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4. Technical Report

Title:	Practices and problems associated with economic loading and overflow of dredge hoppers and scows
Authors:	Dredging Research Program (U.S.) Palermo, Michael R. Randall, Robert E., 1940-
Keywords:	Barges Contaminants Dredging Economic loading Environmental effects Hopper dredges Overflow Scows Turbidity Water quality
Publisher:	Environmental Laboratory (U.S.) Engineer Research and Development Center (U.S.)
Description:	Technical report Abstract: Dredge hoppers and scows are commonly filled past the point of overflow to increase the load. Some Corps of Engineers Districts routinely allow overflow to increase the load, while others do not because of actual or perceived environmental and/or economic reasons. No formal Corps policies or regulations governing overflow have been established, mainly because the required studies have not been performed. A survey of District practices indicates that the question of economic loading and overflow is governed by both project-specific considerations and restrictions imposed by resource agencies. Of 21 Districts with significant hopper or scow workloads, 14 reported restrictions on overflow. The majority of the restrictions were requested or imposed by resource agencies because of environmental concerns. In no case were project-specific data on overflow environmental effects available to support the need for restrictions or to technically justify overflow. Technical information related to economic loading of hopper dredges and scows and the nature of overflow is limited. The gain in hopper or scow load and the characteristics of the associated overflow are dependent on the characteristics of the material being dredged and the equipment being used. Overflow with hopper dredges is beneficial when sand is the predominant material because the settling velocity is high enough for the sand to rapidly settle in the hopper during the short filling time. The practice of overflowing when dredging silt and clay with conventional equipment and procedures is questionable because the sediment particle sizes are smaller and settling velocities are lower, which tend to cause the solids to stay in suspension longer. There are no known studies focusing solely on the environmental effects of hopper and scow overflow. However, the environmental effects of overflow would logically be similar to those resulting from disposal of dredged material in open water or from the resuspension of sediment during dredging operations.
Rights:	Approved for public release; distribution is unlimited.
URI:	http://hdl.handle.net/11681/4584
Appears in Collections:	Technical Report