Sedimentation is steadily depleting reservoir capacity worldwide, threatening the reliability of water supplies, flood control, hydropower energy and other benefits that form the basis of today’s water-intensive society. The strategies available to combat reservoir sedimentation may be classed into four broad categories. Three proactive categories seek to improve the sediment balance across reservoirs by: (a) reducing sediment yield from the watershed, (b) routing sediment-laden flows around or through the storage pool, and (c) removing deposited sediment following deposition. The fourth category (d) consists of strategies that adapt to capacity loss, without addressing the sediment balance. Successful management will typically combine multiple strategies. This paper presents a comprehensive classification of both proactive and adaptive strategies, consistent with current international practice. Functional descriptions and examples are given for each strategy, and criteria are provided to differentiate between them when there is potential for ambiguity. The classification categories can be used as a checklist of strategies to consider in evaluating sediment management alternatives for new designs as well as remedial work at existing sediment-challenged reservoirs. This will also help practitioners to more clearly describe and communicate the nature of their management activities. Widespread application of both active and adaptive strategies is required to bring sedimentation under control to sustain benefits of water storage for today’s and future generations.

Reservoir sedimentation, a global challenge causing an annual loss of 0.8–1% of reservoir storage capacity, disrupts fluvial sediment continuity and impacts ecology and societal needs. This study focuses on the Pulangi IV reservoir in the Philippines, a shallow and wide reservoir facing significant sedimentation issues. The research aims to investigate drawdown flushing and dredging of a flushing channel for future sustainable drawdown sluicing. A test flushing event was conducted and monitoring data, including discharge, suspended sediment concentration, bathymetry, and grain size distribution, were collected. Laboratory analyses, such as critical shear stress tests, were performed for model calibration. A 3D reservoir model and a 1D sediment transport model were applied incorporating cohesive sediment behavior. Scenarios were simulated to assess drawdown flushing, dredging and downstream impacts. Results highlight the importance of drawdown level, with cohesive sediment properties playing a critical role. Sedimentation downstream of the dam, resulting from dumped or flushed sediments, was low. However, downstream ecological and morphodynamic monitoring was found to be essential for all modeled strategies. This study demonstrates potential for establishing a flushing channel enabling future sustainable drawdown sluicing during floods by conducting repeated drawdown flushing in combination with dredging in the upper reservoir.

This paper outlines the engineering controls designed and installed to stabilize a river bank segment of approximately 350 m at Río Gurabo in Puerto Rico using rock vanes. The design strategy consisted on providing a sustainable, environmental friendly, and economically feasible structural control to stabilize the bank and prevent future erosion. Structural controls includes the installation of seven rock vanes to redirect the erosive forces from the river bank toward the center of the channel, and the construction of a rock bench which serves as an adequate structure to tie in the rock vanes, and provide additional protection to the bank toe. This document summarizes the planning, geomorphologic and engineering evaluations, permitting, design, and construction phase of the project. System performance of the flood event associated with Hurricane María on September 20, 2017, is discussed.

A conjunctive use strategy is described for the 104 year-old Patillas Reservoir on the south coast of Puerto Rico, which has lost 57% of its storage capacity to a combination of sedimentation (39%) plus forced drawdown due to dam safety concerns (18%). A new reservoir operating rule is described which offsets storage loss by allowing the diversion, on average, of 11% of reservoir inflow for storage by aquifer recharge in Salinas Municipality. Salinas is 100% dependent on groundwater for municipal water supply, and experienced water rationing (intermittent service) during the 2015 drought in the face of increasing dissolved solids, attributed to saline intrusion. Of 7.8 mm³/yr diverted to recharge, only 0.6 mm³/yr comes from reduced reservoir firm yield while the remaining 7.2 mm³/yr represents reduced spills to the Caribbean Sea.