iit dam analysis – why it is subjective

8/3/2019 IIT Dam Analysis – Why it is subjective

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IIT Dam Analysis Why it is completely

subjective



Objective

Show what inputs are needed for Dam break

analysis and why the analysis is completely

subjective



Some terms for understanding

Breach Breaking of dam / embankment

Piping failure Failure of dam by Erosion of

the structure - erosion will be faster as thebreach grows due to hydraulic flow. It is the

most common method of dam failure. The

other dam failure method is toppling.

HEC RAS Software developed by US Army

corps and used by IIT for Dam break analysis



Step by Step

1. Download HEC RAS software (Freeware) which wasused by IIT for dam break analysisused by IIT for dam break analysis from here:http://www.hec.usace.army.mil/software/hec-ras/

2. Install the examples folder when prompted. Create anew project or open an existing project (Eg: BaldEagle Creek)

3. If you are creating new project click Enter geometricdata icon , add River reach and to represent thedam add Inline structure (screen shots in next slide)



1. Click to add River, Name it (Eg Periyar)

2. Click to add Dam and enterVarious parameters. Best

option is to check existing

example



3. Click Breach Plan data to see inputs



Arbitrary inputs

Piping Coefficient is arbitrary so by

Changing this, results can be changed drastically

This is the time of breach in hours from

start of breach to finish. Reducing this will

show faster breach and breaking of dam



Arbitrary inputs

Instead of Water surface elevation (WS

Elev) Specific time or date can be selectedleading to an arbitrary dam break time

Even the Starting Water surface elevation

can be reduced to show faster breach!

Entering higher value for bottom width of

breach at its max size will show bigger

piping failure



As we saw in the previous screen shots, pretty

much all important data are arbitrary and

requires lot of experimentations before it can

be used for uniquely constructed Mullaperiyar

dam. It is important to note that HEC RAS

has been successfully used only in earthen

dam and weirs breaching simulations.Simulations with other material structures are

questionable.



Signs of arbitrariness

Report of half the Dam breaking in 12 minutes is

a sure sign that all or some of the arbitrary input

parameters are wrong. Surkhi has a density of

2473 kg/cu.m- close to cement mortars density;

how can piping failure occur so fast ?

No modeling or experiments has been carried out

to ascertain surkhi piping failure so neither fullformation time nor piping coefficient will be

correct.



Hydro-metreo map of Kerala (5b)

The Probable Maximum flood (calculated in

another report by IIT) data used for modelingbreach does not conform to hydro-meteorology sub

zone map of India.



Conclusion

While the final dam analysis report is not

public, it is prudent to consider the fact that

the hypothetical dam break analysis is fraught

with experimental and arbitrary inputs. This

does not confirm to scientific reporting norms.

iit dam analysis – why it is subjective

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