Experimental Verification of Groyne Theory

In order to check the results of Bakker's theory [1], [2] concerning the influence of groynes on a sandy beach, a comparison is made with experimental results obtained in model tests performed in the Delft Hydraulics Laboratory [3], and in the Laboratorio Nacional de Engenharia Civil, Portugal [4]. The theory gives the bathymetric development in terms of a set of two schematized contour lines, representing the onshore and offshore parts of the model where longshore sand transport occurs. As input in the theory the characteristics of the undisturbed sand transport should be known, i.e. without groynes. This is achieved by computing the longshore sand transport acoording to Bijker's method [5] and the transverse sand transport according to Swart's method [6], starting from the hydraulic conditions as measured in the model without groynes. In order to make a comparison with the theoretical lines, the bathymetric development as measured in the model with groynes is also schematized to a set of two contour lines. In some cases the result is quite good, whereas in other conditions the theory does not even show the right trend; see [7] for details. Possible causes are discussed, and shortcomings of the model as well as of the theory are mentioned.