There are many reservoirs where storage loss due to sedimentation is severe, and where these limitations can be overcome. In these circumstances flushing may offer a viable means of recovering and maintaining storage capacity especially when the costs are compared with those of other options.

The report
The report aims to assess the feasibility of flushing sediment from reservoirs using simple criteria that require readily available data. By applying these criteria, reservoirs at which flushing might be viable can be identified, and a preliminary estimate of the sustainable storage capacity can be made. More detailed studies can then be undertaken for those reservoirs.

What it covers
The report discusses the processes involved in reservoir flushing and derives methods to quantify two key requirements for effective flushing:

1. The quantity of sediment removed during flushing should at least match the quantity of sediment that deposits in the reservoir during the periods between flushing operations

2. The useful storage capacity that can be maintained should be a substantial proportion (above about 50%) of the original capacity.

Simple quantitative criteria for assessing the feasibility of flushing sediments from reservoirs are developed. They are designed to determine whether, at a particular site, there is the potential to restore lost capacity and to maintain a usable storage volume in the long term. Development of the criteria, and their calculation procedures, are described. The criteria were applied to fourteen reservoirs that have been flushed and observations of its effect are available, in order to establish how closely the predicted behaviour matches observed behaviour. A detailed example of an application of the criteria is presented in an appendix.

Contributors
HR Wallingford Ltd, UK.

Intended users
The report is useful for reservoir or scheme managers and reservoir design engineers.

Atkinson, E, 1996. The feasibility of flushing sediment from reservoirs. HR Wallingford, UK. Report no. OD 137.