The TASS project is being carried out by HR Wallingford and DRL on behalf of the SSB and Rijkswaterstaat.

The research has sought to identify all of the mechanisms by which sediment is released during dredging and to develop models that predict the rates of release. Little theoretical work on the subject has been conducted to date, and accurate field measurements of losses are not available, although some measurements are available which can be used to derive an initial order of magnitude calibration.

A detailed review of published reports on sediment release from dredging operations revealed that field measurement methods were inconsistent and frequently failed to collect all of the data required to assess losses with different types of plant working in different soil and rock conditions. The inconsistencies prevent direct and meaningful comparison between the measurements and thus reduce their value.

As a result of the work, protocols have been developed for each of five main dredger types, and two field trials have been carried out, one on a grab dredger working in the River Tees in the UK, the other a trailing suction hopper dredger working at Rotterdam, in The Netherlands.

International co-operation is presently being sought to assist with the large number of calibration exercises that are required to give confidence in the models, and future work will focus on gathering accurate field measurements of sediment release, using conventional and innovative methods, to calibrate and refine the predictive components of the software package. Currently, the SSB and Rijkswaterstaat are focusing on trailing suction hopper dredgers.

In the next few years, five field trails will be carried out around this kind of dredger to provide a calibrated and validated TASS model.