Dam Break Studies for Gandhi Sagar and Rana Pratap Sagar Dams

B P Roy, Member

J N Nanda, Non-member

Protecting the public from the consequence of dam failures has taken on increasing importance as populationhas concentrated in areas vulnerable to dam break disasters. This has created general interest in the damsafety analysis in recent years. There is codal provision (IS code 11223-1985) for insisting on dam breakstudies. The preventive measures in avoiding dam disaster are either issuing flood warning to the publicdownstream, or regulating reservoir in such a fashion so that there may not be hydrologic dam failure. Theseare difficult during the time of occurrence, and hence hypothetical situation is a necessary exercise. TheUnited States National Weather Services DAMBRK' program attempts to represent the current state-of-the-art in understanding dam failures and utilising hydrodynamic theory to predict the dam break wave formationand downstream progression. This paper presents the use of DAMBRK' program in finding the inflowhydrograph at dam site improbable maximun flood condition, using the distributed model. The same programhas been used to find the safe impingement level in probable maximum flood condition for Gandhi Sagar Damand to visualise the downstream situation under different dam failure conditions.

Keywords : Distributed model; Dynamic routing; Safe impingement level; Inflow hydrograph; Outflow rating

INTRODUCTION

More and more dams have come up, or are being constructed,with the aim of using the available water resources optimallyfor developmental purposes, or for protecting lives andproperties from the fury of floods. With the assured waterresources facility and flood protection provided by the dam,the increase in population and the encouragement for im-proving the overall economy of the country have led tovarious developmental activities downstream of the dam.This has resulted in the settlement of large population andproperties on the flood plain and adjoining areas. However,in the eventuality of a dam failure, the disaster would becatastropic with the flood flow not only occupying theerstwhile flood plain area, but the area adjoining it.

The dam break analysis involves the following componentsteps :

development of identification of the inflowhydrograph to the reservoir at the time of failure,

routing the inflow hydrograph through the reservoir,

development of the failure condition of the dam,

calculating the outflow hydrograph from the faileddam, and

(v) modelling the movement of the flood wavedownstream to determine the magnitude of maxi-mum discharge and maximum water level, and theirarrival time, inundated area, etc.

This study has been carried for Gandhi Sagar and RanaPratap Sagar Dams of Chambal Basin. The Chambal ValleyDevelopment Project was conceived and executed in threestages as a joint venture of the Governments of Rajasthanand Madhya Pradesh. The various projects under thisdevelopment programme in different stages are as givenhere.

B P Royis with National Institute of Hydrology, Roorkee 247 667 andJ N Nanda is with Planning Commission, New Delhi.

This paper (revised) was received on July 7, 1995. Written discussion on thepaper will be entertained till June 30, 1997.

In the first stage, Gandhi Sagar Dam, a 63.7-m high masonrydam for a gross storage of 7746 Mm 3 of water and hydro-power station with an installed capacity for generating 119MW of power, along with Kota Barrage were completed inNovember, 1960. In the second stage the 44.8-m high RanaPratap Sagar Dam, at Rawatbhata in Rajasthan, about 48 kmdownstream of Gandhi Sagar Dam and 48 km upstream ofKota Barrage, with a gross storage of 2899 Mm 3 water anda powerhouse with an installed capacity of 172 MW werecompleted in 1970. In the third stage, the 44.8-m highJawahar Sagar Dam to create a head of 36.5 m for power.generation only, with an installed capacity of 99 MW wascompleted in 1972 about 26 km upstream of Kota Barrage.Fig 1 shows the location of the various projects.

For Gandhi Sagar Dam, it was informed that design floodhas exceeded ten times since date of completion. Rana PratapSagar Dam is hydrologically related with Gandhi SagarDam, hence, hydrological safety of both the dams were con-ducted. This paper presents the general principles behind themathematical models used for dam break analysis, discussesthe various available models for darn break analysis and theirspecial features. Also a brief description of a case study ofdam failure using US National Weather Services DAMBRKmodel is presented.

RATIONALE FOR THE STUDIES

The Gandhi Sagar Dam has been designed to accommodatea design peak flood inflow of 212 000 cumecs. This designflood has been exceeded on at least 10 occasions since 1960(Table 1).

In respect of Rana Pratap Sagar Dam, the design flood of184 000 cumecs was derived on the basis of the maximumrelease of 136 000 cumecs from Gandhi Sagar Dam and amaximum discharge of 5900 cumecs from the intermediatecatchment as worked out from Inglis formula. As GandhiSagar and Rana Pratap Sagar dams are in a sequence, anychange in Gandhi Sagar will affect Rana Pratap Sagas. Thisnecessitated a review of design flood. Over and above, it wasfelt that dam break studies of Gandhi Sagar and Rana Pratap

Vol 78, May 1997 7

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