CC - Storm Drainage CalcsCJ-UIB
J•U•B ENGINEERS, INC.
Gorilla Mind
Meridian, Idaho
May 2022
Storm Water Drainage Report
ACHD Project
JUB Project No. 10-22-019
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Kesleigh Massey, PE
fJ/— , 2760 W. Excursion Lane, Suite 400
-VB Meridian, Idaho 83642
208-376-7330
J•U•B ENGINEERS, INC. www.jub.com
Gorilla Mind
Ada County Highway District Operations & Maintenance Manual
Page 2
Site Location
The project site is located adjacent to N Webb Ave between E Pine Ave and E
Commercial Street, in the SW 1/4 of Section 8, Township 3 North, Range 1 East, Boise
Meridian.
Existing Site Characteristics
The 2.91-acre project site located directly north of the existing PKG building with a shared
access road separating the two unique sites. The south boundary of the site is bordered
by the Snyder Ditch, a private irrigation ditch which will remain in place. The overall site
is generally flat with a gentle downward slope to the north.
Soil Conditions
The following geotechnical report was referenced during design of this stormwater
system.
Geotechnical Investigation, Proposed Flex Building, 1835 E Pine Ave, Meridian, Idaho,
dated 23 March 2022, prepared by Atlas Technical Consultants, LLC.
According to the reports, groundwater was not encountered in any of the test pits which
reach depths of up to 15.3 feet below existing surface. Based on the information provided
in the geotechnical report, seeing groundwater during construction of stormwater facilities
is not anticipated.
Based upon the preliminary soils and subsurface investigation for this subdivision, the
existing soils will accept the runoff. Infiltration basins are designed based on assumed
maximum infiltration rate of 8.0 inches per hour provided that sand windows extend to a
depth where free draining soils are, which is approximately 7-8.9 feet below existing
grade.
In the event that during construction the contractor encounters groundwater or rock, or
the field percolation test results are lower than the design infiltration rate, a revised design
may be prepared to meet the field conditions.
Proposed Site Improvements
The proposed improvements include the construction of a proposed office/warehouse
building with sidewalks, parking lot and truck docking areas.
Drainage Design Concept
The project consists of 3 main catchment areas, each with multiple sub -catchments. Each
l
('JU�
J-U-B ENGINEERS, INC.
Gorilla Mind
Ada County Highway District Operations & Maintenance Manual
Page 3
catchment area drains to an infiltration basin either by overland flow or through a piped
connection.
Infiltration Basin
All stormwater catchments shall flow above grade to designed low points where it shall
be collected via curb inlets. The stormwater shall then either pass through a pipe network
and discharge into the infiltration basin or flow through a slot in the back of the catch basin
directly into the basin itself. The basin is sized to retain the 100-year storm event.
Sand Window/Seepage Trench
Storm drainage from catchment A shall flow into Basin A and infiltrate through the
appropriately sized sand window in the bottom of the basin which provides both storage
as well as access to free draining soil which is located several feet below the bottom of
the basin.
Calculation Methods
ACH D
The site was divided into catchment areas based on the proposed grading design. These
catchment areas were analyzed using the rational method to estimate the peak runoff
rates in accordance with ACHD Policy Manual Sections 8000 and 8200 in effect as of
August 2017.
Peak storage volumes were based on the 100-year, 1-hour design storm event of 0.96
inches per hour. Peak flow rates and conveyance flow rates were calculated for each
basin based on the 100-year and 25-year design storms, respectively. The time of
concentration for each basin was used as the design storm duration to calculate both the
peak flow and conveyance flow rates. Time of concentration values were calculated as
a combination of sheet flow from the lots to the road section and gutter flow along the
road. Specific equations are shown in the attached drainage calculations. The
conveyance flow rate was used to size inlets, pipes, and sand and grease traps and to
determine acceptable pipe slopes within the system.
The catchment areas are shown on the Drainage Plan. Calculations are included with
this report for all catchment areas.
l
('J-u�
J-U-B ENGINEERS, INC.
