HomeMy WebLinkAboutCHERRY STREET COTTAGES - PDP - PDP160041 - SUBMITTAL DOCUMENTS - ROUND 2 - STORMWATER-RELATED DOCUMENTS (18)17-06-02_2-yr peak runoff_UD-Rational_Revised.xls, Tc and PeakQ 6/6/17, 8:33 AM
Project Title:
Catchment ID:
I. Catchment Hydrologic Data
Catchment ID = A
Area = 1.01 Acres
Percent Imperviousness = 5.00 %
NRCS Soil Type = C A, B, C, or D
II. Rainfall Information I (inch/hr) = C1 * P1 /(C2 + Td)^C3
Design Storm Return Period, Tr = 2 years (input return period for design storm)
C1 = 28.50 (input the value of C1)
C2= 10.00 (input the value of C2)
C3= 0.786 (input the value of C3)
P1= 0.98 inches (input one-hr precipitation--see Sheet "Design Info")
III. Analysis of Flow Time (Time of Concentration) for a Catchment
Runoff Coefficient, C = 0.08
Overide Runoff Coefficient, C = (enter an overide C value if desired, or leave blank to accept calculated C.)
5-yr. Runoff Coefficient, C-5 = 0.18
Overide 5-yr. Runoff Coefficient, C = (enter an overide C-5 value if desired, or leave blank to accept calculated C-5.)
Illustration
NRCS Land Heavy Tillage/ Short Nearly Grassed
Type Meadow Field Pasture/ Bare Swales/
Lawns Ground Waterways
Conveyance 2.5 5 7 10 15
Calculations: Reach Slope Length 5-yr NRCS Flow Flow
ID S L Runoff Convey- Velocity Time
Coeff ance V Tf
ft/ft ft C-5 fps minutes
input input output input output output
Overland 0.0100 50 0.18 N/A 0.07 11.72
1 0.0100 215 8.50 0.85 4.22
2
3
4
5
265 Computed Tc = 15.94
Regional Tc = 11.47
User-Entered Tc = 12.11
IV. Peak Runoff Prediction
Rainfall Intensity at Computed Tc, I = 2.16 inch/hr Peak Flowrate, Qp = 0.17 cfs
Rainfall Intensity at Regional Tc, I = 2.51 inch/hr Peak Flowrate, Qp = 0.19 cfs
Rainfall Intensity at User-Defined Tc, I = 2.45 inch/hr Peak Flowrate, Qp = 0.19 cfs
(Sheet Flow)
20
Shallow Paved Swales
Sum
CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD
Gilmartin - Cherry: Pierce Subdivision
A: Onsite
Paved Areas &