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<br />4.2 LIMITED CHANNEL IMPROVEMENT <br /> <br />A scaled-down version of the full channel improvement option also was considered, <br />utilizing essentially the same configuration as the full channel inlprovement, above, but with <br />improvements focused on the most non-uniform areas. Table 4-4 shows costs for the limited <br />channel improvements. These could be implemented as an interim step to alleviate capacity <br />problems. While the underlying channel shapes from which these limited configurations were <br />derived are based on channel stability concepts, they are not presented as long-term solutions <br />since they were developed based on conveyance only. <br /> <br />Table 4-4. Approximate earthwork costs for the Limited Channel Improvement alterna!ive. <br />Problem Length Cut Fill Earthwork Cost per mile <br />Area (mi.) (cu. yd.) (cu. yd.) Cost ($) ($) <br /> <br />3 9.0 322,lOO 1,037,600 18,140,600 2,017,500 <br />4 2.3 26,900 0 349,900 152,400 <br />5 8.l 0 414,900 6,233,700 764,800 <br />6 4.1 204,500 62,700 3,285,300 807,900 <br />7 2.6 19,900 4,600 304,lOO 1l5,900 <br /> <br />4.3 FLOODW A Y IMPROVEMENT <br /> <br />Agricultural practices along the Arkansas River have steadily encroached upon the <br />floodway: former riparian areas have been separated from the floodway by berms and then <br />placed into production. While agricultural encroachment has contributed greatly to observed <br />channel instability, high river stages, and decreased conveyance capacity, it has already <br />occurred. The two Floodway Improvement alternatives outlined below look at enhancement of <br />the system already in place. While continued encroachment of the floodway is strongly <br />discouraged, these alternatives would at least provide for 3,000 cfs operational releases and <br />promote sediment transport at higher discharges and maintenance of conveyance capacity. <br /> <br />The impetus for the current study was inundation of agricultural fields during the spring <br />runoff period in 1997. As hydraulic modeling progressed, it became apparent that several <br />agricultural areas within the five study reaches showed a potential for surface-water inundation <br />during a peak release of 3,000 cfs. (The term "agricultural" as used here refers to production <br />cropland [e.g., alfalfa, com, sorghum, winter wheat] and does not include pasture). Actual <br />inundation of most of these areas was, in fact, confirmed during conversations with landowners <br />and irrigation district personnel. <br /> <br />36 <br />