HomeMy WebLinkAboutOaks Subdivision No. 6 - H-2017-0016-Drainage CalcsPROJECT NO. 10-17-007
DRAINAGE CALCULATIONS
FOR
The Oaks Subidivions No. 6
City of Meridian
Ada County, Idaho
February 2017
2
Of
'N.
J -U-6 ENGINEERS, INC.
250 S. Beechwood Drive, #201
Boise, Idaho 83709
208-376-7330
PROJECT NO. 10-17-007
The Oaks Subidivions No. 6
SITE OVERVIEW
The Oaks Subdivision No. 6 is located at the southwest corner of W. McMillan Road and N. Rustic
Oak Way in Meridian, Idaho. The proposed development consists of 20 single family residential lots
located on approximately 13.2 acres.
EXISTING DRAINAGE
The existing project site presently consists of a vacant agricultural field. The site is bounded by
developed single family residential properties to the north and east, and agricultural land to the
west and south. The ground slopes gently from northeast to southwest at grades generally less than
2%.
DRAINAGE DESIGN CONCEPT
The proposed stormwater improvements include the installation of roadways, pipe networks,
stormwater treatment systems, and storage facilities. The surface flow will be directed to and
contained within the road sections to designed low points where inlets will capture the stormwater
and convey it through a pipe network to a discharge location. A treatment system will be installed
for each pipe network prior to allowing the stormwater to be be discharged to the storage facility.
The site was divided into catchment areas based on the inlet locations. Each catchement area was
analyzed for the 25 -year flow rate for conveyance, the water quality event for treatment and the
100 -year runoff for storage.
CALCULATION METHODS
Calcualtions were prepared in accordance with the current edition of the Ada County Highway
District Stormwater Policy Manual using the rational method (Q=CIA). The catchment areas are
shown on the Drainage Catchment Plan. The average rainfall intensity is estimated from the
"Rainfall Intensity -Duration -Frequency Relationship" figure for each storm event noted. The time of
concentration is determined using the TR -55 method and combines the longest overland grass flow
time to gutter flow time. Calculations and spreadsheets are included with this report for all
catchment areas.
SOIL CONDITIONS
Based upon the preliminary soils and subsurface investigation provided in the soils report for this
subdivision, the existing soils will accept the runoff. However, in the event that during construction
the contractor encounters either groundwater or rock, a revised design will be done based upon
field conditions.
FAProjects\JUB\10-17-007-Oaks No 6\Drainage\Oaks 6 Drainage-Copy.xlsx
IT
Om
N
Cl)
>
r
N
7
r
d
d
f0
00
c
O
O
� w
N
O 00
V
tD
(Y O
O
O O
O
O
O
co
m
Q
�
O
@
0:N
0
0
m
a
H
N
Cl)
'O
II)o E
Q
O
_
C C V
o
4.1
d
C
E c
Gr
m00
V.O..
M
r-
0
rn
00
r
L
p
y O
O
O
O
O
N (�5 (D
0
=
Em' '
U)
O
0 C: o ,n
'�'�
N N
�
r
O
O
Of` L:
0)C
4)
CD
p =
N O
10
Vr
O C
0
\!
M
N
C
� �UCOO
11
H
U
0
�j o
w
U
C\!LO
13 13 11 IN O O
N
O
O
O
O
U
> >
V
O
O
N
N
LO
f`
N
L
N
M
Ci
O
M
cl)
CY OOH
M
N
M
N
Lq
3
O
O
0) N
(0 'U
V
O
O
Q
G')
I�
N
O co
M
M
ch
(D
N
O
O
N N
o
N
°U
ootcoN
OD
Y O O0
C
N
N
N
N
Q W C C
U
U Il� �F�
N
Lorn
CO
Ln N
00
�n
II II II II
C
0
F
Cf aC) Q
6)
O
O
r -
C
-
O
O
Ll)
O
LQ
U
�
0
C)
O
o
L)
O
N
U) 3 ma
3 D o
O J 00N
C
N
V
V
Ln
^
W M
E
N
(D
L'7
h
41
O
3 v L 0
c d
J
(D
co
(N
(D
N
N
M
Iq
C
D Q
li'%
II
In
Ln
in
in
N
(n
0
0
O
O
LLLLiii
�'
O
O
O
O
r
C
E
O
M
r
Mr�
0
0
y�,�
N N
.�
N
0
0
0
O
0
O
C3
o
N
V
O -J V a
in
O
a:Ci j N N L N
J,
Ln
N
O
L7
N
LO
C
o
a r-- °) a)
(�
m O oN C O N O
O a m n i a
w
01 0 L N m
o0
0
0
d
0 N C� � m
m LL
O
O
O
O
C
O J O Q
