Role of Physical Wave Models in Optimization of Breakwater for Development of Harbours on Open Coast

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Breakwaters are sound massive structures devised for providing tranquil conditions to facilitate loading and unloading operations at the berths, wharfs and jetties in harbour areas. The cost of breakwater construction governs about 70–80% of total capital cost of the coastal engineering project. Considerable economics can be achieved by using small-scale physical models which help in avoiding disastrous mistakes in prototype design. The present study emphasizes on the role of physical wave models for establishing wave tranquility conditions for the development of a jetty and passenger cruise terminal at Bhagwati Bunder in Ratnagiri district, Maharashtra, India. The part construction of west or commercial breakwater up to a length of 457 m was over in 1973. Maharashtra Maritime Board has proposed development of cruise terminal and jetty to cater to passenger ships with length of 245 m and draught of 7.9 m. The permissible wave limit for berthing operations at passenger jetty has been considered as 0.50 m. The physical wave model studies at geometric similar scale of 1/120 were conducted at CWPRS which consists of a three-dimensional model tray shallow wave basin equipped with the Random Sea Wave Generation facilities with SCADA control. The physical wave model studies were conducted for 100 m as well as 200 m extension of the existing breakwater for the three predominant wave directions, viz. WSW (Hs = 4.0 m, Tp = 12 s), West (Hs = 4.0 m, Tp = 12 s) and North West (Hs = 1.8 m, Tp = 6 s). The studies indicated that about 70–80 days will be lost for operation at the passenger berth during the monsoon season under existing condition. With 100 m extension of existing breakwater, the downtime will be about 10 days at the passenger berth during the monsoon season. The 200 m extension will provide just adequate wave tranquility throughout the year at the passenger berth for ship size of 245 m length with wave permissible limit as 0.50 m. The physical model studies were very useful in visualizing the complex interaction of wave patterns inside the harbour which helped in evolving the wave tranquility conditions at different berths, jetties, wharfs, etc.