CC - DrainageReport_2020-05-05 MERIDIAN , IDAHO
Pine I4 Subd iv is ion I C) s 2
Stormwater Drainage Report
May 2020
1 892
OF
Prepared by:
CJOU@IB ,
JmUmB ENGINEERS , Inc .
250 South Beechwood Avenue , Suite 201
Boise , ID 83709-0944
208m376- 7330
www . JUB . com
J =U = B Project No . 10 =20 =019
SITE LOCATION
The project site is located approximately 1,500 feet south of E. Fairview Avenue and 350 feet E.
of N. Locust Grove Road. The site is located in the NW 1/4 of Section 8, Township 3 North,
Range 1 East, Boise meridian.
EXISTING SITE CHARACTERISTICS
The project site presently consists of relatively flat non-irrigated land and slopes gently down-
gradient to the south with grades less than 1%.
PROPOSED SITE IMPROVEMENTS
The proposed improvements include the construction of 54 residential lots, 3 common lots, 2
commercial lots and associated streets, sidewalks, and infrastructure.
SOIL CONDITIONS
The following geotechnical reports were referenced during design of this stormwater system.
Geotechnical Report for the Pinebridge Development. Pine Street, Eagle to Locust Groave
Road, Meridian Idaho, dated 4 February 2008, prepared by Bob J. Arnold, P.E.
Based upon the preliminary soils and subsurface investigation for this subdivision, the existing
soils will accept the runoff. Seepage beds are designed based on assumed maximum
infiltration rate of 1.0 inch per hour. Groundwater at the nearest test pit was recorded at 9 feet
below the existing ground.
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.
DRAINAGE DESIGN CONCEPT
The drainage area included within these calculations encompasses portions of the development
located in future phases and covers approximately 8.7 acres. The project consists of 2
catchments labeled A through B.
Catchment A stormwater shall flow above grade to designed low points where it shall be
collected via curb inlets. The stormwater shall then discharge into a sub-surface seepage bed
for infiltration through a sand filter into the groundwater network.
Catchment B stormwater shall flow above grade to designed low points where it shall be
collected via existing curb inlets. The stormwater shall then discharge into an expanded sub-
surface seepage bed for infiltration through a sand filter into the groundwater network.
The two commercial lots are not included in the design described in this report. Stormwater in
these two lots shall flow to separate infiltration system(s) which shall not collect water from the
public roadway and shall not discharge water into public storm drain systems. These system(s)
shall be designed during the final development of these two lots.
Stormwater Drainage Report
Pine 34 Subdivision No. 2
CALCULATION METHODS
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 and pipes
and determine acceptable pipe slopes within the system.
Sizing the expansion of seepage bed B was accomplished by assuming that the existing
storage volume completely captures the previous design with no additional storage capacity.
Flow rates for the existing pipes between the affected catch basins and the seepage bed have
been recalculated and are presented to show that these pipes have not exceeded capacity.
The catchment areas are shown on the Drainage Plan. Calculations are included with this
report for all catchment areas.
Stormwater Drainage Report
Pine 34 Subdivision No. 2
Catchment A Pine 43 Phase 2
Project No.10-20-019
Gutter Flow Rational Method (TR-55)
Sub- Elev. 1 Elev. 2 1-gutter Intercept Slope(Sp Vgutter T,gutter
