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