Catchment A
Gorilla Mind
Project No. 10-22-019
Catchment Parameters
Sub-
catchment
C1
Area,
(ac)
C2
Area2
(ac)
C3
Area3
(ac)
Cq
Area4
(ac)
CT
AreaT
(ac)
1
0.95
0.14
0.20
0.01
0.90
0.15
2
0.95
0.16
0.20
0.03
0.83
0.19
3
0.95
0.08
0.95
0.08
4
0.95
0.78
0.20
0.03
0.92
0.81
5
0.95
0.08
0.95
0.08
6
0.95
0.09
0.95
0.09
7
0.95
0.09
0.95
0.09
8
0.95
0.09
0.95
0.09
Total A
1.58
Comp. C
0.92
Sheet Flow Calculation
Gutter Flow
Sub-
catchment
n
(unitless)
L
(ft)
5
(ft/ft)
Tc-sheet
(min)
Slope
(ft/ft)
1-gutter
(ft)
Interc.
Coeff.
Vgutter
(fps)
Tc-gutter
(min)
Tc
(min)
1
0.011
60.0
0.01
1.6
0.004
100
0.62
1.29
1.29
10.0
2
0.011
56.0
0.01
1.5
0.004
142
0.62
1.29
1.83
10.0
3
0.012
60.0
0.06
0.9
0.005
60
0.62
1.44
0.69
10.0
4
0.011
76.0
0.01
1.9
0.004
211
0.62
1.29
2.73
10.0
5
0.011
95.0
0.01
2.5
10.0
6
0.011
95.0
0.01
2.5
10.0
7
0.011
95.0
0.01
2.5
10.0
8
0.011
95.0
0.01
2.5
10.0
sign Storm Intensities
Design Storm Flow Rates
Sub-
catchment
i2
(in/hr)
i25
(in/hr)
iso
(in/hr)
itoo
(in/hr)
Q2
(cfs)
Q25
(cfs)
Qso
(cfs)
Q100
(cfs)
1
0.69
1.85
2.20
2.58
0.09
0.25
0.30
0.35
2
0.69
1.85
2.20
2.58
0.11
0.29
0.35
0.41
3
0.69
1.85
2.20
2.58
0.05
0.14
0.17
0.20
4
0.69
1.85
2.20
2.58
0.52
1.38
1.64
1.93
5
0.69
1.85
2.20
2.58
0.05
0.14
0.17
0.20
6
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
7
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
8
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
F-
Vgutter = 3.281kSp'5
1.00
Lgutter
Tc-gutter = 60 • V
gutter
0.007 (nL)0-8
Tc-sheet = (p2)0.SS0.4
2.68 3.20 3.75
Tc = Tc-gutter + Tc-sheet
V.2020-03-17
Catchment A
Gorilla Mind
Project No. 10-22-019
Seepage Trench
DESIGN OPTIONS
Account for 1st hr of infiltration? No
Is the bed inside the right-of-way? No
Design Infiltration rate 8.00 in/hr
METERS
Design Storm frequency
100
-year
Design Storm duration
1
-hour
Weighted Runoff Coefficient (C)
0.92
Design Storm Inentsity
0.96
in/hr
Catchment Area
1.58
ac
Sediment factor
0
%
Required Storage Volume (V1oo)
2,180
ft3 (This is the excess storage required for pond)
iN
Width =
4 ft
Pipe
dia (in)
quantity
Depth =
6 ft
Inlet
18
0
Void Ratio (v)=
40 %
Overlfow
12
0
RESULTS DESIGN CHECKS
Bed length' =
228
ft
Bed Capacity (V) =
2,189
ft3
1st hr Inf =
0
ft3
Adj. V100 =
2,180
ft3
V >_ Adj. V1oo PASS
Time to Drain 90% =
3.2
hr
t90 <_ 48 PASS
Min. allowed inf. rate2 =
0.50
in/hr
DNAL MULTIPLE SUB -BEDS
Sub -Bed # Length Max allowed bed length = 386 ft
1 ft
2 ft
3 ft
4 ft
Total Length (JLsJ= ft Single bed design
1 Itterative calculation of the equations shown below
Z Since bed length is the next 1-ft increment larger than the minimum length, this value represents the
minimum infiltration rate that the as -designed bed can tollerate. For reference only. Not for design.
