Author
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Bouwer, Herman |
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Submitted to: Biennial Symposium on the Artificial Recharge of Groundwater
Publication Type: Proceedings Publication Acceptance Date: 6/1/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Artificial recharge of groundwater by infiltration basins requires permeable soil materials, like sand and gravels. Such soils, however, are not always available where artificial recharge is desired and finer soils like sandy loams and loams may be all that is available. For such soils, expected recharge rates or infiltration rates must be predicted rather accurately so that land requirements, evaporation losses, and economic feasibility can be assessed and preliminary project designs can be made. In some cases the main purpose of the recharge is to store water underground for long periods (water "banking") and conjunctive use of surface water and groundwater. Estimates must then be made on how much water can be "banked" before groundwater levels rise too high and groundwater pumping must be initiated to avoid unduerises in the recharge area. Techniques have been developed and tested to predict infiltration rates, to manage recharge systems in finer soils for maximum hydraulic capacity, and to predict when and where groundwater pumping must begin and at what rates to avoid waterlogging in the recharge area. These findings enable water resources managers to obtain the benefits of artificial recharge and integrated water management under "challenging" soil conditions. Technical Abstract: The finer the soils that are available for groundwater recharge, the more important it is to get a good idea of the infiltration capacity of the soil so that land requirements and evaporation losses for planned recharge systems can be estimated with some confidence and the feasibility of recharge via surface infiltration can be assessed. Also, finer soils are more vulnerable to surface clogging than coarse soils, so that recharge systems in finer soils must be carefully designed and managed to minimize infiltration reductions. After infiltration, the water must be able to move freely down through the vadose zone to the aquifer, without being impeded by high groundwater levels that may be caused by rising perched water above less permeable layers in the vadose zone or by mounding of groundwater on the aquifer itself. Equations were developed to predict groundwater rises in response to recharge so as to determine the maximum hydraulic capacity of the system, the optimum layout of the infiltration area, and where and at what rate groundwater must be pumped to maintain adequate lateral flow in the aquifer away from the infiltration area. Techniques were developed to measure infiltration rates by correcting results from single cylinder infiltrometers for water depth in cylinders, lateral flow in soil below cylinder, and limited depth of wet front penetration so as to predict long-term infiltration rates for large recharge basins. Field tests showed good agreement between predicted and observed infiltration rates for basins. Special aspects of managing infiltration basins in finer soils for maximizing infiltration rates were defined, including fine-particle movement. |
