DAM BREAK SIMULATION OF MANDIRA DAM AND FLOOD RISK ASSESSMENT USING MIKE FLOOD MODEL

Abstract

Dams are manmade hydraulic structures built over water courses for the utilisation of human being. Failure of dams always results in a great loss to life, economy and property. Moreover, it is more critical to estimate the exact process of failure of the dam. Therefore the analysis for dam break is carried out in advance for various possible scenarios and subsequently flood risk maps should be developed as part of the disaster management programme. In India the Dam Rehabilitation and Improvement Project (DRIP), is taken up to assess the need for rehabilitation and improvements of about 223 large dams. In this study dam break analysis of Mandira dam, built across Sankh river in Odisha is carried out. The earthen dam is a zoned embankment of about 426.72 m length with height of about 35.38 m from the foundation. The design flood hydrographs for 100 year return period is calculated using SUH approach (CWC, 1997) and hydrologic modelling in HEC-HMS. The estimated peak flow to Mandira dam is about 11590.2 m3/s and time to peak is 32 hr. (hour). Similarly, the estimated peak flow for Koel river is about 19229.2 m3/s and time to peak is 33 hr. The hydrodynamic model in Mike-11 of the river from Mandira dam to a distance of 118 km is developed. The 1-D model is calibrated and validated by comparison of simulated and observed water level at Gomali gauging site. The Nash–Sutcliffe model efficiency is 0.937 for manning’s coefficient of 0.035 is during calibration and 0.86 for the validation period. It is observed that about 15.5 ht. is required for peak flow to reach downstream located at 100 km. The simulated discharge also shows that there is very high discharge just below the dam location and it gradually reduces towards downstream. The output from the hydrodynamic modelling in the form of floods characteristic maps viz. flood depth, velocity, time to peak etc. are used for hazard assessment. Further, the Land Use Land Cover (LULC) map is overplayed to obtain risk map. The flood risk is dividing in to five classes. The sensitivity analysis of dam breach model parameters viz. breach width, time of breach is carried out by comparing the combined outflow from dam for different cases. It is observed that the variation in flood hydrographs decreases as the flood wave moves downstream from the dam site. It is expected that, the result of this study in form of flood risk map will help to create the Emergency Action Plans (EAP) for dam failure scenario. However, in this study limited river cross sections and SRTM DEM is used for modelling, this can be further improved by incorporation more number of river cross sections and high resolution DEM.