Wave measurements in the dump area of the Constanta breakwater project

Abstract

The crew of the Razende Bol had experienced that their work conditions were worse than measured by the waverider. They concluded that the wave height measured by the waverider should be multiplied with a factor of 1.5 to find the real wave conditions in the working area. A number of reasons have been discussed, but only a hypothesis was prevailing. It was questioned how the waves are influenced by the half-finished-breakwater. Because a lot of uncertainties exist in theoretical predictions, it was decided to do measurements. A simple pressure meter was available to do these measurements; the wave logger. Measuring waves based on their pressure has its limitations. Small, short waves may not be measured since they do not induce enough pressure. On top of that the device also produces noise, which makes it necessary to throw a part of the data away. The performance of the wave logger decreases as the depth of deployment increases. Altogether, this results in limited areas to deploy the pressure meter, and limited wave conditions able to measure. Taking into account these limitations, the wave logger was placed on top of the core material of the breakwater, at -7 meter. The device collected data for 13 days. The most appropriate wave conditions were chosen to analyse. The measurements of the wave logger are compared to measurements of the Waverider. The Waverider measures the wave conditions that are unaffected by the half-finished underwater construction. The comparison of the wave spectra gives most insight in the situation. It was noticed that the waves lost energy when passing the breakwater core, especially for the larger periods. This corresponds with the expectations that the larger periods are subject to stronger reflections.