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PROJECT
SITE
VICINITY MAP
NOT TO SCALE
APPENDIX A
VICMTY MAP
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5.2 Drainage Concept
This project was designed in order to minimi�.e the number of drainage structures
required, to maintain the overall drainage pattern to the greatest extent possible and to
conform to previous criteria placed on this site. This has been accomplished by utilizing
overland And gutter flow, maintaining flow patterns where possible and providing an on
site detention and water quality pond.
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6. REFERENCES
1. Larimer County, Colorado, "Larimer County Storm -Water Management Manual",
prepared by Resource Consultants, Inc., dated May, 1979.
2. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria
Manual", Volumes 1, 2, and 3 dated March, 1969, and Volume 3 dated
September, 1992.
' 3. Final Drainage Study for Fossil Lake, P.U.D. First Filing, Larimer County,
Colorado, prepared by Northern Engineering Service, Inc. dated January 28, 1999.
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prevent dust nuisance, which 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 plans, on right-of-way or elsewhere.
4.3 Tracking Mud
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. A stabilized construction entrance is required per the detail
1 shown on the detail sheet with base material consisting of 6" coarse aggregate. The
1 contractor will be responsible for clearing tracked mud on a daily basis.
4.4 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. Maintenance is the
responsibility of the developer.
4.5 Permanent Stabilization
I All soils exposed during land disturbing activity (stripping, grading, utility installations,
stockpiling, filling, etc.) shall be kept in a roughened condition by ripping or disking
along land contours until mulch, vegetation or other permanent erosion control is
installed. No soils in areas outside project street rights of way shall remain exposed by
land disturbing activity for more than thirty (30) days before .required temporary or
permanent erosion control (e.g. seed/ mulch, landscaping, etc.) is installed.
1 5. CONCLUSIONS
5.1 Compliance with Standards
Criteria from Section 2.4.1 of the Larimer County Storm —Water Management Manual
and the Final Drainage Study for Fossil Lake P. U.D. First Filing, prepared by Northern
Engineering Services, Inc. have been complied with for the preliminary design of this
project.
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collected in a sump inlet (Inlet #3) in the southern portion of the site and is then
conveyed in Storm 1 to the detention pond.
Basin 4 consists of the eastern 1/3 portion of the project. The basin is bounded on the
east by Fossil Lake First Filing. This basin contains several buildings and access drives in
the eastern portion of the site and the detention area in the southeast corner of the site.
Runoff from this basin will flow in swales and curb to a curb opening and will then enter
the detention area.
Basin 5 is a small basin in the southwest portion of the site. This basin includes the
I south half of two buildings and landscaped area. Runoff from this basin is collected in a
swale and is conveyed east to an area inlet (Inlet #4). The runoff then enters Storm 2
and is conveyed to the detention area.
IBasin 6 is a small basin in the south central portion of the site. This basin includes
I portions of two buildings and landscaped area. Runoff from this basin is collected in a
swale and is conveyed south to an area inlet (Inlet #5). The runoff then enters Storm 2
and is conveyed to the detention area.
Runoff from Basins 1-6 enter the detention pond and the flow is released at a rate of 0.5
cfs per acre or a total of 3.59 cfs. Water quality extended detention is also incorporated
into the detention pond. Release from this pond will flow through a water quality outlet
structure into Storm 3 which will convey the flow to the existing 15' type `r' inlet in
Shallow Pond Drive. From this point, the water is conveyed in a storm system designed
and constructed with the Fossil Lake First Filing.
4. EROSION CONTROL
4.1 Erosion and Sediment Control Measures
IErosion and sediment will be controlled on -site by use of straw bale barriers in the
proposed swales, inlet protection at all inlets, a gravel construction entrance and silt
fence along the perimeter. See the Drainage and Erosion Control Plan.
' The measures are designed to limit the overall sediment yield increase due to
construction. Straw bale dikes will be utilized in limited areas adjacent to any stripping
stockpiles that are created during grading. They will also be used to slow runoff around
' the perimeter of the site.
4.2 Dust Abatement
During the performance of the work required by these plans, the Contractor shall carry
out proper efficient measures wherever and as necessary to reduce dust nuisance, and to
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Following is a summary table of rational method calculations for the developed drainage basins on
r site:
TABLE 3.1 DEVELOPED DRAINAGE SUMMARY TABU'.'.
Des.
Point
Basin
Designation
Area
(ac)
C
tc (2)
(min)
Q (2)
cfs
tc (100)
min)
Q (100)
cfs
1
1
2.15
1 0.64
7.0
3.5
5.7
16.4
2
2
0.90
0.57
11.4
1.1
9.0
15.8
3
3
0.65
0.59
5.0
1.1
5.0
4.7
4
4
3.02
0.60
6.6
4.7
5.5
21.8
5
5
0.38
0.44
7.5
0.4
6.7
1.9
6
6
0.08
0.65
5.0
0.1
5.0
0.6
Hydrologic calculations in Appendix B provide a more detailed presentation of
calculations and results.
