Groundwater is an integral part of natural hydrologic systems. Humans have used groundwater for thousands of years. Its use has increased greatly over time, but only in the last few decades has our appreciation of the limitations of its supply and its vulnerability to contamination grown to the point where steps are being taken to protect this valuable resource. One of the most important components in any assessment of groundwater supply or aquifer vulnerability is the rate at which water in the system is replenished – the rate of recharge.

A number of textbooks are devoted to hydrogeology, groundwater flow, and contaminant transport (e.g. Freeze and Cherry, 1979; Domenico and Schwartz, 1998; Todd and Mays, 2005). The importance of recharge is cited in all of these textbooks, but only limited information is provided on the description and analysis of techniques for estimating recharge. Similarly, undergraduate and graduate courses on hydrogeology, groundwater flow, and contaminant transport are offered at many universities, but we know of no university level courses specifically devoted to groundwater recharge. This book attempts to fill these gaps by providing a systematic and comprehensive analysis of methods for estimating recharge.