Flood Hazard Assessment and Mitigation in the Tigris River: An HEC-RAS Approach (Al-Kut Dam to Al-Musandawq)

This study addresses the critical issue of flood hazard management in the Maysan region of Iraq, a city highly susceptible to recurrent and devastating floods, as tragically demonstrated by the ۲۰۱۹ flood event. Focusing on a ۱۶۹ km reach of the Tigris River downstream of the Al-Kut barrage, including the Al-Musandawq channel, this research investigates the impact of riverine obstacles on flood dynamics. The primary objective is to assess and mitigate flood hazards through advanced hydrological modeling. The study employed the HEC-RAS model, utilizing ۱۶۹ cross-sections surveyed in ۲۰۱۷ and incorporating digital elevation model (DEM) data. Model calibration, using hydrological and topographical inputs, yielded a Manning’s roughness coefficient of ۰.۰۳۱ for the Tigris River and ۰.۰۲۸ for the Al-Musandawi channel. High accuracy was confirmed by Nash-Sutcliffe Efficiency (NSE) indices of ۰.۹۷۹ and ۰.۹۸۶, respectively, alongside other error metrics (RMSE, MAE). Model simulations revealed that flood waves were primarily delayed, reaching Maysan city with minimal dispersion, leading to inundation. To mitigate these risks, two management approaches were considered: (۱) removal of islands and sidebars within the river reach, and (۲) construction of a weir. Due to the high cost and limited effectiveness of removing natural obstacles, the focus shifted to structural solutions. Scenarios were developed to design a weir with an optimal crest elevation. The goal was to prevent downstream flow to Maysan city from exceeding ۷۰۰ m³s during flood seasons, while ensuring a minimum flow of ۲۵۰ m³s during dry seasons. Simulations of peak flow rates (۴۰۰۰, ۲۵۰۰, ۱۰۵۰, ۵۳۳, and ۲۵۰ m³s) established an optimal weir crest elevation of ۹.۴ meters. This study provides crucial insights into flood mitigation strategies for the Tigris River, offering a data-driven approach to protect vulnerable downstream areas.

کلیدواژه ها:

Flood hazard management ، HEC-RAS ، Tigris River ، Flood control ، Flood wave routing ، Hydraulic modeling