Management Of Shoreline Morphological Changes Consequent To Breakwater Construction

摘要

The coastal stretch from Veli to Varkala along Thiruvananthapuram coast, which was in dynamic equilibrium, has two identifiable sediment cells separated by the Muthalapozhi inlet with harbour breakwaters on either side of the inlet. Construction of breakwaters to develop a fishing harbour at Muthalapozhi has caused erosion immediately north of the inlet and beach build up south of the inlet. In addition, the harbour mouth gets blocked due to deposition of sand, virtually making the harbour unusable. In the present study, the processes of shoreline morphological changes along the high energy coast are analyzed using numerical models to propose management options to tackle morphological modifications. Shoreline changes, nearshore processes and beach characteristics along this sector are studied through extensive field observations. The data is used to calibrate and validate sediment transport and shoreline change models for this coast. Sediment transport and shoreline changes are simulated using different modules of LITPACK model. The LITDRIFT module is used to calculate annual sediment transport. The LITLINE module is used for shoreline evolution during fair season and the behaviour of coast during monsoon is simulated using the module LITPROF. The calibration of the model is done with field observations. It is found that beach sediments get deposited on southern side of the breakwater and bypassed sediment gets deposited at the inlet mouth. The model after validation is used to simulate the processes with different designs and a groin field of smaller transitional lengths comparable with the surf zone width. The groins having lengths 40, 30 and 20 m at 120, 220 and 300 m south of breakwater, has been found best suited to control the chocking of harbour mouth due to sediment deposition during beach building period.