Quantification of aquifer recharge distribution using environmental isotopes and regional hydrochemistry

Abstract

A mathematical model is proposed to estimate annual recharge rates from various sources into an aquifer, based on chemical and isotopic data. The aquifer is divided into mixing cells. For each mixing cell, annual mass balance equations are written which express the conservation of water, dissolved chemicals, and stable environmental isotopes. These equations are solved simultaneously for unknown recharge rates by quadratic programming. A similar approach was used earlier to estimate inflows into a river reach which acts as a single mixing cell. The sensitivity of the model to input errors is analyzed by applying it to synthetic data corrupted by artificial noise. The ability of the model to deal with real data is illustrated by applying it to the semiarid Aravaipa basin in southern Arizona.