Sediment management strategies
Management activities to address reservoir sedimentation may be classified into four broad types of methodologies:
These strategies are outlined in the figure below, which may be used as a checklist for ensuring that all strategies have been considered at a given site.
A combination of strategies will usually be used, and the techniques most suitable for implementation will change over time as a reservoir fills with sediment.
The optimum sediment management strategy may consist of a sequence of different techniques to be applied as the reservoir volume diminishes.
Reducing upstream sediment yield
Two basic strategies may be used to reduce sediment yield entering the reservoir from the upstream watershed: (1) control soil and channel erosion at its source or (2) trap eroded sediment upstream of the reservoir.
Sediment routing refers to a family of techniques that take advantage of the timewise variation in sediment discharge, managing flows during periods of highest sediment yield to minimise sediment trapping in the reservoir.
Sediment bypass strategies include: 1) diverting clear water into a reservoir while selectively excluding sediment-laden flood flows, and 2) bypassing sediment-laden flood flows around an onstream reservoir.
Sediment pass-through strategies include 1) reservoir drawdown to pass sediment-laden floods through the impoundment at a high velocity to minimise deposition, termed sluicing, and (2) venting of turbid density currents through a low-level outlet.
In all cases the objective is to release sediment-laden water and impound clear water.
Sediment routing techniques require that a fraction of the river inflow be dedicated to transporting sediment around or through the reservoir, and is not feasible if all the inflow is being captured and stored. However, as reservoir capacity is diminished by sedimentation, sediment routing strategies become increasingly feasible. Therefore, it may become a viable future strategy at sites where it is not currently feasible.
Redistributing or removing sediment deposits
There are three main strategies to redistribute or remove sediment deposits. The principal technique used to modify the sedimentation pattern, or to redistribute deposited sediment, is to manipulate water levels in the reservoir by modifying the operating level.
There are several dredging techniques used to remove sediment from beneath the water. Hydraulic scour or flushing occurs when a submerged low-level outlet is opened to release sediment while the reservoir level is high, producing a localised scour cone immediately above the pressure flushing outlet.
Adaptive strategies are actions to mitigate the impacts of sedimentation but that do not involve handling the sediment. They may be used along with or instead of active sediment management.
The strategies which are featured in the case studies drop-down list classification are below. As more case studies will be included, we will include more strategies.
Case study classification
The case studies featured on this website are classified according to the following categories. As more case studies will be included on this website, we will include more strategies.
Reduce sediment yield from upstream
Remove or redistribute sediments