Abstract
Major dam and reservoir development within the Brazos River Basin is correlative with a significant decrease in the suspended sediment load of the river and with increased coastal erosion rates near the Brazos delta. A hydrologic analysis of the river discharge, by use of cumulative frequency curves, shows that discharge control by dam regulation has reduced the frequency of high discharges, thus smoothing out the river hydrograph and reducing the amount of sediment the river is able to carry and deliver to the coastal zone. In addition, the reservoirs are presently trapping about 76% of all sand produced within the basin. The amount of sand denied access to the coastal zone through changing geologic processes is estimated to be 30 mcf/yr and, through the loss of the river's transporting ability and reservoir entrapment, has been determined to be an additional 60 mcf/yr. The increase in the coastal erosion rates in the study area, at least since 1941, can be related to the construction of water resource structures. Sand losses brought about by the construction of reservoirs on the Brazos River, or one of its major tributaries, can be predicted from a relationship between the ratio of sand load (tons) to discharge (acre-ft) to the effective drainage basin (area of the basin below the water resource structures).
