HomeMy WebLinkAboutDrainage Reports - 03/18/1992Cry
Fina pproved Report
FINAL DRAINAGE REPORT
FOR
TOYS "R" US AND WESTERN AUTO STORES
SOUTH COLLEGE AVENUE AND BOCKMAN DRIVE
FORT COLLINS, COLORADO
JUNE 4, 1991
(REVISED JANUARY 14, 1992)
PREPARED FOR:
ROSENBAUM/DEAN
101 North Cascade Suite 400
Colorado Springs, Colorado 80903
719-630-0066
PREPARED BY:
PARSONS & ASSOCIATES CONSULTING ENGINEERS
432 Link Lane Plaza
Fort Collins, Colorado 80524
303-221-2400
PROJECT NO. 91.03 TOY
FINAL DRAINAGE REPORT
FOR
TOYS "R" US AND WESTERN AUTO STORES
SOUTH COLLEGE AVENUE AND BOCKMAN DRIVE
INTRODUCTION
This drainage investigation has been prepared along with 'final
plans for the Toys "R" Us and Western Auto Store to be located
northeast of the intersection of South College Avenue and Bockman
Drive. - This study was prepared in accordance with the City of Fort
Collins "Storm Drainage Design Criteria and Construction Standards"
and based on the site plan prepared by Masterplans Design Concepts,
Inc., a topographic survey completed by Rick Lewis, P.L.S.'and
preliminary review comments completed by the City of Fort Collins
staff.
SITE DESCRIPTION
The study area is situated in the Northwest Quarter of Section
36, Township 7 North, Range 69 West of the 6th Principal Meridian,
City of Fort Collins, Larimer County, Colorado. The site is
bounded by: South College Avenue on the West, Western Wardrobe and
Larimer County #2 Canal on the North, JFK Parkway on the East and
Bockman Drive on the South.
The site comprises approximately the, northern one third of
Superblock 5 plan prepared for South College Properties. The
Western Auto Store site is located approximately in the.area of the
previous South Grove S.I.D. The site is presently undeveloped
except for an abandoned house and an existing lumber yard which
will be relocated. The, site slopes generally to the North and
Northeast at 0.5% to 6%. Vegetation consists of native grasses and
brush along with a few scattered trees.
HISTORIC DRAINAGE
The project area falls within the limits of the Heart Special
Improvement District (S.I.D.) Final Drainage Report completed in
January, 1985. This area (shown in Figure 1) includes the 2.4 acre
Western Auto site, the 5.4 acre Toys "R" Us site and approximately
5.1 acres of undeveloped area to the south.
-1-
I
Three different.subbasins contribute to the historical runoff.'
Existing Area #1 is a sliver of land which drains into South
College Avenue. This. area is approximately .4 acres and is the
area between the East curb of south college Avenue and the front of
buildings in this area. Existing Area #2 is approximately 2.0
acres in area and covers a level area just East of South College
Avenue along Area #1. Flows here continue to the North where they
are intercepted by the Western Wardrobe, Wendy's, and Palmer House
drainage system and held in a retention pond behind the Palmer
House. The remainder of the flows in Area #3 are surface flows
which continue Northeasterly before they are intercepted by the
Larimer #2 Canal. Once intercepted by the canal they are
transported in the canal Southeasterly to either Warren Lake or the
Larimer #2 extension ditch. A small 0.38 acre portion of this area
north of the Larimer #2 Canal continues to.drain to the north away
from this project.
These existing basin patterns are modified by the development
of this project. Existing area #1 will be reduced by approximately
one-half as the Western Auto Store grading and landscaping are
completed. The runoff from Area #2 will be totally contained on
the Western Auto Store site and will eliminate any runoff to the
existing commercial properties to the north. Area #3 will continue
to discharge into the Larimer #2 Canal; however, through controlled
outlets at reduced flow rates.
MASTER DRAINAGE
Following the guidelines developed under "Master Storm
Drainage Report For the Landings P.U.D." by Cornell Consulting
Company and reaffirmed by "Final Drainage Report for Heart Special
Improvement District" by Engineering Professionals, Inc., only a
two year historic discharge should be allowed into the Larimer #2
Canal. This discharge was further defined by the Heart S.I.D.
final report at a limit of 0.87 cfs/acre of development. This
release rate was used to compute the required detention volumes for
each basin identified in this report.
