HomeMy WebLinkAboutDrainage Reports - 07/18/2005i'
1
North Star
�*a., de -sign, inc.
May 23,2005
Basil Hamdan
City of Fort Collins Stormwater
700 Wood Street =
Fort Collins, CO 80522-0580
RE: Drainage Report for Liberty Common School Track Project
Proj : 205-02
Dear Basil,
inal Raplx4t
Date ., 7)i��6
The Liberty Common School (LCS) is proposing to build a track and field adjacent to March
Court and Riverbend Court in Prospect Industrial Park. This: project -will construct the track and
field, relocate the private drive connection to Midpoint Drive (from March Court), and build
some additional parking. March Court will be reconstructed with the project under a separate
plan' set. This letter and attached calculations show the existing and proposed drainage
conditions for the area and will serve as the drainage report for the project. An Erosion Control
Plan has been included in the plan set for City comment, no erosion control calculations have
been prepared. This letter will demonstrate that drainage conditions will be improved with this
project.
Existing Conditions:
the area to undergo construction activities,,, there are three distinct. -,drainage basins. These
basins are shown on the "Existing Drainage Basins" exhibit.
Basin EXl is in the northwest portion of the project and drains north to the existing Liberty
Common School parking area on the west side of the building. There is an existing curb inlet in
the parking lot that will remain as the outfall for this area. This area has a private drive and the
remaining portion of the basin is impervious.
Basin EX2 is in the northeast portion of the project and drains overland to March Court. From
March Court, runoff flows east to Sharp Point Drive and the ponds to the east of Sharp Point
Drive. This basin includes a portion of the private drive, and the portion of March Court that
will be rebuilt with the project. The remaining portion of the basin is impervious.
Basin EX3 includes the south portion of the project. This basin consists of Lot 3 and Lot 6 of
Prospect Industrial Park which are presently undeveloped. This basin presently drains southeast
to Lot 7, Prospect Industrial Park. There is an underground drainage system on this lot, but it is
unknown if the system was sized to accept any flows from .Lots 3 and 6. During the Utility
700 Automation Drive, Unit I Windsor, Colorado 80550
970-686-6939 Phone 9 970-686-1 188 Fax
A
Coordination Meeting for this project, it was stated that the City would prefer that this area drain
to Riverbend Court.
Proposed Conditions: _
This project will add impervious area to the overall project area. The drive, parking and track
will be paved with asphalt. The existing private drive and a portion of March Court will be
removed with the project.: The overall flow to the three design points will be reduced with the
construction of the project because of the reduction in drainage area from Basin 1 and Basin 2
and the use of the track and field area as a detention pond for Basin 3. These basins are shown
on the "Proposed Drainage Basins" exhibit. A more detailed description of each basin follows:
Basin PI - is in the northwest portion of the project and drains north to a curb inlet in the
existing Liberty Common School parking area on the west side of the building. The new parking
area and a portion of the new drive are within this basin. Drainage from this basin will continue
to flow north, but the basin size has been substantially reduced. The amount of paved area in this
basin has also been reduced. There is no possible location to add water quality -facilities to this
basin; but because the paved area is reduced, technically, the existing water quality should be
improved.
Basin P2 is in the northeast portion of the project and includes the remaining portion of the new
private drive, a paved play area, and the reconstructed portion of March Court. It is proposed
that this area will drain in a concrete trickle pan to a new sidewalk culvert and into March Court.
It is City standard to not allow substantial drainage over the public sidewalk, and the proposed
sidewalk culvert will accomplish this. Drainage from this basin will continue to its historic
location (March Court), but the basin size has been substantially reduced. The amount of paved
area in this basin has also been reduced. There is no possible location to add water quality
facilities .to;this basin; but because the paved area .is reduced, technically, the existing water
quality should be improved.
Basin P3 includes the entire proposed track and field. Tracks are designed with no longitudinal
slope (the entire inside edge of the track is at the same elevation). To provide for drainage, tracks
have a subsurface drainage: system on this inside perimeter. This site does not have any adjacent
subsurface storm drainage system to tie to, so the only option for an outfall is to find the lowest
existing surface outfall. It is the City's desire for this area to drain to Riverbend Court, so it is
proposed to install a sidewalk culvert into the cul-de-sac, and have the track drainage system
outfall to this point. A gravel trench drain with two 4" perforated pipes (at about 0.15%) will be
installed around the inside of the majority of the track. At the north end of the track a sloping
PVC trench drain in a concrete header will be installed. This will provide very slow, but positive
drainage for the track and field to Riverbend Court.
The track cross slope is inward at 1.5% toward the trench drain and the field will have a 2%
crown draining to the trench drain as well. In large storms, when the drainage system cannot
convey the rainfall, water will pond staring at the trench drain and then up onto the track and the
field. This, by default, will create detention for the area. It has been calculated that the volume
between elevation 4996.35 (the top of the trench drain) and elevation 4996.70 (the outside edge
of the track) is 0.21 acre-feet. The FAA Detention Method was iterated to find the pond
discharge for the track's C value and the available detention volume. It was found that if the
pond release is 2.5 cfs, the detention volume will be utilized. A 10" PVC pipe at 0.68% has a
capacity of 2.6 cfs and has been used for the outfall from the track to Riverbend Court.
This basin is larger than the existing Basin 3 and will have more impervious area than existing
conditions, but because of the detention provided, the peak flow will be reduced and will no
longer be routed through Lot 7. ' No water quality facilities are proposed for this basin, but all
runoff will flow through several hundred feet of very flat gravel trench drain, and the asphalt
track, unlike an asphalt parking lot, will not have any vehicles on it spilling oil, etc. The only
issue with this "pond" is that there will not be a spillway. If the track were completely
overwhelmed, it would spill evenly over the entire perimeter of the track (more that 1,000 feet) at
a very shallow depth. Based on this, no damage to any adjacent facilities or properties would be
anticipated.
