Experimental investigation of a moored, circular pipe breakwater

Authors: ROSSELL, WILLIAM - University Of Mississippi; OZEREN, YAVUZ - University Of Mississippi; Wren, Daniel

Submitted to: Journal of Waterway, Port, Coastal and Ocean Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2021
Publication Date: 5/31/2021
Citation: Rossell, W., Ozeren, Y., Wren, D.G. 2021. Experimental investigation of a moored, circular pipe breakwater. Journal of Waterway, Port, Coastal and Ocean Engineering. 147(5):04021019.

Interpretive Summary: Irrigation reservoirs are used to reduce dependence on limited groundwater resources in the Mississippi river alluvial floodplain, particularly in the state of Arkansas. The earthen embankments that enclose the reservoirs can be eroded by wind-generated waves, resulting in expensive repairs by agricultural producers to protect the levees. Floating wave barriers can reduce the energy of waves that impact shorelines and the resulting erosion, but there is not enough previous research available to design floating wave barriers for small water bodies like irrigation reservoirs. In particular, there is little information on how to anchor the floating barriers in place, including the strength of cables needed to connect barriers to their anchors. In order to obtain the needed information, laboratory experiments were used to study the motions of a floating wave barrier model, including measurements of how hard the waves pulled on the lines that held them in place. Floating wave barriers were shown to reduce wave heights by up to 60%. Wave barriers connected to anchored cables worked best when fully-submerged close to the surface of still waters. Slack in the cable reduced the capability of the barrier to reduce waves and the amount of force the system can absorb. The results of this work will be useful in the design of levee protection measures for agricultural producers who rely on irrigation reservoirs as a water resource that reduces their dependence on groundwater for crop irrigation.

Technical 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 proposed the use of a moored cylindrical floating breakwater constructed from corrugated irrigation pipe and investigated 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 ARS, National Sedimentation Laboratory in Oxford,MS. 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 within the range of approximately 87% to 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.