Abstract
Design flood has been estimated for rivers of Saurashtra region contributing into the Gulf of Khambhat using deterministic as well as statistical approach for planning, design and management of hydraulic structures. By comparing the results obtained by these approaches, one can easily estimate the flow rate or peak discharge to a given design return period and can establish the suitability of approach for this study area. Nine river basins with 20 dams of Saurashtra region were analyzed in this study. Though Saurashtra is one of the most water scarce regions of India yet it suffers from the flooding problem, as the numbers of rainy days are very less and the rainfall intensity is very high. Due to being a regulated basin, dam wise study was preferred. Deterministic approach was carried out using synthetic unit hydrograph (SUH) and regional flood formulae (RFF) methods for subzone-3a provided in Central Water Commission (CWC) report, 2001. Statistical approach was carried out using Rainfall frequency analysis employingGumbel’s EV1distribution. As there is no spill by these hydraulic structures and the annual flood data for the nine river sites are heavily affected by the storage dams in the upstream. Hence these data violate the basic principle of virgin flow. Hence the analysis of these data was not attempted further. The main objective of study was to carry out the rainfall frequency analysis for these river basins to get 24 hour rainfall for a return period of 25, 50 and 100 years for an individual basin instead of using the value obtained by iso-pluvial map to estimate the design flood. The overall results reveals that due to construction of number of dams in 9 river basins, design flood estimation on each dam by using deterministic approach is more feasible.Revised design floods using SUH and RFF method on the basis of estimated rainfall indicates over-estimated and under-estimated design floods. Since the percentage difference is very less between revised SUH and revised RFF method. So, for safety purpose one with higher value should be used.
Highlights
Flood, a natural disaster is responsible for loss of life and property world over
In this study initially the above approach are used for 20 dams as well as for 9 river basins on the basis of 24 hour rainfall for T year return period given in the iso-pluvial map
It is revised only for dams because these basins are heavily affected by dams situated on upstream
Summary
A natural disaster is responsible for loss of life and property world over. Floods damage property and endanger the lives of humans and animals and affect the environment and aquatic life negatively. Floods have been occurring repeatedly in India. 40 million ha area (12%) in India has been identified as flood prone[18]. For mitigating the flood disasters, various structural and non-structural measures are adopted. Structural measures include protection works and flood embankments while non-structural measures include flood forecasting, flood warning and flood plain zoning. Design flood estimates are required for the design of various hydraulic structures such as weirs, barrages, dams, embankment etc. Flood protection / relief schemes[5, 14].
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