V100 = C * i * A * 3600 * (1 + f)
Vbed — (Vrock — EVpipe) * V + a p2ipe,in + zVpipe,over —Vinf
Vrock = Lbed - W - D 2
TCdpipe
Vpipe = (Lbed — 1) * 4
Vinf = Lbed . W 1l2
V.2020-03-17
Catchment A
Gorilla Mind
Project No. 10-22-019
Pond
Design Storm frequency
100
-year
Design Storm duration
60
-minutes
Soil Infiltration rate (rf)
8.00
in/hr
Weighted Runoff Coefficient (C)
0.92
Design Storm Inentsity (i)
0.96
in/hr
Catchment Area (A)
1.58
ac
Req. Storage Volume (V100)
5,024
ft3 V = C * i * A * 3600
Infiltration area (AF) = 912 ft2 Account for 1st hr of infiltration? Yes
Pond infiltration rate (PF) = 608.00 ft3/hr
Time for 90% infiltration (t90%) = 7.44 hr t90%< 48 PASS
First hour infiltration (F1) = 608 ft3
Adj. Req. Storage Volume (VAd) = 4,416 ft3
Mainbay volume (VR) = 2,845 ft3
Forebay Size Forebay Required = FALSE
Required volume (VR) = ft
Forebay volume (VF)1 = ft3 VF > VR N/R
Seepage Trench Capatcity (See Separate Calc Sheet) Seepage Trench Required = TRUE
Required volume (VR) = 2179.5 ft
Seepage Trench volume (VF)1 = 2,189 VF > VR PASS
Total Pond Volume (VT)
Check: VT > VAdi
Equations
rf
P-- d-•—
5,033 ft3
PASS
17Adj — T'loo 7-
V. 2020-03-17
Catchment A-3
Gorilla Mind
Project No. 10-22-019
Sand and Grease Trap
Peak Flow Design Storm
Peak Flow Rate (QPeak)
uesign Laicuiations
100 -year
0.20 cfs QwQ = C * iwQ * A
Vault Size =
1000
gallon
Peak Throat Velocity (VPeak) =
0.03 ft/sec
No. of S&G Traps =
1
Baffle Spacing =
20
inch
Allowed Max Flow rate (QMax,A) =
3.33 ft3/sec
Throat Width =
48
inch
Max Flow rate (QMax) =
0.20 ft3/sec
Total Throat Area =
6.67
ft'
Bypass Flow Rate =
0 ft'/sec
Checks: VPeak < 0.5 PASS
Bypass Required FALSE
FLOW
FLOW
Modified ro
ISPWC SD-6:
Peak flow less than 0.5 cfs. SDMH may be used in lieu of S&G Trap
esypass caicivavons
Inlet
Bypass
Flow rate = 3.33
0.00 ft3/sec
Mannings =
(unitless)
Pipe dia =
in
Pipe slope =
%
Flow depth = 0.00
0.00 ft Difference = ft
V.2020-03-17
Catchment B
Gorilla Mind
Project No. 10-22-019
Catchment Parameters
Sub-
catchment
C1
Area,
(ac)
CZ
Areal
(ac)
C3
Area3
(ac)
Cq
Area4
(ac)
CT
AreaT
(ac)
1
0.95
0.23
0.20
0.06
0.79
0.29
2
0.95
0.10
0.95
0.10
3
0.95
0.40
0.20
0.13
0.77
0.53
4
0.95
0.09
0.95
0.09
5
0.95
0.09
0.95
0.09
6
0.95
0.09
0.95
0.09
7
0.95
0.09
0.95
0.09
Total A
1.28
Comp. C
0.84
Sheet Flow Calculation
Gutter Flow
Sub-
catchment
n
(unitless)
L
(ft)
s
(ft/ft)
Tc_sheet
(min)
Slope
(ft/ft)
1-gutter
(ft)
Interc.
Coeff.
