Spreading of thin layers of cap material over large areas can also be accomplished by gradually opening a conventional split-hull barge while underway by tow. Use of barges for spreading cap materials may not be suitable in shallow water depths, because of the water depths needed for barge draft, door openings and consideration of the propeller wash from tug boats. Hydraulic Washing of Coarse Sand Figure 11 . This technique produces a gradual buildup of cap material, prevents any sudden discharge of a large volume of sand, and may be suitable for water depths as shallow as 10 feet or less. Where granular cap material is excavated by a hydraulic dredge or transported in a slurry form through a pipeline, spreading placement capping operations can be easily accomplished with surface discharge by an energy dissipating device such as a baffle plate or sand box attached to the end of the pipeline.
Hydraulic placement is well-suited to placement of thin layers over large surface areas.
Figure 12 . Spreader place for hydraulic pipeline discharge. First, as the pipeline discharge strikes the plate, the discharge is sprayed in a radial fashion and the dscharge is allowed to fall vertically into the water column. The decrease in velocity reduces the potential of the discharge to erode material already in place. Second, the angle of the plate can be adjusted so that the momentum of the discharge exerts a force which can be used to swing the end of the floating pipeline in an arc.