Drainage Water Reuse Potential in Arid Irrigation Projects Using DRAINMOD Simulations

Introduction: Drainage water reuse can improve water-use efficiency in arid irrigation projects, but elevated salinity may reduce crop yield and accelerate soil salinization if reuse is not managed carefully. This study assessed the potential and limitations of drainage water reuse as an irrigation-water source in two data-poor agricultural projects in southern Libya: the Eshkeda Agricultural Project (EAP) and the Hammam Agricultural Project (HAP).

Methods: DRAINMOD simulations were used to evaluate crop response under drainage water reuse scenarios. The reuse scenarios were developed by progressively increasing irrigation water salinity to represent drainage water qualities equivalent to two, three, and four times the original irrigation water salinity. The baseline irrigation water salinity was 1.25 dS m⁻¹ in EAP and 3.91 dS m⁻¹ in HAP. Simulations were conducted using the drainage design scenario that represented the optimum water-management condition for each project, allowing the analysis to focus on the effect of salinity degradation under reuse. Relative yield responses were evaluated for wheat, beans, maize, and soybeans.

Results: Drainage water reuse potential was strongly site- and crop-dependent. In EAP, yield reduction was mainly observed for beans and maize, with relative yield ranging from 100% to 60% and from 100% to 78%, respectively. In HAP, where baseline irrigation water salinity was already higher, yield penalties were much more severe. Beans declined from 73% to 0% relative yield as salinity increased from 3.91 to 15.64 dS m⁻¹, while maize declined from 88% to 2% and soybeans from 98% to 40%. Wheat was the most tolerant crop, maintaining 79% relative yield at the highest salinity level.

Conclusions: Drainage water reuse in arid regions should not be treated as a universal water-saving strategy. It requires site-specific salinity assessment, crop selection, blending strategies, and long-term monitoring to avoid yield loss and soil degradation.