V gutter
(fps)
T c-gutter
(min)
T c
(min)
1
0.011
65.0
0.02
1.6
0.004
128
0.62
1.29
1.65
10.0
2
0.011
65.0
0.02
1.6
0.004
32
0.62
1.29
0.41
10.0
3
0.011
54.0
0.02
1.4
0.004
155
0.62
1.29
2
10.0
4
0.011
65.0
0.01
1.8
10.0
5
0.011
60.0
0.01
1.7
10.0
6
0.011
60.0
0.01
1.7
10.0
7
0.011
100.0
0.01
2.6
10.0
Design Storm Intensities
Design Storm Flow Rates
Sub-
catchment
i2
(in/hr)
i25
(in/hr)
i50
(in/hr)
iioo
(in/hr)
Q2
(cfs)
Q25
(cfs)
Q50
(cfs)
Qioo
(cfs)
1
0.69
1.85
2.20
2.58
0.16
0.43
0.51
0.59
2
0.69
1.85
2.20
2.58
0.07
0.18
0.21
0.25
3
0.69
1.85
2.20
2.58
0.28
0.75
0.89
1.05
4
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
5
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
6
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
7
0.69
1.85
2.20
2.58
0.06
0.16
0.19
0.22
Vgutter = 3.281kSp'5
0.75
Lgutter
Tc-gutter - 60 • V
gutter
0.007 (nL)0-8
Tc-sheet - (p2)0.5S0.4
2.00 2.37 2.77
Tc = Tc-gutter + Tc-sheet
V.2020-03-17
Catchment B
Gorilla Mind
Project No. 10-22-019
Pond
Design Storm frequency
100
-year
Design Storm duration
60
-minutes
Soil Infiltration rate (rf)
2.00
in/hr
Weighted Runoff Coefficient (C)
0.84
Design Storm Inentsity (i)
0.96
in/hr
Catchment Area (A)
1.28
ac
Req. Storage Volume (V100)
3,716
ft3 V = C * i * A * 3600
Infiltration area (AF) = 2013 ft2 Account for 1st hr of infiltration? Yes
Pond infiltration rate (PF) = 335.50 ft3/hr
Time for 90% infiltration (t90%) = 9.97 hr t90%< 48 PASS
First hour infiltration (F1) = 336 ft3
Adj. Req. Storage Volume (VAd) = 3,380 ft3
Mainbay volume (VR) = 3,755 ft3
Forebay Size Forebay Required = FALSE
Required volume (VR) = ft
Forebay volume (VF)1 = ft3 VF > VR N/R
Seepage Trench Capatcity (See Separate Calc Sheet) Seepage Trench Required = FALSE
Required volume (VR) = FALSE ft
Seepage Trench volume (VF)1 = FALSE VF > VR N/R
Total Pond Volume (VT)
Check: VT > VAdi
Equations
rf
P-- d-•—
3,755 ft3
PASS
17Adj — V100 7-
V. 2020-03-17
Catchment C
Gorilla Mind
Project No. 10-22-019
Catchment Parameters
-----------
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2 IN
Sheet Flow Calculation
Gutter Flow
Sub-
catchment
n
(unitless)
L
(ft)
s
(ft/ft)
Tc_sheet
(min)
Slope
(ft/ft)
1-gutter
(ft)
Interc.
Coeff.
