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Mullaperiyar Dam Break Analysis by IIT Roorkee

Conclusions


The following conclusions can be derived from the study:

1. The literature suggests the HEC-RAS version 5.1.0 model to be quite popular and standard software developed by Hydrologic Engineering Centre of U. S. Army Corps of Engineers for dam break analysis.

2. The consideration of the overtopping mode of failure along with the following breach parameters (as per FERC guidelines) is reasonable for dam break flood generation:

Elevation of Breach (Metres)
Average Breach Width (Metres)
Side Slope of Breach
Breach Development Time (Hours)
Initial
Final
873.26
825.94
195.5
Vertical (1,1)
0.2

3. The generated peak of the dam break flood hydrograph is estimated at 88911.00 cumecs, which is 10.25 times of the peck of Probable Maximum Flood Hydrograph.

4. The depths of flows at different locations within the river reach of 36 km vary from 40.30 m (just below the Mullaperiyar Dam site) to 20.85 at the end of the reach (chainage 36 km from Mullaperiyar Dam).

5. The following table shows the resulting maximum discharges, maximum water surface elevations, and time of occurrence of the maximum water surface elevations in the channel.

Place
Section No.
Location from dam (Metres)
Maximum Water Surface Elevation (Metres) Time of Arrival (minutes)
Velocity (Minutes/second)
Mullaperiyar
1
50
866.90
18
9.47
Vallakkadavu
11
3597
854.35
26
12.41
Vandiperiyar
21
7422
844.77
31
9.36
Upstream of Idukki Reservoir
46
35969
767.26
128
8.50


6. Among the inputs of Manning's roughness (N), Probable Maximum Flood (PMF), dam breach parameters such as breach width and time of breach development and Δx (space) & Δt (time)steps, the Manning's roughness (N) appeared to be the factor most influencing the maximum water surface elevations
. Although conservative a value of N = 0.034 was considered to be reasonable for the reach between Mullaperiyar and Idukki Reservoir.

7. The sensitivity analysis showed the model generated output to be reliable for chosen timed space steps.

Executive Summary

Dam break Analysis-- contents page


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