Coastal defence for Centro Habana

Abstract

Master project report. Havana is protected from the sea’s severity by a seawall which is called the Malecón. The study area of this report is section 4 of the Malecón which more or less matches the coast of the district ‘Centro Habana’. Since the construction of the Malecón the hinterland has frequently been flooded due to storms and hurricanes in the Gulf of Mexico and on the Atlantic Ocean. Recent inundations were caused by hurricanes Michelle (2001) and Wilma (2005). Among the damaged buildings was the Almejeiras hospital, one of Cuba’s most important. The inundations are mainly caused by waves overtopping the seawall. In the present situation the seawall is 4.3 m above MSL and during design conditions 274 litres of water will be discharged per metre over the seawall on time average. Other contributing mechanisms are rainfall and wave penetration into the drainage system, which are in the order of 10 l/s/m. Because the overtopping is the most important cause the main objective of the report is to find feasible alternatives to drastically decrease the overtopping. A solution has to be integrated with the drainage systems to prevent build up of the water mass in the hinterland. First research was done on the causes. With the findings a list of conditions and a list of demands for the solution was formed. Directly after, all sorts of solutions were considered and weighed in a Multi Criteria Analysis, resulting in a berm in front of the seawall and a submerged detached breakwater as the best alternatives. These have been investigated further. Both the berm and breakwater are considered feasible. The berm must be made of rubble with a nominal diameter for the armour layer of 1.0 m. At the crest (MSL + 2 m) the berm is 6 m wide and the bottom ends about 30 m seaward of the wall. Unfavourable aspects of the berm are that it is situated above MSL and that its height makes the permeability performance questionable. The breakwater should be a rubble mound breakwater. A monolithic breakwater proved unfavourable due to the required width and the high transmission. The rubble breakwater is about 90 m off shore. The armour layer consists of 1.5 m rocks, the crest, situated at MSL, is 10 m wide and the height is 7.3 m. The breakwater is more expensive because it requires more material. It matches the list of conditions and demands better and therefore its value is also much higher than the berm’s. The secondary objective of the report is finding hydraulic boundary conditions which are generated by hurricanes. To reach this objective first a literature study on hurricanes was done to gain knowledge of wind generation and wave spectrum generation by wind fields. For this analytical and empirical approaches were investigated. An analysis was done on hurricanes that have past Cuba in the past century. This resulted in parameters that affect the sea severity. The most important parameters are the fetch and the forward speed of the hurricane. From the study on the parameters two worst paths of hurricanes for the Havana coast have been derived.