V gutter
(fps)
T c-gutter
(min)
T c
(min)
1
0.011
101.0
0.03
1.7
0.020
22
0.62
2.88
0.13
10.0
2
0.011
128.0
0.02
2.5
0.008
95
0.62
1.8
0.88
10.0
3
0.011
55.0
0.02
1.1
0.004
33
0.62
1.29
0.43
10.0
Design Storm Intensities
Design Storm Flow Rates
Sub-
catchment
i2
(in/hr)
i25
(in/hr)
i50
(in/hr)
iioo
(in/hr)
Q2
(cfs)
Q25
(cfs)
Q50
(cfs)
Qioo
(cfs)
1
0.69
1.85
2.20
2.58
0.05
0.14
0.17
0.20
2
0.69
1.85
2.20
2.58
0.08
0.21
0.25
0.30
3
0.69
1.85
2.20
2.58
0.05
0.12
0.15
0.17
Vgutter = 3.281kSp'5
0.18 0.47
Lgutter
Tc-gutter - 60 • V
gutter
0.007 (nL)0-8
Tc-she (p2)0.5S0.4
Tc = Tc-gutter + Tc-sheet
0.57 0.67
V.2020-03-17
Catchment C
Gorilla Mind
Project No. 10-22-019
Pond
Design Storm frequency
100
-year
Design Storm duration
60
-minutes
Soil Infiltration rate (rf)
2.00
in/hr
Weighted Runoff Coefficient (C)
0.92
Design Storm Inentsity (i)
0.96
in/hr
Catchment Area (A)
0.28
ac
Req. Storage Volume (V100)
900
ft3 V = C * i * A * 3600
Infiltration area (AF) = 329 ft2 Account for 1st hr of infiltration? Yes
Pond infiltration rate (PF) = 54.83 ft3/hr
Time for 90% infiltration (t90%) = 14.77 hr t90%< 48 PASS
First hour infiltration (F1) = 55 ft3
Adj. Req. Storage Volume (VAd) = 845 ft3
Mainbay volume (VR) = 902 ft3
Forebay Size Forebay Required = FALSE
Required volume (VR) = ft
Forebay volume (VF)1 = ft3 VF > VR N/R
Seepage Trench Capatcity (See Separate Calc Sheet) Seepage Trench Required = FALSE
Required volume (VR) = FALSE ft
Seepage Trench volume (VF)1 = FALSE VF > VR N/R
Total Pond Volume (VT)
Check: VT > VAdi
Equations
rf
P-- d-•—
902 ft3
PASS
17Adj — V100 7-
V. 2020-03-17
Table 3-2. Manning's Roughness Coefficient in) for Overland Sheet Flow.'s'
Surface Description
In
Smooth asphalt
0.011
Smooth concrete
0.012
Ordinary concrete lining
0.013
Good wood
0.014
Brick with cement mortar
0.014
Vitrified clay
0.015
Cast iron
0.015
Corrugated metal pipe
0.024
Cement rubble surface
0.024
Fallow no residue)
0.05
Cultivated soils
Residue cover s 20%
0.06
Residue cover > 20%
0.17
Range (natural)
0.13
Grass
Short grass prairie
0.15
Dense grasses
0.24
Bermuda grass
0.41
Woods'
Light underbrush
0.40
Dense underbrush 0.80
-When selecting n, consider cover to a height of about 30 mm. This is only part of
the plant cover that will obstruct sheet flow.
Table 3.3. Intercept Coefficients for Velocity vs. Slope Relationship of Equation 34. 5
Land Cover/Flow Regime
k
Forest with heavy ground litter: hay meadow (overland flow)
0 076
Trash fallow or minimum bgage cultvation: contour or strip cropped: woodland
(overland flow)
0.152
Short grass pasture (overland flow)
0 213
Cultivated stra ht row (overland flow)
0.274
Nearly bare and unbled overland flow): alluvial fans in western mountain
regions
0,305
Grassed waterway (shallow concentrated flow
0.457
Unpaved (shallow concentrated now)
0.491
Paved area (shallow concentrated flow); small upland gullies
0.619
Table 3.4. Typical Range of Manning's Coefficient In) for Channels and Pipes.
