An urban catchment has a main ditch as shown below. Paths from remote points to the main ditch are also indicated. The
Posted: Wed May 04, 2022 9:41 am
An urban catchment has a main ditch as shown below. Paths from
remote points to the main ditch are also indicated. The
details of each subarea are listed in the table below. Overland
travel times as well as travel time in the ditch are computed by
Kirpich formula. where tc is
the time of concentration in minutes; L
in metres, and S - slope of land
If the 25 year intensity is given by: , where
i is the rainfall intensity in cm/hr and
the duration tc in minutes.
Determine the flood discharge at point G by; The
Rational Method
The Natural Resource Conservation Service (NRCS) curve number
method assuming it had been raining intensely for the past three
days.
Comment on the results obtained by the Rational method and that
of the NRCS method.
Area
Drainage Area (km2)
Type of surface
Average soil infiltration rate (mm/hr
Path
Length (m)
Slope
(%)
1
0.04882
Bare surface, C=0.4
8
AB
800
1.5
2
0.05492
Asphalt paved, C=0.8
5
BD
600
1.0
CD
432.8
2.0
3
0.04800
Lawn, fair condition. C =0.3
8.5
ED
548.6
1.5
4
0.05736
Concrete paved, C=0.9
1
DG
700
1.5
FG
800
0.8
remote points to the main ditch are also indicated. The
details of each subarea are listed in the table below. Overland
travel times as well as travel time in the ditch are computed by
Kirpich formula. where tc is
the time of concentration in minutes; L
in metres, and S - slope of land
If the 25 year intensity is given by: , where
i is the rainfall intensity in cm/hr and
the duration tc in minutes.
Determine the flood discharge at point G by; The
Rational Method
The Natural Resource Conservation Service (NRCS) curve number
method assuming it had been raining intensely for the past three
days.
Comment on the results obtained by the Rational method and that
of the NRCS method.
Area
Drainage Area (km2)
Type of surface
Average soil infiltration rate (mm/hr
Path
Length (m)
Slope
(%)
1
0.04882
Bare surface, C=0.4
8
AB
800
1.5
2
0.05492
Asphalt paved, C=0.8
5
BD
600
1.0
CD
432.8
2.0
3
0.04800
Lawn, fair condition. C =0.3
8.5
ED
548.6
1.5
4
0.05736
Concrete paved, C=0.9
1
DG
700
1.5
FG
800
0.8