HomeMy WebLinkAboutLINCOLN EAST CONVENIENCE CENTER PUD (DIAMOND SHAMROCK) - PRELIMINARY - 40-94D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTLemay will greatly improve the current drainage conditions at this intersection.
In addition, the property to the east will no longer receive the historical flows
0.48 and 1.77 cfs from this property since the developed flows will be safely
routed into the roadside ditch along Lincoln Avenue. All storm inlets and pipes
will be sized in the Final Drainage Study.
Detention has not been provided for this site due to the fact that the site is located
within the 100 year floodplain. Standard practice for developments within the
floodplain area is to release flows from the site as quickly as possible to prevent
further flooding and raising of the base flood elevations. All developed flows
will be routed into the large roadside ditch along Lincoln Avenue. This 15 to 20
foot wide ditch is approximately 5 feet deep and is capable of handling large
flows. Currently, this ditch only receives flows from an existing 12" storm sewer
and runoff from the right-of-way.
A Floodplain Use Permit from the City of Fort Collins will be required prior to
development of this site. In order to meet requirements for the City of Fort
Collins Flood Prevention -and Protection, the site buildings and underground
storage tank slab have been elevated to at least 18 inches above the base flood
elevation of 40.0 feet. The impact of the development will be studied in greater
detail during Floodplain Use Permit Review Process.
• • 1 • 1 • • •
It is determined from the City Reference Manual and Wind Erodibility Zone Map that
the wind erodibility zone is moderate for this site. The potential exists for moderate
erosion during construction. Immediately after overlot grading, gravel mulch is to be
placed in areas that are to be paved, excluding building envelopes. Permanent sod or
seeding with mulch is to be applied immediately after final grading of landscaped areas
calling for grass. Calculations supporting erosion control measures may be found in
Appendix B.
F:\USER\CFS\DRAWAGE\DIAMONDS\DDI 7U EPORTI2.23
B. Developed Site Drainage Racine
The site is divided into seven different basins. The A basins are located within
Lot 1 of the development and the B basins within Lot 2. Three offsite basins
have been examined with this study to help determine the impact of this
development and calculate the combined flows being released into the large
roadside ditch along Lincoln Avenue. The elevation of the site has been lifted
two to five feet with this development to meet Fort Collins Flood Prevention and
Protection requirements for minimum floor elevations of eighteen inches above
the base flood elevation of 40.0. Additionally, the future development of North
Lemay Avenue and Lincoln Avenue was considered in the design grades to
provide smooth transition of the access points for the interim and future
conditions.
Basins A-1, B-1, OSAA, and OSAB are 1.328 acres of landscaping, paving, and
roof area that combines for the 2 and 100 year runoff of 2.55 and 7.32 cfs,
respectively. These basins release into the large capacity roadside ditch along
Lincoln Avenue through a T-0" wide curb opening (design point 1) in the
southeasterly comer of the site.
Basins A-2, B-2 consist of 0.933 acres of landscaping, paving, and roof which
combine for the 2 and 100 year runoff of 1.62 and 4.86 cfs. This combined
runoff, design point 2, is released through the access opening to existing North
Lemay Avenue where area inlets have been provided to capture and route flows
into the roadside ditch along Lincoln Avenue.
The combined flows of basins A-3, B-3, and OS-2 are composed mainly of the
flows within the right-of-way of both Lincoln Avenue and Lemay Avenue. Since
historically these areas have experienced occasional ponding, three area inlets
have been installed along Lemay Avenue to help control runoff in these areas. An
additional storm inlet has been installed along Lincoln Avenue to safely route
right-of-way flows into the roadside ditch once Lincoln is widened. These
combined flows (design point 3) for the 2 and 100 year runoff of 1.62 and 4.29
cfs are routed underground through a series of 18" storm sewers which will tie
into an existing 12" storm sewer along Lincoln Avenue that currently releases
Iinto the roadside ditch. At the point where these storm sewers converge, the 12"
storm sewer will be increased to an 18" pipe and extended under the Lincoln
Avenue access and into the roadside ditch.
Basin B-4 is a small basin located along the north property line that consists of
0.080 acres of landscaping. The 2 and 100 year flow of 0.05 and 0.14 cfs,
respectively, releases into the property located directly adjacent to the north.
