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The pattern of the Vamp a River through Dinosaur National Monument is controlled by the local geology, but the character of the river, its local bed and bank conditions, and the distribution of riparian vegetation are deter- mined by the prevailing streamflow and sediment transport reg.ime. Biological and physical characteristics of this river system are affected by seasonally controlled streamflows and intermittent transport and storage of sediment. Much of the sand- and silt-size material introduced into the canyon reach from Deerlodge Park is mobile at the lowest discharges; however, high discharges, though relatively infrequent and of short duration, transport a large part of the total annual sediment load (fig. 7). Reduced flood peaks and sediment transport through a river reach can result in changes in channel geometry, bed-material size, and bank stability. Schumm (1977, p. 159) summarized the metamorphoses of several rivers in response to changes in mean annual flood, mean annual discharge, and type of' sediment load. Regulation of flood peaks can have pronounced effects on th~ distribution of riparian vegetation as observed on the Green River above the Vampa River (Potter and others, 1983). Dense vegetation encroaching on a channel can promote accumulation of sediment and result in channel-width reduction. A reduction in annual streamflow can have a similar effect on channel geometry, sediment transport, and riparian conditions. The quantity and composition of sediment carried by a river also are significant factors affecting river morphology. When the transport of sedi- ment through a river reach is equal to the amount of sediment supplied to it, the river is said to be in equilibrium, or graded. Changes in the amount of sediment supplied to a reach can disrupt equilibrium and lead to aggradation or degradation of the channe 1. Sediment surplus (or defi ci t) equals the difference between supply to the reach and transport through the reach. Sediment supply may be reduced progressively because of changes in climate or land'management that result in lower sediment yield, or because sediment is being stored upstream in the channel or flood plain. More abrupt reductions in sediment supply occur when sediment is trapped in manmade impoundments. Depletion of annual streamflow due to transbasin diversions may be accompanied by a reduction in transport capacity below a diversion structure, resulting in diminished sediment supplied to downstream reaches. The annual total sediment load can be reduced significantly if the magnitude and duration of the highest increments of streamflow are altered, even though the volume of annual streamflow remains unchanged. Since con- struction of Flaming Gorge Reservoir on the Green River in Wyoming, the magnitUde and duration of high flows have been reduced, while the duration of low flows has increased. Annual streamflow below the dam is equal to pre-dam annual streamflow; but, the annual sediment load measured at a gaging station located 106 mi downstream has declined by 54 percent (E. D. Andrews, U.S. Geological Survey, oral commun., 1983), \lJW h:.f~ tJ~:;::d'd. The potential er'fects of aj ter'ing the distribution of dlsCharge~n sed- iment transport through Deerlcd;2 Park nave oeen examlned for several assumed flow durations of the Yam'Ja Ri'/er. T~e historic duration of streamflows (curve A, fig. 8) was decr~ased or increased by percentages equivalent to the changes observed in the Green River near Jensen, Utah (station 09261000), flow duration following the construction of Flaming Gorge Reservoir. The assumed 23