HomeMy WebLinkAboutSDP200700146 Calculations 2007-11-13RATIONAL METHOD WORKSHEET I'rojec ^: Poplar Glen II
Date: 17/13/2007
Designer:MOS
Watershed ID: Ditch (south end of site)
Drainage Area: 0.57 Acres
c - factor: 0.30 (see worksheet)
tc: 9.65 mins. (see worksheet)
Q(2): 0.71 cfs
Q(10): 0.93 cfs
Time of Concentration Worksheet Weighted c- factor Worksheet
Overland Flow Time Cover Type Area c
Source: Seelye Chart as modified in VDOT Drainage Manual (Fig.Undeveloped (steep)0.57 0.30
1.5.1.1 on Page 1 -13E)
Notes:
1) Length of overland flow always <= 200 ft
2) Calculate a separate Tc for each ground cover condition along the flow path
199.00 Enter Length of Strip (ft)Sample "C" values:c- factor = 0.30
28.66 Enter Slope (% or ft/100ft)0.22 Dense grass
0.30 Enter Rational Method "C" value 0.28 Average grass
0.36 Poor grass
I 8.78IResult Tc (minutes)0.48 Bare soil
0.90 Pavement
Shallow Concentrated Flow Time
Source: SCS Velocity Graph as published in Virginia Erosion and
Sediment Control Handbook, Third Edition (Plate 5 -2 on Page V -12)
Notes:
1) Not intended for well- defined channels - see channel flow calculation
2) Calculate a separate Tc for each ground cover condition along the flow path
508.71 Enter Length of Flow (ft)
36.37 Enter Slope (% or ft/100ft)
I0.87IResult Tc (minutes) IF UNPAVED
0.66 Result Tc (minutes) IF PAVED
Channel Flow Time
Source: Kirpich Chart as modified in VDOT Drainage Manual (Fig. 1.5.1.2 on Page 1 -14)
Notes:
1) For small drainage basins.
2) For concrete channels, use 0.2 *Tc
0.00 Enter Length of Flow (ft)
1.00 Enter Height of most remote point along flow path above outlet
0.001Result Tc (minutes)
Channel Flow Time
Source: Kirpich Chart as modified in VDOT Drainage Manual (Fig. 1.5.1.2 on Page 1 -14)
Notes:
1) For small drainage basins.
2) For concrete channels, use 0.2 *Tc
0.00 Enter Length of Flow (ft)
1.00 Enter Height of most remote point along flow path above outlet
I 0.001Result Tc (minutes)
Rainfall Intensity (Albemarle County, Virginia)
Return Duration Intensity!Period l (mins.) I (in /hr)
2 9.7 4.2
5 9.7 4.8
10 9 7 5.4
25 9.7 6.1
50 9.7 6.5
100 9.7 7.1
Acceptable values for duration are between 5 and 60 minutes. Use values outside this range at risk.
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RATIOS `t Al + METHOD WORKSHEET Project: Poplar Glen fI
Date: 9/28/2007
Designer:MOS
Watershed ID: Ditch (west side of site)
Drainage Area: 0.12 Acres
c- factor: 2.01 (see worksheet)
tc: 7.57 mins. (see worksheet)
Q(2): 1.14 cfs
Q(10): 1.47 cfs
Time of Concentration Worksheet Weighted c- factor Worksheet
Overland Flow Time Cover Type Area c
Source: Seelye Chart as modified in VDOT Drainage Manual (Fig.Undeveloped (steep)0.83 0.30
1.5.1.1 on Page 1 -13E)
Notes:
1) Length of overland flow always <= 200 ft
2) Calculate a separate Tc for each ground cover condition along the flow path
87.33 Enter Length of Strip (ft)Sample "C" values:c- factor = 2.01
12.60 Enter Slope (% or ft/100ft)0.22 Dense grass
0.30 Enter Rational Method "C" value 0.28 Average grass
0.36 Poor grass
7.27 Result Tc (minutes)0.48 Bare soil
0.90 Pavement
Shallow Concentrated Flow Time
Source: SCS Velocity Graph as published in Virginia Erosion and
Sediment Control Handbook, Third Edition (Plate 5 -2 on Page V -12)
Notes
1) Not intended for well- defined channels - see channel flow calculation
2) Calculate a separate Tc for each ground cover condition along the flow path
132.89 Enter Length of Flow (ft)
20.41 Enter Slope (% or ft/100ft)
I0.30 Result Tc (minutes) IF UNPAVED
0.23 Result Tc (minutes) IF PAVED
Channel Flow Time
Source: Kirpich Chart as modified in VDOT Drainage Manual (Fig. 1.5.1.2 on Page 1 -14)
Notes:
1) For small drainage basins.
2) For concrete channels, use 0.2 *Tc
0.00 Enter Length of Flow (ft)
1.00 Enter Height of most remote point along flow path above outlet
0.00 Result Tc (minutes)
Channel Flow Time
Source: Kirpich Chart as modified in VDOT Drainage Manual (Fig. 1.5.1.2 on Page 1 -14)
Notes:
1) For small drainage basins.
2) For concrete channels, use 0.2 *Tc
0.00 Enter Length of Flow (ft)
1.00 Enter Height of most remote point along flow path above outlet
I 0.00IResult Tc (minutes)
Rainfall Intensity (Albemarle County, Virginia)
Return Duration Intensity
Period I (mins.) I (in /hr) I
2 7.6 4.6
5 7.6 5.3
10 7.6 5.9
25 7.6 6.6
50 7.6 7.1
100 7.6 7.7
Acceptable values for duration are between 5 and 60 minutes. Use values outside this range at risk.
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