HomeMy WebLinkAboutHARMONY RIDGE, 2ND FILING - PDP - 49-95F - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI REFERENCES
City of Fort Collins Storm Drainage Criteria Manual, Department of Public Works and Water
Utilities Storm Drainage Division, May 1984
Final Drainage Report for Harmony Ridge P.U.D., TST, Inc. Consulting Engineers, January
1999
National Engineering Handbook NEH 4, prepared by Soil Conservation Service, U.S.
Department of Agriculture, April 21, 1993.
Preliminary Subsurface Exploration Report — Harmony Ridge Filing II, Earth Engineering
Consultants, Inc., May 2004.
Urban Storm Drainage Criteria Manual, Denver Regional Council of Governments,
dated 1969, Volumes 1, & 2
Urban Storm Drainage Criteria Manual, Volume 3 — Best management Practices,
Denver Regional Council of Governments, Urban Drainage and Flood Control District,
September 1999
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EPROIECC FDESLA4DL350
HARMONY RIDGE MDOCSL350 DRAMAGE REPORT.DOC
Drainage and Erosion Control Reportfor Harmony Ridge Filing l!
Febnawry 23, 20034 Page 10
The detention pond was designed using the release rate from Basin C-1 from the TST analysis
for Harmony Ridge I. TST calculated a historic 2-year discharge of 5.65 cfs. Using 5.65 cfs as a
release rate for the pond, a storage volume including water quality capture volume (WQCV) of
1.28 acre-feet is required. The existing outlet structure for the pond will be lowered to the pond
invert elevation of 5084 to maximize storage capacity and eliminate the stagnant water that exists
with the current invert out elevation of 5087.6. With 4:1 side slopes, 1.28 acre-feet of storage
can be achieved with a water surface elevation of 5090.71, providing 1.29 feet of freeboard.
Outlet structure calculations will be provided in the final drainage report.
EROSION CONTROL
A temporary erosion control plan is to be implemented for the site during construction. During
construction, straw bale barriers will be placed at regular intervals in the swales to dissipate
energy, and ultimately intercept and detain sediment (to be presented in the final drainage
report). In addition, silt fences are to be constructed in accordance with the UDFCD Manual (V.
3) along the perimeter of the site to further limit transport of sediment off -site (see Erosion and
Sediment Control Plan). A single construction entrance with vehicle tracking control on
Centennial Drive is proposed.
WETLAND DETERMINATION AND REVIEW
A small wetland is located in the northwest corner of the site. No disturbance is proposed to the
wetland.
CONCLUSIONS
The Harmony Ridge Filing II Drainage Report has been prepared to comply with the present
City of Fort Collins Storm Drainage Criteria Manual and the USDCM. The drainage plan
presented in this report is intended to effectively and safely convey storm runoff through the
proposed site. No variances are requested.
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ETROFECr FnL SLL 1350 HA CW RIDGE MDOCSU350 DR AGEREPORT.DOC
'Drainage and Erosion Control Report for Harmony Ridge Filing II
February 23, 20034 Page 9
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Drawing Name:
2350 ENG GRADWG CURRENT
Project Number
2350
Date
06-0-04
Global Holdings, LLC
Fort Collins, CO. Sheet j of 1
Storm Drainage Criteria Manual). Rational Method discharge calculations for the 2-year and
100-year events are presented in Tables A5 and A6, respectively. These tables include routed
discharges and discharges for each drainage sub -basin. The "comments" column on each of the
Rational Method tables indicates the basins from which storm runoff was routed. Table A7
presents an extrapolation procedure to extend the City of Fort Collins IDF duration data to 225
minutes for purposes of calculating pond storage requirements. The pond storage requirement
calculations are presented in Table A8. Table A9 presents water quality capture volume
(WQCV) and pond grading calculations. Street capacity calculations and inlet capacities are
presented in Appendix B.
