Artifical Recharge of Ground Water in Colorado

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Artificial Recharge of Ground Water in Colorado A Statewide Assessment Surface Infiltration Surface infiltration is simply the impoundment of water at the ground surface to allow it to soak into the underlying near - surface, unconfined aquifer. Surface - infiltration recharge systems are suitable for unconfined aquifers where water levels are relatively shallow and impermeable layers are absent between the ground surface and the base of the aquifer. Receiving aquifers typically have relatively high transmissivities to accommodate lateral flow away from the recharge area and thus prevent the formation of high ground -water mounds. Varying in shape from symmetrical ponds to long linear ditches, and in size from several acres to several hundred acres, surface infiltration design is highly dependant on surface conditions. Structures can be entirely constructed on flat land or can take advantage of natural topography. Surface infiltration systems may cover large areas, but can be relatively simple to construct. The structures can coexist with other uses such as recreation and wildlife habitat, but compatibility with adjoining land use is an important consideration. As in surface -water reservoirs, evaporative losses must be considered. The general types of surface infiltration structures, illustrated in Figure IV -1, are described below. Infiltration ponds and spreading basins — Circular or rectilinear structures into which water is directed and allowed to infiltrate through the bottom. These may be constructed above grade or excavated below grade and often take advantage of existing excavations such as gravel pits or water storage reservoirs that naturally leak. Terminology typically refers to small structures as infiltration ponds or basins and larger scale structures as spreading basins. • Infiltration ditches —Water is directed into linear structures and allowed to infiltrate through the bottom. Often, these take advantage of existing water conveyance ditches and canals that naturally leak. They can be adapted to topographic conditions that prohibit large infiltration ponds and basins. • Stream channels — Water is directed to natural ephemeral or perennial streams. Dry stream channels may require little modification in situations where the channel morphology and highly permeable streambed material allow for rapid infiltration. This method may also involve construction of dams or low weirs across the channel to back the water up and increase the wetted surface area of the streambed or floodplain, providing a larger area for infiltration into the ground. • Playa lakes —These ephemeral lakes are natural topographic depressions where water is directed for recharge. Surface modification may be required to increase lakebed permeability. • Land application — This involves over - irrigation of fields at rates at which excess soil moisture infiltrates down to the underlying aquifer. 15