Estimating accumulation rates and physical properties of sediment behind a dam: Englebright Lake, Yuba River, northern California

Abstract

[1] Studies of reservoir sedimentation are vital to understanding scientific and management issues related to watershed sediment budgets, depositional processes, reservoir operations, and dam decommissioning. Here we quantify the mass, organic content, and grain-size distribution of a reservoir deposit in northern California by two methods of extrapolating measurements of sediment physical properties from cores to the entire volume of impounded material. Englebright Dam, completed in 1940, is located on the Yuba River in the Sierra Nevada foothills. A research program is underway to assess the feasibility of introducing wild anadromous fish species to the river upstream of the dam. Possible management scenarios include removing or lowering the dam, which could cause downstream transport of stored sediment. In 2001 the volume of sediments deposited behind Englebright Dam occupied 25.5% of the original reservoir capacity. The physical properties of this deposit were calculated using data from a coring campaign that sampled the entire reservoir sediment thickness (6-32 m) at six locations in the downstream $3/4 of the reservoir. As a result, the sediment in the downstream part of the reservoir is well characterized, but in the coarse, upstream part of the reservoir, only surficial sediments were sampled, so calculations there are more uncertain. Extrapolation from one-dimensional vertical sections of sediment sampled in cores to entire threedimensional volumes of the reservoir deposit is accomplished via two methods, using assumptions of variable and constant layer thickness. Overall, the two extrapolation methods yield nearly identical estimates of the mass of the reservoir deposit of $26 Â 10 6 metric tons (t) of material, of which 64.7-68.5% is sand and gravel. Over the 61 year reservoir history this corresponds to a maximum basin-wide sediment yield of $340 t/km 2 /yr, assuming no contribution from upstream parts of the watershed impounded by other dams. The uncertainties and limitations of the estimates of overall sediment quantities are discussed. Implications for watershed management and future reservoir sedimentation studies are also presented.

Conceptual model of sediment processes in the upper Yuba River watershed, Sierra Nevada, CA

“…Its primary purpose was to contain sediment from anticipated future hydraulic mining. Hydraulic mining resumed for a brief period after completion of the dam (James, submitted for publication); however by May 2001 Englebright Lake had accumulated 21.9 million m 3 of sediment (Childs et al, 2003;Snyder et al, 2004). One of the primary goals of this paper is to identify major sediment sources in the upper Yuba River and the reservoir sediment volume is an ideal gauge that suggests the relative magnitude of sediment deliveries integrated over the past 62 years.…”

Channel and Floodplain Change Analysis over a 100-Year Period: Lower Yuba River, California

“…The lower Yuba River flows from Englebright Dam, through the Yuba Gold Fields over Daguerre Point Dam, to the Feather River at Marysville (Figure 2). Englebright Dam traps most sediment leaving the mountains and has arrested the delivery of reworked hydraulic mining sediment to the Valley since it was constructed in 1941 [15,20,21]. Most sediment transport in the lower Yuba River is produced from mining sediment stored downstream of Englebright, where the valley is wider, gradients decrease and much HMS was deposited.…”

Seasonal Accumulation and Depletion of Local Sediment Stores of Four Headwater Catchments

“…This is especially true in California where 60 percent of the water comes from the Sierra Nevada and most of the major river systems contain dams where storage area can be greatly reduced by accumulating sediment [19]. Several case studies on California reservoirs have shown that the fine sediment fraction (silt, clay, and sand), which can cause turbidity in headwater reaches, accounts for the majority of accumulated sediment in reservoirs [20,21]. Sediment and sediment transport also play a key role in nutrient cycling, aquatic-habitat quality, flood-control and water-supply infrastructure, and contaminant transport [22].…”