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I I I I I I I I I I I I I I I I I I I LAWMA WELL DEPLETIONS The ground water in the alluvial and bench aquifers in the main stem area are hydraulically connected to the Arkansas River. In general, the ground water in these aquifers is in transit down gradient toward the Arkansas River. These aquifers are recharged with water from several sources, including precipitation, deep percolation from irrigation, and leakage from the surface streams in the area. They are discharged also through several phenomena, including water consumption by phreatophytes and subirrigation, discharges into tributaries and drains in the area, and water consumption from well pumpage. Pumping wells constructed into these aquifers intercepts the ground water as it flows toward the Arkansas River. The actual depletion to the flow in the Arkansas River from this well pumping, however, is typically less than the consumption of the well water because not all the ground water in transit would otherwise make it to the Arkansas River. Part of this ground water is consumed by phreatophytes and subirrigation, by evapotranspiration in and along the tributaries and drains in the area, and by diversions from the tributaries and drains. Most of the well depletions affect Colorado surface rights. Some affect the flow at the Stateline, either directly or through reduced return flow from Colorado surface rights. Not all flow at the Stateline is usable in Kansas, so not all depletions at the Stateline are depletions to usable flow. The augmentation program formulated in this feasibility study contemplates replacements for well depletions both to Colorado surface water rights and to usable Stateline flow. In order to make these replacements successfully, LAWMA must have procedures for calculating both types of well depletions.. For the purpose of determining depletions to Colorado surface rights, LAWMA's consultants have recommended the application of certain "presumptive well depletion factors" to the main stem irrigation pumping in order to provide a basis for reasonable replacement, yet one which is simple for application. These well depletion factors are 30 percent for supplemental pumping, 50 percent for non-center pivot sole-source pumping, and 75 percent for center-pivot sole-source pumping. It is noted also that these well depletion factors have been suggested in connection with the augmentation plan proposed for well owners in the Southeastern Colorado Water Conservancy District. Additionally, LAWMA will calculate depletions for the municipal and commercial pumping that affect Colorado surface rights on 12