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THIS LAND GROUP, INC.
YMCA Modular Building
Siena Elementary School
Meridian, Idaho
Storm Water Management &
Engineering Drainage Report
Treasure Valley Family YMCA
Contact: Robert Park
1177 W. State St.
Boise, Idaho 83702
Ph: 208.344.5502
Engineer
The Land Group, Inc.
462 A
aldaho 83616
e, Suite 100
EagleContact: Jason Densmer, PE
Ph: 208.939.4041
141- OF ��,'�'
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June 26, 2014
Project No. 114105
Site Planning • Landscape Architecture - Civil Engineering - Golf Course Irrigation & Engineering - Graphic Design - Surveying
462 E. Shore Drive, Suite 100 • Eagle, Idaho 83616 • P 208.939.4041 - F 208.939.4445 - www.the.landgroupinc.com
r THE LAND GROUP, INC.
Report Purpose
YMCA Modular Building
Meridian, Idaho
Storm Water Management Report
The following report addresses the storm drainage systems proposed for the YMCA Modular Building to
be located in the southeast corner of the Siena K8 Magnet School which is located on the north side of E.
Rome Dr. in Meridian, Idaho. Calculations are provided demonstrating that the project provides suitable
drainage systems to accommodate anticipated stormwater flows.
Peak Precipitation Rates
The drainage systems have been designed to store the 100 -year, 1 -hour event. The drainage calculations
are shown in Appendix A.
Peak Stormwater Flows & System Performance
Site Drainage Areas
The site comprises a single tributary area. Generally, the drainage from the building roof and attached
planter beds. The runoff will sheet flow from the roof area to rain gutters flowing to four downspouts,
one at each corner of the building. The downspouts will drain into a grated inlet that is piped to a
subsurface piping system. Direct rainwater that is collected in the planter beds will infiltrate through
topsoil and be collected in the storm drain piping system. The subsurface piping system will direct the
runoff to a subsurface seepage bed designed to hold the 100 -year event storm runoff. Over time the
seepage bed will allow the runoff to infiltrate into the natural sub -soils.
The following calculations show that the proposed facilities are adequately sized to accommodate the
expected storm water runoff from the site.
Ar
Site Planning • Landscape Architecture • Civil Engineering • Golf Course Irrigation & Engineering • Graphic Design • Surveying
462 E. Shore Drive, Suite 100 - Eagle, Idaho 83616 • P 208.939.4041 • F 208.939.4445 • www.thelandgroupinc.com
• THE LAND GROUP, INC.
Appendix A
5tormwater Calculations
YMCA Modular Building
Meridian, Idaho
Storm Water Management Report
A,
Site Planning • Landscape Architecture • Civil Engineering • Golf Course Irrigation & Engineering • Graphic Design • Surveying
462 E. Shore Drive, Suite 100 • Eagle, Idaho 83616 • P 208.939.4041 • f 208.939.4445 • www.thelandgroupinc.com
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THE LAND GROUP, INC.
YMCA (Siena Elementary) (PN 114105)
Storm Drainage Calculations
Drainage Area
Total Area =s.f.
Impervious Area =s.f.
Landscape Area =s.f.
wt. C =1E
8.0
C = 0.95
C = 0.20
4.0
50.0
2.85
Retention System Design
Infiltration Trench Characteristics
Infiltration Rate =
Bed Bottom Width =
Bed Bottom Length =
Storage Depth =
Bed Bottom Area =
Voids =
A perc. =
Q perc. =
8.0
in/hr`
ft.
ft.
ft.
s.f.
s.f.
cf/hr
4.0
50.0
2.85
200.0
40%
200
133
June 26, 2014
Storage Volume Required (100 Year Return Period)
Time (hr)
Time
(min)
Time
(sec)
Intensity
(in/hr
Q dev.
(cfs)
V dev.
(c. f)
V inf.
(cf
. )
V St. (c.f.)
0.17
10
600
3.11
0.25
153
22
131
0.25
15
900
2.62
0.21
193
33
160
0.33
20
1,200
2.28
0.19
224
44
180
0.50
30
1,800
1.82
0.15
268
67
202
0.67
40
2,400
1.37
0.11
269
89
180
0.83 1
50
3,000 1
1.17
0.10 1
287
111
176
1.0
60
3,600
1.15
0.09
339
133
206
2.0
120
7,200
0.66
0.05
389
267
122
3.0
180
10,800
0.48
0.04
425
400
25
6.0
360
21,600
0.36
0.03
637
800
-163
12.0
720
43,200
0.19
0.02
672
1,600
-928
24.0
1,440
86,400
0.12
0.01
849
3,200
-2,351
Site Planning - LandscapeArchiteaure - Civil Engineering - GoofCowse Irrigation & Eogineering • Graphic Communication - Surveying
462E. ShoreDrive, Ste. 100, Eagle, Idaho 83616 - P208.939.4041 F208.939.4445 - navw.thelandgroupinccam
On Site Drainage (continued)
VSp =1 228 I c.f.
Infiltration Volume Check:
V(90%) = 764 cf
Vperc = 3,200 cf
Seepage Bed Recovery Time:
Vs Max= 849 cf
Q perc = 133 cf per hr
THE LAND GROUP, INC.
, Required Storage Volume
Total Volume Provided
,90% of maximum runoff developed in 24 -hours
—Total Percolation Volume in 24 -hours
,Maximum Runoff Developed
Site Planning -Landscape Architecture - Ciad Engineering Golf Course Irrigation 6—Engineenng , Graphic Communication Surveying
462E. ShoreDrive, Ste. 100, Eagle, Idaho 83616 P 208.939.4041 F 208.939.4445 - wwruthelandgroupinc.co>n