Numerical Modelling for Coastal Structures Design and Planning. A Case Study of the Venetian Harbour of Chania, Greece

Abstract

Wave energy harnessing is associated with high cost, compared to established renewables such as wind and solar. In order to make the technology commercially attractive, electricity production could be coupled with secondary functions, such as coastal defence. An innovative concept is the integration of wave energy converters (WECs) in caisson breakwaters, offsetting the initial high cost of WECs with coastal defence. Here, the functionality of Chania’s Venetian harbour offshore breakwater was assessed under typical wave conditions. We used measurements from a Nortek AWAC ADCP, deployed in the nearshore, to numerically simulate the wave conditions induced by a typical low energy storm (M_dir=360^o, H_m0=1 m and T_p=5.5 s) inside the Venetian harbour. We employed the Boussinesq-type wave model MIKE 21 BW and simulated cases with and without the breakwater. In both cases, H_m0 reached 0.4 m, just inside the harbour’s entrance and, in general, similar wave conditions were observed. Therefore, results indicate that the existing offshore breakwater provides little protection to the entrance and the south part of the harbour from waves coming from the north, which are the vast majority of the winter waves according to the field measurements. Thus, an extension or other modifications are required, so as to provide adequate protection to the entrance and the south part of the harbour. We also used the ADCP measured data for a preliminary analysis of the local wave power potential. During winter 2011-2012, the maximum significant wave height (H_m0) recorded by the AWAC was 3.85 m, whilst peak periods (T_p) higher than 10 s were observed. These wave characteristics yielded mean (P_mean) and maximum (P_max) wave power values close to 4.8 kW/m and 72 kW/m, respectively. Therefore, integrating a WEC in future breakwater designs might be a feasible alternative, given also the minimal tidal range of a few cm. Apart from offsetting the WEC’s high initial capital expenditure to coastal defence, the electricity from the waves could power the harbour’s lighthouse. Coupled with interpretive displays of the wave energy technology, this could also stimulate additional (eco)tourism opportunities.