Mine Scour, Burial, and Migration as a Function of Wave and Current Forcing


Investigators

Casey Church, Steve Elgar, Robert Guza

Funding Source

Naval Research Laboratory

Objectives

The overall objective is to understand the behavior of small, potentially mobile objects (eg, mines)within the surf zone and inner shelf. Specific research goals of this pilot project include observing the migration and the scour and burial of the objects as a function of wave and current hydrodynamic forcing, location within the swash and inner surf zone, and geometry of the object. Information from this pilot study will be used to evaluate the potential utility of a deterministic mine burial model for operational Navy requirements and to design future experiments.

Approach

Small inert mines will be monitored as they respond to waves and currents in the inner surf and swash zones. Single mines (with small marker buoys attached for visual tracking) will be deployed for periods of several hours under a range of wave and current conditions. Burial depths, scour, and horizontal migration will be monitored with video imaging and with detailed bathymetric surveys in the immediate mine vicinity. Visiblility permitting, mine scour and burial will be monitored continuously with underwater video. It is important to distinguish between mine burial owing to the complex interactions between mine, fluid, and sediment motion, and mine burial owing to general accretion of the beach, bar movement, or ripple formation. Supporting observations from the nearby cross shore transect of sonic altimeters, pressure gages, and current meters will determine the presence or absence of general accretion/erosion, bar movement, and ripples, as well as provide background environmental information.

The experiment will be conducted during September when interference with DUCK94 experiments and sensors will be minimal. Mine loss (and possible subsequent interference with October experiments) will be minimized by the wading depth/swash zone deployment of the mines coupled with close monitoring.

Initial Results

Conditions during the study period varied greatly, ranging from small to moderate wave heights and current velocities. The predominant process observed was the migration of the anti-tank mines, with burial occuring much less frequently than expected. Video image analysis is in progess and will be used to quantify the mine's movement which will be combined with the wave and current data obtained from the in situ current meters and pressure gages. The resulting understanding will be used to produce a predictive model for the redistribution of mines likely to be encountered during an amphibious landing of naval forces.

For a list of addresses of the investigators involved in Duck 94 click here.