Open Channel Flow Ass 2 V 2 Final Ver
Open Channel Flow Ass 2 V 2 Final Ver
Open Channel Flow Ass 2 V 2 Final Ver
Suman SAHA
Student ID Number: 6726143
Determine a stage discharge relationship for the road crossing of Wilsons Creek.
3
Rural
I Y3
/s
Discharge (Q)
ARI(Y)
(year/s)
) values for ARI 1, 2, 5, 10, 20, 50, 100 year/s for Beechworth
Urban
(mm/hr)
0.599
2.97
8.55
0.904
4.13
11
1.44
6.09
14
10
1.85
7.41
15.8
20
2.4
9.16
18.2
50
3.16
12.10
21.5
100
3.92
14.44
24
Where I Y is 3 hours rainfall intensity in mm/hr for ARI of y years. These values are obtained from the rainfall frequency
distribution data for; Beech worth in task 1 (based on the 9 parameters inputted into the IFD software).
Creek Channel Properties (Case 2) :
Parameters
Case 2
0.56.I 53
0.48
0.19.I 53
0.34
Channel depth
S0 (in m/km) =
4.57I 23
0.18
Slope of channel
WLB=WRB(in
metres) =width of
flood plain
3.2I100
0.53
Given
= 14 mm/ hr,
= 11mm/hr
WMC (m) =
0.56.I 53
24mm/hr
0.48
0.19.I 53
= 0.56
= 1.9876 m
0.34
YC (m) =
= 0.19
4.57I 23
= 0.4661m
0.18
S0 (m/km) =
= 4.57
3.2I100
= 2.968 m/km =
0.53
S.SAHA
m /m =0.002968 m/m
= 17.2449m 17.25m
Page 1/12
Computed Value
1.99
0.466
0.02968
17.25
Channel Cross-Section
From Mannings n Tables for Main Channel,
n = 0.045 (max) i.e. clean, winding, some pools and shoals
The flood plain is predominantly composed of light brush and trees (both in summer and winter).
Therefore, from Mannings n Tables for Floodplains,
n (winter) = 0.06 (maximum)
and
Assumptions
(I) Uniform depth along the depth of the channel. Depth (YC) for the main channel and depth (y YC) uniform adopted
across the flood plains.
(II) In general, the Mannings parameter n accounts for roughness (friction) between the water surface and the
channel or flood plain.
(III) For the worst case scenario, adopt the maximum column for Mannings parameter n for either the main
channel or flood plain. This is because the higher Mannings parameter n caters for high flow/ discharge downstream
(more potential flooding) as a result of less flow on the adjacent flood plains.
(IV) Moreover due to the presence of shoals at some sections during summer period (dry season), the flow rate is reduced
which consequently results in an increase in the water level. Hence it is critical that a higher Mannings parameter n
is adopted for the worst case due to gradual increase of water flow in the main channel (increased friction/roughness)
which will eventually overflow unto the surrounding the flood plains.
(V) For flood plain, n summer is the critical since the winter period is usually characterised by dormant growth of
vegetative cover such as light bushes and trees compared to the summer period. The vegetative cover is essential in
reducing the flow / discharge rate, thereby resulting in an increase discharge downstream (rise in water level in main
channel). Consequently over time, this results in flooding of the adjacent flood plains of the road embankment.
(VI) Given; the slope of the embankments on either side of the main channel and the flood plains are 1 Horizontal: 2
Vertical.
S.SAHA
Page 2/12
WMC = 1.99m/m
YC=0.47m
1 2 Yc =0.47m
x
(Not to scale)
= (WMC +
WMC)
By Phythagoras theorem;
YC
2(WMC + x)
YC= (WMC + x)
YC
S.SAHA
YC
YC =
= WMC +
WMC = 2
)=
WMC =
)=
)=
+ WMC
Page 3/12
The parameter for one section of the flood plain is computed as shown below;
WLB=WRB = 17.25m/m
y
y
y
2
2
1
YC) =
WLB)
2WLB +
{WLB + (
} (y YC )= {WLB + (
By Pythagoras theorem; l
)} +WLB)
}
YC
((2WLB
))
YC
YC)
)= =
)=
WLB =
WLB
S.SAHA
==
Page 4/12
However if y >
ie water flow has overtopped the main channel and flooded the two adjacent flood plains.