This development and the installation of the storm sewer to both Lincoln and
The Lincoln East, P.U.D. is bounded by North Lemay Avenue on the west, East
Lincoln Avenue on the south, and undeveloped land on the north and east, owned by
Webster Associates. It is located in the NW 1/4 of Section 32, Township 7 north, Range
68 west of the Sixth Principle Meridian, City of Fort Collins, Larimer County, Colorado.
The Lincoln East, P.U.D. contains 2.31 acres and is presently two single family
residences and agricultural land. The topography of the site generally slopes from west to
east at approximately 0-0.8 percent. The property is situated in the fringe area (zone A-4)
of the 100 year designated flood hazard area according to the Flood Insurance Rate Map
Community Panel No. 080101-0179 C dated March 18, 1986.
Il. Drainage,. Design Criteria
A. Regulations
This storm drainage and erosion control study has been prepared using the City of
Fort Collins Storm Drainage Design Criteria, dated May, 1984 and the City of
Fort Collins Erosion Control Reference Manual, dated January, 1991.
B. Hydrological Criteria
The Rational Method for determining surface runoff was used for the project site.
The 2 year and 100 year storm even criteria were used in calculating runoff
flows. Times of concentration were calculated using the overland flow equation
and estimates of average flow velocity. Composite runoff coefficients were
calculated for individual site basins and the overall site. Calculations are included
in the Appendix A to this report.
III. Drainage. FarilitV Design
A. C,eneral Concept and Offsite influences
Historically, the land for this site drains to the southeast and eventually into the
large roadside ditch along the north R.O.W. of Lincoln Avenue. The entire site
has been divided into two major basins, A and B.
Basin A, 0.80 acres, is located adjacent to the right-of-way of both Lincoln and
Lemay. Offsite flows from the adjacent one-half of Lemay flow into the site and
travel southeasterly combining with the offsite flows from the Lincoln right-of-
way and release the combined 2 and 100 year runoff of 0.65 and 2.46 cfs,
respectively, into the large roadside ditch along Lincoln Avenue. The land along
the east R.O.W. of Lemay Avenue drains poorly and has received occasional
ponding.
The remaining 1.51 acres has been identified as Basin B. This basin is composed
of the northern and eastern areas of the property and releases the largely
unconcentrated flows of 0.48 and 1.77 cfs, respectively, into the adjacent
property along the east property line.
I
Thble of Contents
pp.scription Page
I. General Location and Description 1
II. Drainage Design Criteria 1
A. Regulations 1
B. Hydrological Criteria 1
III. Drainage Facility Design 1
A. General Concept and Offsite Influences 1
B. Developed Site Drainage Basins 2
IV. Erosion Control Study 3
Appendix A
Vicinity Map
A.1
Rainfall Intensity Duration Curve
A.2
Estimate of Average Flow Velocity
A.3
Runoff Computations: 2 Year Developed
A.4
Runoff Computations: 100 Year Developed
A.5
Composite Runoff Coefficients for Developed Basins:
2 Year
A.6
100 Year
A.7
Runoff Computations: 2 Year Historic
A.8
Runoff Computations: 100 Year Historic .
A.9
Composite Runoff Coefficients for Historic Basins
A.10
Appendix B 11
Rainfall Performance Standards for Fort Collins B.1
Rainfall Performance Standard Evaluation B.2
Effectiveness Calculations B.3 - B.12
Construction Schedule B.13
Erosion Control Cost Estimate B.14
Galloway, Romero & Associates
Design Engineering Planning
Preliminary Drainage and Erosion
Control Study
for
Diamond Shamrock, Inc.
Lincoln East, P.U.D.
at
North Lemay Avenue & East Lincoln
Avenue
Fort Collins, Colorado
December 19%
Prepared for:
Diamond Shamrock, Inc.
520 East 56th Avenue
Denver, Colorado 80216
(303) 297-9777
Attn: Dan Lamb
Prepared by:
Galloway, Romero & Associates
5350 DTC Parkway
Englewood, Colorado 80111
(303) 770-8884
Attn: Carl T. Schmidtlein