For guidance, use the procedure for the Standard Step Method as outlined in Chap
ID: 1709994 • Letter: F
Question
For guidance, use the procedure for the Standard Step Method as outlined in Chapter 3, p3-13 to p3-16 and Example 3.20. A water stage elevation gauge is located at River Station cross-section 1.0 which has measured the Water Surface Elevation to be 1505.0 ft for the 100-year storm. Based on this WSEL, the following information was already determined for you for cross-section 1.0: Column 3: Computer WSEL 1505 ft Column 4: A- 696 ft^2 Column 5:R = 3.25 ft Column 6: You calculate Column 7: You estimate Manning's n for main channel Column 8: K = 64, 756 Next, use the value of flow (Q) that you determined in the last homework, to complete Columns 15 and 16. Then, compute the Water Surface Elevation (WSEL) for cross-section 2.0. For your first trial, use an assumed WSEL = 1509.89 ft and A = 342.24 ft^2 and R = 3.20ft and a reach length of L 250 ft. Determine the computed WSEL. It may not be within 0.5ft of your assumed WSEL of 1509.89ft. STOP here. The purpose of this exercise is to appreciate the time and effort required for multiple iterations.Explanation / Answer
Please find the solution in the excel file attached since discharge was not available in a
This is an example of using the standard step method to do a backwater calculation for a rectangular channel
Standard step method
CROSS SECTION 2 CALCULATION
Values in yellow boxes are required for each different problem
Enter the values and press the button
Inputs
Depth
Area
Perimeter
EG (m)
Sf
(So-Sf)mean
DelE (m)
Iterations
EC (m)
Distance (m)
Assumed
Flow (m3/s)
30.0
48.7300
19.4920
97.8600
48.8507
0.0326
48.8507
0.0
Assumed
Manning n
0.04
48.8879
19.5552
98.1758
49.0079
0.0324
-0.0315
0.1574
1
49.0081
-5.0
Assumed
Slope
0.001
49.0448
19.6179
98.4895
49.1639
0.0322
-0.0313
0.1563
1
49.1642
-10.0
Width (m)
0.4
49.2006
19.6802
98.8011
49.3190
0.0320
-0.0311
0.1553
1
49.3192
-15.0
Initial depth (m)
48.7
49.3554
19.7421
99.1107
49.4731
0.0318
-0.0309
0.1543
1
49.4733
-20.0
Step (m)
5.0
49.5091
19.8037
99.4183
49.6261
0.0316
-0.0307
0.1533
1
49.6263
-25.0
Length (m)
76.0
49.6619
19.8648
99.7239
49.7782
0.0314
-0.0305
0.1523
1
49.7784
-30.0
Tolerance
0.0010
49.8138
19.9255
100.0276
49.9293
0.0312
-0.0303
0.1514
1
49.9295
-35.0
49.9647
19.9859
100.3293
50.0795
0.0310
-0.0301
0.1504
1
50.0797
-40.0
50.1146
20.0458
100.6292
50.2287
0.0308
-0.0299
0.1495
1
50.2290
-45.0
50.2636
20.1054
100.9272
50.3771
0.0306
-0.0297
0.1485
1
50.3773
-50.0
50.4117
20.1647
101.2233
50.5245
0.0304
-0.0295
0.1476
1
50.5247
-55.0
50.5589
20.2235
101.5177
50.6710
0.0303
-0.0293
0.1467
1
50.6712
-60.0
50.7052
20.2821
101.8103
50.8167
0.0301
-0.0292
0.1459
1
50.8169
-65.0
50.8506
20.3402
102.1012
50.9615
0.0299
-0.0290
0.1450
1
50.9617
-70.0
50.9952
20.3981
102.3903
51.1054
0.0297
-0.0288
0.1441
1
51.1056
-75.0
correct unit so taken as 30m3/s and all other parameters are converted into SI unit. If the discharge is different change the Value in the excel file and you will get the solution
This is an example of using the standard step method to do a backwater calculation for a rectangular channel
Standard step method
CROSS SECTION 2 CALCULATION
Values in yellow boxes are required for each different problem
Enter the values and press the button
Inputs
Depth
Area
Perimeter
EG (m)
Sf
(So-Sf)mean
DelE (m)
Iterations
EC (m)
Distance (m)
Assumed
Flow (m3/s)
30.0
48.7300
19.4920
97.8600
48.8507
0.0326
48.8507
0.0
Assumed
Manning n
0.04
48.8879
19.5552
98.1758
49.0079
0.0324
-0.0315
0.1574
1
49.0081
-5.0
Assumed
Slope
0.001
49.0448
19.6179
98.4895
49.1639
0.0322
-0.0313
0.1563
1
49.1642
-10.0
Width (m)
0.4
49.2006
19.6802
98.8011
49.3190
0.0320
-0.0311
0.1553
1
49.3192
-15.0
Initial depth (m)
48.7
49.3554
19.7421
99.1107
49.4731
0.0318
-0.0309
0.1543
1
49.4733
-20.0
Step (m)
5.0
49.5091
19.8037
99.4183
49.6261
0.0316
-0.0307
0.1533
1
49.6263
-25.0
Length (m)
76.0
49.6619
19.8648
99.7239
49.7782
0.0314
-0.0305
0.1523
1
49.7784
-30.0
Tolerance
0.0010
49.8138
19.9255
100.0276
49.9293
0.0312
-0.0303
0.1514
1
49.9295
-35.0
49.9647
19.9859
100.3293
50.0795
0.0310
-0.0301
0.1504
1
50.0797
-40.0
50.1146
20.0458
100.6292
50.2287
0.0308
-0.0299
0.1495
1
50.2290
-45.0
50.2636
20.1054
100.9272
50.3771
0.0306
-0.0297
0.1485
1
50.3773
-50.0
50.4117
20.1647
101.2233
50.5245
0.0304
-0.0295
0.1476
1
50.5247
-55.0
50.5589
20.2235
101.5177
50.6710
0.0303
-0.0293
0.1467
1
50.6712
-60.0
50.7052
20.2821
101.8103
50.8167
0.0301
-0.0292
0.1459
1
50.8169
-65.0
50.8506
20.3402
102.1012
50.9615
0.0299
-0.0290
0.1450
1
50.9617
-70.0
50.9952
20.3981
102.3903
51.1054
0.0297
-0.0288
0.1441
1
51.1056
-75.0
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