HomeMy WebLinkAboutCC - Storm Drainage Calcs DRAINAGE CALCULATIONS
FOR
ARTEMISIA SUBDIVISION
ADA COUNTY, IDAHO
July 28, 2021
ENGINEERING SOLUTIONS, LLP
1029 N. Rosario Street, Suite 100
Meridian, Idaho 83642
(208) 938 -0980
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Job Numbers: 190715
Artemisia Subdivision Drainage Report
Artemisia Subdivision is a single - phase commercial development. The project is
generally located in the Section 14, T.3N., R.1 W., B.M., Meridian, Ada County,
Idaho. Artemisia Subdivision is located on the north side of W. Overland Road, on
the west side of future S. Linder Road and on the south side of 1-84. Artemisia is
comprised of 7 commercial lots on approximately 19.3 acres. The storm drainage
from this project will be intercepted by drop inlets, will flow through a storm drain
system including a 1000-gallon sand and grease trap, then into a seepage bed
located within ACHD ROW.
Assumptions used for this drainage report are as follows:
1. Rational Equation used to estimate storm runoff(Q= CIA)
2. SCS: TR-55 Method used to determine Time of Concentration (Tc)
3. Coefficient of Runoff used is C = 0.50 this is from ACHD Section 8011.2.1
Coefficients of Runoff. Residential Single Family 0.35-0.50. I used
maximum.
The rational method was used to determine the peak discharge. This method uses
a"C" value of 0.90 for pavement and sidewalks and 0.20 for landscape areas,
Time of Concentration (Tc) calculated by SCS TR-55 methods and rainfall
Intensity Duration Frequency (IDF) curves for the Boise Front from the ACHD
Storm Water Design Manual. The rainfall intensity is determined from the IDF
curve where "I" is selected at the calculated Tc and the 100-year return.
I used the latest ACHD spreadsheet Version 10.5, November 2018.
Artemisia Subdivision is divided into two runoff collection zones. The
contributing areas are depicted on the attached drainage map. The assumption is
that the front of the lot (approximately 15') will flow to the street, but since it is
commercial each lot will retain on site the parking and roof runoff.
The peak discharge is used to determine the capacity of the pipes and drop inlet.
A minimum value of 10 minutes is used to select the "I" in the peak discharge
calculations. Per ACHD policy, the volume calculations were determined using
Tc of 60 minutes, therefore; I=0.96". I have used the ACHD worksheets Version
10.5 dated November 2018 to determine the peak discharge, bed sizes required,
volumes of the seepage beds and time to drain.
Proposed Drainage
The proposed drainage system improvements consist of drop inlets, a storm pipe
network and a seepage bed.
Areas 1 and 2 will be picked up in drop inlets and piped into a 1000 - gallon sand
and grease trap. An 18"pipe goes 5' into the seepage bed. An 18" top only
perforated pipe extends through the seepage bed. The seepage bed has 1.5' of
filter sand below it. The seepage bed is designed to have 3' of separation from
high groundwater.
Seepage Bed
The seepage bed system is sized for the 100-year storm. The seepage bed is sized
for a seepage bed located in ROW or the 100-year storm plus 25%. The seepage
bed has clean drain rock wrapped in filter fabric to facilitate drainage, an 18"pipe
perforated on the top only and 1.5' of sand underneath the clean drain rock. The
seepage bed also contains a monitoring well inside the bed and one outside of the
bed. The seepage bed was sized using a percolation rate of 4"/hr. The bed was
designed to have 3' of separation from high groundwater based on the
groundwater monitoring report that was provided.
