Floating breakwaters increase operating time for offshore beach nourishment dredging alternatives
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
R. Randall and B. Koo
Abstract: The operating time of dredging equipment such as cutter suction pipeline dredges, hydraulic unloaders, spider barges, and booster pumps for offshore beach nourishment projects is often limited by the ocean wave conditions. The limiting wave condition for dredging equipment, other than hopper dredges, is commonly 1 m (3 ft) and when the waves exceed this limit dredging must be stopped and consequently the operating time is reduced. In some severe weather conditions, (e.g. hurricanes and winter storms) the dredging equipment must be moved from the offshore location to protected waters. Floating breakwaters are devices that can be moored offshore to protect the dredging equipment from ocean waves. These breakwaters can reduce the wave height by as much as 50 percent. A review of floating breakwaters is described and these devices might be considered for reducing the downtime for dredging and decreasing the length of time for beach nourishment projects. Examples of proposed beach nourishment locations along the upper Texas coast in the United States are used to illustrate the improvement in operating time for several dredging equipment alternatives. Ocean wave data offshore of Galveston, Texas are summarized to illustrate possible dredge operating time improvements using floating breakwaters. Using the common limiting significant wave height for the cutter suction dredge of about 1 m (3.28 ft), the down time of cutter suction dredge is about 35 %. The wave height transmission coefficient for a typical floating breakwater is 0.50.4, and using a floating breakwater could reduce the down time to 2 % in the significant wave height environment off the Texas coast.
Keywords: beach nourishment, floating breakwaters, equipment operating time, dredging equipment