C150150 Feasibility Study - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I wells. LA WMA' s primary service area is the Arkansas River mainstem below John Martin Reservoir, although it has members in the Big Sandy Creek and Two Butte Creek basins and a few members above John Martin Reservoir. LA WMA membership also includes several municipal and rural domestic water suppliers that rely on Dakota and Cheyenne aquifer wells which are considered non- tributary and are not subjectto the Arkansas River Use Rules. III. Replacement Water Requirements LA WMA' s replacement waterrequirements are annually determined in its Arkansas River Use Rules replacement plan using an accounting model of the Arkansas River basin prepared by the State Engineer's office. The model is broken down into 18 segments between Pueblo Dam and the State line. Well pumpage by LA WMA members affects only the lower 9 segments of the State Engineer's model which represent the area from the Las Animas Consolidated Canal above John Martin Reservoir to the State line. The stream segments can be logically reduced to (1) the segment between the Las Animas Consolidated Canal headgate and John Martin Dam, (2) the segment between John Martin Dam and the Lamar Canal headgate, (3) the drainage ditches and small creeks which contribute water to the Amity Canal, (4) the segment between the Lamar Canal and Buffalo Canal headgates, and (5) the segment between the Buffalo Canal headgate and the State line. Figure 1 is a schematic drawing of the Arkansas River from La Junta to the State line and shows these features as well as others. Pursuant to the State Engineer's Arkansas River Use Rules, a presumptive depletion factor is assigned to each irrigation well based on whether the well supplements ditch deliveries of surface water or provides a full supply of water for the owner's fields. Wells providing supplemental supplies are assigned a 30% depletion factor, and wells providing the full supply are assigned a 50% or 75% depletion factor for flood irrigation methods and sprinklers, respectively. Currently, LA WMA's irrigation members in the mainstem area include 254 supplemental wells, 149 sole-source wells, and 35 wells which are used as part of a compound or complex system. Tributary Areas. LA WMA covers the 50 irrigation wells and the 24 municipal wells and commercial wells in the tributary areas, primarily the Big Sandy and Two Butte Creeks basins. . Two Butte Creekjoins the Arkansas River at Holly, downstream of any Colorado ditch. The confluence of Big Sandy Creek and the Arkansas River is located about 8.5 miles upstream from the Buffalo Canal diversion. Big Sandy Creek normally is intermittent except during major precipitation events. The stream flow during these events is reduced by an amount of additional groundwater recharge induced by the well pumping. Otherwise, the pumping affects evapotranspiration (ET) by native vegetation in the creek valley. The depletions with respect to the Arkansas River from LA WMA member well pumping in these tributary areas were estimated to be equal to 4% of the wellhead depletions on an annual basis (1996, Helton and 1997, Helton) and are replaced to the Arkansas River. The pump age from the tributary areas totaled 5,148 acre-feet in 2002, representing 131 acre- feet of potential depletions. The 5,148 pump age volume is a good estimate of future pump age in the tributary areas by LA WMA's present membership. 2