Sediment loads in the Ventura River Basin, Ventura County, California, 1969-81

To estimate the replenishment of beach sands by fluvial transport from the Ventura River, sediment data collected during a 12-year period were used to develop relations between bedload and coarse-suspended-sediment loads and streamflow.These relations were used to calculate coarse-and total-sediment loads from the Ventura River, and to assess the effects of major storms on sediment transport.Sediment data collected on an unregulated tributary over a 2-year period were used to assess effects of dam construction on sediment loads and to identify major sediment-source areas in the Ventura basin.Total-sediment load from the Ventura River for the 12 years of data collection was 12,800,000 tons, of which 5,100,000 tons, or 40 percent, consisted of coarse material potentially available for replenishment of beach sands.Suspended-sediment transport was the dominant process supplying sediment to the coast, accounting for more than 98 percent of the total-sediment load and 96 percent of the coarse-sediment load.Higher streamflows carried proportionately more coarse-suspended sediment than low flows.Major storm events transported more than 96 percent of both total-and coarse-sediment annual loads during three high-flow years.The sequence of storm events may influence storm-period sediment transport, as sediment removed rapidly during high flows is gradually replenished by hillslope processes.The sediment yield of the unregulated part of the basin was higher than that of the regulated part.Consideration of the trap efficiencies of reservoirs in the basin, however, indicates that actual yields may be highest in areas affected by impoundments.