Basin Resonance Study for Colombo South Harbor Through Long-Wave Studies for Enhanced Port Operations

The design and construction of breakwaters are effective measures to protect harbors from the impact of wind-generated short waves and swell waves. These structures enable safe and efficient harbor operations. However, the same solution does not adequately address the challenges posed by long waves. Long waves exhibit a high wave period and relatively low wave height, making it easier for them to enter the harbor basin through the harbor entrance. Consequently, the harbor may experience oscillations when incoming long waves resonate with the harbor's natural oscillation period. Such oscillations can lead to increased downtime and mooring difficulties, even though other adverse wave effects have been already successfully addressed for short-period waves. While the scientific literature extensively covers short waves, there has been limited research on long waves and harbor resonance. This study focuses on Colombo South Harbor (CSH), which was designed in 2005, and construction works were completed in 2012. Although basin resonance studies for CSH considered the original terminal arrangement, the east and west terminals remain incomplete, with plans for completion in the future. Consequently, the study of basin resonance for the intermediate period becomes crucial, emphasizing the harbor basin's existing configuration and depths. Our study aims to identify the oscillation modes generated by long waves in CSH using numerical simulation methods, specifically the MIKE 21 BW (Boussinesq Wave) model. Through white noise simulations, we identified the most sensitive frequency bands prone to long waves. Further simulation and analysis of long waves within these identified frequency bands allowed us to discern the natural oscillation modes of the harbor in both the longitudinal and transverse directions, considering the wavelengths and harmonics involved. In summary, our research sheds light on the phenomenon of long-wave oscillations of CSH for the existing harbor configuration and depths. By identifying and understanding these oscillation modes, we contribute valuable insights to harbor operations in the face of diverse long-wave conditions.