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<br />hydraulic analysis, This program is applicable to steady, gradually varied flow conditions. It
<br />was assumed that the controlling hydraulic conditions were represented within the boundaries
<br />of the geometry provided, i,e" that conditions downstream of the areas would not substantially
<br />influence the profiles within the computer models, The downstream boundary condition was
<br />calculated using the Slope-Area method, Cross-section geometry was provided in ASCII
<br />format by Kucera International, Inc" under contract to CWCR Reach lengths between cross-
<br />sections were scaled from the contact prints. Bridges and diversion structures were not
<br />modeled since the corresponding geometry was not provided, This should not significantly
<br />effect the results for the relatively low discharges modeled, Manning's "n" roughness values
<br />were assigned based on a combination of previous studies, field conditions, sediment transport
<br />theory, and engineering judgement Channel "n" values were adjusted using Brownlie's bed
<br />roughness equation to account for bed forms, The specific "n" values for the individual
<br />problem areas are shown in Table 3-2. Contraction and expansion coefficients used were 0,1
<br />and 0,3, respectively,
<br />
<br />Table 3-2. Manning's roughness values,
<br />Problem Area Left Overbank
<br />
<br />Channel
<br />
<br />3
<br />4
<br />5
<br />6
<br />7
<br />
<br />0,065,0.1 00
<br />0.050-0,065
<br />0,050-0,070
<br />0,070-0.1 00
<br />0,090,0.100
<br />
<br />0,035
<br />0,032
<br />0,032
<br />0.033
<br />0,033
<br />
<br />Right Overbank
<br />
<br />0,050-0.1 00
<br />0,045-0.1 00
<br />0,070-0,100
<br />0,070-0.100
<br />0,080-0.1 00
<br />
<br />The 3,000 cfs operational peak discharge was modeled to indicate potential problem
<br />areas under current conditions, The flow area extents for this discharge (i,e" the points where
<br />the water surface "daylights" with ground) were connected to generate "pseudo-floodplains"
<br />and plotted over the photographic images, The figures generated are for illustrative purposes,
<br />and are not true floodplains, since they were produced without sufficient topographic
<br />information, The following assumptions were used to create these:
<br />
<br />I) Flow was initially confined to the generally bermed flow corridor.
<br />2) Flows that escaped the corridor were allowed to spread out at subsequent
<br />upstream cross-sections, unless one of these upstream cross-sections showed a
<br />strong likelihood of returning flows to the bermed flow area,
<br />3) Correspondingly, potential ponding outside of berms at cross,sections
<br />downstream from a "break-out" location were ignored,
<br />
<br />These simplifying assumptions were necessary due to the lack of topographic detail between
<br />cross-sections. In actuality intervening features, or the lack thereof, would have a bearing on
<br />
<br />17
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