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8/3/2019 IIT Dam Analysis – Why it is subjective
http://slidepdf.com/reader/full/iit-dam-analysis-why-it-is-subjective 1/12
IIT Dam Analysis Why it is completely
subjective
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Objective
Show what inputs are needed for Dam break
analysis and why the analysis is completely
subjective
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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
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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)
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1. Click to add River, Name it (Eg Periyar)
2. Click to add Dam and enterVarious parameters. Best
option is to check existing
example
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3. Click Breach Plan data to see inputs
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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
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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
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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.
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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.
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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.
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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.