Abstract
The increasing number of extreme climate events has impacted the operation of reservoirs, resulting in drastic changes in flow releases from reservoirs. Consequently, downstream riverbanks have experienced more rapid and frequent changes of the river water surface elevation (WSE). These changes in the WSE affect pore water pressures in riverbanks, directly influencing slope stability. This study presents an analysis of seepage and slope stability for riverbanks under the influence of steady-state, drawdown, and peaking operations of the Roanoke Rapids Hydropower dam on the lower Roanoke River, North Carolina, USA. Although the riverbanks were found to be stable under all the discharge conditions considered, which indicates that normal operations of the reservoir have no adverse effects on riverbank stability, the factor of safety decreases as the WSE decreases. When the role of fluvial erosion is considered, riverbank stability is found to reduce. Drawdown and fluctuation also decrease the safety factor, though the rate of the decrease depends more on the hydraulic conductivity of the soils rather than the discharge pattern.
Highlights
Slope stability is generally expressed in terms of its factor of safety (FS), which is defined as the ratio of the available shear strength of the soil to the equilibrium shear stress that is required to maintain a just-stable slope [1]
Riverbank stability at all five sites was analyzed for the steady-state flow conditions listed in Table 4, representing typical operational modes in different seasons, including one overbank flow condition
Transient seepage and slope stability analyses were performed to highlight the influence of dam operations on downstream riverbank stability using input parameters determined by laboratory tests, in situ tests, and empirical methods
Summary
Shown, are located on the lower Roanoke River near. Sites 2, 4, and 5 are located on relatively straight reaches, while Site 1 and 3 are situated on the outer and inner banks of meander bends, respectively. These sites were close enough to the dam to be directly affected by its peaking releases. Hupp et al [8] observed and documented bank erosion and mass failure in their study of the same reach. The USGS monitored bank erosion at several locations along the study reach between 2005 and 2009 [9]
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