The project involved a large capital investment and a total of volume of 300,000 cubic meters had been used in the nourishment process. The sand used to nourish the beach was offshore sand dredged using a vessel anchored far away from the coastal zone. This is important because, using sand in the coastal zone itself would have been ineffective. The dredged sand had been pumped via pipeline and released as a slurry onshore and the beach reconstructed using earth moving equipment. Several offshore breakwaters had also been constructed with the intention of retaining the nourishing sand. While the project seemed to be an initial success with positive results shown in surveys carried out immediately before and after the project, over a period of time it is evident that the nourishment has not changed the rate of erosion. At present, the beach has once again severely eroded and continues to erode despite the breakwaters.
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| Severe erosion of the nourished sand |
The success of a beach nourishment program depends on many factors. Coastal processes such as waves, near-shore currents, tides and even wind affect the nourishment process. Parameters such as beach profile and gradient and grain size of sand also matters in this regard. For this reason, a beach nourishment effort is site specific and all these site specific data needs to be considered when planning a nourishment program. In addition, it also vital to continuously monitor the performance of the beach after nourishment and to take necessary remedial action to maintain the project.
While most of the above information had been gathered prior to the nourishment project at Uswetakaiyyawa, the effort has fallen short in post project monitoring. The construction of breakwaters to retain the sand being a tried and tested method, has failed to perform properly possibly due to incorrect layout and dimensions of the breakwaters. Our final year research project aims to assess the performance of this nourishment effort and to provide a solution to the problems faced in this project.
To do this, beach profile measurements are taken using a dumpy level and total station along transects perpendicular to the nourished coastal strip. This process is done during several visits to the area covering the main seasonal cycle of the country. This data is used to model the beach profile and to analyse the sand volume changes with respect to time. A particle size analysis is performed on samples collected at each transect and will be used to determine the direction and severity of the sand transport. In addition to this, a temporal analysis of satellite images is also expected to be incorporated in the research in order to further enhance the field data. Using these findings, our research team expects to propose a suitable solution to minimize the rate of erosion and provide a methodology to effectively monitor beach nourishment programs in Sri Lanka. This would be of immense use in future nourishment projects in the country.