A multi-model approach for optimizing drainage water reuse sustainability in arid and semi-arid regions: a case study of El-Salam Canal project in Egypt

Sustainable drainage water reuse (DWR) in agriculture requires integrated assessment of water quality, soil dynamics, leaching requirements, and crop productivity. This study developed a novel multi-model framework integrating expert knowledge, multi-criteria decision analysis, hydraulic modeling (HEC-RAS), and soil–water-atmosphere-plant simulation (SWAP) to optimize operational strategies for Egypt's El-Salam Canal project. Three water supply reliability scenarios were evaluated: planned baseline, 95% reliability, and 75% reliability with seasonal variability. Model validation demonstrated robust performance (HEC-RAS: NSE = 0.88–0.94; SWAP: R 2 = 0.89, RMSE = 0.23 dS/m). The 75% reliability scenario achieved transformative improvements, including a 188.4% increase in integrated water quality score, a 25.5% reduction in Sodium Adsorption Ratio (from 7.15 to 5.33), and a 33.5% decline in Total Dissolved Solids (from 1706 to 1134 mg/L). Seasonal optimization, prioritizing high-quality drainage sources (El-Serw, Farskor, Hadous, El-Matria) during critical summer cropping periods, outperformed uniform year-round allocation. The planned scenario resulted in critical root zone salinity (ECe: 7.17 dS/m), causing predicted yield losses of 8.3% (wheat) and 38.9% (maize), while requiring intensive leaching (15.5% of irrigation). The 75% reliability—summer-oriented scenario reduced soil salinity by 49.1% to 3.65 dS/m (P < 0.001), maintained yields within 5% of optimal, and decreased leaching to 8.5%, saving 610 m 3 /feddan/year. This framework provides actionable decision support for sustainable drainage water management in water-scarce regions, directly advancing SDGs 2 (Zero Hunger) and 6 (Clean Water and Sanitation) by maintaining crop yields, conserving water, and enhancing climate resilience through reduced soil salinity and freshwater dependence while preserving soil health.