Author(s): Sanjeewa Wickramaratne; Imalka Abeygoonasekara

Linked Author(s): Sanjeewa Wickramaratne

Keywords: Beach Stabilization; Unawatuna; Modelling

Abstract: Unawatuna bay, a famous tourist destination in southern Sri Lanka underwent an uneven coastal erosion and accretion which had been exacerbated due to climate change. An adhoc groyne placed in the west side of the bay further hindered the alongshore sediment movement. Thus, stabilization of Unawatuna beach was a subject of discussion for its significant impact to the environment, stakeholders and to the economy in general. A numerical modelling study completed in 2014, which is the base for this technical paper, considered four distinct alternatives for coastal stabilization, inclusive of: removal of existing breakwater and sand nourishment, an establishment of a groyne field, a single submerged groyne, and an offshore submerged breakwater. Three mathematical models namely, wave transformation, hydrodynamic and sediment transport were simulated in progressive steps to scientifically interpret morphological repercussions of each of the alternative in their post-implementation period. Wave transformation simulations revealed that removal of breakwater permits larger unbroken waves to reach nearshore with a relatively wide directional spectrum. Hydrodynamic analyses confirmed that once the breakwater is removed, moderately high currents would help reduce the accreted area in the west, and disperse water currents uniformly across the bay. The morphologic model study clearly promotes removal of breakwater over the other alternatives for its superlative performance particularly in reverting the status quo back to the normalcy. In this context, removal of breakwater coupled with sand nourishment is found as the most desired option in the morphological perspective. This alternative is contested, although not closely, by the offshore breakwater option. Other alternatives are not recommended on the basis of them falling short of the expected hydrodynamic and morphologic performance. Beach nourishment and removal of breakwater was completed in March 2015, and ten years on, the Unawatuna Bay has still been able to retain sand volumes upto 65-70% of the original nourishment.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1958-cd

Year: 2025