3.3 Specific Flow Routing
A summary of the drainage patterns within each subbasin is provided in the following
paragraphs.
DEVELOPED BASINS
Basin 1 consists of the western 1/3 portion of the project. The basin is bounded on the
west by the Ziegler Road and contains a several buildings and access drives in the
western portion of the site. Runoff from this basin will flow from north to south to Inlet
#1. This inlet is ongrade and will capture approximately 5 cfs. The remaining flows will
enter Basin 2.
Basin 2 consists of the west half of the middle portion of the proposed site including the
eastern half of several buildings and the west half of Dripping Rock Lane. The runoff
'. from this basin is collected in a sump inlet (Inlet #2) in the southern portion of the site
and is then conveyed in Storm 1 to the detention pond.
Basin 3 consists of the east half of the middle portion of the proposed site including the
western half of several buildings and the east half of Dripping Rock Lane. The runoff is
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3. DRAINAGE FACILITY DESIGN
3.1 General Concept
Runoff from the site currently flows from northwest to southeast. It is proposed to
maintain this runoff pattern to the greatest extent possible. Property and conveyances
downstream of this site have been designed to accommodate attenuated flows from this
t site. Detention and water quality are being proposed onsite for this development and are
provided in the southeast corner of the site.
3.2 Hydrologic Analysis of the Existing Drainage Conditions
The Rational Method was used to determine the 2-year and 100-year runoff values for
the developed condition. The Rational Method utilizes the equation:
Q = CCJA
(1)
` Where Q is the flow in cubic feet per second (cfs), A is the total area of the basin in acres,
C is the runoff coefficient, and I is the rainfall intensity in inches per hour.
The historical C value was calculated for the basin using runoff coefficients from Table.
4.2.6-1 of the Larimer County Storm -water Management Manual.
In order to determine the rainfall intensity, the time of concentration is required. The
following equation was used to determine the time of concentration.
tc = ti + tt (2)
' where t. is the time of concentration in minutes, t, is the initial or overland flow time in
minutes, and t, is the travel time in the channel, pipe, or gutter in minutes. The initial or
overland flow time is calculated with the equation:
ti = [1.87(1.1- CCf)Los]/(S)0s3 (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 is the runoff coefficient.
The rainfall intensity was calculated using formulas defined in the Final Drainage Study
for Fossil Lake P. U.D. First Filing, prepared by Northern Engineering Services, Inc. The
formulas were generated specifically for Fossil Lake Village P.U.D. using the computer
program "Watershed Modeling", by Eagle Point.
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2. DRAINAGE DESIGN CRITERIA
2.1 Regulations
This report was prepared to meet or exceed the "City of Fort Collins Storm Drainage
Design Criteria Manual" specifications as well as the Final Drainage Study for Fossil
Lake P. U.D. First Filing, prepared by Northern Engineering Services, Inc. Where
applicable, the criteria established in the "Urban Storm Drainage Criteria Manual"
(UDFCD), 1984, developed by the Denver Regional Council of Governments, has been
used.
2.2 Development Criteria Reference and Constraints
The site is accounted for in the Final Drainage Study for Fossil Lake P. U.D. First
Filing, prepared by Northern Engineering Services, Inc. This site is included as Basin 1
in the Northern Engineering report and runoff from the undeveloped lot is
accommodated in .the First Filing calculations. The drainage patterns outlined in the
study have been maintained to the extent possible.
Runoff from this site will be carried to the detention pond by curb, gutter, storm pipe and
drainage swales. The flow will be released from this site by through a proposed pipe
which will be tied into the existing 15' Type `R' inlet (Inlet 1 on Storm Line 1-1 in the
Northern report) in Shallow Pond Drive at the southeast comer of the site. The flow
will then be conveyed in the storm system (Storm Line 1-1) installed with the Fossil Lake
First Filing improvements. This storm system was sized to accommodate detained
release from this site.
The detention release for this site was set by the Final Drainage Study for Fossil Lake
P. U.D. First Filing and was determined to be 0.5 cfs per acre. The amount of release
allowed from the detention pond on this site is 3.59 cfs.
2.3 Hydrologic Criteria
Runoff computations for developed runoff were prepared for the 2-year minor storm and
the 100-year major storm frequency utilizing the rational method. Hydrologic
l calculations associated with the developed runoff are attached in Appendix B.
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2.4 Hydraulic Criteria
Storm drainage pipes have been sized to convey flows from the proposed site to the
detention pond in the southeast comer of the site. The pipes have been sized using
StormCad by Haestad Methods.
