HomeMy WebLinkAboutSTETSON CREEK, FIFTH FILING - PRELIMINARY - 16-89K - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT}„ STETSON CREEK 5T" FILING
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JUNE 159 1998
ROCKY MOUNTAIN CONSULTANTS, INC.
FINAL STORM DRAINAGE
AND
EROSION CONTROL STUDY
FOR
STETSON CREEK 5"' FILING
FORT COLLINS, COLORADO
Prepared For:
THE WRITER CORPORATION
Northern Colorado Division
1600-A Water Valley Parkway
P.O. Box 40
Windsor, CO 80550
Prepared By:
ROCKY MOUNTAIN CONSULTANTS, INC.
8301 E. Prentice Ave., Suite 101
Englewood, Colorado 80111
June 15, 1998
RMC Reference No. 2431.061.00
TABLE OF CONTENTS
DESCRIPTION
SECTION I - STORM DRAINAGE STUDY
Introduction
General Location and Description
Historic Drainage Pattern
Drainage Design Criteria
Drainage Facility Design
Conclusion
SECTION II - STORM WATER QUALITY AND EROSION CONTROL
Introduction
Site Specific Conditions
Erosion Control
Conclusion
APPENDIX A - Exhibits
APPENDIX B - Runoff Calculations
APPENDIX C - Detention Sizing
APPENDIX D - Erosion Control Performance Calculations
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' SECTION I - STORM DRAINAGE STUDY
I INTRODUCTION
' This study has been prepared to provide hydrologic and hydraulic design data for
proposed storm drainage facilities required to develop this project. This site contains
I approximately 13.4 acres and will be developed into 101 Multi -Family (Townhomes)
residential units and related infrastructure. All required storm drainage facilities will be
addressed in this report.
GENERAL LOCATION AND DESCRIPTION
This site consisting of approximately is located in the west half of Section 5, Township
6 North, Range 68 West of the 6 h Principal Meridian, City of Fort Collins, County of
Larimer, State of Colorado. The site will be the 5m Filing of the Stetson Creek
' Subdivision.
This site is bounded on the west by Timberline Road, on the south by Stetson Creek
' Drive and Stetson Creek First Filing, on the east by Stetson Creek Fourth Filing and on
the north by Timber Creek First Filing. The site is currently undeveloped but is
planned to be developed as single family residential. The site is sparsely vegetated
and has been used for occasional earth stockpiling.
HISTORIC DRAINAGE PATTERN
The site drains from the Northwest to the Southeast overland to Stetson Creek Drive.
Into the existing Stetson Creek Drive gutter and storm sewer system. Stetson Creek
Drive drains to a low point to the east and discharges into an existing regional Storm
Detention Facility. The entire site and existing facilities are tributary to the McClellands
Basin Drainageway.
A previous drainage report was prepared by RBD Inc. for the entire Stetson Creek
P.U.D. The proposed Fifth Filing was accounted for in the RBD report as Single Family
Residential. The RBD report accounted for approximately 10.5 acres of the site
(Basins 520, 521, 522 & 523) draining into Stetson Creek Drive to RBD Design Point
No. 523. The RBD report accounts for the remaining 2.9 acres of the site (A portion of
Basin 701) to drain to the east to RBD Design Point No. 701.
RBD DISCHARGE SUMMARY:
Design Point No. 2yr Peak Discharge 100yr Peak Discharge
523 10.34cfs 38.04cfs
701 3.70cfs 14.00cfs
No portion of this site lies within a designated regulatory flood plain. The current
F.E.M.A. Flood Insurance Rate Map Flood Zone designation for this site is "Zone X' as
shown on F.I.R.M. Community Panel No. 080102 0014 C.
DRAINAGE DESIGN CRITERIA
This report has been prepared to be in conformance with the City of Fort Collins Storm
Water Utility, Storm Drainage Design Criteria and Construction Standards. The
Hydrologic analysis will be based on the "Rational Method" for peak runoff calculations.
The minor storm analysis will be based on the 2 year flood frequency event and the
major storm analysis will be based on the 100 year flood frequency event. Rainfall
intensity information was obtained from the "City of Fort Collins Rainfall Intensity
Duration Curves, Nov. 1975. Composite "C" values where calculated for each basin
based on the City of Fort Collins Storm Water Utility, Storm Drainage Design Criteria
and Construction Standards.
Storm Water Detention for this site has already been provided for in the regional
Detention Facility designed by RBD Inc. This Detention Facility was designed
assuming that the Fifth Filing Was to be developed as Single Family Residential.
