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Drainage Study For
King Soopers Shopping Center
Fort Collins, Colorado
Page Four
Area "C"
Drainage Area "C" is located in the east central half of the
development. The area consists of 5.87 acres of commercial
buildings and paved roadway. This total acreage will produce
39.6 cfs from a 50-year storm. The historic 50-year storm
runoff is 10.2 cfs.
To provide, adequate storage of the runoff from Area "C", a
detention' facility will be required. A pond is to be
constructed in the parking area in the central portion of the
property to contain drainage from Area "C". The detention
volume of 22,830 cubic- feet is required for the area'. Total
rooftop storage of 4,754 cubic feet, and detention in the
parking area of 22,780 cubic feet, will provide adequate
detention of 27,534 cubic feet. Release of the drainage will
be through a 12-inch in Taft Hill Road as indicated on the
plan. The reduction of runoff from 39.6 cfs to cfs in the
12-inch RCP and 10.9 overland through the. entrances for the
drainage areas involved is much less than the historic value.
CONCLUSION
With development of this property, there will be an increase in the
total 50-year runoff from 20.3 cfs historical to 65.0 'cfs
developed. The drainage policy set forth by the City. of Fort
Collins is to detain the difference between developed and
historical 50-year flows on -site. With this policy in mind,
detention of the excess will be accomplished by rooftop detention
and detention in sump areas in the parking lots. The sump areas
during a 50-year storm would have water ponding to a maximum of one -
foot in depth. The developed runoff flow has been reduced from 65.0
cfs to 20.2 cfs as required by drainage policy.
This Drainage Study is submitted for review and approval.
GENGE/MEURER, SERAFINI AND MEURER, INC.
Prepared by: ✓
William H. Keller
Design Engineer
Reviewed by:
amen. uarney
r ct Manager
Mr WHK:sc
Drainage Study For
King Soopers Shopping Center
Fort Collins, Colorado
Page Three
The peak runoff generated within Area "A" will be partially
detained on -site by rooftop storage with controlled release.
Since it is impractical to have a detention pond behind the
building to contain a minor amount of water, the excess will
be allowed to pass overland to Taft Hill Road.
The available building storage for Area "A" is 1,294 cubic
feet and the required' storage is 1,176 cubic feet. However,
the actual building storage to be used is 160 cubic feet. The
reason for this small amount of storage is due to the aerial
extent of the building versus the basin areas. The remainder
of the SO -year runoff, 7.6 cfs.,. will be allowed to flow
overland to Taft Hill Road as mentioned in the above
_ paragraph.
Area "B"
Drainage Area "B" ,is located in the northwest corner of the
site. The area consists of 3.27 acres of commercial
buildings, residential homes, and paved loading areas. The
total acreage, will produce 16.2 cfs for a SO -year storm. The
historic 50-year storm runoff is 6.1 cfs.
The peak. runoff generated within Area "B" will be detained on -
site (rooftop and loading areas) with controlled maximum
release not to exceed historic peak flows. The detention
volume computations were based on the triangular hydrograph
method.
A detention volume of 4,9SO cubic feet is required for Area
"B" (Exhibit 4). This volume of water will be detained on -
site by rooftop storage of 3,087 cubic feet and in sump areas
behind the buildings in the southeast corner of the basin.
Total available storage for Area "B" is more than adequate for
the 50-year runoff. The release of runoff (1.7 cfs) from the
detention areas will be by means of a 12-inch RCP that will
drain under the buildings to Area "C" inlet, to the southeast,
in a pipe as shown on the plans.
s
Drainage Study For
King Soopers Shopping Center
Fort Collins, Colorado
Page Two
The detention ponds, outlet structures, and pipes are, sized to
regulate the amount of storm runoff to be released from. the site.
during a 50-year storm. The size 'of the sewer pipes to be used was
determined by using the "Design Manual" published by the American
Concrete Pipe Association.
The area inlets called for in this report are to be situated in sump
areas as .indicated on the plans. They are sized to release the
historic runoff value of storm waters from the drainage area. The
detention and controlled release of storm runoff from the 'rooftops
of buildings has been designed into the drainage system. The
required available detention on rooftops was estimated on an
average depth of 1.5-inches of water over the plan surface area of
the building. The actual configuration and grade of the roof, as
well as the number and locations of roof drains, would determine
their .size ,and design. At the time of this study, such information
was not available. The roof drains should be designed as the
information becomes available.
DISCUSSION
The results of the drainage analysis are shown on the drainage map
enclosed at the back of this report, and in the computation sheets
in the Appendix. It should be noted that the drainage areas' peak
flows, etc., may change slightly during the final design of the
project.
Area "A"
The proposed site was divided into three drainage basins, A
through C. Drainage Area "A" consists of 1.71 acres along the
west and south side of the proposed development. The. area
drains from west to east along the south side of the proposed
building. The area consists of commercial buildings,
residential homes, and paved roadways. The 50-year historic
flow for Area "A" is 3.2 cfs and the developed flow will be 8.1
cfs.
DRAINAGE STUDY
FOR
KING SOOPERS SHOPPING CENTER
. FORT COLLINS, COLORADO
INTRODUCTION
a
This Drainage Study has been prepared for a proposed shopping
center. The site is south and west of the intersection of West
Elizabeth Street and Taft Hill Road, City of Fort Collins, County
of Larimer, State.of Colorado. It is bounded on the North by West
Elizabeth Street, on the .East by Taft Hill Road, and on the South
and West by Miller Brothers Subdivision, Filing No. 6. The area
consists of approximately 7.9 acres .to be developed into retail
stores with parking facilities. The runoff from the developed site
for the 50-year return period is 65.0 cfs, while the historic value
is 20.3 cfs. The difference between developed and historic flow
will be detained on -site in the parking areas and on the building
rooftops.