DRAINAGE UNDER DEVELOPED CONDITIONS
The final site layout and grading are attached as Figure 2.
In general, the grading plan will follow the contour of the
existing slopes, tipping to the northeast. A summary of the
proposed drainage basins follows:
-3-
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.Dk.9//(/AGE
A t
BASIN Al (Western Auto South Parking Area)
Basin •A, includes the South parking lot of the Western
Auto store site, the north one-half of Bockman Drive from
South College Avenue to Mitchell Drive,and the west one-
half of Mitchell Drive from Bockman Drive to the first
driveway entrance. This basin is 1.20 acres large and
will require 10,260 ft.3 of detention volume discharging
at 1.17 cfs (See Table 1).
BASIN A, (Western Auto Building and North Parking Area
Basin AZ includes approximately the north parking area,.
the west one-half of the Mitchell Drive right-of-way from
the southerly entrance to the northerly entrance, and the
roof drainage from the proposed building. This basin is
1.05 acres large and will require 6,840 ft.3 of detention
volume discharging at 0.78 cfs (See Table 2).
BASIN A-, (South College Avenue)
The proposed site plan shows three graded and landscaped
berms along the South College Avenue curb line along the
west edge of the Western Auto site. The area which will
flow from the side of these berms towards South College
Avenue is reduced from .4 acres to .2 acres. In
addition, the runoff :from these grassed areas will be
substantially less than the exposed .dirt and packed
gravel areas which now exist. We feel that this will
allow us to improve the drainage conditions along South
College Avenue.
Existing flows in South College Avenue will continue to
flow from South to North. A valley gutter at the
intersection of Bockman Drive and South College Avenue
will allow flows to continue Northerly without being
diverted into this site. Bockman Drive grades increase
from South College Avenue at a grade of 1.67% for a
distance of over 150 feet. This is reflected in the
street design for Bockman Drive as part of the site
construction plans. A curb inlet has been provided in the
curb line along South College Avenue. This inlet has
been sized to intercept and divert a portion of basin A3
flows into basin Al. The detention pond for subbasin Al
will be sized to detain these flows. Only a small
portion of subbasin A3north of this curb inlet will flow
offsite.
-5-
BASIN A4 (North End of Mitchell Drive)
Due to the grades established by the design of Mitchell
Drive through the Feeney Subdivision immediately North of
this site it will be impossible to contain all of the
Mitchell Drive runoff on site. Approximately .03 acres
will be undetained at the North end'of Mitchell Drive.
In the short term, this runoff will be diverted to the
East by a drainage swale and discharged into the Larimer
#2 Canal. Ultimately, as Mitchell Drive is built, this
area will drain into the Northerly Mitchell Drive
improvements.
BASIN B, (Toys "R" Us Parking Area)
Basin Blincludes all of the Toys "R" Us site to the west
of the building, the east one-half of Mitchell Drive and
the north one-half of Bockman Drive from Mitchell Drive
to the approach at the west edge of the Toys "R" Us
building. This basin is 2.42 acres large and will
require 16,590 ft.2 of detention volume discharging at
2.00 cfs (See Table 3).
BASIN B,
Basin B2 includes the remainder of the .Toys "R" Us site
which includes the roof drainage, the north one-half of
Bockman Drive from the .approach at the west end of the
building to JFK Parkway, the areas directly north and
east of the proposed building and the east one-half of
the JFR right-of-way from Bockman Drive to the Larimer #2
canal. This basin is 2.24 acres large and will require
15,186 ft3 of detention volume discharging at 1.90 cfs
(See Table 4).
BASIN B3
Basin B3 includes a 0.38 acre parcel at the northeast
corner of the site which is north of the Larimer # 2
canal. This piece will be maintained in its natural
state, (0.10 acres drain into the canal and 0.28 acres
drain to the northeast). It is anticipated that
detention needed for this area will be included in
development to the north of this site.
