Profile development of a nourishment behind a submerged breakwater

A literature review is undertaken to understand the causes and the effects of the first process. Using the resulting equations, the UNIBEST-TC program is verified for the process of wave transmission over and through a submerged breakwater. Due to the fact that only impermeable breakwaters can be implemented in the program, deviations occur. For conventional breakwaters the agreement is quite good. For reef breakwaters it is not accurate enough. Due to the fact that a conventional submerged breakwater will be used, the approximations as computed with UNIBEST-TC will suffice. The cause and results of the second process are qualitatively more or less known. However, more quantitative data are needed. The third process is very important because it causes a spatial difference between the point of breaking and the position of maximum return flow. It determines the amount and effect of scour just bebind the breakwater. It seems that these effects are slightly overpredicted by the program. Model tests and extensive measurements will be needed to verify this assumption. All three processes together result in asteeper slope of the nourishment bebind the breakwater, as compared to the reference slope. The amount of shoreline retreat is computed for a nourishment bebind breakwaters with the crest located at NAP -2 m and NAP -4 m. A stability analysis on the primary armour layer as used on these two breakwaters was carried out. Using the results of that analysis, a rough estimate of the costs for both breakwaters is derived. Adding these figures to the costs needed for the nourishments bebind the breakwaters, a comparison is made between these two protected nourishments and an unprotected nourishment. Both result in a more or less stabie coast enlargement of 1000 m. The conclusion is that the protected nourishment is economically a better option than the unprotected one. Due to the fact that the overall costs for the two protected nourishments do not differ much, the one with the lower crest (NAP -4 m) is recommended.Hydraulic EngineeringCivil Engineering and Geoscience