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(r 1. GENERAL LOCATION AND DESCRIPTION
1.1 Location
Fossil Lake P. U.D., Fourth Filing is a proposed 5.9 acre medium density, multi -family
�. residential development located in the west''/2 of Section 9, Township 6 North, Range 68
West of the Sixth Principal Meridian in Larimer County, Colorado.
This site is located within the Fossil Lake P.U.D., south of Shallow Pond Drive, east of
Trilby Road and west of Snowy Creek Drive. Please refer to the Vicinity Map in
Appendix A. Twelve (12) 4-plex buildings are proposed for the site. The project will
access from Shallow Pond Drive on the north and have one internal street that ends in a
cul-de-sac in each direction.
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1.2 Description of Property
The site consists of approximately 7.5 acres of land. The land is currently undeveloped
with single-family lots (Fossil Lake Second Filing) to the south and east. The area to the
north is undeveloped and Ziegler Road exists along the west boundary of the site.
The site has topography generally ranging from 0.9% to 3.5% slopes. Runoff currently
flows from northwest to southeast and into Shallow Pond Drive along the southern
boundary of the site.
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Runoff from Ziegler Road on the west and Shallow Pond Drive on the south has been
accounted for with the Final Drainage Study for Fossil Lake P.U.D. First Filing by
l' Northern Engineering. Detention is not provided for these streets in Fossil Lake Fourth
Filing.
C! The project site is located within the Fossil Creek Drainage Basin as defined on the
Fort Collins Storm Water Basin Map and Fossil Creek Master Drainageway Planning
Study. No part of this site is within a FEMA flood hazard area.
The drainage patterns for this site should not be changed greatly with this development.
I Final grading will be completed with final design for this project and required to conform
to the Final Drainage Study for Fossil Lake P. U.D First Filing, prepared by Northern
Engineering Services, Inc. Dated January 28, 1999.
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ITABLE OF CONTENTS
TABLEOF CONTENTS........................................................................................................... iii
1.
GENERAL LOCATION AND DESCRIPTION
�.
1.1 Location...............................................................................................................1
1.2 Description of Property ........................................................................................1
1 2.
DRAINAGE DESIGN CRITERIA
2
2.1 Regulations..........................................................................................................
2.2 Development Criteria Reference and Constraints..................................................2
2.3 Hydrologic Criteria..............................................................................................2
2.4 Hydraulic Criteria.................................................................................................2
3.
DRAINAGE FACILITY DESIGN
3.1 General Concept..................................................................................................
3
3.2 Hydrologic Analysis of the Existing Drainage Conditions ..................................... 3
3.3 Specific Flow Routing..........................................................................................4
4.
EROSION CONTROL
4.1 Erosion and Sediment Control Measures..............................................................
5
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4.2 Dust Abatement...................................................................................................
C4.3
Tracking Mud......................................................................................................
6
4.4 Maintenance..................................................:.......................................................6
4.5 Permanent Stabilization........................................................................................6
5.
CONCLUSIONS
5.1 Compliance with Standards.................................................................................6
5.2 Drainage Concept................................................................................................7
1 6. REFERENCES................................................................................................................7
APPENDICES
l A VICINITY MAP
B HYDROLOGIC CALCULATIONS
C HYDRAULIC CALCULATIONS
D DETENTION & WATER QUALITY POND CALCULATIONS
E EXCERPTS FROM PREVIOUS REPORTS
F TABLES AND FIGURES
iii
North Star
'® design, inc.
fJuly 30, 2002
Basil Hamdan
City of Fort Collins Stormwater
700 Wood Street
Fort Collins, CO 80524
RE: Final Drainage and Erosion Control Report for Fossil Lake P.U.D., Fourth Filing
Dear Basil,
I am pleased to submit for your review and approval, this Final Drainage and Erosion Control
Report for Fossil Lake P.U.D., Fourth Filing. I certify that this report for the drainage design was
prepared in accordance with the criteria in the City of Fort Collins Storm Drainage Manual.
I appreciate your time and consideration in reviewing this submittal. Please call if you have any
questions.
,Sincere '
Patricia Kroetch, P.E.
700 Automation Drive, Unit I Windsor, Colorado e0550
870-686-6939 Phone 0 970-686-1188 Fax
FINAL DRAINAGE &
EROSION CONTROL REPORT
FOSSIL LAKE P.U.D., FOURTH FILING,
FORT COLLINS, COLORADO
Prepared for:
KEM BUILDERS, LLC
3000 South College Ave.
Fort Collins, CO 80525
Prepared by:
NORTH STAR DESIGN, INC.
700 Automation Drive, Unit I
Windsor, CO 805550
(970) 686-6939
July 30, 2002
Job Number 111-05