At the middle section, the test starts with 20 of the largest waves, followed by a stepwise decrease. When choosing the volume to start with, the results obtained for the lower section are decisive. The initial wave volume will be one level higher than the wave volume at which a significant erosion rate occurred (in the order of 5 cm or more for 10 waves). This is to be estimated by Deltares and to be decided with the local test leader. However, if the series of waves at this higher volume in the lower section has not been completed because the test had to be aborted, then a lower initial volume may be chosen. This decision was taken in the field, by the local test leader and the advisor of Deltares.
Three examples:
1. Suppose on the lower section no (or only little) erosion occurred during the 10 waves of 1500 l/m, an estimated increase of more than 5 cm during the 10 waves of 2000 l/m, the same during the 10 waves of 2500 l/m and that the test has been aborted after 7 waves of 3000 l/m. Then the test on the middle section will start with waves of 2500 l/m.
2. Suppose on the lower section hardly any erosion occurred during the 10 waves of 1500 l/m, there was a clear increase of the erosion during the 10 waves of 2000 l/m, and the test has been aborted after 3 waves of 2500 l/m. Then the test on the middle section will start with waves of 2000 l/m.
3. Suppose that in total only about 15 cm of erosion has occurred (as measured indicatively at the end of the test of the lower section), without a significant increase at any stage, and the lower section will remain open. Then the test on the middle section will start with waves of 3400 l/m.
At every level, 20 waves will be applied, with a maximum 60 second interruption after every 10 waves. In the most extreme case (i.e., a situation like example 3 above), this means first 2 x 10 waves of 3400 l/m, followed by 2 x 10 waves of 3000 l/m, etcetera, and finally 2 x 10 waves of 500 l/m. The total ‘wave time’, including 13 x 60 seconds interruptions, will be about 1.5 hours.