Fieldwork coastal engineering: Preliminary design of a floating marina, Varna, Bulgaria

Abstract

The beach in front of the hotel Sirius is suffering from a retreating coastline. Bathymetry and beach profiles were measured. With the data from previous years the long term evolution of the coast was analyzed. The main conclusions were that the beach in front of the Sirius hotel is still suffering from erosion and if this erosion trend continues it will damage the hotel itself in just a few years. More to the south the beach was actually a little bit accreting. The reason why only the beach in front of the hotel is eroding is probably because the beach there is at the leeside of the breakwater, which causes a gradient in the longshore sediment transport The hotel owner of Azalia, located at the Azalia beach north of Sirius beach, observed a retreating coastline during some months in the year. Therefore also here the bathymetry and beach profiles were measured. Unfortunately there were no previous measurements to compare the data with. From the beach profile we can conclude that there is probably a seasonal variation in the coastline. During winter the coastline is retreating due to the more severe wave climate. Yet in summer the beach is accreting. It can be possible that sometimes the beach has not accreted enough at the moment the touristic season starts. This can be a problem for the hotel owner because the beach is not wide enough then. A solution then can be found by some minor dredging operations in the form of beach nourishments. The sand can be recovered from deeper water or from shoals at the same beach. It can be assumed that the nourishment is not necessary at the moment but might be a good idea in the next years. Furthermore the owner of hotel Azalia wants to build a new marina a few kilometers to the south of St Constantine. Due to difficulties in obtaining a building permit it will be a floating marina which can be removed in winter, which must be protected by a breakwater. By a Multi Criteria Analysis a floating breakwater that will be removed during winter proved to be the best solution in this case. This breakwater can be designed with the milder wave conditions during summer which is a serious advantage.