CRITERIA
The peak runoff quantities were estimated by the "Rational Method",
as described in the "Urban Storm Drainage Criteria Manual"
published by the Denver Regional Council of Governments (DRCOG),
and according to the City of Fort Collins drainage criteria. -
The design of the detention system is based on the difference in
runoff of the 50-year historic. storm and the 50-year developed
storm. The coefficients used in the drainage system design are
from 0.50 to 0.90 for building areas and 0.9 for paved areas. A
composite coefficient was calculated where a combination of
different types of areas existed in the same basin. The
coefficients were increased by 20% for the 50-year storm analysis.
The initial times of concentration used in determining rainfall
intensities are calculated from the overland flow curves (Exhibit
2) from the DRCOG Drainage Manual. To the overland flow time was
added the time of flow in the street and over the parking lots by
using the flow pathlength divided by the average velocity. The
rainfall intensity -duration -frequency curves (Exhibit 3) were from
information provided by the Engineering Department of the City of
Fort Collins.
DRAINAGE STUDY
m;
KING SOOPERS SHOPPING CENTER
FORT COLLINS, COLORADO
April,. 1977
+Job'Number 46650
-Prepared By-
GENGE/MEURER'SERAFINI AND MEURER, INC.
570 West 44th Avenue
Denver, Colorado 80216
(303) 455-7321
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The existing 12 inch RCP storm sewer from the existing catch basin to the existing
manhole will be relocated to the new catch basin ( see drawing ).
The design of the detention system in the previous report is based on the 50 year storm
event and not the 100 year storm required by the new regulation. For the 100 year storm a
detention volume of 19,338 cubic feet of storage is required for Basin `B" ( see mass
diagram for detention volume, Basin `B"). The total available storage of 20,503 cubic
feet is adequate. If storm runoff raise above the detention elevation in the relocated and
existing catch basins, overflowing will occur to prevent water from entering the finished
elevation of the building.
The proposed expansion has no impact on Basins "A" and "C". However, the previous
drainage study only provide adequate detention storage for the 50 year storm event.
Present- City drainage criteria requires 10 and 100 year storm detention. In Basin "A', the
increased flow for the 100 year storm runoff will flow overland to Taft Hill Road. Except
for a small amount of roof storage no detention area is available. For Basin "C", the
existing parking area used as detention pond is inadequate to provide for the 100 year
storm runoff. The required storage of 56,616 cubic feet exceeded the available storage of
39,498 cubic feet ( see mass diagram for detention volume ). However, the additional
storm runoff will flow overland through the shopping center entrance into Taft Hill Road
when the parking area / detention pond reaches capacity.
IV. EROSION CONTROL
This development lies within the Moderate Rainfall Erodibility Zone and the Moderate
Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists for
minor erosion problems during construction of the King Soopers building expansion. It is
anticipated that the project site improvements will be subjected to both wind and rainfall'
erosion before the new building is erected. This project will comply with the City's erosion
control specification.
V. CONCLUSION
The proposed King Soopers store expansion to be constructed on an area that is paved
and will not create any additional impervious surface area. Based on the recent topo
information of the entire shopping center, the effects of the expansion has no adverse
impact on the existing grading / drainage patterns and the drainage basins.
Storage volume for Basin "B" is adequate for the 100 year storm. For Basins "A" and
"C", the increase storm runoff will be allowed to flow overland into Taft Hill Road.
PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY
FOR
KING SOOPERS STORE #9 EXPANSION
FORT COLLINS, COLORADO
L INTRODUCTION
A. Project Location
The King Soopers store is located in the Cedarwood Plaza Shopping Center on the
southwest corner of West Elizabeth Street and Taft Hill Road. More specifically, this site
is situated in the Southeast quarter of Section 16, Township 7 north, Range 69. west of
the 6th Prime Meridian in Fort Collins, Colorado.
B. Description of Property
The proposed King Soopers store expansion lies on the south side of the existing building.
The expansion consisted of 5165 square feet of new retail space in an area that has-been
paved. Renovating 5625 square feet of existing retail space directly adjacent to the south
of the existing King Soopers store will also be included in the expansion.
II. DRAINAGE DESIGN CRITERIA
A. Regulations
The City of Fort Collins Storm Drainage Design Criteria will be use for the subject
expansion where it is applicable.
B. Design Criteria
The Rational Method for determining surface runoff was previously used for analysis of
the Cedarwood Plaza Shopping Center site. The 50 year storm was used in calculating
runoff values for this site. The previous Drainage Study prepared in 1977 have been
included in the appendix of this report. However, the 10 and 100 year storm is being used
for this study in accordance with City regulations.
III. DISCUSSION
The existing site is divided into drainage basins A, B and C ( see previous drainage study
in the appendix ). The proposed expansion will be located entirely in Basin "B" with an
area of 3.27 acres. The new building will abut the existing King Soopers store and existing
paved loading area on two sides. All the storm runoff from the building expansion will be
collected in the roof drain system. The existing 12 inch RCP storm sewer that runs
beneath the existing building will be extended on the west end to accommodate the
expansion. A new catch basin will be installed at the low point to retain the overland flow.
PRELIMINARY
DRAINAGE AND EROSION CONTROL STUDY
KING SOOPERS # 9 EXPANSION
FORT COLLINS, COLORADO
Prepared for :
Zylstra Baker Surveying, Inc,
1510 West Tufts Avenue
Englewood, CO 80110
Prepared by :
Chang Engineering Co., Inc.
10210 S. Progress lane
Parker, CO., 80134
Tel: 303-841-8887
June 10, 1997