Assessment and Prioritization of Flood Protection Levees along the Lower Tapi River, India

Surat city, located on the banks of the Tapi River near the Arabian Sea in India, has faced the wrath of severe flooding in the recent past. There has been an alarming reduction in the safe carrying capacity of the river at Surat, which is primarily responsible for the increase in severity of flood disasters. This study conducts an on-site flood frequency analysis using the annual peak discharge series of the lower Tapi River observed at Kathor/Ukai (from 1939 to 2013), and quantifies flood quantiles corresponding to 25- and 100-year return periods for design of levees as per defined standards. A one-dimensional steady-flow hydrodynamic model, based on the standard step method, is developed using numerical code in MATLAB and HEC-RAS for prediction of water levels along the lower Tapi River. The performance of the models is analyzed by comparing respective simulated stages with observed stages at Kakrapar Weir, Mandvi Bridge, Ghala, and Nehru Bridge (in Surat city). The simulation results of the developed numerical code are then used to determine the design levee heights along the lower Tapi River. The proposed levees along the lower Tapi River are prioritized for implementation using the improved analytical hierarchy process (AHP) based on three attributes, namely mean levee height, population density, and mean elevation of the area adjacent to the riverbank lines.