jw��
CO
co
co
F
m
Q
Q¢
mm
Basin A
Contributing Catchment Areas: A
Required Water Quality Volume: 1,720 ft'
Required Water Quality Flow Rate: 0.88 cfs
Required Storage Volume: 4,856 ft'
Seepage Bed
Th
Sai
PROJECT NO. 10-17-007
The Oaks Subidivions No. 6
Volume Calculations
Storage Duration
Box Volume =
Depth =
4 ft
Interior Box Width =
48 in
Length =
203 ft
Infiltration Area =
812 ft2
Width =
15 ft
Infiltration Rate =
8 in./hr
Void Ratio =
40 %
Trench Infiltration =
541 ft'/hr
Trench Volume =
4,872 ft'
Time for 90% Percolation =
2.86 hr
Id and Grease Trap calculations
Box Volume =
1000 gallon
Interior Box Width =
48 in
Qwo = 0.88 ft'/sec
Baffle Separation =
20 in
Throat Velocity = 0.13 ft/sec
Number of Boxes =
1
Throat Area =
6.67 ft2
Throat Velocity must be < 0.50 ft/sec
F:\Projects\JUB\10-17-007-Oaks No 6\Drainage\Oaks 6 Drainage-Copy.xlsx Page 4 of 7
Basin B
Contributing Catchment Areas: B
Required Water Quality Volume: 1,236 ft'
Required Water Quality Flow Rate: 0.60 cfs
Required Storage Volume: 3,491 ft3
Seepage Bed
Sar
PROJECT NO. 10-17-007
The Oaks Subidivions No. 6
Volume Calculations
Storage Duration
Depth =
4 ft
Length =
182 ft
Infiltration Area =
728 ft
Width =
12 ft
Infiltration Rate =
8 in./hr
Void Ratio =
40 %
Trench Infiltration =
485 ft3/hr
Trench Volume =
3,494 ft'
Time for 90% Percolation =
2.29 hr
d and Grease Trap Calculations
Box Volume = 1000 gallon
Interior Box Width = 48 in QWQ = 0.60 ft3/sec
Baffle Separation = 20 in Throat Velocity = 0.09 ft/sec
Number of Boxes =
Throat Area = 6.67 ft' Throat Velocity must be < 0.50 ft/sec
F:\Projects\JUB\10-17-007-Oaks No 6\Drainage\Oaks 6 Drainage-Copy.xlsx Page 5 of 7
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3DO by Autodesk, Inc.
PIPE BASIN Al -A2
Circular
Diameter (ft) = 1.00
Invert Elev (ft)
= 100.00
Slope (%)
= 2.74
N -Value
= 0.010
Calculations
Compute by:
Known Q
Known Q (cfs)
= 2.34
Elev (ft)
102.00
101.50
101.00
100.50
99.50
0
1
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section
Reach (ft)
2
Thursday, Jan 26 2017
= 0.38
= 2.340
= 0.27
= 8.52
= 1.33
= 0.66
= 0.97
= 1.51
Depth
2.00
1.50
1.00
0.50
M
-0.50
3
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.
PIPE BASIN A2
Circular
Diameter (ft) = 1.00
Invert Elev (ft)
= 100.00
Slope (%)
= 0.50
N -Value
= 0.010
Calculations
Compute by:
Known Q
Known Q (cfs)
= 1.61
Elev (ft)
102.00
101.50
TiI1
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section
Thursday, Jan 26 2017
= 0.50
= 1.610
= 0.39
= 4.08
= 1.57
= 0.54
= 1.00
= 0.76
99.50 —'
0
1
Reach (ft)
2
Depth
2.00
1.50
M
MIN
L — -0.50
3
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.
PIPE BASIN 131-132
Circular
Diameter (ft) = 1.00
Invert Elev (ft)
= 100.00
Slope (%)
= 2.65
N -Value
= 0.010
Calculations
Compute by:
Known Q
Known Q (cfs)
= 1.59
Elev (ft)
102.00
101.50
101.00
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section
Thursday, Jan 26 2017
= 0.31
= 1.590
= 0.21
= 7.60
= 1.18
= 0.54
= 0.93
= 1.21
99.50 -'
0
1
Reach (ft)
2
Depth
2.00
1.50
1.00
0.50
M
'- -0.50
3
Channel Report
Hydraflow Express Extension for Autodesk@ AutoCADO Civil 3D@ by Autodesk, Inc.
PIPE BASIN B2
Circular
Diameter (ft) = 1.00
Invert Elev (ft)
= 100.00
Slope (%)
= 0.50
N -Value
= 0.010
Calculations
Compute by:
Known Q
Known Q (cfs)
= 1.23
Elev (ft)
102.00
101.00
100.50
100.00
1
Highlighted
Depth (ft)
Q (cfs)
Area (sqft)
Velocity (ft/s)
Wetted Perim (ft)
Crit Depth, Yc (ft)
Top Width (ft)
EGL (ft)
Section
Reach (ft)
FA
Thursday, Jan 26 2017
= 0.43
= 1.230
= 0.33
= 3.78
= 1.43
= 0.47
= 0.99
= 0.65
Depth
2.00
1.50
1.00
0.50
11 10
-0.50
3
■
...........
I