-6-
BASIN #B4 (North End of Mitchell Drive)
Due to the grades established by the design of Mitchell
Drive through the Feeney Subdivision immediately North of
this site it will be impossible to contain all of the
Mitchell Drive runoff on site. Approximately .03 acres
will be undetained at the North end of Mitchell Drive.
In the short term, this runoff will be diverted to the
East by a drainage swale and discharged into the Larimer
#2 Canal. Ultimately, as Mitchell Drive is built, this
area will drain into the Northerly Mitchell Drive
improvements.
BASIN C
Basin C includes all of the area south of Bockman Drive
between South College Avenue and the proposed JFK
Parkway. The southerly limits of the basin extend
approximately 450' south of the centerline of Bockman
Drive to an existing ridge line. Approximately 5.1 acres
contributes runoff to the southwest corner of Bockman
Drive and the proposed JFK Parkway. A channel has been
provided here to convey historical flows around the Toys
"R" Us .site and into the Larimer #2 Canal. The
preliminary design of the JFK Parkway and Bockman Drive
intersection includes inlets and storm drains which will
carry JFK runoff and detention pond releases from this
area to the Larimer #2 Canal. Drainage from the South
one-half of the Bockman Drive right-of-way is intercepted
by this channel as well. The channel for this basin will
convey the 100-year historic flow which is calculated as
7.2 cfs. Any detention or storm drainage improvements
for this sub -basin will be constructed as the site
develops or as the JFK Parkway is constructed.
-7-
-SUMMARY
The total developed Toys "R" Us - Western Auto site includes
approximately 7.72 acres. As per the allowed release rate of 0.87
acre/feet per acre, this site would be allowed 6.72 cfs of runoff
in the 100 year event. To meet this requirement, several detention
ponds with controlled outlets have been provided. The total runoff
from the developed site (as summarized in the following table) is
6.97 cfs.
Actual runoff from this site exceeds the allowable by .25 cfs.
We feel that this is within the accuracy of the calculations. In
addition, this is a temporary situation. Flows from Basins A4, B3,
and B4 will be collected by detention ponds rin future developments
to the north. This means that approximately 1.12 cfs from these
three basins will ultimately be detained. We feel that this is an
effective and conservative solution to the Toys "R" Us drainage
conditions. We request a variance to allow this .25 cfs to be
discharged from the Toys "R" Us and Western Auto site in a 100 year
storm.
-8-
0
SUBBASIN SUMMARY
Drainage
Area
Allowed
Actual
Req.
Avail
Ori-
Remarks
Subbasin
(Ac)
Runoff
Runoff
Deten
Deten
fice
(On-
(0.87
From
(Ft3)
(Ft3)
Area
Site)
CFS/
Site
(S.
ACRE)
(CFS)
F.)
Al
1.20
1.04
1.17
10260
11056
.111
Detention in
parking lot
A2
1.05
0.91
0.78
6,840
6,925
4i�
Detention in
0,073
parking lot
A3
0.37
0.32
---
None
---
---
Diverted into
Basin Al
A4*
0.03
0.03
0.22,
None
---
---
Undetained
area of
Mitchell Drive
B1
2.42
2.00
16590
16305
.118
50 Year Storm
12.11
Detention
Underground
B2
2.24
1.95
1.90
15180
16125
.118
50 Year Storm
Detention
Underground
B3*
0.38
0.33
0.68
---
---
---
Natural area
North of Canal
B4*
0.03
0.03
0.22
None
---
---
Undetained
area of
Mitchell Drive
(On-
7.72
6.72
6.97
---
---
---
---
Site)
Total
Drainage
Subbasin
(off -
site)
C
5.10
4.44
---
---
---
---
Flow is Q-100
detention is
part of future
IL
developement
* Note: Runoff from B4 and A4 will eventually continue down Mitchell Drive and
be detained in detention ponds constructed as part of Palmer House Improvements.
Runoff from the north end of Subbasin B3 will be detained by future development
along the JFR Parkway.
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4.
