SUBMARINE BORROW PITS AS CONTAINMENT SITES FOR DREDGED SEDIMENT.

Sand-mining operations in New York Harbor have left several large pits on the harbor floor. Two of these were examined. The pits are typically 7-10 m deeper than the ambient seafloor and have side slopes of between 10 and 25 degree . The technology is available to deposit dredged sediment into the pits. Hopper dredged disposal operations may be used to forecast the short-term behavior of the dredged sediment during the emplacement process. The side slopes of the pits in New York Harbor should be sufficient to prevent the spread of dredged sediment outside of the pit until the pit is about half filled. The dredged-material deposit will have low side slopes ( less than 3 degree ). The most effective form for the deposit would be a truncated cone or pyramid in order to maintain a shallow trough around the inside edge of the pit. While the thickness of the mud deposit is small compared to the depth of the pit, the naturally high sedimentation rate will enhance containment, alternatively the surface might be covered, or capped, with sand.