HomeMy WebLinkAboutGATEWAY AT HARMONY ROAD PUD, 3RD FILING, LOTS 1 & 2, M & O TIRE AUTOMOTIVE - PRELIMINARY & FINAL - 1-88G - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT I
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DRAINAGE AND EROSION CONTROL REPORT
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M & O TIRES, P.U.D.
FORT COLLINS, COLORADO
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DRAINAGE AND EROSION CONTROL REPORT
II FOR
M & 0 TIRES, P.U.D.
FORT COLLINS, COLORADO
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Prepared for:
II Mr. J. Paul Heffron
Real Estate Investment Services Corp.
750 17th Street
Boulder, Colorado 80302
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1111 Prepared by:
Water, Waste & Land, Inc.
111 2629 Redwing Road, Suite 200
Fort Collins, Colorado 80526
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III April 24, 1995
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gill WATER 2629 Redwing Rd. Suite 200,Fort Collins,Colorado 80526-2879
(303) 226-3535
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WASTE fax(303)226-6475
& LAND
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April 24, 1995 WWL #95431.100
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I Mr.Glen D. Schlueter
City of Fort Collins
Utility Services Stormwater
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235 Mathews
Fort Collins, Colorado 80522
RE: M & 0 TIRES, P.U.D.- FINAL DRAINAGE AND EROSION CONTROL REPORT
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Dear Mr. Schlueter:
Transmitted herewith is a copy of the subject report for your review and approval.
All calculations for this report have been made in accordance with criteria established by
111 the City of Fort Collins.
If you have any questions or require any modifications please call me.
Thank you.
Sincerely,
WATER, WASTE & LAND, INC.
1111
Tom Knostman, P.E.
Project Engineer
Civil Engineering Division
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Consulting Engineers and Scientists
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DRAINAGE AND EROSION CONTROL REPORT
FOR
M & 0 TIRES, P.U.D.
FORT COLLINS, COLORADO
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DEVELOPMENT LOCATION AND DESCRIPTION
1111 Location
M & 0 Tires P.U.D will construct a masonry building to serve as a retail tire outlet and
automotive service center. The facility will be located at Mason and Kensington
Streets shown on Figure 1 . The site will consist of Lots 1 and 2 of The Gateway at
Harmony P.U.D., Third Filing consisting of 1 .045 acres. The site lies in the southeast
quarter of Section 35, Township 7 North, Range 69 West of the sixth P.M., City of
Fort Collins, County of Larimer, State of Colorado.
Property Description
The property M & 0 Tires (the Site) will occupy is currently undeveloped but is
surrounded by city right-of-way (R.O.W.) on two sides and private access roads on
two sides. It is presently covered with gravel or is barren and slopes from the
northwest to southeast at a gradient of less than 1 to 3 percent. Historic drainage
from the Site was to the south, southeast to Mail Creek.
DRAINAGE BASIN IDENTIFICATION
Description
The site is within the McClellands/Mail Creek Basin and drainage is carried to Mail
Creek via a 42" Storm Sewer located in the west R.O.W. of South College Avenue.
The precedent for drainage control in this area was set by the approved drainage report
for The Gateway to Harmony Road P.U.D., prepared by Stewart and Associates in
1989 [1]. This plan sets the detention requirement for the property at the difference
between an allowed runoff of 0.5 cubic feet per second (cfs) per acre and 100-year
storm event. The released water shall flow to the 42" storm drainage main via a new
storm sewer connection as detailed on the drainage study attached to this report
(Drawing 5).
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III WATERINTI FIGURE 1 APR 1995
y? WASTE M&O AUTOMOTIVE project:
& LAND SITE MAP 95431100
IIIII INC.
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DRAINAGE DESIGN CRITERIA
Regulations
The City of Fort Collins Storm Drainage Design Criteria [2] is being used as the basis
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Development Criteria Constraints
1111 Neither off site detention nor downstream drainage capacity for the 100-year storm
event exist for Basins 1. Therefore, Lots 1 and 2 will have to detain stormwater on
site and release at 0.5 cfs per acre for storm events up to the 100-year storm event.
Hydrologic Criteria
11111 The Rational Method was used to predict the peak and cumulative runoff from the
proposed development. Calculations are included in Appendix I.
UCalculations
All calculations for this report have been made in accordance with criteria established
by the City of Fort Collins.
