Title: Head-Independent Time-Invariant Infiltration Rate in Aquifer Recharge with Treated Municipal Wastewater

Abstract: Means to increase water resources are essential in regions grappling with water scarcity and growing populations. Soil aquifer treatment (SAT) is a cheap, low maintenance, low-energy method to supply water for irrigation of crops consumed raw or even for drinking purposes. However, the most expensive cost-component of SATs is the land use, the infiltration basins the area of which is inversely proportional to the infiltration rate, the most important characteristic of SAT basins design and operation, which until now was believed to be time-dependent and, therefore, difficult to predict. Focusing on the Shafdan SAT in Israel as a showcase and using a decade's worth of data from 50 recharge basins, we study the time dependence of the infiltration rates. The study reveals a noteworthy consistency in the decline of effluent levels during the drainage phase across various flooding events, signifying a constant, head-independent infiltration rate. 97% of over 40,000 flooding events showed this behavior. Furthermore, the infiltration rate calculated in this manner provides good predictions of the average infiltration rate during the entire wetting phase.
The water-level-independent infiltration rate is a general feature. It was found in all the 50 studied basins, regardless of the soil sand content, commissioning year, operation conditions and season. The constant infiltration rate law revealed in this study simplifies the prediction of the flooding cycle duration and will facilitate simplified predictive modeling of multiple basins SAT systems. Our research may extend beyond SAT systems, offering insights applicable to other managed aquifer recharge methods, crucial for effective water resource management, ensuring environmental compatibility.