Since the Fifth Filing will be developed as Multi -Family Residential which has a slightly
higher percent of impervious area, we have designed a storm detention facility on site
to reduce peak discharge rates to those accounted for in the RBD study. Normally
Storm Detention facilities are designed to restrict the 10 year and 100 year Storm
events. In this case the purpose of the on site Detention facility is to reduce the peak
discharge from the site to the existing Street and Storm Sewer system which was
designed to convey the 2 year and 100 year events. Therefore the proposed on site
Detention Facility for this development has been designed to detain the 2 year and 100
year events.
Storm water quality enhancement for the entire Stetson Creek development has been
provided for in the regional detention facility. Development of this project will not
change water quality loading rates already anticipated for this site.
DRAINAGE FACILITY DESIGN
Basin Al which is primarily half of Timberline Road begins approximately 310 ft. north
of the NW corner of the site drains from north to south in the street gutter and turns
east onto Stetson Creek Drive. Basin A2 drains overland and in the gutter to Inlet No. 1
a 10' Type R inlet. Inlet No. 1 will intercept the entire minor storm flow (2.4cfs) and
62% of the major storm flow (5.3cfs intercept, 3.3cfs bypass, 8.6cfs total). Intercepted
flows will be conveyed in an 18"RCP conduit to Inlet No. 2 (D.P.-1). Basin A3 drains
overland and in the gutter to Inlet No. 2 a 10' Type R inlet. Inlet No. 2 will intercept the
entire minor storm flow (1.7cfs) and the entire major storm flow (4.9cfs). Intercepted
flows from Inlet No. 1 and Inlet No. 2 will be conveyed in an existing 18"RCP conduit to
and existing 10' Type-R inlet (D.P.-4) in Stetson Creek Drive.
Basin A4 drains overland and in the gutter to a low point in Alder Creek Drive and
thence thru a cross pan to Basin A5. Basin A5 Drains overland and in the gutter to a
lowpoint at Inlet No. 3. Inlet No. 3 a 5' Type-R inlet (D.P.-3) will accept both the minor
storm flow (2.Ocfs) and the major storm flow (7.1 cfs) without overtopping the curb.
Flows from Inlet No. 3 will be conveyed to an existing inlet (D.P.-4) in an 18"RCP
conduit.
Basin A6 will sheet flow directly to Stetson Creek Drive and along the gutter to the
existing inlet at D.P.4. At Design Point 4 flow from Basin A6 as well as bypass from
Design Point 2 will be intercepted by an existing 10' Type-R inlet. The existing inlet at
Design Point 4 will intercept 100% of the minor storm flow (2.3cfs) and 58% of the
major storm flow (6.2cfs). Intercepted flows for the minor storm (7.4cfs) as well as the
major storm (21.5cfs) at Design point 4 will be conveyed to Design Point 10 (RBD D.P.-
523) in an existing 18"RCP conduit. Bypassed flows for both the minor and major
storms will be conveyed in the gutter to Design Point 7.
Basin A7 drains overland and in street gutters to a cross pan at the intersection of
Alder Creek Drive and Stetson Creek Court. The cross pan will convey both the minor
storm flow (2.4cfs) and the major storm flow (8.6cfs) to Basin A9. Combined runoff from
Basins A7 and A8 (Design Point 5) will be intercepted by Inlet No. 4 a 10' Type-R inlet.
Inlet No. 4 will intercept 70% of the minor storm flow (3.6cfs intercept, 1.6cfs bypass,
5.2cfs total) and 60% of the major storm flow (10.9cfs intercept, 7.2cfs bypass, 18.1 cfs
total). Intercepted flows will be conveyed to design Point 6 in an 18"RCP conduit.
Basin A9 will flow in the street gutter to Inlet No. 5 a 5' Type-R inlet. Inlet No. 5 will
Intercept 100% of both the minor storm flow (0.6cfs) and the major storm flow (1.5cfs).
Intercepted flows from Design Point 6 will be conveyed to the on site detention pond by
an 18"RCP conduit.
3
Basin Al will sheet flow directly to Stetson Creek Drive and in the street gutter to
Design Point 7. At Design Point 7 Combined flows from Basin A10, bypass from D.P.-4
and bypass from Design Point 5 will flow thru an existing cross pan to the east to
Design Point 10.
Basin Al will flow overland and in the private drive system to a low point and cross
pan in the private drives between units 54 & 55. Basin Al2 will flow overland and in
the private drive system to a low point at Design Point 8 (Inlet No. 6). Inlet No. 6 a 10'
Type-R inlet will collect both the minor storm flow (3.3cfs) and the major storm flow
(11.7cfs) without overtopping the curb. Collected flows from Inlet No. 6 will be
conveyed to the proposed detention pond in an 18"RCP conduit. Basin A13 will flow
directly as sheet flow and shallow swale flow to the proposed detention pond.
