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This addition to The Basics of Recharge and Discharge series deals with the surface water balance approaches that form the traditional basis of hydrological investigations. It explores both field methods and modelling methods for measuring or estimating the different parts of the water balance, including rainfall, evaporation, run-off and soil water storage. The authors discuss the concepts required to understand a surface water balance result or to set up an experiment. As water balance studies can be both time-consuming and expensive, this report will give readers a better understanding of water balance approaches and the considerations before going into a water balance study for the purpose of deep drainage.
Deals with the surface water balance approaches that form the traditional basis of hydrological investigations. It explores both field methods and modelling for measuring or estimating the different parts of the water balance, including rainfall, evaporation, run-off and soil water storage.
In view of the rapidly expanding urban, industrial and agri cultural water requirements in many areas and the normally associated critical unreliability of surface water supplies in arid and semi-arid zones, groundwater exploration and use is of fundamental importance for logical economic development. Two interrelated facets should be evident in all such groundwater projects : (a) definition of groundwater recharge mechanisms and characteristics for identified geological formations, in order to determine whether exploitation in the long-term involves 'mining' of an es sentially 'fossil' resource or withdrawal from a dynamic supply. A solution to this aspect is essential for development of a re source management policy: (b) determination of recharge variability in time and space to thus enable determination of total aquifer input and to quantify such practical aspects as 'minimum risk' waste disposal locations and artificial recharge potential via (e.g.) devegetation or engi neering works. However, current international developments relating to natural recharge indicate the following 'problems' ; no single comprehensive estimation technique can yet be iden tified from the spectrum of methods available; all are reported to give suspect results.
To face the threats to the water supply and to maintain sustainable water management policies, detailed knowledge is needed on the surface-to-subsurface transformation link in the water cycle. Recharge flux is covered in this book as well as many other groundwater issues, including a comparison of the traditional and modern approaches to determine groundwater recharge. The authors also explain in detail the fate of groundwater recharge in the subsurface by hydraulic and geologic means, in order to stimulate adapted groundwater-management strategies.
A Soil-Water-Balance (SWB) computer code has been developed to calculate spatial and temporal variations in groundwater recharge. The SWB model calculates recharge by use of commonly available geographic information system (GIS) data layers in combination with tabular climatological data. The code is based on a modified Thornthwaite-Mather soil-water-balance approach, with components of the soil- water balance calculated at a daily timestep. Recharge calculations are made on a rectangular grid of computational elements that may be easily imported into a regional ground- water-flow model. Recharge estimates calculated by the code may be output as daily, monthly, or annual values.