Proposed cross -pans, channels, and sidewalk chases will be analyzed with Flowmaster®
software as part of the final report. Swales have been analyzed for freeboard conditions. The
freeboard condition has been defined as the 100-year discharge plus an additional 33%
(1.33.1100-year discharge.) Storm sewers will be analyzed with Stormcad®. Per City of Fort
Collins criteria, all swales and sidewalk chases will be designed for the 100-year event.
DESCRIPTION OF THE DRAINAGE PLAN
The historic drainage plan for the Harmony Ridge Filing H site is illustrated in Figure 2. Figure
3 illustrates the developed condition drainage plan including grading and drainage basin
delineations.
Drainage Basins 1 and 2 contain portions of Fromme Prairie Way. Discharge from Basin 1 will
be routed to Basin 4. Ultimately runoff from Basins 1 and 4 will combine with runoff from
Basins 3, 5, and 8 to flow into the area inlet in the landscape median in the downstream end of
Basin 8. Routed discharge to the inlet in Basin 8 for the 2-year and 100-year events will be 2.26
cfs and 17.23 cfs, respectively. In the event that the area inlet in Basin 8 should become
obstructed during a flooding event, a cross -pan will route runoff to Basin 11 within ponding
depth criteria for minor and major events.
The outlet to the landscape depression in Basin 11 will route minor event discharges from Basins
1, 2, 3, 4, 5, 8, 9, 10, 11, and offsite basin 01. Total routed discharges for the 2-year and 100-
year events to Basin 11 are 7.45 cfs and 30.4 cfs, respectively. Mite Basin 02 and Basin 13
will contribute flows to the natural channel downstream of Basin 12 and into the pond to the
southeast.
Street capacity calculations are presented in Appendix B. Street capacities were calculated for
' average slopes in each basin. Calculations were presented for 24-foot cross -sections and 30-foot
cross -sections with roll-over and vertical curbs, where applicable. All streets flow depths will be
within criteria presented in Appendix B for both minor and major events.
f Basins 6 and 7 will contribute 6.57 cfs and 17.88 cfs for the 2-year and 100-year events
respectively. The Linear sediment traps will be located upstream of the Trilby Lateral in
locations where flows will be more concentrated from Basins 6 and 7 as part of the erosion
' control plan to be prepared as part of the Final Drainage and Erosion Control report.
Historically, 19.51 cfs is contributed to the Trilby Lateral.
Drainage and Erosion Control Report for Harntony Ridge Filing 11
E:TROIECf F MANDV.350 HARMONY RIDGE MDOCS2350 DRARJACE REPOU DOC Febnary 23, 20034 Page 6
STORM DRAINAGE CRITERIA
Storm drainage design criteria were referenced from the City of Fort Collins Storm Drainage
Criteria Manual. Additional reports and manuals referenced in this report include the Final
Drainage Report for Harmony Ridge P.U.D prepared by TST in Fort Collins (January 1999),
Preliminary Subsurface Exploration Report — Harmony Ridge Filing II prepared by EEC (May
2004), and Urban Drainage and Flood Control District's "Urban Storm Drainage Criteria
Manuals, Volumes 1, 2, and 3. "
Per Table 3-1 in the Fort Collins Storm Drainage Criteria Manual, Initial (minor) and Major
storm return periods for all residential development are the 2-year and 100-year events,
respectively. Design storms were based on 2-hour rainfall events. The Rational Method,
appropriate for calculating runoff for basins less than 160 acres, was used to estimate peak runoff
values for various basins on this site. The Fort Collins Storm Drainage Criteria Manual presents
runoff coefficients increased in 1999.
Storm sewers will be required to effectively convey runoff on the Harmony Ridge Filing II site.
Two area inlets and two single Type-R inlets are required to convey minor event discharge.
Gutters at vertical and roll-over curbs, cross -pans, and swales will be the primary means of
transporting remaining minor event storm discharges to landscaped areas. Major event
discharges will also be conveyed across the site through surface infrastructure.
