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<br /> <br />22 <br /> <br /> <br />. <br /> <br />original streambed is deduced trom the boundaries between finished <br />and unfinished concrete on the abutments and wingwa11s. Comparison <br />of widths of the main channel shown on the base map with those <br />determined by field surveys in the spring of 1962 indicates that <br />there has been a very large amount of erosion since 1950 or 1951, <br />when the base maps were compiled. For example, the base map shows <br />a width of about 60 feet at tne cross-section 1,400 feet below <br />Hover Road, although the widtn at the same section at the time of <br />the field surveys was 450 feet. Much of the erosion at the Hover <br />Road bridge and in the channel probably occurred during the floods <br />of May 1957 (see figure 7). <br />The present Sunset Drive bridge, constructed in 1958, has not <br />been subjected to large floods, so the effects of erosion are not <br />readily apparent. However, the collapse of the former bridge in <br />May 1958 was probably due to abutment failure induced by erosion <br />in 1957 and 1958. The levee on the north bank of the main channel <br />just downstream from Sunset Drive appears to have been damaged by <br />fairly recent floods. Timber cribbing has been constructed along <br />its streamward face, presumably in an attempt to prevent further <br />damage. <br />There is some evidence of substantial erosion fairly recently <br />under the railroad bridge where several timber piles, evidently <br />the r~manents of a previous bridge, extend aS'much as three feet <br /> <br />above the present streambed. presumably, these piles were cut at <br />