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<br />The prescribed channel improvements demonstrate an approach to achieving a more <br />uniform, gradually varying and stable river channel system in terms of sediment transport whik <br />maintaining the necessary conveyance capacity for water deliveries and flood control <br />operations. They are, however, mathematical models and implementation must be considered. <br /> <br />To get an idea of the costs associated with these improvements some preliminary <br />earthwork quantities were calculated and rough dollar figures associated with them. Table 4-2 <br />shows the costs estimated for the earthwork involved. It is important to note that these <br />estimates are crude due to time and scope constraints. The alignments have not been optimized <br />and other factors have not been considered. They do, however, allow some comparison of the <br />five areas and ranking of them. <br /> <br />Table 4-2. Approximate earthwork costs for the Channel Improvement alternative. <br />Problem Length Cut Fill Earthwork Cost per mile <br />Area (mi.) (cu. yd.) (cu. yd.) Cost ($) ($) <br />3 9.0 458,300 2,l69,700 36,2ll,200 4,027,200 <br />4 2.3 19l,200 0 2,485,600 1,082,700 <br />5 8.1 402,800 0 18,821,900 2,313,000 <br />6 4.l 317,400 1,040,000 5,325, 1 00 l,30l,400 <br />7 2.6 l40,600 119,900 2,599, 1 00 990,100 <br /> <br />Based on these preliminary costs, Problem Areas 4 and 7 stand out: they are less <br />expensive per unit length than the others. Problem Areas 5 and 6 require further study because <br />of the diversion within Area 5 and the suspiciously high transport rates of Area 6. Area 3 is <br />the most expensive of the five, both in terms of unit length and overall because of the large <br />volume of earthwork involved. <br /> <br />As described above, channel improvements include the reshaping of the entire 1,000- to <br />I ,500-cfs river channel (approximately 865 acres) throughout the five Problem Areas. To <br />attain the requisite flow depth for channel stability, the 3,000-cfs corridor also would require <br />reshaping (see typical cross-sections on Plates II through 15). The entire overbank area <br />(approximately l,800 acres) would be modified through excavation, fill placement, and the <br />removal (and subsequent re-establishment) of all riparian vegetation. Over all five Problem <br />Areas, the post-project area of river channel and riparian habitats would be within oi3% of the <br />existing acreage; however, pre- YS. post-project area varies widely among individual Problem <br />Areas (Table 4-3). <br /> <br />34 <br />