Erosion control measures will be specified in the final drainage analysis. Anticipated measures
required for the site include silt fencing, vehicle -tracking control, straw bale barriers in swales,
inlet protection, riprap, and re -vegetation of disturbed areas with crimped straw.
DRAINAGE FACILITY DESIGN
RUNOFF CALCULATIONS
Storm runoff calculations for the Harmony Ridge Filing II Development are presented in
Appendix A. Table A.1 presents composite runoff coefficients for the 2-year and 100-year
precipitation events. Runoff coefficients were referenced from the City of Fort Collins Storm
Drainage Criteria Manual.
The time of concentration calculations are presented in Table A.2 for the proposed condition.
The travel time velocities were referenced from Figure 3-3 of the Fort Collins manual. Table
A.3 presents the historic drainage analysis for 2-year and 100-year events. Rainfall intensity -
duration data is presented in Table A.4. Rainfall intensity -duration data was calculated from
linear interpolation of time -intensity data presented in Figure 3-1 of the Fort Collins manual.
Time of concentration values for each basin were assumed to be equal to the storm duration (a
standard assumption, as discussed in the Urban Drainage and Flood Control District Urban
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EAPR07ECr Fa.ESV. NDV350 HARMONY RIDGE MDOCSL350 DRAINAGE REPORT.DOC
Drainage and Erosion Control Report for Harmony Ridge Filing II
February 23, 20034 Page 5
FIGURE 1 — VICINITY MAP
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E TROJECf FILESLL., Q350 HARMONY RJDGE MOCS12350 DRAJNAGE REPORT.DOC
Drainage and Erosion Control Reportfor Harmony Ridge Filing //
February 23, 20034 Page 4
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GENERAL DESCRIPTION AND LOCATION
The Harmony Ridge Filing II site is approximately 14 acres in size. The site is located in
southwest Fort Collins, off Fromme Prairie Way (Old Harmony Road) and west of Seneca Street
in the northwest quarter of Section 3, Township 6 North, Range 69 West of the Sixth P.M.,
Larimer County, Colorado. The project proposes 45 single-family lots and 13 multi -family
townhome lots. The single-family residences are to be patio homes located on small lots and
intended to fit with the topography of the site. The multi -family units will face north toward
Fromme Prairie Way.
EXISTING CONDITIONS
1 The site is currently vacant land. Existing elevations on the property range from approximately
5150 feet at the high point in Fromme Prairie Way along the north property line to 5090 along
the Trilby Lateral meandering along the south side of the site. Prairie Ridge Drive is stubbed to
the site on the east side. No surface irrigation infrastructure is present on the Harmony Ridge
Filing II site.
According to the Preliminary Subsurface Exploration Report for Harmony Ridge Filing II, Fort
Collins, Colorado by EEC, 2 to 4 inches of topsoil were encountered on the site. Brown sandy
lean clays were found underneath the topsoil. Soils exhibited increasing sands, gravels, and
cobbles with depth.
DRAINAGE BASINS AND HISTORIC RUNOFF
' Harmony Ridge II has been divided into two historic drainage basins. Both basins ultimately
drain to the Trilby Lateral at the base of the ridge. The drainage concept for the developed
condition provides 100-year event discharges that are less than the 100-year historic contributing
discharge to the Trilby Lateral.
One detention pond southeast of the site is required for the site. The pond was initially analyzed
as part of the Harmony Ridge Filing I project by TST in 1999. The majority of developed runoff
I from the Harmony Ridge Filing II site drains to the pond with some runoff from the west side of
Harmony Ridge Filing 1.
The drainage analysis for the Harmony Ridge Filing II project is comprised of 13 drainage
basins. The site will drain to ultimately two outfall locations. Runoff from most of the site will
be routed to the pond while remaining discharge will flow south to the Trilby Lateral.
Three landscape medians have been designed with landscape depressions as part of a
stormwater-conservation concept to encourage infiltration of runoff within the site. Although the
increased infiltration will decrease peak storm discharge, no reduction of the total discharge has
been considered in this analysis for conservative measure.
