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A survey of methods for groundwater recharge in arid and semi-arid regions
The rate of recharge is the single most important factor in the analysis and management of groundwater resources in arid and semi-arid regions. At the same time, it is also the most difficult quantity to determine. This document, which is the result of a course held in Niamey, Niger, in 2000, presents an overview of all the methods identified to date for estimating groundwater recharge, including an assessment of the accuracy and suitability of each. It then looks in more depth at a selection of methods best suited to arid and semiarid environments. Among these are the chloride method, the CFC and Tritium tracer methods, and the radiocarbon method. Excel spreadsheets and programmes are provided for calculating soil water balances, conducting geochemical analyses, dating environmental tracer concentrations, and building comprehensive groundwater flow and transport models. The key to the successful estimation of groundwater recharge lies in the utilisation of a variety of independent methods. Every method has its strengths and weaknesses, but combined they become much stronger. By bringing together environmental tracers, modern measurement techniques, automatic monitoring equipment, DGPS and remote sensing in a comprehensive groundwater model, the study of the hydrology of arid and semi-arid environments can enter a new era.