Conduit Material
Manning's n'
Close Conduits
Concrete pipe
0.010 •0.015
CMP
0.011 - 0 037
Plastic smooth
0 009.0 015
Plastic Corru ated
0.018. 0.025
Pavement/gutter sections
0.012 - 0.016
Small Open Channels
Concrete
0011 .0015
Ruble or nprep
0,020 - 0 035
vegetation
0 020 - 0 150
Bare Sal
0 016 - 0 025
Rook Cut
0o25 - 0 045
Natural channels (minor streams, top width at (food stage <30 m (100 111)
Fairly re ular section
0.025 - 0 050
inegul or aeptgn with pools
O 040 . 0.150
'Lower values are usually for weft -constructed and rnwntmned (smoother) pipes
and Channels
Estimated Runoff Coefficients for Various Surfaces
Type of Surface
Runoff Coefficients "C'
Business
Downtown areas
0.70-0.95
Urban neighborhoods
0.50-0.70
Residential
Single Family
0.35-0.50
Multi -family
0.60-0.75
Residential (rural)
0.25-0.40
Apartment Dwelling Areas
0.70
Industrial and Commercial
Light areas
0.80
Heavy areas
0.90
Parks Cemeteries
0.10-0.25
Playgrounds
0.20-0.35
Railroad yard areas
0.20-0.40
Unimproved areas
0.10-0.30
Streets
Asphalt
0.95
Concrete
0.95
Brick
0.95
Roofs
0.95
Gravel
0.75
Fields: Sandy soil
Soil Type
slope
A
B
C
D
Fat: 0-2%
0.04
0.07
0.11
0.15
Average: 2-6%
0.09
0.12
0.15
0.20
Steep:�6%
0.13
0.18
0.23
0.28
Adaptedfrom ASCE
Recommend Standards for Wastewater Facilities
Table 33.41 Recommended Minimum Slopes
Nominal Setter Size
Minimum Slope in Feet
Per 100 Feet m( 100 m)
8 inch (200 mm)
0.40
10 inch (250 mm)
0.28
12inch (300 mm)
0.22
14 inch (350 mm)
0.17
15 inch (375 mm)
0.15
16 inch (400 mm)
0.14
18 inch (450 mm)
0.12
21 inch (525 mm)
0.10
24 inch (600 mm)
0.08
27 inch (675 mm)
0.067
30 inch (750 mm)
0.058
33 inch (825 mm)
0.052
36 inch (900 mm)
0.046
39 inch (975 mm)
0.041
42 inch (1050 mm)
0.037
ACHD Intensity -Duration -Frequency
Intensity (inches per hour)
Design Storm 2 5 10 25
Tc lhr) Tdminl
50 100
0.17
10
0.69
1.15
1.48
1.85
2.20
2.58
0.25
15
0.59
0.97
1.22
1.56
1.86
2.18
0.33
20
0.49
0.81
1.01
1.30
1.54
1.81
0.42
25
0.43
0.71
0.89
1.14
1.35
1.58
0.50
30
0.41
0.67
0.85
1.08
1.29
1.51
0.58
35
0.34
0.56
0.70
0.90
1.07
1.25
0.67
40
0.31
0.51
0.64
0.82
0.98
1.15
0.75
45
0.29
0.48
0.60
0.77
0.91
1.07
0.83
50
0.27
0.45
0.56
0.72
0.85
1.00
0.92
55
0.26
0.43
0.54
0.69
0.82
0.96
1.00
60
0.26
0.43
0.54
0.69
0.82
0.96
2.00
120
0.16
0.25
0.31
0.39
0.46
0.54
3.00
180
0.13
0.19
0.23
0.29
0.34
0.40
6.00
360
0.09
0.12
0.14
0.18
0.21
0.25
12.00
720
0.06
0.08
0.10
0.12
0.14
0.16:::]
24.00
1440
0.04
0.06
0.06
0.08
0.09
0.10
Intensity Duration Frequency
3.00
------- z
-x- 5
-x- 10
2.50
-� 25
50
2.00
-❑
100
L
L
c
1.50
x\
x
X
1.00
�x\x
c
'X�x�x�
0.50
- x x
----- ----- -�x_x_X_ x\
---- ------------ ----- - -----------� -----
0.00-
---- ----
10 15 20 25 30 35 40 45 50 55 60 120 180
360 720 1440
Duration (minutes)
0
Ic O
B-3
/ 0.52
A-5 B-4
0.08 10091
0.0910091 0.09
0.0910091 10091
A-3
0.18
A-4
0.82
J
F
ii
0 60 120
C
J
SCALE
LEGEND
— - -
—PROJECT BOUNDARY
CATCHMENT BOUNDARY
- - - - -
- - SUB -CATCHMENT BOUNDARY
—_
FLOW DIRECTION
®
POND LOCATION
Al
CATCHMENT ID
Ll 2a
CATCHMENT AREA (AC)
_s� HANNCATCHMEHANSEN RICE
STORM DRAIN CATCHMENT MAP
„ 1-U-B ENGINEERS, INC.