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IE:TROFEGT FTLESILAND12550 HARMONY RIDGE I100CS050 DRAINAGE REPORT.DOC
Drainage and Erosion Control Report for Harmony Ridge Filing II
June 11, 2004 - Page 3
ENGINEER'S CERTIFICATION BLOCK
I hereby certify that this Drainage and Erosion Control Report for the drainage design for the
Harmony Ridge Filing U Site was prepared by me (or under my direct supervision) for the
owners thereof and meets or exceeds the criteria in the City of Fort Collins Storm Drainage
Criteria Manual.
O O
V:� O.•d
• W 37724 7-1 •
Eric M. Skowron
Registered Professional Engineer
State of Colorado No. 37724
FTR03ECf FaY-SU,vurn2350 nnrtMor RIDGE
Drainage and Erosion Control Reportfor Harmony Ridge Filing I!
February 23, 20034 Page 2
I TABLE OF CONTENTS
Tableof Contents............................................................................................................................ 1
Engineer's Certification Block....................................................................................................... 2
General Description and Location.................................................................................................. 3
ExistingConditions..................................................................................................................... 3
Drainage Basins and Historic Runoff............................................................................................. 3
Figure1 — Vicinity Map........................................................................................................... 4
StormDrainage Criteria.................................................................................................................. 5
DrainageFacility Design................................................................................................................ 5
RunoffCalculations..................................................................................................................... 5
Description Of The Drainage Plan......:....:..:............................................................................... 6
Figure 2 — Historic Drainage Patterns at the Harmony Ridge Filing II Site ............................ 7
Figure 3 — Developed Drainage Plan For the Harmony Ridge Filing H Site ........................... 8
ErosionControl............................................................................................................................... 9
Wetland Determination And Review.............................................................................................. 9
Conclusions..................................................................................................................................... 9
References..................................................................................................................................... 10
Appendices.................................................................................................................................... 11
APPENDIX A: RUNOFF AND DRAINAGE CALCULATIONS .......................................... 12
APPENDIX B: HYDRAULIC CALCULATIONS.................................................................. 13
APPENDIX C: REFERENCED INFORMATION AND SUPPORTING DOCUMENTS...... 14
jpio
EAMIECT FR.ES V;DU50 HARMONY RIME R00CM350 DRAINAGE REIVRT.DOC
Drainage and Erosion Control Reportfor Harmony Ridge Filing 11
June 11, 2004 - Page I
A
s
June 11, 2004
LinA npedn-lii(ntnn
Li gintyury
&-imnmmtal f Conunimiy Awnuti g
Mr. Basil Hamdan
Light & Power, Stormwater, Wastewater, Water
700 Wood Street
PO Box 580
Fort Collins, CO. 80522
RE: Harmony Midge Filing II Preliminary Drainage and Erosion Control Report
JSD Project No. 2350
Dear Mr. Harridan:
Please refer to our enclosed "Preliminary Drainage and Erosion Control Report for the Harmony
Ridge Filing U." This report has been prepared in accordance with the drainage guidelines .
presented in the City of Fort Collins Storm Drainage Criteria Manual.
Please feel free to contact our office at (970) 484-1921 at your convenience if you have any
questions regarding this report. We thank you for your time and consideration in reviewing this
drainage report submittal.
Sincerely,
JIM SELL DESIGN,'INC. _
Eric Skowron, P.E.
Project Engineer
Enclosure
cc: Jim Newcomb
File .
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PRELIMINARY DRAINAGE AND EROSION CONTROL REPORT FOR:
HARMONY RIDGE FILING II
FORT COLLINS, COLORADO
Prepared for:
'JIM NEWCOMB '
932 E. PITKIN ST.
GLOBAL HOLDINGS OF COLORADO, LLC
FORT COLLINS CO 80524
(970) 221-3076
. R
0
Project #2350
June 11, 2004
Prepared by:
153 West Mountain Avenue
Fort Collins, Colorado 80524
FAX 970.484.2443
970.484.1921
T