At Design Point 9 developed flows for both the minor storm and the major storm from
basins A7, A8, A9, A11, Al and Al will be detained to reduce the peak discharge at
Design Point 10 (RBD D.P.-523) to the expected rates in the RBD report.
POND DATA:
Storm
stage
storage
developed
release rate
event
( ft.)
(cu.ft.)
Inflow (cfs)
(cfs)
2 year
4932.05
5,582
7.5
2.0
100 year
4933.20
14,422
24.3
9.0
Storm water quality enhancement for this site has already been provided for in the
existing regional detention facility. Since water quality detention volumes are based on
capturing the first'/" of runoff irregardless of land use or ground cover, water quality
volume requirements for this site will be no different for Multi -Family housing. No
additional storm water quality is needed for this site.
Basin A14 will sheet flow directly to Stetson Creek Drive and along the gutter to Design
Point 10. Basin A15 will flow in Madison Creek Drive gutters to Design Point 10.
Total Peak discharge from the site at Design Point 10 will be less than accounted for in
the previously approved Drainage Report by RBD Inc.
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SUMMARY DISCHARGE COMPARISON:
Design 2 year Peak 100 year Peak Approx. Tc
Point (cfs) (cfs) min.
RBD Data 523 10.3 38.0 20.2
RMC Data 10 10.1 37.4 17.9
RBD Data 701 3.7 14.1 -----
RMC Data — 0.0 0.0 -----
CONCLUSION
This final drainage report for Stetson Creek Fifth Filing was prepared to be in
conformance with the City of Fort Collins Storm Water Utility, Storm Drainage Design
Criteria and Construction Standards (Ref. 1). This Drainage design and concept is
adequate to handle developed flows from this project without overloading downstream
drainage facilities.
SECTION II - EROSION CONTROL
INTRODUCTION
The purpose of this section of the report is to develop a comprehensive site erosion
control plan for the Stetson Creek Fifth Filing. This plan is based on the City of Fort
Collins Storm Water Utility, Storm Drainage Design Criteria and Construction
Standards (Ref. 1). This report and enclosed plan will be used to satisfy The City of
Fort Collins Storm Water Utility, Storm Drainage Design Criteria and Construction
Standards and the State of Colorado Grading and erosion control permit requirements.
The Storm Water Discharge Permit requires a Storm Water Management Plan (SWMP)
based on Best Management Practices (BMP). This plan shall be considered to be for
SWMP application to the Colorado Health Department for a general permit under the
Colorado Discharge Permit System (CDPS).
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SITE SPECIFIC CONDITIONS
The site being studied will be developed into 101 multi -family residential housing units
and related infrastructure. The Final Drainage and Erosion Control Plan (see back
pocket) defines the locations of all drainage basins onsite and offsite.
The site will be cleared and graded at one time with the construction of utilities,
pavement, walkways, curb and gutter to follow shortly thereafter. Dwelling Units will be
constructed in two phases.
The potential for pollution sources during construction other than sediment transport is
negligible. An occasional spill while fueling or oiling construction equipment should be
the only other potential pollution source from this site. This type of pollution could
occur at any location within the site. Handling of these types of materials is addressed
in the projects specifications under "Materials Handling and Spill Prevention", as
required by local, state and federal requirements.
There may be non -storm water components of discharge anticipated with this project in
the form of landscape irrigation return flows generated by the housing being
constructed. The "Landscaping Contractor' will be required to address return irrigation
flows until construction is complete. Therefore, this permit plan does not anticipate any
non -storm water flows when infrastructure improvements are completed.
EROSION AND SEDIMENT CONTROL MEASURES
Approximately 13.4 acres will be disturbed during over lot grading. All disturbed areas
that are not to be covered by pavement or buildings will be sodded or seeded. A wide
variety of erosion control measures both temporary and permanent will be utilized on
this project. Perimeter controls such as silt fence, straw bale barriers, vehicle tracking
controls and temporary sediment traps will be installed prior to commencement of
grading operations. Other measures such as inlet protection and surface roughening
will be utilized during and after grading operations. The contractor will be responsible
for washing soil off of all vehicles before leaving the site. Any soil or other deleterious
material tracked onto existing public streets during construction will be cleaned off on a
daily basis.
0
CONCLUSION
The above -described erosion and sediment control measures are industry accepted
standards for capturing and filtering sediment laden runoff. The STORM WATER
management systems will be inspected a minimum of every 14 days of after each
significant rainfall event that may cause surface erosion. Based upon the criteria
established by City of Fort Collins Storm Water Utility, Storm Drainage Design Criteria
and Construction Standards, this application meets of exceeds all applicable
standards. All supporting documentation and calculations are enclosed with this
submittal.
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APPENDIX A
EXHIBITS
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