) Lgutter
catchment (ft) (ft) (ft) Coeff. (k) N (fps) (min) Tc-gutter = 60 V
Al 2608.05 2610.48 527 0.619 0.46 1.38 6.36 gutter
A2 2608.05 2610.98 542 0.619 0.54 1.49 6.06 0.007(nL)0.8
Tc-sheet - (p2)0.SS0.4
= 3.281kSp0'S
Vgutter
Tc = Tc-gutter + Tc-sheet
Q = CiA
Sheet Flow Calculation Total Tc Catchment Parameters
Sub- n L P2 s Tc-sheet Tc C, Area, C2 Areal CT AreaT
catchment (unitless) (ft) (in) (ft/ft) (min) (min) (ac) (ac) (ac)
Al 0.24 60 1.2 0.01 20.4 26.8 0.50 1.30 0.50 1.30
A2 0.24 57 1.2 0.01 19.5 25.5 0.50 2.02 0.50 2.02
Total Area 3.32
Comp.C 0.5
Design Storm Intensities Design Storm Flow Rates Soil Parameters
Sub- i2 i25 iso iloo Q2 Q25 Qso QZoo Infil. Rate
4.00 in/hr
catchment (in/hr) (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) (cfs) (F)
Al 0.42 1.12 1.33 1.55 0.27 0.73 0.86 1.01
A2 0.43 1.13 1.34 1.57 0.43 1.14 1.35 1.59
0.70 1.87 2.21 2.60
V.2019-05-09 10 Apr 2020
Catchment A Pine 43 Phase 2
Project No.10-20-019
Seepage Bed (BMP-20)
DESIGN OPTIONS
ris
count for 1st hr of infiltration? Yes
the bed inside the right-of-way? No
PARAMETERS
Design Storm frequency 100 -year
Design Storm duration 1 -hour
Design Infiltration rate(Fr) 4.00 in/hr
Weighted Runoff Coefficient(C) 0.50
Design Storm Inentsity(i) 0.96 in/hr
Catchment Area (A) 3.32 ac
Sediment factor(f)= 0 %
Required Storage Volume(V100) 5,737 ft3 V = C * i *A * 3600 * 1 +
DESIGN
Width (W)= 10 ft
Depth (D)= 6.5 ft
Void Ratio(e)= 40 % Vol (Ve U)= 25.3 ft3
Inlet pipe size(d1)= 18 in Qty(dlq)= 1 Vol (VP1)= 1.77 ft3
Overflow pipe size(dz)= 0 in Qty(d2q)= 0 Vol (VP2)= 0.00 ft3
Infiltration/LF(Fu)= 3.33 ft3
Storage Vol/LF(Su)= 29.51 ft3
Vol based lenth (Lv)= 194.43 ft
Drain based length (Lp)= 35.89 ft
RESULTS DESIGN CHECKS
Min Design
Bed length (L)= 194.43 201.00 ft 368>_L>_Lmin PASS
Bed Capacity(V)= 5,737 5,931 cf water V>_V100 PASS
Time to Drain 90%(t90)= 7.7 hr t90<_48 PASS
Min infil rate(F,r i,) = 0.5 0.6 in/hr
OPTIONAL MULTIPLE SUB-BEDS
Sub-Bed# Length Max allowed bed length= 386 ft
1 36.5 ft
2 75.5 ft
3 89 ft
4 ft
Total Length (ILs b)= 201 ft
EQUATIONS:
F,, iT d2 • dlq rc •dz •d2q
Fu = W - VP1 =12 48 VP2 — 48
V,u = e • ((W •D) — VP1 —VP2) Su = VIU +V21 + VP2 + Fu
_ V100 _ V100
Lv SU LD 48 •Fu
V.2019-05-09 10 Apr 2020
Catchment A Pine 43 Phase 2
Project No.10-20-019
Sand and Grease Trap
Peak Flow Design Storm 100 -year
Water Quality Design Storm 25
Peak Flow Rate(QPeak) 2.60 in/hr
Water Quality Flow Rate(QWQ) 1.87 ac QWQ = C * iwQ *A
Design Calculations
Vault Size= 1500 gallon Peak Throat Velocity(VPeak)= 0.31
No.of S&G Traps= 1 WQ Throat Velocity(vN,Q)= 0.22 fps
Baffle Spacing= 20 inch
Throat Width= 60 inch Allowed Max Flow rate(QMax,A)= 4.15 cfs
Total Throat Area= 8.33 ftz Max Flow rate(QMax)= 2.60 cfs
Bypass Flow Rate= 0 cfs
Checks: VWQ<0.5 PASS
Bypass Required FALSE
LI LI
OUTLET BAFFLE WALL
EL. OUT EL. IN-7 FLOW
FL..
INLET BAFFLE WALL
Modified rom
ISPWC SO-624,2017
V.2019-05-09 10 Apr 2020
Catchment A Pine 43 Phase 2
Project No.10-20-019
Pipe Sizing Allowable Limits
Velocity(ft/sec) Flow depth (%)
Min 3.0 0.0
Max 10.0 90.0
Minimum Pipe Slope Maximum Pipe Slope
Pipe Id Design Mannings Pipe Min. V Flow Max. V Flow
Flow Size Slope' Depth Slope Depth
(cfs) (n) (in) (%) (fps) (%) (%) (fps) (%)
CB Al to SDMH Al 0.73 0.010 12 0.37 3.02 34.68 10.80 9.99 14.88
CB A2 to SDMH Al 1.14 0.010 12 0.27 3.03 48.37 7.42 9.99 20.28
SDMH Al through S&G A 1.87 0.010 12 0.22 3.12 71.37 4.96 9.99 28.79
-4
Pipe velocity solved using the Mannings equation at the respective flow depth.
