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:
1Hex Box BreakwatersOn 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.
2Hex 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.
3Hex Breakwater LayoutThe 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 box’s walls.
4Typical 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 allplant 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 breakwater’s 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.
5Breakwater Habitat Smooth cordgrass at high tide inside box. Salt meadow hay planted breakwater.Oysters growing inside box.Natural recruitment of SAV inside box.
6Installing boxes from truck to water. Flatbed trucks can carry 5 boxes.Launching the plugged box.Looking down at the tongue andgroove connection between boxes.Driving 4” concrete pins downthrough the floor of the box.
7Hex 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.
8Hex Boxes at Eagle Bay Dec. 20, 2006 3 days after 1st installation. June 29, more breakwatersadded up river.Jan weeks after 1st installation.Aug 8, 2008 during a storm.
9Installation downriver from 301 Bridge Aug 9, 2007Aug 14, 2007Aug 22, 2007May 23, 2008