Presentation on theme: "Hex Box Breakwaters On Potomac River at low tide. A pier is being built right up to the breakwater and using it to provide calm water for the dock."— Presentation transcript:
Hex Box Breakwaters On Potomac River at low tide. A pier is being built right up to the breakwater and using it to provide calm water for the dock.
Hex Box Characteristics Dimensions: 8 long, 3 to 7 wide, height 4 to 6 Weight varies with height, from 3.6 to 4.5 tons. 11% porosity of wall face from 12 Dia. holes gives wave reflection coefficient of.3 with a 25 foot wave length. This is less than a 1:2 slope rock breakwater and does not consider the extra effects of the angled face on reducing reflection effects. No steel in concrete, Synthetic structural fibers used for reinforcement of the 5000 PSI concrete. Tongue and groove slots in ends lock each box to its neighbor as well as two concrete pins that are driven down through the floor of the box into the riverbed to hold their position.
Hex Breakwater Layout The inside of a hex box fills with sand and allows recruitment of plants and animals in a sunlight, calmer environment. Hex boxes have a higher replacement habitat value than rock, while allowing animals to pass through the large holes in the boxs walls.
Typical Stone Breakwater SAV and grasses cannot grow on rip rap because of the lack of soil and sunlight. They cover up to 5 times the river bottom that a hex box covers, smothering all plant and animal life that may be there under the rock and filter cloth. The large weight of the rock causes settling of the rock into the river bottom and lowering of the breakwaters effectiveness over time, as well as needing maintenance to replace rock that role off in storms. The rock breakwater is hazardous to people walking on them and to boats passing nearby.
Breakwater Habitat Smooth cordgrass at high tide inside box.Salt meadow hay planted breakwater. Oysters growing inside box.Natural recruitment of SAV inside box.
Installing boxes from truck to water. Driving 4 concrete pins down through the floor of the box. Flatbed trucks can carry 5 boxes. Launching the plugged box. Looking down at the tongue and groove connection between boxes.
Hex Breakwaters being towed into position. The boxes have a draft of 3 7 when plugged and floating. This allows distance launching to access areas where you can not reach the shoreline over land. This installation was reached after over a mile of towing from the launch point.
Hex Boxes at Eagle Bay Aug 8, 2008 during a storm. Dec. 20, days after 1 st installation. June 29, more breakwaters added up river. Jan weeks after 1 st installation.
Installation downriver from 301 Bridge Aug 9, 2007Aug 14, 2007 Aug 22, 2007May 23, 2008