October 31, 1991
Mr. Glen Schleuter
Stormwater Utility
City of Fort Collins
235 Mathews Street
Fort Collins, CO 80524
RE: Western Auto Drainage Certification
Dear Glen:
Please find enclosed a revised Toys "R" Us drainage report, survey
notes and "as built" information for the Western Auto site (known
as Tract "A" of the Toys "R" Us/Western Auto P.U.D.). We have made
field inspections of the storm drainage system for Western Auto and
have incorporated this information onto the attached "redline"
prints.
Some changes have occurred through the construction process and are_.
summarized as follows:
INLETS
Minor vertical and horizontal changes have been made to Inlet #1
and Inlet #3 as shown on the "redline" prints. These changes do
not affect the capacity or function of the inlets. The orifice
.plates were measured in place and this information is as follows:
INLET
BASIN
OPENING
OPENING
OPENING
OPENING
NUMBER
SIZE
SIZE
SIZE
SIZE
REQUIRED
REQUIRED
MEASURED
MEASURED
(IN x IN)
(SQ FT)
(FT x FT)
(SQ FT)
# 2
A
4% X 4'r4
1 .141
.37 X .30
.111
# 3
A
3% X 3Y
1 .073
.27 X .27
.073
Although the opening in the inlet #2 orifice plate is slightly
smaller, this reduction in area of the opening results in only
minor changes to the size of the detention pond (see attached
sheets).
Page 2 of 3
October 31, 1991
Western Auto Drainage Certification
STORM WATER
The changed inlet elevations have resulted in grade changes in the
stormwater lines. These changes are as follow:
LINE
-GRADE
GRADE
COMMENTS
(DESIGNED)
(ACTUAL)
B (INLET #1-INLET #2)
0.45%
0.40%
PART OF DETENTION
B (INLET #2-MH #1)
0.44%
0.32%
1.1 CFS
DISCHARGES INTO
THIS LINE
A
0.56%
0.32`k
0.7 CFS
DISCHARGES INTO
THIS LINE
As you can see, the in -place stormwater line grades are generally
flatter than the designed grades. These flattened grades are still
above minimum grades acceptable for 15" PVC storm drain and the
pipe capacities are still adequate to convey the metered discharge
from detention ponds Al and A2.
DETENTION PONDS
Spot elevation in the detention pond areas have been plotted on the
"as built" prints. The revised limits of the detention ponds are
shown based on high water elevations shown on the plan. The
in -place areas were determined using field cross -sections and the
average end area method for determining volumes. The results are
as follows:
REQUIRED
CALCULATED
BASIN
DETENTION
DETENTION
CONCLUSION
VOLUME (FT3)
VOLUME (FT)
OK -
Al
10,260 *
11,056
HW ELEV. = 39.1
SPILL ELEV. = 39.4
OK
A2
6,840 *
6,925
HW ELEV. = 39.05
SPILL ELEV. = 39.05
W
x wajustea =or new ori=ice plate openings ana inlet elevation
changes.
Page 3 Of 3
October 31, 1991
Western Auto Drainage Certification
Based on this information, we feel that the drainage system
constructed on the Western Auto site is built in substantial
conformance to the report and plans approved by the City of Fort
Collins and will provide for the detention of stromwater as
calculated therein.
Sincerely,
Jeff Couch, P.E.
Project Manager
JWC/gbl
CC: Roland Hernandez, Sunwest Construction, Inc.
J � I
November 15, 1991
Mr. Glen Schleuter
Stormwater Utility
City of Fort Collins
235 Mathews Street
Fort Collins, CO 80524
RE: Toys "R" Us Drainage Certification
Our Project Number 91.22 TDC
Dear Glen:
Please find enclosed a revised Toys "R" Us drainage report,
survey notes and "as built" drawings for the Toys "R" Us site
(Tract "B" of the Toys "R" Us/Western Auto P.U.D.). We have made
field inspections of the storm drainage system for Toys "R" Us and
have incorporated our findings onto the attached "redline"
drawings.
Some changes have occurred through the construction process
and are summarized as follows:
INLETS
A 44" diameter round inlet was used in place of the 36" x 36"
square inlet specified on the plans for inlet #4 and inlet #5. The
round inlet provides 10.4 square feet of surface area compared to
9.0 square feet provided by the square inlet. ,
STORMWATER PIPE
The stormwater pipe constructed for the Toy "R" Us site was to
provide additional detention volume and not to convey stormwater
flows.
