Sustainable Sediment Management in Regulated Rivers: Experiences from Five Continents

By interrupting the continuity of sediment transport through rivers systems, dams cause sediment to deposit in reservoirs, resulting in loss of reservoir storage, and depriving downstream reaches of sediments essential for channel form and aquatic ecology. With the explosion of new dam construction throughout Asia, Africa, and South America, there is increasing interest in techniques to pass sediment through or around reservoirs, both to preserve reservoir capacity into the future, and to minimize the impacts of sediment-starved flows on downstream channel form and ecology. We convened 20 experts in managing sediment in reservoirs and systematically compiled their experiences from applying a range of techniques to reservoirs in Asia, Europe, North and South America, and Africa. In some cases with favorable geometry, it is possible to bypass sediment around a reservoir entirely. Where possible, bypassing can avoid sediment entering the reservoir in the first place, and delivers sediment to downstream reaches in the natural seasonal pattern. Drawdown routing, or sluicing, allows incoming sediment to pass through the dam during high flows, without depositing. Flushing involves drawing down the reservoir to re-suspend previously deposited sediment and pass it through the dam., and unlike sluicing, the release of sediment does not necessarily correspond with the natural seasonal patterns. In some cases, sediment-laden density currents can be ';vented' through the dam without having to draw down reservoir stage. To compensate for sediment starvation, sand and gravel has been added to many river channel downstream of dams, but unless the sediment is drawn from the sediment deposits in the reservoir, downstream gravel augmentation does not address the problem of sedimentation within the reservoir. All these techniques have been successfully used in various contexts, notably Japan. Europe, and China, generally more feasible in smaller reservoirs than large.