Variances
A variances is requested to allow Lots 1 and 2 to detain storm drainage from only
those areas within the property boundaries. This would exclude the half street
portions of Mason and Kensington Streets contiguous to the site. The restrictive area
of the site and the elevation of the existing access roadways adjacent to the low areas
of the site make berming restrictive and thus limits the detention volume available.
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DRAINAGE DESIGN
Concept
Drainage from Basin 1 will be conveyed to the area inlet at Point 1 as shown on
Drawing 5 via overland flow across the new parking areas. Drainage from the area
inlet will be restricted by an orifice plate to the allowable discharge for Basin 1 .
Discharge through the orifice plate will be conveyed to the 42" RCP storm drainage
pipe via an 82 foot section of 12" PVC pipe and a 305 foot section of 15" RCP as
shown on Drawing 5. Drainage easements are provided for these pipe sections.
Storm drainage detention will occur in Pond 1 below the 5037.0' contour. An
emergency spillway will be formed by the break in the paving at that elevation with
excessive flows traveling southeast to Mail Creek via the contiguous parking areas.
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Details
Support for the following discussion will be found in the calculations in Appendix I and
on the drawings furnished with this report. As stated above, the Rational Method was
used for drainage estimates.
Lots 1 & 2:
The site was evaluated a one basin (Basin 1) for analysis purposes. A composite
runoff coefficient for developed conditions of 0.826 was estimated for Basin 1 . The
runoff c-value was derived with runoff coefficients of 0.95 for impervious surfaces and
0.35 for pervious surfaces. The area summary at the beginning of Appendix I provides
a breakdown of the types of surface used to estimate the composite runoff coefficient.
The required capacity for Detention Pond 1 was established based on a mass balance
using the post-development runoff coefficient for Basins 1 with the 100-year storm
event and the allowable release rate of 0.523 cfs. Tabular representations of the mass
balances are presented in Appendix I. Based on these estimates the maximum storage
required in Detention Pond 1 is 8,040 cubic feet. The storage volume provided in
ponds A is 10,050 cubic feet.
The hydraulics of the primary spillway for Pond 1 was evaluated using the standard
orifice, head/discharge relationship for sharp edge weir using a discharge coefficient
of 0.60. The maximum head of 4.8 feet was used to estimate the discharge. This
represents the difference between the water surface at maximum storage and the
center of the orifice. Based on these parameters, an orifice opening 3 inches in
diameter was used.
Emergency flows greater that the 100-year storm event will exceed the volume of the
pond and flow south and east from the detention area over the break in pavement at
the 5037.0 foot elevation.
Downstream Discharqe Flows:
Discharge from Pond 1 will be conveyed to the 42" RCP storm drainage pipe via new
storm drainage piping system. The system will consist of an 82 foot section of 12"
PVC pipe at 4,0 percent grade traveling south, southeast across lot 2 to a new
manhole. The depth of flow in this pipe will be 0.18 feet with maximum discharge
from the pond.
From the new manhole drainage will be conveyed east to the existing 42" RCP in the
— west College Avenue R.O.W. via a new 15" R.C.P. connection at 2.0 percent. The
capacity of the 15" RCP at 2.0 percent will be 9.14 cfs. The connection will be made
through a new manhole. This manhole will be fitted with a 15" RCP stub to the
northwest to allow for future connection and drainage of the lot to the east of Lot 2
(Lot 3). An additional manhole will be placed approximately 130 feet west of the 42"
RCP with a 15" stub section to the southwest to allow for future connection and
drainage of Lot 3.
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WIND AND RAINFALL EROSION EVALUATION
The Larimer County, Soil Conservation Service Soils Report identifies the soils as
belonging to the Nunn Clay Loam which is described as having medium rainfall
erodibility. The rainfall erosion season as detailed in the City of Fort Collins, Erosion
Control Reference Manual [2] (the Manual) is between May 1 and October 31. The
natural drainage of the site is from the northwest to southeast where runoff is ponded
north of the east-west access road in a depression. A cover of gravel currently
provides some protection to the northern portion of the site, but for the most part Lots
1 & 2 are barren.
The Manual details the site as having moderate wind erodibility characteristics and
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states the predominant wind direction is from the west-northwest in this area. The
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Site Soils wind erosion season as detailed in the Manual is between November 1st and May
31 st.
