Experimental Investigation of a Moored, Circular Pipe Breakwater

Abstract

Floating breakwaters are commonly used for shoreline protection in coastal areas and may offer a relatively cost-effective method for embankment protection in irrigation reservoirs. This study explored the potential use of a moored cylindrical floating breakwater design constructed from corrugated irrigation pipe and included a preliminary investigation of the performance of a floating breakwater that was subjected to regular waves of varying height and period in a laboratory wave tank. Experiments were carried out at the USDA Agricultural Research Service (ARS), National Sedimentation Laboratory in Oxford, Mississippi. The model breakwater was made of a 17.8-cm outer diameter, high-density polyethylene (HDPE) corrugated pipe section, filled with water and restrained under two mooring configurations using steel mooring lines attached to the floor of the flume, either vertically or at an angle on each side of the breakwater. The draft of the breakwater was varied between approximately 87% and 143% of the outer diameter by adjusting the tension of the mooring lines. Additional controlled experiments were performed using the same pipe section under fixed conditions. Waves were measured using capacitance-type wave staffs located both upwave and downwave of the breakwater, and mooring forces were measured using force gauges. Experimental results indicated that the floating breakwater arrangements studied show potential for usefulness in field application, as wave heights were reduced by as much as 60% in some cases. Cable-moored models performed best when fully submerged relatively close to the still water surface. Mooring line slackness reduced the effectiveness of the model in wave attenuation but also reduced the amount of force incurred by the cable mooring system. The cylindrical model best attenuated shorter waves of low to moderate steepness.