Comparing Methods for Measuring the Volume of Sand Excaveted by a Laboratory Cutter Suction Dredge Using an Instrumented Hopper Barge and a Laser Profiler

The research focuses on the various methods that could be used in the laboratory to determine the values of production from a model cutter suction dredge. The values of production obtained from different methods are compared to estimate the best value. The tests were conducted in an attempt to pave the way to find spillage from the cutter suction dredge. The development of these methods is useful for evaluating the sediment spillage and residuals during dredging. The more accurate the values of production the more accurate would be the values of spillage. For this purpose, the laboratory dredge carriage and dredge/tow tank located at the Haynes Coastal Engineering Laboratory at Texas A&M University is used. During the summer of 2007 and 2008, the laboratory dredge carriage was used to dredge sand (d50 = 0.27 mm) in the sediment pit that is 7.6 m (25 feet) long, 3.7 m (12 feet) wide and 1.5 m (5 feet) deep. A laser profiler, a model hopper barge attached with pressure gauges, a flowmeter and density gauge aid in determining the production from the laboratory model of the cutter suction dredge were used. The before and after bathymetry measurements using a laser profiling system are used to determine the amount of sediment remaining after dredging. The hopper is instrumented with pressure gauges to measure the amount of sediment contained in the hopper. The laboratory dredge system has a magnetic flowmeter and nuclear density gauge that provide data to calculate the amount of sand delivered to the hopper. The difference between the sand volume from the before and after bathymetry is the amount of sand that is resuspended and subsequently resettles in the dredging area (residual) and the sand that is not picked up by the dredge (spillage). Many issues in laboratory testing were found during the course of testing and solutions were found. The production values are compared with reasoning as to why the differences occur. The results demonstrate the ability and difficulty of measuring the amount of material that is dredged and the amount of spillage and residuals that occurs during dredging.