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Construction at the Site is estimated to begin in August 1995 and continue through
December 1995, with the majority of the structural and grading work completed by
October of 1995. This sched'ule places the project within the wind and rain erosion
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seasons.
Performance Standard
1111 The estimated "During Construction" and "After Construction" Performance Standard
for the Site are 81 .0 and 95.3 percent, respectively. For the purpose of estimating the
1111 site's Performance Standard the entire site was broken into two sub-basin areas based
on the final development contours. The sub-basins consist of Lots 1 and 2 as shown
on Drawing 5.
IIII The Performance Standard for the site was estimated using the methods detailed in the
Manual and the estimated, average slope length and slope for each basin. Flow
III lengths and slopes developed for calculation of the "During Construction" Performance
Standard are presented on Standard Form A in Appendix II. The Performance Standard
was taken from Table 5.1 of the Manual. The "After Construction" Performance
Standard is calculated by dividing the "During Construction" Performance Standard by
III 0.85.
IIIPractice Factor Measures
Sediment control practice measures for the M & 0 Tires development will consist of
III the construction of a sediment trap and silt fencing. The location and these features
are shown on Drawing 5.
III Practice factor measures for the site after construction will be dismantled and thus a
weighted P - Factor of 1.0 was used to calculate the effectiveness. The calculations
for the weighted P - Factor for areas contributing to the Pond 1 for both during and
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after construction cases are presented on Standard Form B in Appendix II.
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Cover Factor Measures
Cover factor measures for the site during construction will consist of the building pad
and the existing paving of the adjacent access roads. The building and paved areas
were assigned a C - Factor value of 0.01.
Cover factor measures for the site after construction is completed will consist of
implementation of the landscaping plan. The revegetated areas were assigned C -
Factor values of 0.06 as selected from Table 5.2. Cover factor values for the paved
areas were not changed from during construction conditions. The calculations for the
weighted C - Factor for areas contributing to the Pond 1 for both during and after
construction are presented on Standard Form B in Appendix II.
111 "During Construction" Effectiveness Evaluation
The Effectiveness for the erosion control measures at the site during construction was
U calculated as 81 .4 percent and exceeds the "During Construction" Performance
Standard value of 81.0 percent. Calculations of the basin effectiveness value for the
site are presented on Standard Form B in Appendix II.
"After Construction" Effectiveness Evaluation
1111 The Effectiveness for the erosion control measures at the site after construction was
calculated as-97.9 percent and exceeds the "After Construction" Performance
Standard value of 95.3 percent. Calculations of the basin effectiveness value for the
site are presented on Standard Form B in Appendix II.
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WIND EROSION ANALYSIS
The surface soils at the M & 0 Tires site are rated as moderately wind erodible.
111111 Construction at the site will occur during the windy season of November to May. The
site, with a total disturbed area of less than 1 acre, falls under the exclusion from wind
control requirements. Although the site is excluded from the requirements the
following site features will act to control wind erosion.
• The silt fencing along the east and south margins.
1111 • The cut slope for Pond 1.
• The existing vertical curb along the north and west margins.
INSTALLATION SCHEDULE
Construction of M & 0 Tires is proposed to start in August 1995 and continue during
the fall and winter with the floors, grading and paving completed by of October 1995.
The approximate date of implementation of the erosion control measure during
construction are shown on Standard Form C in Appendix II. As shown on Form C the
silt fence and sediment trap will be constructed prior to overlot grading. Permanent
landscaping will be placed in the late fall prior to the next wind erosion season. The
silt fence will be left in place until landscaping is complete.
EROSION CONTROL SECURITY
The erosion control security requirement for the M & 0 Tires site was estimated based
on the specification of Section 2.0 of the Manual. The cost of the erosion control
measures at the site as detailed above were estimated to cost $848 with a security
requirement of $1 ,272. The estimated cost to revegetate the disturbed areas with a
dryland grass mix according to the city's 1993 mulch and revegetation bid was $680
with a security requirement of $1 ,020. The larger amount is required prior to
construction. Both cost estimates are detailed in Appendix II.
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1111 REFERENCES
1 . Stewart & Associates, INC., Final Drainage Report, The Gateway to Harmony Road
P.U.D., May 1, 1989.
2. City of Fort Collins, Colorado, Storm Drainage Design Criteria and Construction
rStandards, May 1984, Revised January 1991.
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