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ARTEMESIA SUBDIVSION Kinematic Equation from ACHD Spreadsheet
tC=(Ku/p20.4)*(nL/S0.5)0.6
tc= (0.933/0.040.4)*(nL/So.5)0.6
Date:July 28, 2021 tc=3.38*(nL/S0.5)0.6
L= distance traveled, in feet
Job Number: 190715 S= slope, in ft/ft
N= mannings overland roughness coefficient
N =0.24 (dense grass)
N =0.06 (Cultivated Soils)
P2=2 yr 24 hour=0.04
Area Length (ft) Slope (ft/ft) Time of Concentration(min)
1 31 2 9.2
2 31 2 9.2
\\ES-1\Projects\2019\190715\Calcs\190715_Time of Concentration-kin 1-11-21.xlsx
TIME OF CONCENTRATION
COMPUTATION FORM
DRAINAGE VELOCITY TIME
AREA NO. LENGTH/TYPE OF FLOW/SLOPE (f.p.s.) (Minutes)
Project �` -ev) E s I .:��� F
Job No. 1 9 0 "7 1 Sheet I
Master/time comput form By Z fy,) Date I ��
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Artemisia Subdivision
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max) 1
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 0.90 0.59
Acres 1.49
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted AvgJ 0.62
7 User Calculate
Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 min �10 Min. Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"(
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius Flow Residential
Intercept A/Wet Velocity V Flow Time Single Family 0.35-0.50
Multi-family 0.60-0.75
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) (min) Residential(rural) 0.25-0.40
Segment 1:Pipe Flow Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.80
90
Segment 2:Gutter Shallow Concentrated Flow Heavy areas 0.
g Parks,Cemeteries .10-0.25
b 0.619 Playgrounds 0.20-0.35
Railroad yard areas 1 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c
Computed Tc= 0.0
User-Entered Tc= 14.4
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.58 in/hr
y Calculate the Post-Development peak discharge(QPeak) Qpeak 2.39 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 3,207 ft3
V=Ci(Tc=60)Ax3600
11 Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(95th percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 2,004 ft'
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Streets
Surface Storage:Basin Asphalt
Basin Foreba V 321 W Asphalt 0.95
Y Concrete 0.95
Primary Treatment/Storage Basin V 2,886 ft' Brick 0.95
Roofs 0.95
Subsurface Storage
Gravel 0.75
Volume Without Sediment Factor(See BMP 20Tab) V 3,207 (t' Fields:Sandy soil Soil Type
Slope A BY23
Flat:0-2% 0.04 0.0
Average:2-6% 0.09 0.1
Stee :>6% 0.13 0.1
Adapted from ASCE
K:\Data From PC\2019\190715-Artemisia Sub(Kendall Ford)\Calculations\ACHD_SD_CALCS_112018.xlsm 7/28/2021,4:02 PM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's
calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that
meet or exceed these calculations in order to be accepted.
Note this spreadsheet pulls information from the"Peak QV"tab
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Artemisia Subdivision
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100 F.
QV
4 Weighted Runoff Coefficient C 0.62 Linkto: QvTR55
5 Area A(Acres) 1.49 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? No V 4,009 ft3 25%Sediment
8 Set Total Design Width of All Drain Rock W 12.0 ft
9 Set Total Design Depth of All Drain Rock D 5.6 ft
Rock Only,Do Not Include Filter Sand Depth or Cover
10 Void Ratio of Drain Rock Voids 0.4
0.4 for 1.5"-2"drain rock and 3/4"Chips
11 Design Infiltration Rate(8 in/hr max) Perc 4.00 in/hr
12 Size of WQ Perf Pipe(Perf 1800) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 3600),REQD if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 31.1 ft3/ft
15 Calculate Design Length L 129 ft
Override Value Required forChambers
16 Variable Infiltration Window L SWL 129 ft
17 Variable Infiltration Window W SWW 12.0 ft
18 Time to Drain 7.0 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 129 ft
20 Perf Pipe Checks.Qperf>=Qpeak; ,
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers
Note:This assumes chambers are organized in a rectangular layout.
1-StormTech,
1 Type of Chambers SC740
2 Volume to Store V 0 ft3
3 Installed Chamber Width Cw 4•25 ft
Installed Chamber Depth Cd 2.50 ft
Installed Chamber Height Ch 7.12 ft
4 Chamber Void Factor
5 Chamber Storage Volume,Without Rock,Per Manuf 45.90 ft3/Unit
6 Chamber Storage Volume,With Rock,Per Manuf 74.90 ft3/Unit
7 Total Number of Units Required 0 ea
8 Area of Infiltration Aperc ft2
9 Volume Infiltration Vperc 0 ft3/hr
10 Time to Drain hours
90%volume in 48-hours minimum
K:\Data From PC\2019\190715-Artemisia Sub(Kendall Ford)\Calculations\ACHD_SD_CALCS_112018.xlsm 7/28/2021,4:02 PM
Version 10.0,May 2018