Extreme Wave Analysis Within a Confined Harbor Basin: A Case Study of Colombo Port

Designing maritime structures requires calculating design waves for a specific return period. This involves analyzing extreme waves (EWA) using long-term wave data at a specific depth in the sea. Typically, spectral models like MIKE21 SW are used to simulate these long-term wave parameters for EWA. However, when analyzing wave data inside an enclosed coastal area such as a harbor basin, using a spectral wave model may not be suitable due to its limitations in simulating wave processes like reflection and diffraction. Wave heights simulated by MIKE21 SW could be underestimated within the basin due to the influence of structures like quay walls or breakwaters, which affect wave reflection. To address this, our study focuses on EWA within the enclosed basin, utilizing a combination of spectral and Boussinesq wave approaches. Specifically, we selected Colombo Port as our study area and employed the MIKE21 BW module, which can successfully simulate reflection and diffraction processes within the basin. Wave data was hindcast by the MIKE21 SW model at a depth of 20 m in the Colombo Sea for the years 1998 to 2015, and continued EWA. Applying the Peak Over Threshold (POT) technique, we extracted wave heights from storms occurring over 17 years in Colombo for EWA. We employed the Weibull distribution as the best-fitting function to estimate extreme wave heights for return periods of 1, 5, 10, 25, and 50, considering the goodness of fit. These identified extreme wave heights were then transformed using the MIKE21 BW model to the possible development site inside the Colombo Port basin. To estimate the peak wave period for the identified extreme wave heights within the harbor basin, we utilized the relationship between peak wave period and significant wave heights at a 20 m depth. This information provides valuable insights for possible maritime development within the Colombo Port basin.