Author
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Bouwer, Herman |
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Submitted to: Hydraulic Design Handbook
Publication Type: Book / Chapter Publication Acceptance Date: 11/19/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Growing populations demand more water and climates may change. Thus, there more water must be stored in wet or normal years to build "water banks" that can be tapped in dry years. Other tools for drought mitigation are demand management (water conservation, reuse, etc.), and water marketing. The latter requires willing sellers, willing buyers, and protection of third party interests, as well as an adequate infrastructure to move water from where it is to where it is needed. Traditionally, storage has been achieved with dams. However, dams have come under increasing criticism for ecological, environmental, and other reasons. Also, they are not effective for long-term storage (decades, for example) because of evaporation losses. Finally, silt eventually builds behind all dams and, hence, they are not sustainable. Underground storage of water as achieved by artificial recharge of aquifers via surface or deeper infiltration systems, where possible, is the preferred way for building water reserves. The chapter discusses site selection, field investigations and testing, and design and operation of infiltration systems for groundwater recharge. Most systems consist of water spreading or surface infiltration systems in streams or in basins. Recharge can also be achieved with trenches or shafts in the unsaturated zone and with aquifer wells for direct injection into aquifers. Groundwater recharge also plays a significant role in water reuse because sewage effluent or other water of impaired quality used for recharge undergoes significant quality improvements by "soil-aquifer treatment" or "geopurification." This process also enhances the economics and public acceptance of water reuse. This will benefit water districts, consultants, municipalities, planners, regulators, government officials, and the public. Technical Abstract: Underground storage of water via artificial recharge of groundwater has several advantages over surface storage behind dams. The chapter discusses the various types of recharge systems, including surface infiltration systems (in-channel and off-channel), vadose zone systems (trenches and shafts), and aquifer systems (injection wells). Site selection involves infiltration and hydraulic conductivity measurements to predict hydraulic capacities and land requirements, vadose zone studies to make sure that restricting layers do not form perched groundwater mounds that are too high, and aquifer studies to make sure that there is no excessive groundwater mounding. Also, contamination of vadose zones and/or aquifers and how it will affect water quality issues should be checked. Management of artificial recharge systems is primarily aimed at controlling clogging of the infiltrated soil surface. Sands are preferred for surface infiltration systems. However, these soils are not always available, so that finer textured soils such as sandy loams and light loams may have to be used. These present special management challenges for controlling clogging of the soil and maintaining hydraulic capacity. The performance of artificial recharge systems depends on many factors most of which are difficult to predict. Adequate field testing and pilot studies are essential. Environmental and institutional aspects must also be considered. Artificial recharge plays an important role in water reuse because when sewage effluent or other water of impaired quality moves through the underground environment, it receives "soil aquifer treatment" (SAT) or "geopurification." This process enhances the economics and public acceptance of water reuse. |
