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ABSTRACT To hindcast the wave climate at a particular study area in North-western Coast of Sri Lanka, Wave Transformation Matrix and MIKE 21 Spectral Waves (SW) models were used. Directional wave data recorded at 15m ~ 16m depths in Colombo Port during 1998 – 2015 periods was transformed to the study area by using numerical simulation techniques. Thus, representative nearshore wave climate was established at 20 m water depth in the study area (i.e. Wennappuwa in North-western coast). Transformed wave data was analyzed in both annual and seasonal basis. From our analysis, highest percentage of annual waves at 20 m depth in study area has been identified between 250N – 260N directional range. Seasonal wise, southwest monsoon season was recognized as dominant season. Finally, design wave heights for breakwater structures of a proposed harbour were predicted by extreme wave analysis.
INTRODUCTION The coastal wave climate of Sri Lanka has been investigated during the past few decades for the design and construction of many coastal structures and large scale major projects along the coastline. One of a major step forward was the directional wave measurement program off the south-west corner of Sri Lanka by Scheffer et al. (1994). In this program, wave measurements were carried out at 70 m water depth offshore location in Galle. However, successive wave analysis and publication were based only on the first three and a half years data from the program. Since available field measure wave data is limited along the coastline, wave data are transformed from the measurement location to the location where the wave conditions are required, using wave transformation models. Further, wave data measured in early time does not contain wave directions, those data cannot be used for the transformation process. Additionally, underestimation of wave heights due to the limitations of wave measuring instruments questions about the reliability of the recorded data in the past (e.g. due to the rigidity of the mooring, Wave-Rider buoys which was used between 1983 and 1997 in Sri Lanka in near-shore were not able to measure the higher waves (Wikramanayake et al., 2003)). Hence, there is a necessity to carry out wind wave modeling by using the state-of -the-art modeling methodologies for the Sri Lankan coastlines. In the scientific literature, there are some wave climate studies focusing the southern coast of the Sri Lanka (e.g. Thevasiyani & Perera (2014); Laknath & Sasaki (2011), Ranasinghe et al, (2011)). However, similar studies have been done rarely covering the North-western coast line of Sri Lanka (e.g. Bamunawala et al (2015)). Before implementing the Coastal Resource Management Project (CRMP) in Sri Lanka between 2000 – 2006 periods, significant amount of coastal erosion was observed in some coastal stretches in the North-western coast line of Sri Lanka. However, lacks of understanding about the existing coastal processes and high risk have become hindrances for development projects such as fishery harbour construction in North-western coast of Sri Lanka. Consequently, it has been adversely affected to the larger fishery community of the same region. On the other hand, directional wave data has been being recorded for a considerable duration in West coast since 1998, mainly focusing the development and improvements of the main commercial harbour in Sri Lanka (i.e. Colombo Harbour). Hence, use of existing wave data in West coast for the development projects in North-western coast is identified as a wise approach. Accordingly, transformation of recorded wave data in West coast to the Northwestern coast to understand the wave climate in North-western coast of Sri Lanka is the main objective of this study.
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