Head-Independent Infiltration Rate in Aquifer Recharge with Treated Municipal Wastewater

Managed aquifer recharge (MAR) with treated municipal wastewater is a cost-effective, low-maintenance, and energy-efficient method for supplying water for irrigation and drinking purposes. The most expensive component of MAR is land use. Since the area of infiltration basins is inversely proportional to the infiltration rate (Ir), a higher infiltration rate allows for smaller basins, making it the most critical design factor. We examined the dependence of Ir on water levels by analyzing a decade of data from 50 recharge basins of an Israeli SAT as a case study. A positive dependence would imply that high water levels enhance infiltration, while a negative dependence would imply that shallower ponding is preferable. In 97% of over 45,000 flooding events, we observed a linear decline in the effluent level during the drainage phase. This water level-independent Ir was observed in all the studied basins, regardless of commissioning year, operating conditions, or season. Expressing Ir as a function of water level allows the operator to predict accurately the time needed to empty a basin. This also paves the road for developing site-specific predictive models of average Ir as a function of the current and historical operational and environmental conditions. A mechanistic two-resistance model explains the observed pattern, suggesting partial elasticity of the clogging film.