Environmental Hazards of Surface Water Resources due to heavy metals from the wastewater sites: A case study: Integration of HEC-RAS, HEC-HMS, and GIS in Flood Hazard Mapping in Scarcity Rainfall Region, Sohag, Egypt

Only land application is accessible for sewage wastewater disposal in Upper Egypt's Nile Valley. The lowland desert zone, located between the farmed floodplain and the Eocene Limestone plateau, features wastewater disposal installations. These wastewater disposal sites are located in the mouths of wadis, which are vulnerable to flooding. They are located near farmed floodplains, reclaimed lands, residential areas, surface water systems, irrigation canals, and the River Nile. In this work, untreated wastewater forms enormous uncontrolled pools on the ground. Geochemical studies have revealed that wastewater ponds and the surrounding soil are contaminated with heavy metals and bacteria, posing a significant environmental risk. Flood modeling was developed for the Al-Kola Basins, Sohag, Egypt, to generate flood hazard and ecological risk maps by integrating GIS, HEC-HMS, and HEC-RAS techniques. Due to the scarcity of rainfall data, the last recorded rainfall event in 1994 was used as a reference to determine the water runoff rate using HEC-HMS. The study was done using a digital elevation model with 12.5 m resolution. Based on HEC-RAS modeling, it was found that the average water depth increased from 1.48 m to 2.29 m, the average velocity increased from 2.41m/s to 3.76m/s, and the water spread risen from 26–37% of the entire basin area for the first scenario (rainfall = 20mm) and the second scenario (rainfall = 60mm), respectively. Our findings show that heavy metals contaminate the area due to anthropogenic activities, and floodwater can transport these polluted materials towards irrigation canals and the River Nile. Engineering recommendations were made to mitigate these critical environmental risks that could compromise human health.