5.41
0.21
0.24
15.7
15.7
3.0
11.9
6
101.103.105,106
6.64
026
0.33
15.7
15.7
3.7
14.6
4. HYDRAULIC ANALYSIS
4.1 Swale Capacity Analysis
Swale capacities were calculated using Flow Master, developed by Haestad Methods, Inc.
Flow master uses Manning's equation to calculate normal depth for a given cross section.
Triangular sections were used for all swales to minimize the top width of the channel. All
swales have a minimum of 1 foot of freeboard. Capacity calculations are provide in the
Appendix.
4.2 Storm Sewer System
Flow Master was used to size pipes on the site. All pipes have uniform slopes and no bend
so a normal depth analysis is sufficient. Riprap is provided at all pipe outlets. Pipe and riprap
calculations are provided in the Appendix.
5. EROSION CONTROL
5.1 Erosion and Sediment Control Measures
Erosion and sedimentation will be controlled on -site by use of inlet filters, silt fences, straw
bale barriers, gravel construction entrances, and seeding and mulch. The measures are
designed to limit the overall sediment yield increase due to construction as required by the
City of Fort Collins. During overlot and final grading the soil will be roughened and
furrowed perpendicular to the prevailing winds. Straw bale dikes will be placed along
Final Drainage and Erosion Control Report Page 5
Nix Farm February 6, 2001
arm,
3.4 Hydrologic Analysis of the Proposed Drainage Conditions
The Rational Method was used to determine both 2-year and 100-year peak runoff values for
each sub -basin. Runoff coefficients were assigned using Table 3-2 of the SDDCCS Manual.
The Rational Method is given by:
Q = C,CIA
(1)
where Q is the maximum rate of runoff in cfs, A is the total area of the basin in acres, Cr is
the storm frequency adjustment factor, C is the runoff coefficient, and I is the rainfall
intensity in inches per hour for a storm duration equal to the time of concentration. The
frequency adjustment factor, C„ is 1.0 for the initial 2-year storm and 1.25 for the major 100-
year storm. The runoff coefficient is dependent on land use or surface characteristics.
The rainfall intensity is selected from Rainfall Intensity Duration Curves for the City of Fort
Collins (Figure 3.1 of SDDCCS). In order to utilize the Rainfall Intensity Duration Curves,
the time of concentration is required. The following equation is used to determine the time
of concentration
t'=ti+ti
(2)
where t, is the time of concentration in minutes, t- is the initial or overland flow time in
minutes, and t, is the conveyance travel time in minutes. The initial or overland flow time
is calculated with the SDDCCS Manual equation:
t = t1.87(1.1- CCJLo.51/(S)0.33
(3)
where L is the length of overland flow in feet (limited to a maximum of 500 feet), S is the
average slope of the basin in percent, and C and Cr are as defined previously.
All hydrologic calculations associated with the sub -basins shown on the attached drainage
plan are included in the Appendix. A summary of these calculations for the basins is
included in Table 3.1 below.
Final Drainage and Erosion Control Report Page 4
Nix Farm February 6, 2001
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3.2 General Flow Routing
Flows within this site will take the form of sheet, swale, and pipe flow. The existing
drainage patterns have been maintained as much as possible. Stormwater Detention is not
required for the site because it is in the Poudre River Basin. Water Quality will be provided
for the site. A system of swales and pipes has been designed to carry peak 100-yr flows from
the site.
3.3 Proposed Drainage Plan
A qualitative summary of the drainage patterns within each sub -basin and at each design
point is provided in the following paragraphs. Discussions of the detailed design of drainage
facilities identified in this section are included in the following sections.
Runoff from Subbasin 101 will be conveyed via sheet flow to Design Point (DP) 1.
Flows are collected at DP 1 and routed to the water quality pond.
Runoff from Subbasin 102 will be conveyed via sheet flow and swale flow to DP 2.
Flows are routed from DP 2 to the water quality pond in a swale.
Runoff from Subbasin 103 will be conveyed via sheet flow and swale flow to DP 3.
Flows are routed in a system of swales and pipes from DP 3 to the water quality pond.
Runoff from Subbasin 104 will be conveyed via sheet flow and swale flow to DP 4.
Flows are routed from DP 4 to the east in a system of swales and pipes. Flow is release
from the swale and travels overland the existing lake east of the site. Flows from
Subbasin 104 are not treated in the water quality pond, because of the minimal
improvements to the subbasin.
Subbasin 105 is the area tributary to the water quality pond. Flows will be conveyed
via sheet flow to the pond.
Final Drainage and Erosion Control Report Page 3
Nix Farm February 6, 2001
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1.5 Master Drainage Basin
Nix Farm Natural Areas Facility lies in the Poudre River Drainage Basin, but currently
drains to the Spring Creek Drainage Basin through existing ponds east of the site. The City
of Fort Collins Natural Resources Department has future plans to change the outlet point of
the ponds from Spring Creek to the Poudre River. Because of these future improvements the
site was analyzed as a part of the Poudre River Drainage Basin. There is no City of Fort
Collins master plan for the Poudre River Drainage Basin and subsequently no drainage fees
are required. Detention is not required for the basin, however releases from the site must not
cause negative impact to downstream drainage facilities and adequate conveyance must be
shown from this site to a major drainage outfall. Water quality detention is being provided.
