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Title: Assessment of the factors controlling the long-term fate of dredged material deposited in unconfined subaqueous disposal areas
Authors: Basco, David R.
Bouma, Arnold H.
Dunlap, Wayne A.
Keywords: Marine sediments
Dredging spoil
Dredged material
Sediment transport
Sedimentation and deposition
Dredged Material Research Program (U.S.)
Publisher: U.S. Army Engineer Waterways Experiment Station
Series/Report no.: Contract Report (Dredged Material Research Program (U.S.)) ; no. Contract Report D-74-8
Abstract: The distribution or dispersion of unconfined, subaqueous dredged material has received much attention for reasons of economy and pollution. If polluted it may affect the fauna and flora of surrounding areas. On the other hand, the material may quickly return to the dredged channel and require frequent maintenance dredging, proving the use of diked disposal areas to be more economical. The major objective of this literature study was to assess the factors that affect the long-term fate of dredged material deposited in unconfined, subaqueous disposal areas. These fundamental factors are thoroughly discussed in the report. In addition, the present knowledge of various methods and their limitations for determining dredged material dispersion were reviewed. The primary conclusions reached were: (a) Analytical methods do not exist which permit the computation of quantities and rates of spread of finite volumes of dredged material in a flow field, (b) Knowledge of incipient sediment motion is of restricted value since quantities and rates are of direct interest to determine material spread, (c) Previous field experiments failed to adequately monitor the environment during the test, hence were of little value to draw conclusions or generalizations, (d) Future field investigations must employ continuous recording instruments to measure all environmental factors of interest -- particularly during storm periods, (e) Hydraulic model studies and laboratory investigations using flumes, wave tanks, etc., are greatly influenced by scaling effects which result from inabilities to exactly scale the sediments and the environmental factors affecting erosion, transport, and deposition, (f) Because each investigative method (field, laboratory, and analytical) has some limitations, all methods must be employed in a research program to determine generalized expressions for ultimate use in predicting the spread of dredged material. A number of recommendations for priority research to meet the goals of the Dredged Material Research Program were also presented. The major recommendations were to: (a) Conduct field investigations under variable dredging conditions to develop means for predicting percentages of dredged material in various modes (mound, mudflow, and turbidity cloud) from samples of material to be dredged, (b) Study general dispersion patterns of dredged material by currents, waves, and combinations, in laboratory flumes and develop empirical equations for prediction purposes. This must be done for mounds and for bottom mudflows, (c) Conduct combined field, hydraulic model, and mathematical model studies of dredged material dispersion and attempt to generalize results. Use regions where results are applicable to generalization. Use maintenance, noncohesive materials where possibility for mudflow does not exist. Repeat for cohesive materials where mudflows exist. (d) Routinely include geotechnical analyses and bottom surveys of disposal areas in the Corps dredging program. Other, lower priority topics were also recommended and a complete list of possible research topics was included for review. No general policies for the United States were deemed possible due to the wide variety of soils, environments, and water bodies considered. However, regional similarities suggest that some limited generalizations are possible. This report is also recommended as a guide for Corps of Engineers District offices which are planning studies of dredged material dispersion in their areas.
Description: Contract Report
Gov't Doc #: Contract Report D-74-8
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Contract Report

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