(
S.SAHA
Page 5/12
y(m)
A(m^2)
P(m)
R(m)
A'(m^2)
P'(m)
R'(m)
Q(m^3/s)
0.3
0.64128
2.658421
0.241226
0.30085
0.31
0.664206
2.680781
0.247766
0.317212
0.45
0.99567
2.993831
0.332574
0.57862
0.4598
1.019607
3.015744
0.338095
0.59907
0.46
1.020096
3.016192
0.338207
0.59949
0.465
1.032347
3.027372
0.341004
0.61003
0.466
1.0348
3.029608
0.341562
0.612147
0.467
1.037254
3.031844
0.34212
0.034501
34.50224
0.001
0.614501
0.519
1.166245
3.14812
0.370458
1.829905
34.61851
0.052859
0.903802
0.5191
1.166496
3.148343
0.370511
1.83336
34.61874
0.052959
0.90458
0.574
1.305621
3.271103
0.399138
3.731832
34.7415
0.107417
1.431142
0.5748
1.30767
3.272892
0.399546
3.759519
34.74328
0.108209
1.440171
0.6
1.37256
3.329241
0.412274
4.631978
34.79963
0.133104
1.742779
0.6083
1.394072
3.3478
0.416414
4.919475
34.81819
0.14129
1.849943
0.647
1.495282
3.434336
0.435392
6.260881
34.90473
0.179371
2.395968
0.6473
1.496072
3.435007
0.435537
6.271285
34.9054
0.179665
2.40049
0.616
1.41409
3.365018
0.420232
5.18625
34.83541
0.148879
1.952571
0.6831
1.591043
3.515058
0.452636
7.513516
34.98545
0.214761
2.970478
0.6943
1.621017
3.540102
0.457901
7.90241
35.01049
0.225715
3.160881
0.7361
1.733994
3.63357
0.477215
9.354927
35.10396
0.266492
3.920151
0.7
1.63632
3.552848
0.460566
8.100378
35.02324
0.231286
3.259934
0.747
1.763742
3.657943
0.482168
9.733981
35.12834
0.277098
4.130403
0.8388
2.018992
3.863214
0.52262
12.93109
35.33361
0.365971
6.091396
0.8934
2.174804
3.985303
0.545706
14.83664
35.4557
0.418456
7.410782
0.7315
1.721476
3.623284
0.475115
9.194995
35.09368
0.262013
3.832918
0.9598
2.368307
4.133778
0.572916
17.15802
35.60417
0.48191
9.159941
1.0606
2.670485
4.359174
0.612613
20.69047
35.82957
0.577469
12.10286
1.1337
2.89598
4.522631
0.640331
23.25856
35.99302
0.646196
14.44328
S.SAHA
Page 6/12
Q
Rural
(
y Rural
(m)
Q
Urban
y
Urban
(m)
0.599
0.4598
2.97
0.6831
0.904
0.5191
4.13
0.747
1.44
0.5748
6.09
0.8388
10
1.85
0.6083
7.41
0.8934
20
2.4
0.6473
9.16
0.9598
50
3.16
0.6943
12.10
1.0606
100
3.92
0.7361
14.44
1.1337
Comment: As expected the successive y values obtained indicate the discharge (m^3/s) will flow in the main channel and the
consequently unto the flood plains as time proceeds. (Refer to assumption IV)
S.SAHA
Page 7/12
Stage,y (m)
Rural
Urban
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15
S.SAHA
Discharge,Q (m / s)
Page 8/12
Stage,y (m)
0.8
0.6
Rural
Urban
0.4
0.2
0
1
S.SAHA
10
ARI (Year/s)
100
Page 9/12
Stage,y (m)
0.8
Rural
0.6
Urban
Log. (Rural)
Log. (Urban)
0.4
0.2
ARI (Year/s)
0
1
S.SAHA
10
100
Page 10/12
= 0.466
A = (WMC +
YC where
+ WMC =
=
y = ( 1.99 +
+ WMC =
0.465= 1.03
= 3.03m
= 0.34m
= 0.6075
CASE II
y=
= 0.466
A = (WMC +
YC where
+ WMC =
=
y = (1.99 +
+ WMC =
0.466= 1.04
= 3.03m
= 0.34m
S0 (m/m) = 0.02968
= 0.6133
CASE III
y = 0.467 >
A = (WMC +
= 0.466
YC where
+ WMC =
=
y = ( 1.99 +
+ WMC =
0.467= 1.04
= 3.03m
= 0.34m
A = {WLB + (
S.SAHA
} YC = {WLB + (
} (y YC) = {17.25 + (
0.466) = 0.017
Page 11/12
WLB =
+ 17.25 = 17.251m
)
= (0.6133 +
= 0.000985
= 0.61352
Comment:
The slight discrepancy in the computed discharge values obtained from the hand computations and the excel spread sheet are due
to rounding off, Hence the results obtained are accurate, however not precise.
S.SAHA
Page 12/12