  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.
