Stormwater harvesting in ephemeral streams: how to effectively bypass clogging layers and thick vadose zones

In drylands, stormwater is often collected in surface basins and subsequently stored in shallow aquifers via infiltration to cope with water scarcity. These groundwater recharge schemes are often accompanied by high evaporation rates and hygiene problems due to low infiltration rates, which are a consequence of clogging layers on the topsoil and the presence of a thick vadose zone. The present study aims to develop a conceptual solution to increase groundwater recharge rates in stormwater harvesting systems. The efficiency of vadose-zone wells and infiltration trenches is tested using numerical models and sensitivity analyses. The constructed models are conceptualised in the dams built in the channel of ephemeral streams (wadis) and validated utilising analytical equations. The modelling demonstrated that the employment of vadose-zone wells and infiltration trenches contribute to starting the recharge 2250–8100% faster than via infiltration from the wadi dam bed surface. Furthermore, recharge rates are predominantly affected by well length and trench depth as per the sensitivity analyses. In terms of recharge quantity, the well is the most efficient solution contributing to infiltrating up to 1642% more water than an equivalent area of the wadi dam bed surface and between 336 and 825% more than a trench. Moreover, the well can provide the highest cumulative recharge per unit cost and high recharge rates when there are space limitations. The use of analytical equations proved the adequacy of the developed numerical models. The techniques explored can significantly improve groundwater recharge, providing practical solutions to enhance water availability in drylands.