Flood and heavy metal risks from wastewater site in Sohag Governorate, Egypt: integrating hydrological modeling and mapping

Untreated wastewater disposal sites along Upper Egypt’s Nile Valley pose significant environmental and public health threats due to their proximity to flood-prone wadis, cultivated lands, reclaimed areas, residential places, and surface water systems. The present study evaluates flood inundation hazards and heavy metal contamination in the Al-Kola Basins, Sohag, Egypt, by integrating hydrological models and geochemical analysis. Different flood scenarios were simulated using a digital elevation model with a 12.5 m resolution, along with soil and land use maps created using GIS, HEC-HMS, and HEC-RAS techniques. Due to the limited availability of precipitation and flood data in the region, the model’s results were validated using the 1994 rainfall flood event. Results revealed that increasing the rainfall depth from 20 mm to 60 mm resulted in an average water depth increase from 1.48 m to 2.29 m, a rise in flow velocity from 2.41 m/s to 3.76 m/s, an increase in the area inundated from 26% to 37%, and the extreme level of hazard increased from 23% to 42%. To evaluate the heavy metal contamination in the area, eighteen soil samples were geochemically analyzed from the surrounding wastewater sites. Geochemical analysis showed that the concentrations of Pb, Cd, Co, Cu, Ni, and Zn exceeded the international baseline levels. Also, the contamination factors vary from moderate to very high. Statistical analysis confirmed the anthropogenic effects of heavy metal contamination originating from municipal wastewater leakage. Our study, which employed flood inundation models and examined the contaminated soil in the area, suggested that floodwater may transfer these contaminants to irrigation canals and the River Nile. This would significantly exacerbate health and environmental risks. To mitigate the environmental risk problem, some engineering suggestions could be crucial in preventing pollutants from spreading, such as constructing flood control structures, enhancing wastewater treatment plants, and creating buffer zones.