The influence of major dams on hydrology through the drainage network of the Sacramento River basin, California

Abstract

This paper reports basinwide patterns of hydrograph alteration via statistical and graphical analysis from a network of long-term streamflow gauges located various distances downstream of major dams and confluences in the Sacramento River basin in California, USA. Streamflow data from 10 gauging stations downstream of major dams were divided into hydrologic series corresponding to the periods before and after dam construction. Pre-and post-dam flows were compared with respect to hydrograph characteristics representing frequency, magnitude and shape: annual flood peak, annual flow trough, annual flood volume, time to flood peak, flood drawdown time and interarrival time. The use of such a suite of characteristics within a statistical and graphical framework allows for generalising distinct strategies of flood control operation that can be identified without any a priori knowledge of operations rules. Dam operation is highly dependent on the ratio of reservoir capacity to annual flood volume (impounded runoff index). Dams with high values of this index generally completely cut off flood peaks thus reducing time to peak, drawdown time and annual flood volume. Those with low values conduct early and late flow releases to extend the hydrograph, increasing time to peak, drawdown time and annual flood volume. The analyses reveal minimal flood control benefits from foothill dams in the lower Sacramento River (i.e. dissipation of the down-valley flood control signal). The lower part of the basin is instead reliant on a weir and bypass system to control lowland flooding. Data from a control gauge (i.e. with no upstream dams) suggest a background signature of global climate change expressed as shortened flood hydrograph falling limbs and lengthened flood interarrival times at low exceedence probabilities. This research has implications for flood control, water resource management, aquatic and riparian ecosystems and for rehabilitation strategies involving flow alteration and/or manipulation of sediment supplies.

Conceptual Model of Sedimentation in the Sacramento–San Joaquin Delta

“…Flood bypasses were constructed for Central Valley rivers in the early 20th century (Singer and others 2008). Dams were built in most Central Valley rivers in the mid-20th century (Singer 2007). The Sacramento River was stabilized with rip rap mostly during the latter half of the 20th century (USFWS 2000;Florshiem and others 2008).…”

The influence of castanhão reservoir on nutrient and suspended matter transport during rainy season in the ephemeral Jaguaribe river (CE, Brazil)

“…In general, dams alter hydrographs by modifying the frequency and magnitude of seasonal discharges, the storage capacity relative to basin runoff and the influence of tributaries (Batalla et al, 2004;Molisani et al, 2006a;Singer, 2007). Similarly, sediment load is modified when a river is flooded.…”

Characterizing Changes in Streamflow and Sediment Supply in the Sacramento River Basin, California, Using Hydrological Simulation Program—FORTRAN (HSPF)

“…Dams located in the foothills surrounding the valley floor restrict flow in most of the tributaries to the main stem of the Sacramento River. The majority of floodwater in the lower Sacramento River is diverted using a series of passive weirs into a system of flood bypasses, which act as natural conveyance floodplains by transferring excess streamflow directly into the Bay-Delta [8]. The weir and bypass system was built before most of the large dams were constructed in 1920-1970.…”