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Conjunctive Use of Surface and Groundwater - page 9 / 37





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geohydrological investigations aimed at determining more accurately groundwater availability and quality in terms of time and space, using mathematical analysis in order to establish aquifer conditions and behavior;

integration of the physical characteristics and conditions previously collected and analyzed, with economic and social parameters to formulate suitable strategies and policies for subsurface water use, planning and management.

2.2.2 Surface water storage

For surface reservoir management the critical elements to be considered are minimum pool elevation and storage losses due to sedimentation. Generally, minimum pool elevation is not defined solely by hydraulic limitations of the outlet or diversion works; more severe constraints may be imposed by recreational interests, habitat values in the reservoirs or by the adverse water-quality effects if the pool is drawn too low. Loss of storage due to silting is normally significant only if based on projections of 50 or 100 years, so regular sediment surveys (at least once every 10 years) are important aspects of the process.

To account for these factors, generally, a two-step design process is adopted (McMahon, 1992). In the first step, a number of potential reservoir sites are examined, not only for construction requirements, but also in terms of hydrologic patterns in order to establish capacity-yield relationships. This procedure leads to the “preliminary design” framework. In this phase simplifying assumptions are normally made: reservoir releases are assumed constant, evaporation is ignored in temperate and humid regions, seasonal flows may not be taken into account, and so on. In the second step, leading to

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