On estimation of wave forces on seawater intake caisson in high energy environment using field investigations

The nonlinear wave impact forces on marine structures can lead to severe damage even collapse of the structures. The seawater intake caisson of the desalination plant located at Agatti Island, UT of Lakshadweep, India experienced high wave breaking forces resulting in the strengthening of the structure. When a wave breaks directly on the intake structure, the resulting impact wave force is severe and wave pressure distribution on the intake structure depends on the nonlinear wave transformation over finite water depth. A clear understanding of these impact wave forces on the caisson is required to optimize the design of similar structures in future. Hence, an attempt is made to undertake full scale investigations in field to measure the dynamic wave pressures on the caisson and compare the results with the existing theoretical and numerical methods. These measurements are intended to validate the existing formula for estimating design wave load and to construct a numerical model for the real field condition, which is required for design of similar structures in other islands of UT Lakshadweep. This paper treats a full scale measurement of pressure fields on a vertical wall under wave impacts which also present complete experimental setup at filed and results of investigations carried out to estimate the wave forces on the vertical wall of seawater intake caisson. Pressure measurements and derived force calculations on the vertical wall of seawater intake caisson were compared with the existing formula of Goda (1974). The time series of the variations in the dynamic pressure over the vertical wall indicates that the caisson experienced a maximum force during extreme wave action. The analysis indicates that formula of Goda overestimates the force on the caisson by about 30% during pre-monsoon for highest significant wave height of 1.44m and wave period of 12sec and underestimates the force by about 55% during monsoon for highest significant wave height of 2.76m and wave period of 15sec. This study highlights the estimation of wave loads on this structure during pulsating and impulse conditions of wave regime.