HEC-HMS Exercise
****************
O
7
7
7
7
3
1
A
B
2
4
C
14
5
D
14
E
6
14
F
7
7
G
Fig1: Basin/Sub-Basins for Rainfall-Runoff Analysis
Objective: To determine hydrological Response of the given basin for 500 years
return period. This analysis consists of following two parts:
1. To estimate the IDF-curve & Design storm applying suggested
methodology.
2. To determine the hydrological response of the design storm over the basin
using software tool HEC-HMS and to reduce the peak flow by adjusting
elevation & length of the spillway.
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TRAINING FOR OFFICIALS OF “FLOOD WARNING SECTION” ROYAL GOVT. OF BHUTAN (20-24 April 2015)
Table 1: Rainfall Data (Maximum rainfall in 24 hrs. extreme events of the years)
Year
Rainfall mm
Year
Rainfall mm
Year
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
124
66.4
52.1
40.1
76.5
73.4
47.4
82.2
34.2
48.5
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
54.4
63.6
52.5
29.7
112.6
42.8
46.6
48.3
230.1
67.2
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Cumulative
rainfall. mm
Rainfall. mm
Rainfall mm
61.9
97.5
82.4
55.5
63.6
31.3
63.5
87.1
77.7
60.1
Table 2: IDF Curve Data
Duration in
hrs
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
70
Multiplying
factor
Intensity
mm/hour
Alt. Block
T = 500 years
  T 
y = − ln ln
 
  T −1
N = 30
y: f(T)
x n = 0.536
s n = 1.112
Frequency factor
k=
y − xn
k: f(T,N)
sn
P24 = x − kσ
Expression of Synthetic IDF
 280.1 − D 0.1 

280.1 −1 


P
I ( D, T ) = 24 RF 
24
I: Intensity (mm/h)
P24: 24 hours rainfall
D: Duration (h)
RF: Regional Factor = 10
TRAINING FOR OFFICIALS OF “FLOOD WARNING SECTION” ROYAL GOVT. OF BHUTAN (20-24 April 2015)
Table 3: Spillway elevation Vs Reservoir Area
Elevation
(M)
Area
(M2)
0
30
50
70
80
84
88
92
96
100
0
250
500
700
900
1800
3600
7200
14400
28800
 L 
Tc = 0.3 0.25 
J

0.76
Tlag = 0.35Tc ⋅ 60
Ia = 0.2S
S=
25400
− 254
CN
Table 4: Sub-basins
subbasin
Length
(KM)
1
2
3
4
5
6
7
slope
Area
(KM2)
Tc
(Hrs)
Tlag
(Min)
S
(mm)
Ia
(mm)
CN
66
71
66
71
71
69
69
0.03
0.02
0.03
0.02
0.02
0.01
0.01
Muskingum Equation: S= K[x I + (1-x) Q]
Where, S= storage, I=Inflow, Q=Outflow discharge, K= storage time constant, x=
weighting factor.
K = 0.6Tc
Table 5: Reaches (Routing)
Reach
AD
BD
DF
CF
EF
FG
Length
(KM)
Slope
Tc
(Hrs)
Musk. K
(Hrs)
Musk. x
0.25
0.25
0.22
0.22
0.22
0.20
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TRAINING FOR OFFICIALS OF “FLOOD WARNING SECTION” ROYAL GOVT. OF BHUTAN (20-24 April 2015)
Gumbel Extreme Value Distribution
SCS Curve Number Estimation
SCS Curve Number Groups
Hydrologic Soil
Group
72
Soil Group Characteristics
A
Soils having high infiltration rates, even when thoroughly
wetted and consisting chiefly of deep, well to excessivelydrained sands or gravels. These soils have a high rate of
water transmission.
B
Soils having moderate infiltration rates when thoroughly
wetted and consisting chiefly of moderately deep to deep,
moderately fine to moderately coarse textures. These
soils have a moderate rate of water transmission.
C
Soils having slow infiltration rates when thoroughly
wetted and consisting chiefly of soils with a layer that
impedes downward movement of water, or soils with
moderately fine to fine texture. These soils have a slow
rate of water transmission.
D
Soils having very slow infiltration rates when thoroughly
wetted and consisting chiefly of clay soils with a high
swelling potential, soils with a permanent high water
table, soils with a claypan or clay layer at or near the
surface, and shallow soils
TRAINING FOR OFFICIALS OF “FLOOD WARNING SECTION” ROYAL GOVT. OF BHUTAN (20-24 April 2015)
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TRAINING FOR OFFICIALS OF “FLOOD WARNING SECTION” ROYAL GOVT. OF BHUTAN (20-24 April 2015)
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TRAINING FOR OFFICIALS OF “FLOOD WARNING SECTION” ROYAL GOVT. OF BHUTAN (20-24 April 2015)