Flood analysis using HEC-RAS 1D model for the delta of Brahmani river, Odisha, India

The Brahmani river is the important and the second largest river network of the Odisha state, India and it is in the state of vulnerable condition during heavy flood in the river. Frequent embankment failures are common features in its delta region, since the homogenous flood embankments along the river are extremely vulnerable to floods. The most common feature in its delta is inundation of vast areas on both sides of the river. Bureau of Indian Standards (2000), in its Indian Standard Guidelines for Planning and Design of River Embankments (Levees), IS 12094:2000 has recommended the adoption of flood of 25 years frequency in the case of predominantly agricultural areas and flood of 100 years frequency for works pertaining to protection of town, important industrial and other vital installations, for design of flood embankments. Also, it recommends that in certain special cases, where damage potential justifies, the maximum observed flood may also be considered. Keeping this in view, flood scenarios of return periods 10, 30, 50, and 100 years, were simulated to provide an insight into future flood risks. Also, investigation is done in this study to examine the effects of three critical flood events which occurred in July 2001, July 2005, and September 2011 on embankments of the major tributaries of Brahmani river, with the use of the 1D HEC-RAS model. Different flow characteristics such as Water Surface Elevation, Flow area, Flow discharge, and Flow velocity, were assessed for both the left and right embankments at various cross sections. From the experiment it is revealed that floods have a greater impact on the right embankment of the upper reach of the Kharasuan and Brahmani rivers than on the middle and lower reaches. At most of the locations, the WSE exceeded the height of both left and right embankments. Since the danger level at Jenapur, the Delta head of Brahmani river is at RL 23 m, and even the water levels during floods of return period less than 10 years are exceeding it, the result is the severe flooding of Delta area. Hence, it is recommended that the flood embankments on both sides of the rivers Kharasuan and Brahmani be raised to have a safeguard against incessant flooding.