Punaise

ERDC TN-DOER-T1

February 2000

require a stand-alone pump and delivery system. Jet cutting is accomplished by injecting high-

velocity water into the sediment just before the intake of the draghead. The fluidization accomplishes

two objectives: (1) increased cutting action and (2) more efficient entrainment of bottom materials.

The jet cutting action more efficiently moves the dredged sediment to the intake while reducing the

difference in pressure between the suction head and the ambient water. The reduction in pressure

reduces the friction forces between the draghead and the bottom, which reduces the force the dredge

must overcome while dredging. With the increased efficiency and reduced friction the dragheads

have become wider to take advantage of the jet cutting action.

Punaise. The Punaise is a completely submersible system that can pump free-flowing sand or silt.

Primary use in the United States would be to use the Punaise for sand bypassing or beach

nourishment projects. The system works best in free-flowing sand with the sand layer around 10 m

in depth. Since the Punaise is submerged, it can work in high sea conditions, which limit

surface-piercing dredge plant. Several locations within the United States have been considered for

the use of the Punaise including Boca Raton, FL, the Mississippi River, and the mouth of the

Columbia River. The Punaise would be extremely effective in locations where relatively small

volumes of sand are dredged by a hopper and can be stockpiled offshore. After two or more dredge

cycles the Punaise could be used to more efficiently move the sand to the shore.

There are currently three Punaise models, the PN 200, PN 250 and PN 400. All equipment required

to mobilize each model can be transported via containers. The PN 200 and PN 250 can also be

transferred within containers, while the PN 400 must be transported through conventional shipping.

Container shipping reduces mobilization/demobilization costs. The PN 250 and PN 400 have

onboard pumps, and the PN 200 requires alternate pumping facilities.

Cable systems and pumping distances currently limit the operation of the Punaise to within 1,000 m

of the shoreline discharge point for beach nourishment projects. For remote channel operations, a

barge can be utilized to operate the surface equipment. The Punaise is operated remotely by electrical

cables. From the remote location, the operator can monitor and manage production rates, tempera-

ture, and fuel mixture, as well as ballast and other vital operating parameters. It is estimated that for

beach nourishment approximately three to four self-contained buildings will be located on the beach

for offices, generators, and fuel. The number of buildings can be reduced if alternate energy sources

can be utilized.

Environmental Dredges. Because of years of industrialization, many of the rivers in Europe have

become contaminated and require specialty cleanup jobs. To dredge these sediments, several

dredges have been developed to make precise cuts, reduce spillage, and decrease turbidity. For

example, during the testing phase for the Kettelmeer Project (described in a following paragraph)

three different dredges were tested to determine production, spillage, and turbidity generation. The

dredges were designed to dredge between 25,000 to 50,000 cu m per week. The three dredges tested

included the HAM 291, the WADDENZEE, and the disc cutter VECHT.

All three dredges use a conventional suction dredge platform with different cutting heads. The HAM

291 has a sophisticated dredge head that can articulate and rotate into the face of the cut and provide

maximum cut on both swings of the draghead. The pumps and swing speed are computer controlled

to obtain the density required for the project. The Ballas Nedam dredge, WADDENZEE, has a suction