The software package RESSASS (REServoir Survey Analysis and Sedimentation Simulation) was developed and is Output 1 of the project. Tutorials were developed and a manual was prepared.

For Output 2, a method for assessing the feasibility of flushing was developed and published. The method allows engineers to assess, with the minimum of data, whether flushing is likely to prove successful in restoring or maintaining reservoir storage capacity. For more detailed investigations of the impact of flushing, a numerical model 'RESFLUSH' was developed. RESFLUSH predicts sediment movements in reservoirs during flushing operations. The flushing model is separate from, but fully compatible with, the RESSASS software. Finally, a user manual was prepared for RESFLUSH.

Flushing sediment deposits from reservoirs is one of the very limited options available for recovering storage losses in reservoirs. Flushing works by the opening of low level gates in a dam which draws down reservoir water levels and so enables a channel of fast flowing water to develop. This scours away the sediment deposits. An advantage in the method is that it does not require dredging plant nor mechanical energy inputs. Flushing has proved successful at some sites but has failed to produce significant benefits at others. A method has been developed which enables the feasibility of flushing to be assessed before the expense of constructing low level gates, or emptying an impoundment, is incurred. Data from fourteen reservoirs where flushing has been attempted have been collated and the method correctly identified those reservoirs where flushing proved successful, see the figure attached. A numerical model has been developed which models the flushing process in detail. The model can also be used to predict the long term effects of flushing in a reservoir so that, for example, the relative impacts of flushing annually and flushing every second year can be compared.

measure sediment deposition and storage loss in reservoirs more accurately and quickly - by using the volume analysis and section editing facilities,

predict future deposition - either by using the quick and relatively simple volume prediction facility or by using the more accurate technique based on calibrating and applying the numerical model,

manage future deposition through appropriate reservoir operation - by assessing the options available with the numerical model.

At those reservoirs where flushing is feasible, it can be an economically attractive means of managing past and future deposition. Application of the method for assessing the feasibility of flushing, and subsequent application of the numerical model for flushing, will help to identify the reservoirs where flushing is suitable. /td>

The feasibility of flushing sediments from reservoirs', E Atkinson, Report OD 137, HR Report

'Measuring, predicting and managing reservoir sedimentation: RESSASS user manual', Report OD ITM 56, HR Report

'Flushing sediment from reservoirs: RESFLUSH user manual', E Atkinson, Report OD ITM 54, HR Report

'Looking a little flushed', article by Ed Atkinson in International Water Power and Dam Construction, February 1998.

'Reservoir operation to control sedimentation: techniques for assessment', E Atkinson, British Dam Society, Bangor Conference, 1998.

A paper publicising the work was produced and submitted to 'Water Power and Dam Construction', and an article on the software RESSASS will appeared in 'Water'.

The RESSASS software was distributed free of charge to government agencies in the following countries:

Philippines	Thailand
Indonesia	Vietnam
India	Pakistan
Kenya	Tanzania
Zimbabwe	South Africa

The action above was funded by HR Wallingford. Training in RESSASS has also been given to agencies in South Africa, Vietnam and China.

Tel: +44 1491 835381
Fax: +44 1491 826352
Email: dfid-kar-water@hrwallingford.co.uk