HomeMy WebLinkAboutSW5180501_Calcs_20180523DOCUMENT TITLE:
PROJECT NAME:
COMPLETED BY: CHECKED BY:
RATIONAL METHOD CALCULATIONS:
Q = CiA; evailuated for the 10-yr, 24-hr storm event
C: Runoff Coefficient
i: Rainfall Intensity (in/hr)
A: Watershed Area (acres)
1. Assumptions:
Evaluate only LOD Area, 44 acres
Pre-Const C-value = 0.30 (Table 1: lawns, heavy soil >7% slopes)
Post-Const C-value = 0.31 (Weighted for minor project improvements; see calculation below)
2. Weighted C-value Calculation for Post-Project Condition:
Project LOD Area 44 ac C-values
Lawns, heavy soils > 7% slopes 1916640 sf 0.30
Minor Project Improvement Areas
Steel Piles 866 sf 1.00
Concrete Equipment Pads/Driveways 1,598 sf 0.95
Asphalt Paving (Siler Business Dr.)4,259 sf 0.95
Gravel (Onsite Roads)76,992 sf 0.65
Subtotal (Minor Impvts)83,715 sf
Cw = [((Alawn - Aimpvts)x 0.30) + (Apiles x 1.0) + (Aconcrete x 0.95) + (Aasphalt x 0.95) + (Agravel x 0.65)]/(Project LOD Area)
Cw = 0.32
3. Runoff Calculation Results:
Drainage
Area Desciption Area
(Acres)
Runoff
Coefficient
Intensity
(10-yr, 24-
hr) (in/hr)
Q10 (cfs)
1 Undisturbed; existing conditions 44.0 0.30 7.4 97.7
Drainage
Area Desciption Area
(Acres)
Runoff
Coefficient
Intensity
(10-yr, 24-
hr) (in/hr)
Q10 (cfs)
1 Vegetated; minor improvements 44.0 0.32 7.4 104.2
>The slight increase in runoff (+6.5 cfs) may be considered negligible due to the weighted C-value; however,
it should be noted that the concrete driveway and paved cul-de-sac will sheet flow into existing swales
on each side of Siler Business Drive. Onsite, once revegetation is completed within the disturbed areas
the majority of the site will closely resemble the existing conditions beneath the solar panels.
EROSION CONTROL CALCULATIONS
SILER SOLAR, LLC
DATE:5/11/2018
ALLY PATRICK MARIO CARREON, PE
3.1 Pre-Construction Condition
3.2 Post-Construction Condition
20180511_Siler Solar_Rational Method Calculations Page 1 of 2
DOCUMENT TITLE:
PROJECT NAME:
COMPLETED BY: CHECKED BY:
EROSION CONTROL CALCULATIONS
SILER SOLAR, LLC
DATE:5/11/2018
ALLY PATRICK MARIO CARREON, PE
4. Reference:
20180511_Siler Solar_Rational Method Calculations Page 2 of 2