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was tested against hand computations for simpl'9' verification (See "Model Confirmation' SElction). The equilibrium sediment transport values lor each discharge were aggregated into an event hydrograph and a total sediment volume for each eVElnt was determined. The individual event sediment yield estimates were integrated to determine an average annual sediment yield for comparison to the previously computed PSIA methodology e,stimate of average annual sediment yield. This integration was performed by plotting a curve of total sediment yield for each event against the probability of the event recurrence and determining the arEla beneath the curve which represents average annual sediment yield. (See 'Ave I~nnual Yield' Sec;tion.) fA,NjDIKE SYSTEM ANALYSIS Th'3 previously described hydrograph and event specific sediment inflow was used to evaluate the, effects of the West Range Wash Dike system 011 the sediment transport oj the 1oo-year ElVElnt. HEC-6 requires that a hydrograph and a sediment rating curve bEl input into the model as a boundary condition. The sediment yield r.ating curve was developed basEld on the fan Elquilibrium transport capacity computations used to develop the event specific yield estimates described above. ThEl HEC-6 model began at the apex of the alluvial fan with the apex flow hydrogn~ph and an assumed sediment load. (See "System MOdel" Section.) Flows down the alluvial fan were modeled USing the previousiy described channel of constant cross-section. Flows were modeled down the fan where they reached equilibrium and Wl3re eventually interc:epted by the West Range Wash Dike. The model cross-section was modified to' reflect the geometry of the channel along the upstream toe of the dike and the slope along the dike as it traverses the fan. A 1:20 foot wide unlined channel with 3:1 side slopes was assumed along the upstream toe 01 the dike. Two longitudinal bed Slopes were simulated which l"epresented the extremes of the conditions encountered along the dike. (0.5 percent and 1.0 pelJ'cent). HEC-6 determines the equilibrium sediment transport down the fan and, based on a comparison with the computed equilibrium sediment transport along the dike, the total volume of deposition is computed for each time step. Because 01 intermediate cCJmputational instabilities, it was not possible to determine the total volume of deposition which occurred at the peak flow by interpreting HEC-6 directly. An intermediate computation basecj on a mass curve of sediment transport was required which determined that ~~8% of the total deposition occurred at the peak discharge. (See "Deposition Percelntage" Section) HEC-6 computes equilibrium transport at each cross-section and Ciannot distribute deposition throlJgh a channel reach. The methodology prese,nted in Desi(ln of Small Dams for evaluating the (leometry and longitudinal length of a scour hole was modified slightly and applied here to estimate the length of deposition and the maximum depth of the, deposited materials at the 100- yr pElak flow (See "Transition Model" section). This methodology was compared to a parabOlic vertil~al curve of a comparable length and resulted in a good correlation for the maximum depth. A transition length of approximately 1,100 feet Cind a depth 01' deposition of 5.9 feet was computed. WATER SURFACE PROFILE DETERMINATION The computed transition and deposition were incorporated into a HEC-2 run to deltermine the water surface through the transition section. A horizontal transition between the re,ctangular