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5.2.1 Bed Material The bed material gradations used for the long-term simulation discussed in Chapter 4 were obtained from 1946 data published in the report "Arkansas River and Tributaries above John Martin Dam" (4). A bed material inspection was performed in January 1984 by Fox and Associates of New Mexico, Inc. for the Corps of Engineers' Albuquerque District. Bed samples were taken in the vicinity of La Junta at the following river mile locations: 1197.6, 1198.6, 1199.6 and 1200.6. The bed material gradation varied from location to location (see Figure 5.2). These most recent bed material gradations were incorporated into the HEC-6 input data set for the single-event analyses. 5.2.2 InflowinK Load A small amount of data for the mean annual total sediment volume passing La Junta was presented in the report "Sedimentation in John Martin Reservoir" (6). The standard project flood has a peak flow of 212,000 cfs but the observed data (from 5) were usually for flows less than 3,000 cfs. The total sediment load for the higher single-event flows was developed by using two methods. The first method determined sediment loads that were in equilibrium with the bed material for specific flow rates. (This procedure is explained in Section 4.2.2.) The second method determined the sensitivity of the river bed profile to changes in the inflowing load. The equilibrium load for the peak SPF flow was used as an upper bound. The load curve was then adjusted downward to provide five hypothetical inflowing load curves shown in Figure 5.3. A sensitivity analysis was performed and the load curve that gave the most stable solution was chosen to be used in the single-event simulations. This curve is indicated in Figure 5.3. 5.2.3 Total Load Gradation The total inflowing load is composed of the suspended load and the bed load. Average suspended load gradation data was obtained from reference 5, Plate 42. It was assumed that the suspended load was 90~ of the total load. The gradation of the bed load was considered to be the same as the gradation of the bed material shown in Figure 5.2. The gradation of the total load was calculated by taking a weighted average of the suspended load and bed load gradations. The resulting total load gradation is shown in Figure 5.4. 5.3 Development of Flood Hydrographs Hydrographs for three flood events were provided to HEC by the Albuquerque District. The single-event analyses were performed using both existing and project conditions for all three flood magnitudes. The hydrographs correspond to standard project, 100-year and 50-year floods with peak flows of 212,000 cfs, 94,000 cfs and 64,000 cfs, respectively (see Figure 5.5). The hydrographs were discretized for use in the HEC-6 computer program. 51