Flow depth solved using itterative solutions of the Manning's equation
1.49 2 1
Q = .A . R3 . $2
n
D Cr hl Y
r = — h = 2r —y 9 = 2 arccos /I _
r2(9 — sin B) A r
A = TC • r2 — 2 Rh = P P = 2rcr — rO
h
Note:
'Slightly decreased slopes may be considered where the depth of flow will be 0.3 of the diameter or greater for design average flow. (10-State Standards, Paragraph
Z Maximum slopes greater than 20%require additional restraint. (10-State Standards, Paragraph 33.46)
V.2019-05-09 10 Apr 2020
Catchment B Pine 43 Phase 2
Project No.10-20-019
Gutter Flow Rational Method (TR-55)
Sub- Elev. 1 Elev. 2 1-gutter Intercept Slope(Sp Vgutter T,gutter
) Lgutter
catchment (ft) (ft) (ft) Coeff. (k) N (fps) (min) Tc-gutter = 60 V
61 2610.98 2608.87 241 0.619 0.87 1.89 2.13 gutter
B2 2610.98 2608.87 241 0.619 0.87 1.89 2.13 0.007(nL)0.8
Tc-sheet - (p2)0.SS0.4
= 3.281kSp0'S
Vgutter
Tc = Tc-gutter + Tc-sheet
Q = CiA
Sheet Flow Calculation Total Tc Catchment Parameters
Sub- n L P2 s Tc-sheet Tc C, Area, C2 Areal CT AreaT
catchment (unitless) (ft) (in) (ft/ft) (min) (min) (ac) (ac) (ac)
131 0.24 52.5 1.2 0.01 18.4 20.5 0.50 0.66 0.50 0.66
B2 0.24 52.5 1.2 0.01 18.4 20.5 0.50 0.61 0.50 0.61
Total Area 1.27
Comp.C 0.5
Design Storm Intensities Design Storm Flow Rates Soil Parameters
Sub- i2 i25 iso iloo Q2 Q25 Qso QZoo Infil. Rate
4.00 in/hr
catchment (in/hr) (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) (cfs) (F)
131 0.48 1.28 1.52 1.79 0.16 0.42 0.50 0.59
B2 0.48 1.28 1.52 1.79 0.15 0.39 0.46 0.55
0.31 0.81 0.96 1.14
V.2019-05-09 10 Apr 2020
Catchment B Pine 43 Phase 2
Project No.10-20-019
Seepage Bed (BMP-20)
DESIGN OPTIONS
ris
count for 1st hr of infiltration? Yes
the bed inside the right-of-way? No
PARAMETERS
Design Storm frequency 100 -year
Design Storm duration 1 -hour
Design Infiltration rate(Fr) 4.00 in/hr
Weighted Runoff Coefficient(C) 0.50
Design Storm Inentsity(i) 0.96 in/hr
Catchment Area (A) 1.27 ac
Sediment factor(f)= 0 %
Required Storage Volume(V1oo) 2,195 ft 3 V = C * i *A * 3600 * 1 +
DESIGN
Width (W)= 32 ft
Depth (D)= 6.5 ft
Void Ratio(e)= 40 % Vol (Ve U)= 81.8 ft3
Inlet pipe size(d1)= 18 in Qty(dlq)= 2 Vol (VP1)= 3.53 ft 3
Overflow pipe size(dz)= 0 in Qty(d2q)= 0 Vol (VP2)= 0.00 ft3
Infiltration/LF(F,)= 10.67 ft3
Storage Vol/LF(Su)= 94.22 ft3
Vol based lenth (Lv)= 23.30 ft
Drain based length (Lp)= 4.29 ft
RESULTS DESIGN CHECKS
Min Design
Bed length (L)= 23.30 24.00 ft 368>_L>_Lmin PASS
Bed Capacity(V)= 2,195 2,261 cf water V>_V100 PASS
Time to Drain 90%(t90)= 7.7 hr t90<_48 PASS
Min infil rate(F,r i,) = 0.5 0.6 in/hr
OPTIONAL MULTIPLE SUB-BEDS
Sub-Bed# Length Max allowed bed length= 386 ft
1 ft
2 ft
3 ft
4 ft
Total Length (ILs b)= ft Single bed design
EQUATIONS:
F,, 7T d2 • dlq rc •dz •d2q
Fu = W - VP1 =12 48 VP2 — 48
VeU = e • ((W •D) — VP1 —VP2) Su = Veu +V21 + VP2 + Fu
_ V100 _ V100
Lv SU LD 48 •Fu
V.2019-05-09 10 Apr 2020
Catchment B Pine 43 Phase 2
Project No.10-20-019
Sand and Grease Trap
Peak Flow Design Storm 100 -year
Water Quality Design Storm 25
Peak Flow Rate(QPeak) 1.14 in/hr
Water Quality Flow Rate(QWQ) 0.81 ac QWQ = C * iWQ *A
Design Calculations
Vault Size= 1500 gallon Peak Throat Velocity(VPeak)= 0.14
