Estimation of potential nutrient fluxes from the Wadi Gaza catchment into the Mediterranean Sea with emphasis on flooding events

The coastal catchment of Wadi Gaza is the main surface water basin that flows downstream to Gaza’s coastal plain zone and drains into the Mediterranean Sea. The model-based assessment of the Wadi Gaza hydrological system is an essential endeavor for more efficient management of water resources and ensuring water security in terms of climate changes and anthropogenic processes. The hydrological simulation of the basin was performed using the SWAT model between 1984 and 2020. The outputs of the simulation predicted an average discharge that varies between zero in the summer months and about 15 m³/s in the winter with a maximum recorded discharge of about 130 m³/s. The model predicted average sediment and nutrient discharge to the sea as 3673, 177, and 62 tons per month of sediments, total nitrogen (TN), and total phosphorus (TP), respectively. The average dissolved inorganic nitrogen discharges were predicted to be 4, 13, and 1 tons per month for Nitrate (NO₃), Ammonium (NH₄), and Nitrogen dioxide (NO₂), respectively during the rainy season. The constructed model is used to predict flood volumes and associated TN and TP for return periods (T) of 2, 25, 50, and 100 years. These return periods corresponded to total water discharges of 18, 91, 105, and 127 m³/s, respectively, accounting for 1,142, 5,773, 6,915, and 8,059 tons of TN, and 414, 2,092, 2,505, and 2,919 tons, of TP respectively.