Enhancing rainwater harvesting efficiency in karst terrains: The role of road intercepted soil-epikarst lateral flow

In karst landscapes, where sustainable water management is increasingly challenged by drought-induced water scarcity, the adoption of road-based rainwater harvesting (RBWH) systems has emerged as a promising solution for improving water accessibility. Despite the growing implementation of such systems, the effectiveness of many RBWH projects in karst terrains remains suboptimal due to an inadequate understanding of runoff generation mechanisms associated with hilly road networks. This study focuses on quantifying the contributions of intercepted surface runoff (SR) and soil-epikarst lateral flow (SEF) from a newly exposed road-cut slope in a dolomite hillslope, with data collected across 156 rainfall events from May 2019 to May 2022. Our findings revealed that SEF, with an annual average volume of 2.065 × 10⁶ L for the experimental karst catchment (with a projected area of 7850 m²), was the main contributor to road-cut slope flow (RCF), significantly surpassing SR, which accounted for an annual average of 0.283 × 10⁶ L. The annual runoff coefficients for SR, SEF, and RCF were quantified at 2.2%, 16.0%, and 18.2%, respectively. Both rainfall depth and antecedent soil moisture content were identified as pivotal factors influencing SEF, indicative of a saturation-excess runoff mechanism within the context of the karstic road-cut slope. Notably, the contribution of SEF to the overall runoff was approximately twice that of SR from both the upslope and road surface combined. These findings highlight the importance of incorporating the rainstorm runoff potential of road-cut slopes into the design and optimization of RBWH systems within dolomitic karst terrains. To improve water collection efficiency for various purposes in such initiatives, it is essential to consider the hydrological characteristics of the upslope terrain and the geometric properties of the soil-epikarst interface in the planning process.