No.of S&G Traps= 1 WQ Throat Velocity(vN,Q)= 0.10 fps
Baffle Spacing= 20 inch
Throat Width= 60 inch Allowed Max Flow rate(QMax,A)= 4.15 cfs
Total Throat Area= 8.33 ftz Max Flow rate(QMax)= 1.14 cfs
Bypass Flow Rate= 0 cfs
Checks: VWQ<0.5 PASS
Bypass Required FALSE
LI LI
OUTLET BAFFLE WALL
EL. OUT EL. IN-7FLOW
FLOW
III—
INLET BAFFLE WALL
Modified rom
ISPWC SO-624,2017
V.2019-05-09 10 Apr 2020
Catchment B Pine 43 Phase 2
Project No.10-20-019
Pipe Sizing Allowable Limits
Velocity(ft/sec) Flow depth (%)
Min 3.0 0.0
Max 10.0 90.0
Minimum Pipe Slope Maximum Pipe Slope
Pipe Id Design Mannings Pipe Min. V Flow Max. V Flow
Flow Size Slope' Depth Slope Depth
(cfs) (n) (in) (%) (fps) (%) (%) (fps) (%)
Ex CB 131 to Ex SDMH B3 0.53 0.010 12 0.47 3.00 27.60 14.19 9.99 11.95
Ex CB B2 to Ex SDMH B3 0.54 0.010 12 0.46 3.00 28.02 13.96 9.99 12.10
EX SDMH B3 to Ex SDMH B2 1.07 0.010 12 0.28 3.02 46.15 7.83 9.99 19.40
EX SDMH B2 to Ex SDMH B1 2.70 0.010 12 0.30 3.65 89.17 3.73 9.99 37.62
Pipe velocity solved using the Mannings equation at the respective flow depth.
Flow depth solved using itterative solutions of the Manning's equation
1.49 2 1
Q = .A . R3 . $2
n
D Cr hl Y
r = - h = 2r -y 9 = 2 arccos /I _
r2(9 - sin B) R A r
A = TC • r2 - 2 h = P P = 2rcr - rO
h
Note:
'Slightly decreased slopes may be considered where the depth of flow will be 0.3 of the diameter or greater for design average flow. (10-State Standards, Paragraph
Z Maximum slopes greater than 20%require additional restraint. (10-State Standards, Paragraph 33.46)
V.2019-05-09 10 Apr 2020
ACHD Intensity-Duration-Frequency
Intensity(inches per hour)
Design Storm 2 5 10 25 50 100
Tc(hr) Tc(min)
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 2
-)K-5
-x-10
2.50 -�25
t 50
2.00 100
i
t
1.50
c
' x
1.00 � \x
x\X,x\x--x�
\)K- _ x�
0.50 - � � )\
-.-.- -------------x------ �
=�„
0.00 1---
10 15 20 25 30 35 40 45 50 55 60 120 180 360 720 1440
Duration (minutes)
Table 3.2. Manning's Roughness Coefficient(n)for Overland Sheet Flow." Estimated Runoff Coefficients for VafiOUS Surfaces
Surface Description n Type of Surface Runoff Coefficients"C"
Smooth asphalt 0.011 Business
Smooth concrete 0,012 Downtown areas 0.70-0.95
-Ordionary concrete lining p_013 Urban neighborhoods 0.50-0.70
Good wood 0.014 Residential
Brick wqh cement mortar 0.014 Sirtgie Family 0.35-0-50
Multi-family 0.60-0.75
Vitrified clay 0.015 Residential(rural) 0.25-0.40
Cast iron 0.015 Apartment Dwelling Areas 0.70
-Corrugated rnetal pipe 0.024 Industrial and Commercial
Cement rubble surface 0,024 Light areas 0.80
Fallow no residue) 0.05 keavyareas 0.90
Cultivated soils Parks,Cemeteries 0.10-0.25
Residue covers 20/ 0.06 Playgrounds 0.20-0.35
Residue covers 200l 0,17 Railroad yard areas 0.20-0.40
Unimproved areas 0.10-0.30
Range(natural) D-13 Streets
Grass Asphalt 0.95
Short grass prairie 0.15 Concrete 0.95
Dense grasses 0,24 Brick 0.95
Bermuda rass 0.41 Roofs 0.95
Woo d s' Gravel 0.75
Light underbrush 0-40 Fields:Sandy soil soirType
Dense underbrush ❑-190'When selecting n,consider cover to a height of about 30 m Slope A B C ❑
m- This is only part of
the plant Cover that will obstruct sheet flow. Sly:0-2% 0.007 D.11 0.15
0.15 0.15
Average:2-6°d 0.094 0.
