HomeMy WebLinkAboutSW4070701_Calcs (ToC)_20200213Watershed Basin Number Average
Total Drainage Area 0.5
Rational Method for Flow RUNOFF COEFFICIENT
Subarea A acres 0.3
Subarea A Runoff Coefficient 0.9 LAND USE C
Subarea B acres
0.21
BUSINESS:
DOWNTOWN AREAS
NEIGHBORHOOD AREAS
RESIDENTIAL:
SINGLE FAMILY AREAS
MULTI UNITS, DETACHED
MULTI UNITS, ATTACHED
SUBURBAN
0.7-0.95
0.5-0.7
0.3-0.5
0.4-0.6
0.6-0.75
0.25-0.4
Subarea B Runoff Coefficient
0.2
Subarea C acres
Subarea C Runoff Coefficient
Subarea D acres
Subarea D Runoff Coefficient
Weighted Runoff Coefficient
0.62
2-vear Rainfall Intensitv (IDF)
5.27
Q2 Flow 1.634 LIGHT AREAS
0.5-0.8
Q10 Flow 2.6 HEAVYAREAS
0.6-0.9
PARKS, CEMETARIES
0.1-0.25
PLAYGROUNDS
0.2-0.35
RAILROAD YARD AREAS
0.2-0.4
UNIMPROVED AREAS
0.1-0.3
STREETS:
ASPHALT
0.7-0.95
CONCRETE
0.8-0.95
BRICK
0.7-0.85
DRIVES AND WALKS
0.75-0.85
ROOFS
0.75-0.85
LAWNS:
SANDY SOIL, FLAT, 2%
0.05-0.1
SANDY SOIL, AVE., 2-7%
0.1-0.15
SANDY SOIL, STEEP, 7%
0.15-0.2
HEAVY SOIL, FLAT, 2%
0.13-0.17
HEAVY SOIL, AVE., 2-7%
0.18-0.22
HEAVY SOIL, STEEP, 7%
0.25-0.35
AGRICULTURAL LAND:
BARE PACKED SOIL
SMOOTH
0.3-0.6
ROUGH
0.2-0.5
CUL TI VATED RO WS
HEAVY SOIL NO CROP
0.3-0.6
HEAVY SOIL WITH CROP
0.2-0.5
SANDY SOIL NO CROP
0.2-0.4
SANDY SOIL WITH CROP
0.1-0.25
PASTURE
HEAVYSOIL
0.15-0.45
SANDYSOIL
0.05-0.25
WOODLANDS
0.05-0.25
Revised 11/25/2008 TGH
Solving for Time of Concentration
Kinematic Wave Theory _
User Data Calculated Value
Length of overland flow
100.000
Surface Mannin s n
Mannin s "n" for surface
0.011
Smooth Surface
0.011
Bare Earth
0.020
Average watershed sloe
5.000
ft./ft.
Fallow
0.050
Constant alpha
302.886
Cultivated, <= 20% Residue
0.060
Constant m
1.667
Cultivated, > 20% Residue
0.170
Wei hted Runoff Coefficient 0.62 Grass, Short
Grass, Dense
Grass, Bermuda
Woods, Light
Woods, Dense
0.150
0.240
0.41n
0.400
0.800
iAM
Trail Time of Duration I Rainfall Intensity(IDF)I Calculation of Time of Concentration
tr (minutes) i (Inches/hour) tc (minutes)
5
8.45
0.32
10
6.73
0.35
15
5.69
0.37
30
4.21
0.42
60
1 hour
2.81
0.49
120
2 hours
1.75
0.59
180
3 hours
1.27
0.68
360
6 hours
0.814
0.81
720
12 hours
0.511
0.97
1440
(24 hours) 1
0.3
1.15
Enter the Rainfall Intensity Values for the Corresponding Times of Duration from the NWS hyperlink provided.
Select the smallest Trial Time of Duration
that is equal to or less than the calculated Time of Concentration, or the Calculated
Time of Concentration if it is less than 5 minutes. This is the overland flow component of the Time of Concentration.
Overland Flow Itc (minutes)
Calculate the shallow concentrated flow component of the Time of Concentration.
Calculate the channel flow component of the Time of Concentration.
Sum these three components.
This is the total Time of Concentration.
Shallow Concentrated Flow
Channel Flow 0
Paved
Flow Length
1
Flow Length
100
Slope
1
Sloe 1
5
tc (minutes)
0.0
Hydraulic Radius
0.584
Unpaved
Mann nag n
0.24
Slope 1
tc (minutes) _ 0.0
Total Time of Concentration
Jarrett Shortcut, for Bare Soil
:IIII
Area A
acres