Page 2 `Of 3
November 15, 1991
Toys Drainage Certification
With minor changes :the stormwater lines were constructed at the
location and grade called for on the plans. Minor changes in
elevation and pipe lengths are shown on the "redline" drawings.
DETENTION PONDS
Spot elevations in the detention pond areas have been plotted
on the "redline" drawings. The revised limits of the detention
pond areas are shown based on actual field measurements and the
high water elevation shown on the plans. Volumes were determined
for the irregular shaped areas by planimetering contours at .5 feet
intervals. The results are as follows.
BASIN
REQUIRED
-MEASURED
MEASURED
TOTAL
COMMENTS
DETENTION
DETENTION
DETENTION
VOLUME
VOLUME
VOLUME IN
VOLUME
(FT')
PIP S
ABOVE
(FT
GRO1
(FT
Bi
16,590
8,206
8,099
i6,305
See Note:
HW EL = 37.6
SPILL EL = 37.6
B2
15,180
13,252
2,873
16,125
Adequate
Detention
HW EL = 35.0
SPILL EL = 35.0
NOTE: Basin Biis 285 cubic feet short of providing the
required detention volume. Basin Bi will spill into
Basin B2 if it should overflow. Basin B2 has
additional volume necessary to provide the
necessary detention.
Page 3 of 3
November 15, 1991
Toys Drainage Certification
ORIFICE PLATES
Orifice plates have not yet been attached to the outside edge
of the retaining wall for bsins B1 and B2. These plates are
fabricated; however they have not been installed due to standing
water in the irrigation ditch. Connell Resources is under contract
to install these items and will do so when they can gain access to
the irrigation ditch.
Based on this information, we feel that the drainage system
constructed on the Toys "R" Us site is built in substantial
conformance to the report and plans approved by the City of Fort
Collins and will provide for the detention of stormwater as
calculated therein once orifice plates are installed.
Sincerely,
Jeff Couch, P.E.
Project Manager
JWC/gbl
cc: Bill Pyle, To
November 27, 1991
Mr. Glen Schlueter
Stormwater Utility
City of Fort Collins
235 Mathews
Fort Collins, Colorado 90524
RE: Toys "R" Us Drainage Certification
Our Project Number 91.22 TDC
Dear Glen:
Toys "R" Us has recently installed the orifice plates on the
ends of Line "D" and Line "E" to finish the work required.on their
drainage system. We have field verified these improvements and
determined the following:
LOCATION
MEASURED
OPENINGS
(INCHES)
CALCULATED
AREA
(SQ. IN.)
REQUIRED
OPENING
SQ. IN.
COMMENTS
Plate attached
4 1/8
properly to
Line "D".
x
17.02
17.02
retaining wall
4 1/8
and is adequate
size.
Plate attached
4 x 4%
17.00
17.02
properly to
Line "E"
retaining wall
and is adequate
size.
This should complete the information required for the Toys "R"
Us drainage certification. Please include this information with
our original submittal and contact me should you have any
questions. ----
Sincerely,
Jeff Couch, P.E.
Senior Engineer
JWC/gbl
cc: Bill Pyle, Toys "R" Us
rf 1
Utility Services
Stormwater
City of Fort Collins
December 23, 1991
Jeff Couch .
Parson & Associates
425 Link Lane Plaza.
Fort Collins, CO 80524
RE: Toys R Us Drainage Certification
Dear Jeff:
I have reviewed the "as -built" material you submitted for the Toys
R Us site drainage, dated November 15 and November 27, 1991. These
letters with the additional material submitted is acceptable and
certifies that the site drainage improvements have been
substantially constructed in conformance with the design plans.
The Stormwater Utility hold on the certificate of occupancy has
been released.
If you have any questions or concerns, please feel free to contact
me.
Sincerely,
,(xV._jjt&Zk
Glen D. Schlueter
Civil Engineer II
cc: Dave Stringer
235 Mathews • P.O. Box 580 • Fort Collins, CO 80522-0580 • (303) 221-6589 • FAX (303) 221-6239