Table 3-3. Intercept Coefficients for Velocity vs.Slope Relationship of Equation 3-V" Steep:>696 0.13 0-18 0.23 0.29
Land Cover)Flow Regime k Adapted from ASCt`
Forest with heavy ground litter:hay meadow{overland flowh 0-076 Recommend Standards for Wastewater Facilities
Trash fallow or minimum tillage cultivation:contour or strip cropped:wowiland OA52
overland Row Table 33.41 Recommended Minimum Slopes
Short grass pasture overland flaw] 0,213 Minnnum Slope m Feet
Cultivated straig hi raw[overland fknv) 0,274 Nominal Seger Size Per 10D Feet mi( '100 m)
Nearly bare and unfilled[overland flow);alluvial fans in wastem mountain ions 0.305 8 i -h(200 mm) 0 40
Grassadwaterwa shallow omcentrated now 0.457
Unpaved(shallow oonoentrated flow) 491 ID nch(25D nun) D.28
Paved area shallow concentrated flow);small upland gullies O.St9 12 inch(300 rnm) 0.22
Tabra S4. TyPlell Rargh o!Llannlny^1 C-M.Iara 4.)for Ch.-U■.a Pip- 14 inch(350 nun) 0.17
Conduit moreael Mvnnina'* - 15 inch(375 rnm) 0.15
a-d cendwls 16 inch(4DO nun) 0.14
c_ a.ura-a.ass ISuich(450mm) 0.12
CIWP 0.011-0.o37
vleasic am Dour a.aos-a.ofs 21mch(525nun) O.1D
Plli.i -etas)) o.ora-0.026 24=h(6DO nun) 0.08
Paw Vpunar aaalona O.er2-0.016
smau own cnanaels 27 inch(675 nun) 0.067
co..car t. a.or+-o.o1a 30 inch(750 nun) 0.058
punele era p a.020.-tr.oas 33 inch(825 nun) 0.052
V -ion 01.020
sere Seal e.urd-0-026 36 inch(900 nun) 0.D46
Racy cut 0,025-0.043
Natwal ctfennsls(rnlnw aVearna-Sop width er flood siege tsa m(TOO it)) 39 inch(975 tnm) 0.041
Fain . ularsecnpn a.o2s-e-oaa 42mch(1D50mm) 0.037
lOQWOI srarion wlrn pools [ILLY:/r lwldl-Ldnudl uUIIirwdxewdrelxdnudl ub.pui
t Owar valusa era usuaNy rpr wee-C4neVu clad arw mai nteiaaQ Is^tpplharl pipes
anO chann.as
• 0 50 100
SCALE IN FEET
LEGEND
Al
® , •• 1.30 \\ — — PROJECT BOUNDARY
•
♦ \ \ \ CATCHMENT BOUNDARY
wl — — — — — — — SUB-CATCHMENT BOUNDARY
1 —� FLOW DIRECTION
INFILTRATION BED LOCATION
x o1 2.02 , \ \
m \ Al I CATCHMENT ID
o ♦ \ 1.24 CATCHMENT AREA (AC)
LLII
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DELAWARE PARK, SUBDIVISION NO. 2, UNIT 5
B � CALDWELL, IDAHO
o o STORM DRAIN CATCHMENT MAP
a J-U-B ENGINEERS,INC.