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<br />areas investigated, the profile of this reach is fairly well-behaved. A profile plot of this area is <br />shown in Plate 3. <br />The planform of the river exhibits two different forms in this area. Downstream of the <br />irrigation diversion the channel shows a pronounced meandering channel pattern form with <br />sandy point bars. Upstream of the diversion the river channel is much less sinuous until the <br />upper end of the reach, with fewer and smaller point bars and more braiding. This is consistent <br />with a change in the sediment transport regime and is due to the diversion of a larger <br />proportion of water than sediment. No attempt to quantify this effect was made because of <br />inadequate data. <br /> <br />The "Bristol Bridge" particle size distribution was used for this sub-reach for sediment <br />transport calculations. The sediment yield for this problem area under existing conditions was <br />30,200 tonslyr with a mean daily load of 83 tonslday (averages of below and above diversion). <br /> <br />Problem Area 6. Hydraulic modeling of Problem Area 6 indicated that the capacity <br />within the active channel banks is approximately 1,500 cfs. This is the value above which flow <br />begins to significantly inundate the overbank areas adjacent to the river channel. Potentially <br />damaging flows begin above approximately 2,500 cfs at some cross-sections. The next <br />potentially damaging flow occurs at approximately 3,500 cfs, upstream of a severe constriction <br />caused by agricultural encroachment. 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 previously, and are <br />shown on Sheet 4. <br /> <br />Examination of the profile indicated by the survey shows varying slopes between <br />adjacent cross-sections, though not to the degree of area 4. The reach-length weighted average <br />slope for the problem area is 0.00l29, but the individual values range from a relatively steep <br />0.00615 to flat. There are no adverse slopes within this reach. Compared to other areas <br />investigated, the profile of this reach is reasonably well-behaved. A profile plot of this area is <br />shown in Plate 4. <br /> <br />The planform of the river reveals extensive encroachment along the reach, with one <br />area near the downstream end where this is particularly extreme (shown in Figure 7). In this <br />area, a circle-irrigation plot, coupled with its appurtenant levee and one on the other side of the <br />river, has restricted most flows (i.e., well above the channel capacity) to a width of only 200 <br />feet. This severely reduces the area available for overbank flows and eliminates channel <br />sinuosity. Without extensive bank stabilization and maintenance, this area can be expected to <br />be very problematic. As mentioned above, this constriction also causes lowered capacity <br />upstream with its backwater effect. A projection of an average slope through the reach shows <br />that the channel bottom is overly deep in the area of this constriction. Again, this is likely the <br />result of the actual channel work performed (probable over-excavation) and the channel's <br />response to it. <br /> <br />2l <br />