Author
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Bouwer, Herman |
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Submitted to: International Symposium Artificial Recharge of Ground Water
Publication Type: Proceedings Publication Acceptance Date: 9/25/1998 Publication Date: N/A Citation: N/A Interpretive Summary: An improved method has been developed to predict soil infiltration rates for artificial recharge of groundwater with infiltration basins or other facilities. Normally, cylinders with a diameter of about 1 ft are pushed into the ground and flooded for several hours to measure how fast water moves into the ground. The results tend to overestimate basin infiltration nrates, even when "buffered" by a larger outer cylinder. Small test basins have also been used, but those are much more expensive. In the new method, single cylinders with a diameter of 2 ft are used. The results are then corrected for lateral flow in the soil and limited depth of wetting. Continued recharge without groundwater pumping from the aquifer system will eventually lead to excessive groundwater level rises in the recharge area. Equations have been developed that will indicate where and to what depth groundwater must be pumped and how much water can be stored or "banked" underground for the long term. Coarse soil materials like sands and gravel in river beds or flood plains are preferred for artificial recharge of groundwater. However, these soils are not always available and less permeable soils like sandy loams to loamy sand as often found in agricultural or desert areas must be used. These soils present difficult management challenges to maintain infiltration rates at potential values. Local experimentation using concepts and principles developed for agricultural soil management must be used. These findings and recommendations will benefit local, state, and federal agencies in water resources management, consultants, and planners. Technical Abstract: Artificial recharge of groundwater with fresh water and sewage effluent can be expected to increase worldwide. A simple technique has been developed to correct infiltration rates measured with single cylinder infiltrometers for lateral flow in the soil (divergence) and limited depth of penetration of the wet front to obtain the final infiltration rate for large flooded areas slike recharge basins. In a field test, the corrected infiltrometer rates accurately predicted long-term infiltration rates for two 0.2 ha test basins. Thus, the simple infiltrometer technique can be used for feasibility studies and system design. Prolonged recharge can cause undue groundwater mound rises below the recharge area. Steady-state equations were developed for strip-type and cluster-type (round or square) recharge areas to estimate where groundwater must be pumped and to what depth groundwater levels must be pumped down to prevent the groundwater mound from rising beyond an acceptable level. Sands and gravels are preferred fo recharge systems, but they are not always available and less permeable soils in the range of loamy sands so sandy loams may have to be used. These soils are more likely to get infiltration reductions due to clogging. Also, there may be erosion-deposition problems in the basins with segregation of particle sizes as suspended material settles, fine particle movement in the soil itself, crusting, hardsetting, collapsing, self mulching, compaction, and other problems. Effective management is necessary to maintain adequate infiltration rates on these soils. Concepts developed for agricultural soil management must be used. |
