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<br />are generated using the same procedures, The impacts of channel changes can be qualitatively,
<br />if not quantitatively, predicted.
<br />
<br />Problem Areas - Existing Conditions
<br />
<br />Problem Area 3, Hydraulic modeling of Problem Area 3 indicated that the capacity
<br />within the active channel banks is approximately 1,500 cfs, This is the flow above which water
<br />begins to significantly inundate the overbank areas adjacent to the river channel. Several cross-
<br />sections within the model indicate flows in excess of2,500 cfs could cause damage to the
<br />adjacent agricultural area, The 3,000 cfs operational discharge was modeled to indicate
<br />potential problem areas under current conditions, The flow area extents for this discharge were
<br />connected to generate pseudo-floodplains, as described above, and are shown on Sheet L
<br />
<br />Examination of the profile indicated by the survey shows widely varying slopes
<br />between adjacent cross-sections. The reach-length weighted average slope for the problem area
<br />is 0,00 I 05 (flIft), but the individual values range from a relatively steep 0,00505 to an adverse
<br />(and also steep) -0,00415, More disturbingly, the values change sign quite often, with one
<br />stretch of sixteen consecutive cross-sections and another of eleven being the longest
<br />consecutive runs of positive slope within the model, but more typically averaging three to four
<br />sections, This indicates inaccurate mapping information, since these values represent the water
<br />surface and the numerous adverse slopes could not exist. Their occurrence is, nonetheless,
<br />troubling and could be indicative of disequilibrium, The region in the center of this problem
<br />area exhibits considerably more agricultural encroachment than the upstream or downstream
<br />ends, but no apparent correlation was observed with the slope changes and adjacent land
<br />practices or structures, Also, the sinuosity of the active channel decreases significantly
<br />upstream of a tributary at cross-section 3030. Just downstream of this point, the active channel
<br />has straightened, leaving a small oxbow lake, It is not known if this occurred naturally or was
<br />accomplished mechanically, A profile plot of this area is shown in Plate I,
<br />
<br />Area 3 is suspected to be aggrading, although this can not be stated with certainty at this
<br />point. This is consistent with the apparent downstream movement of an aggradational trend
<br />observed in the degradation rangelines.
<br />
<br />The "JR2" particle size distribution was used for this sub-reach for sediment transport
<br />calculations, The sediment yield for this problem area under existing conditions was 4, I 00
<br />tons/yr with a mean daily load of II tons/day,
<br />
<br />Problem Area 4, Hydraulic modeling of Problem Area 4 indicated that the capacity
<br />within the active channel banks is approximately 1,500 cfs, This is the flow above which flow
<br />begins to significantly inundate the overbank areas adjacent to the river channel. Some cross-
<br />sections within the model indicate flows between 1,500 and 3,000 cfs could potentially cause
<br />damage to the adjacent agricultural area. The 3,000 cfs operational discharge was modeled to
<br />indicate potential problem areas under current conditions, The flow area extents for this
<br />discharge were connected to generate pseudo-floodplains, as described above, and are shown
<br />on Sheet 2,
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<br />19
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