Coastal areas are subjected to geomorphological changes due to natural and manmade activities. Artificial reef is considered an effective way in preventing coastal erosion due to its multipurpose benefits. Artificial reefs are human made underwater structure built to promote marine life, coastal protection and recreational activities. Submerged wrecks are the most common form of artificial reef. Submerged reefs dissipate the incoming wave energy by forcing waves to break on top of the reef. Wave attenuation also occurs due to turbulence and nonlinear interaction between the reef and the incoming waves. Waves in the leeward side will be shorter and smaller and help in accumulation of sediments. These types of offshore reefs are custom-designed to trap sediment for each unique zone for different application.
In this paper the experimental investigation of a submerged reef under regular and random waves for different water levels carried out is presented. The reef is designed for conditions of south east coast of India. The reef makes an angle of 13° with respect to the shore line and envisaged to trap the sediments from the long shore sediment transport. The submerged reef has a triangular wedge shaped structure with armour stones and concrete cubes, the first of its kind in India. The model studies are carried out in 1:10 model scale in shallow wave basin (19.36 m×15 m×1 m) at IIT Madras, India. The shallow wave basin has 5 piston type paddles on one side which can generate both regular and random waves and a wave absorber on another side.The main part of the submerged reef is triangular shaped steel wedge weighing 900 t (in prototype scale) with dimensions 60 m×50 m×2.5 m with slope on either side resting on stone bed. Since the wedge is having sloping sides the waves will tend to break on either sides during the North East and South west monsoon. The studies are carried out for head sea condition with for regular and random waves with wave height 5 cm to 15 cm with wave period 6 s to 9 s. Armour stones are provided around the wedge to prevent the scour, followed by concrete cubes with holes
The wave transformation over the reef is measured using wave gauges. The waves undergo transformations and breaks on the reef compared to other waves which breaks on the beach. Since the waves break over the reef the wave energy is reduced and thus it does not cause any erosion in leeward side. In the model study the stability of the structure for 3 hour storm duration is carried out. Based on the experimental study the details of wave height transformation over the submerged reef and stability of reef are presented.