Numerical modelling of the spatial variation of sediment transport using wave climate schematization method - a case study of west coast of Sri Lanka

This study quantifies the variations in wave characteristics and the resulting variations in potential longshore sediment transport rate along the coastline between Mount Lavinia and Negombo, Sri Lanka. Over the last 25 years, this coastal belt has been subjected to dramatic interventions due to the influence of rapid social-economic development in the country such as construction of the Colombo South Harbor jetty, ongoing Colombo Port City Project and mega sand dreading off Negombo coast. For the wave transformation, SWAN (Simulating Waves Nearshore) numerical model was applied, forced by offshore wave/wind. The Delft3D-FLOW model was used to estimate the longshore sediment transport rates and related morphodynamics using input reduction and morphological acceleration techniques. Results of the alongshore sediment transport capacity computations clearly indicate the variable characteristics of different parts of the study zone. The annual alongshore sediment transport capacity computed in the study area oriented northward, comply very well with the observations. The coastal belt between Mount Lavinia and Colombo, the wave climate, and subsequently the annual alongshore transport reached the highest values indicating a relative dynamic environment and there after decreased with a strong gradient northward. The explanation for these negative steep gradients and the environmental forcing/human interventions that govern the regional sediment transport are discussed in this paper.