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18 I I I I I I I I I I I I I I I I I I I the actual floodplain, Some upstream areas would, no doubt, have break-outs more confined than what is shown and some downstream areas wO\1ld exhibit ponding that is not indicated. Hence, the term "pseudo-floodplain", It is hoped that this methodology is indicative of potential surface water flooding under current operation conditions and that the graphical products are useful. Sediment Modeling Sedimentation was modeled using Hydraulic Design Package for Channels (USACE 1997), also known as SAM, This is an integrated sY$tem of programs developed to aid engineers in analyses associated with designing, op~rating, and maintaining flood control channels and stream restoration projects, SAM provides the computational capability to include erosion, entrainment, transportation, and deposition 'of sediment in channels. The hydraulic, sediment transport and sediment yield modules of the program were used in this study, The results of the HEC-2 hydraulic models were imported into SAM and used to describe a set of hydraulic parameters for sediment t,ransport calculations, This was accomplished by specifying a portion of each sub-reach as representative of the hydraulic conditions and calculating average values for velocity, depth, width, and energy slope for each discharge value. These parameters were then used, a)ong with bed material particle distribution information, to generate sediment transport rating cUrves for the sub-reaches. The Brownlie sediment transport equation was used to calculate transport, This equation was used because the Stable Channel geometries are calculated with this equation, thus preserving theoretical consistency, The Brownlie sediment transport equation would not necessarily be the first choice for transport calculation, but it is applicable tp sand-bed rivers such as the Lower Arkansas, The resulting sediment transport values ~or the chosen stable design discharge, 1,000 cfs, (discussed in Section 4) were also used toigenerate tables of stable channel dimensions for the channel improvements. The improved channel models were similarly used to generate new sediment transport rating curves, The resulting rating curves were then integrated with a discharge-duration curve to calculate sediment yields for each sub-reach, for each condition. The discharge-duration for the post-1981 period was used for this, since it was felt that this represented the current operational scenario. The calculated sediment yield$ can then be compared to evaluate the functioning of the improved channel and to assess maintenance requirements, \ The actual yield values should not be consid'ilred definitive, by any means, Reliable sediment transport rating curves would require careful selection of a transport function, calibration to measured data and more detailed analysis outside the scope of this study. Additionally, only two particle size distribution curves were used for the five areas, based on the proximity of the problem area and the sample lo\:ation, The three most downstream sub- reaches show considerably higher yields than the fir~t two. A large degree of this is due to the finer particle sizes more prevalent in the downstremv sample. However, the values calculated do have value in that differing conditions for the Saf\le sub, reach can be compared, since they