All of the runoff and_ detention pond calculation are attached to the back of this report.,,...A
summary of the 'ezisting and proposed drainage conditions are provided in the table below:
BASIN
EX 1
P1
EX2
P2
EX3
P3
AREA
0.54 Ac.
0.30 Ac.
1.33 Ac.
0.65 Ac.
1.86 Ac.
2.85 Ac.
"C" 100
0.56
0.60
0.52
0.82
0.25
0.58
" " 100
2.2 cfs
1.8 cfs
5.6 cfs
4.7 cfs
3.3 cfs
11.1 cfs*
* - Basin P3 peak flow is reduced to 2.5 cfs with 0.21 acre-feet of detention storage.
In summary, peak flows; will be reduced with this project to the three receiving points. Basin 3::_>
will be rerouted to the public right of way rather than through Lot 7 of Prospect Industrial Park.
If you have any questions, please feel free to call me.
Sincerely,
Michael Oberlander, P.E., L.S.I.
- / -
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North Star
design, inc.
_ 700 Automation Drive, Unit I
Windsor, Colorado 80550
Phone: 970-686-6939
Fax: 970-686-1188
LIBERTY COMMON
SCHOOL TRACK* PROJECT
EXISTING DRAINAGE BASINS
5-23-05
------------
00 50 0 100 200
North Star
design, inc.
700 Automation Drive, Unit I
Windsor, Colorado 80550
Phone: 970-686-6939
Fax: 970-686-1188
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'.M1 YGY/SAbK PI,K
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LIBERTY COMMON
SCHOOL TRACK PROJECT
PROPOSED DRAINAGE 13;4SINS
5-23-05
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TRACK OUTLET PIPE 10" PVC
Worksheet for Circular Channel
Project Description
Project File
d:\haestad\fmw\culvert.fm2
Worksheet
CULVERT
Flow Element
Circular Channel
Method
Manning's Formula
Solve For
Channel Depth
Input Data
Mannings Coefficient
0.009
Channel Slope
0.6800 %
Diameter
10.00 in
Discharge
2.50 cfs
Results
Depth
7.8
in
Flow Area
0.46
ft2
Wetted Perimeter
1.81
ft
Top Width
0.69
ft
Critical Depth
0.70
ft
Percent Full
78.43
Critical Slope
0.005957 ft/ft
Velocity
5.45
ft/s
Velocity Head
0.46
ft
Specific Energy
1.11
ft
Froude Number
1.17
Maximum Discharge
2.81
cfs
"Full Flow Capacity
2.61
cfs
Full Flow Slope
0.006241 ft/ft
Flow is supercritical.
05/20/05 , FlowMaster v5.15
09:22:00 PM Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 (203) 755-1666 Page 1 of 1
MINIMUM DETENTION VOLUME REQUIRED
FAA METHOD
(100-YEAR)
LOCATION: LIBERTY COMMON SCHOOL
PROJECT NO: 205-02
COMPUTATIONS BY: MPO
SUBMITTED BY: North Star Design
DATE: 5/20/05
Equations:
Qo = CiA
V; = T*CiA = T*Qp
Vo = K*QPo*T
S=V; -Va
Rainfall intensity from City of Fort Collins IDF Curve
A trib. To pond =
Cioo =
Developed C*A =
QPo =
K=
2.85. acre
0.58
1.7 acre
2.50 cfs
1 (from fig 2.1)
Storm
Duration, T
(min)
Rainfall
Intensity, i
(in/hr)
Qo
(cfs)
Vol. In
V;
(ft3)
Vol. Out
Vo
(ft3)
Storage
S
(ft3)
Storage
S
(ac-ft)
5
9.95
16.4
4934
750
4184
0.10
10
1 7.72
12.8
7657
1500
6157
0.14
20
5.60
9.3
11108
3000
8108
0.19
30
4.52
7.5
13449
4500
8949
0.21
40
3.74
6.2
14837
6000
8837
0.20
50
3.23
5.3
16018
7500
8518
0.20
60
2.86
4.7
17019
9000
8019
` 0.18
70
2.60
4.3
18051
10500
7551
0.17
80
2.34
3.9
18566
12000
6566
0.15
90
2.17
3.6
19370
13500
5870
0.13
100
1.99•
3.3
19737
15000
4737
0.11
110
1.87
3.1
20401
16500
3901
0.09
120
1.75
2.9
20828
18000
2828
0.06
130
1.66
2.7
21403
19500
1903
0.04
140
1.57
2.6
21800
21000
800
0.02
150
1.48
2.4
22018
22500
-482
-0.01
160
1.42
2.3
22534
24000
-1466
-0.03
170
1.35
2.2
22762
25500
-2738
-0.06
180
1.29
2.1
23030
27000
-3970
-0.09
Required Storage Volume: 8949 ft3
0.21 acre-ft
PROPOSED POND VOLUME
LOCATION: LIBERTY COMMON SCHOOL
_ PROJECT NO: 205-02
COMPUTATIONS BY: MPO
SUBMITTED BY: North Star Design
DATE: 5/20/05
10-Year Detention required =
100-Year Detention Required =
Total Detention Required =
100-Year WSEL
0.00 ac-ft
0.21 ac-ft
0.21 ac-fit
Stage
(ft)
Surface
Area
(ft2)
Incremental
Storage
(ac-ft)
Total
Storage
(ac-ft)
4996.35
0
4996.4
7400
0.003
0.00
4996.5
22400
0.033
0.04
4996.6
37300
0.068
0.10
4996.7
52100
0.102
0.21