2. HISTORIC (EXISTING). DRAINAGE
The historic (existing) flows for Nix Farm Natural Areas Facility consist of overland flow
from the site. The drainage pattern for the property is via overland flow in a east to
northeasterly direction at approximately 1 percent slope. The site has a good ground cover
of native grasses and weeds.
According to the City of Fort Collins Cache La Poudre River Floodway Analysis (Ayres
2000), the site lies out of the 100-YR Floodplain. A copy of the floodplain map is provided
in the Appendix.
3. LOCAL DEVELOPED DRAINAGE DESIGN
3.1 Method
Since the subbasins are less than 160 acres, the Rational Method was used to determine both
the 2-year and 100-year runoff rates for the sub -basins indicated in this drainage report.
Drainage facilities were designed to convey the 100-year peak flows. A detailed description
of the hydrologic analysis is provided in Section 3.4 and the Appendix of this report.
Final Drainage and Erosion Control Report Page 2
Nix Fann February 6, 2001
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1. INTRODUCTION
1.1 Project Description
Nix Farm Natural Areas Facility is a proposed re -development of an existing farm. The site
is located east of the Burlington Northern Railroad Tracks, North of Timberline Road, West
of the Cache La Poudre River, and south of Lemay Avenue. The site is located in the Poudre
River Drainage Basin and contains approximately 27.48 Acres. The site is zoned POL,
Public Open Lands. The project is a portion of Section 18, Township 7 North, Range 68
West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado.
A location map is provided in the Appendix.
1.2 Existing Site Characteristics
According to the "Soil Survey for Larimer County Area, Colorado" (USDA) soils for onsite
and off site basins include: Kim loam (54), Satanta loam (95) & Stoneham loam (103).
Runoff ranges from slow to rapid and erosion ranges from slight too severe for the soils. A
soils map is provided in the Appendix. The site is within the moderate wind erodibility zone
according to the Wind Erodibility Map for the City of Fort Collins.
1.3 Purpose and Scope of Report
This report defines the proposed drainage and erosion control plan for Nix Farm Natural
Areas Facility. The plan includes consideration of all on -site runoff and the design of all
drainage facilities required for this development.
1.4 Design Criteria
This report was prepared to meet or exceed the submittal requirements established in the City
of Fort Collins' "Storm Drainage Design Criteria and Construction Standards" (SDDCCS),
dated May 1984. Where applicable, the criteria established in the "Urban Storm Drainage
Criteria Manual" (UDFCD) dated 1984, developed by the Denver Regional Council of
Governments have been utilized.
Final Drainage and Erosion Control Report Page 1
Nix Farm February 6, 2001
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TABLE OF CONTENTS
aPAGE
TRANSMITTAL LETTER............................................................................................................. i
TABLEOF CONTENTS................................................................................................................ ii
1. INTRODUCTION.............................................................................::...................................1
1.1 Project Description .................................................. ..1
1.2 Existing Site Characteristics...........................................................................................1
1.3 Purpose and Scope of Report ..........................................................................................1
1.4 Design Criteria................................................................................................................1
1.5 Master Drainage Basin....................................................................................................2
2. HISTORIC (EXISTING) DRAINAGE................................................................................2
3. LOCAL DEVELOPED DRAINAGE DESIGN...................................................................2
'
3.1 Method............................................................................................................................2
3.2 General Flow Routing.....................................................................................................3
3.3 Proposed Drainage Plan ..................................................................................................3
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3.4 Hydrologic Analysis of the Proposed Drainage Conditions
...........................................4
4. HYDRAULIC ANALYSIS.....................................................................................................5
4.1 Swale Capacity Analysis.................................................................................................5
5. EROSION CONTROL...........................................................................................................5
5.1
Erosion and Sediment Control Measures........................................................................5
5.2
5.3
Dust Abatement...............................................................................................................6
Tracking Mud on City Streets.........................................................................................6
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5.4
Maintenance....................................................................................................................6
5.5
Permanent Stabilization., ......:.........................................................................................7
7. REFERENCES.......................................................................................................................8
Appendix
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J-R ENGINEERING
A Subsidiary of Westrian
February 6, 2001
Mr. Basil Harridan
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
MRE: Final Drainage and Erosion Control Report for Nix Farm Natural Areas Facility.
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Dear Basil,
We are pleased to submit to you for your approval, this Final Drainage and Erosion Control Report
for Nix Farm Natural Areas Facility, zoned POL (Public Open Lands). The site is located in the
Poudre River Drainage Basin and currently drains to the Spring Creek Drainage Basin. All
computations within this report have been completed in compliance with the City of Fort Collins
Storm Drainage Design Criteria.
We greatly appreciate your time and consideration in reviewing this submittal. Please call if you
have any questions.
Sincerely,
Prepared by,
William F. Strand
Project Engineer, P.E.
attachments
Reviewed by,
Randall Provencio
Project Manager
2620 East Prospect Road, State 190, Fort Collins, CO 80525
970-491-9888 - Fax: 970-491-9984 - w Jrengineering.corn
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FINAL DRAINAGE AND
EROSION CONTROL REPORT
NIX FARM NATURAL AREAS FACILITY
Prepared for:
City of Fort Collins
Natural Resources Department
Mark Sears, P.E.
P.O. Box 580
Fort Collins, Colorado 80522
(970)416-2096
Prepared by:
JR Engineering,LLC
2620 E. Prospect Road, Suite 190
Fort Collins, Colorado 80525
(970)491-9888
February 6, 2001
Job Number 9023.27
777777777