Dredging Operations Technical Support Program. Evaluation of Clamshell Dredging and Barge Overflow, Military Ocean Terminal Sunny Point, North Carolina

The 1987 maintenance dredging for the Military Ocean Terminal, Sunny Point MOTSU, project was performed by mechanical clamshell dredge, with material placed in barges and transported to an open-water ocean disposal site. This work was the first major use of mechanical clamshell equipment in North Carolina. Since resource agencies were concerned with operational procedures for clamshell dredges from the standpoint of potential resuspension of sediment during the dredging process and overflow of barges to increase load, a field study was conducted to give site-specific information on the MOTSU clamshell operation. Barge loading characteristics for both overflow and nonoverflow conditions and potential gain in load due to overflow were determined for three barge loads. The load gained during the period of overflow varied from 1.4-3.2, with corresponding times of overflow from 9 to 28 min. The load gained by filling the disposal barge in one test from a level 1 ft below the coaming to the point of overflow was approximately 6.9. This, added to the load gained during overflow, corresponded to a total increase in load of 10.1 for this test. The suspended solids concentration of the overflow increased with time of overflow. Plumes from the clamshell bucket spillage were observed to be patchy in nature, were advected downcurrent, and mixed with the ambient water downstream. At this site, suspended sediment levels observed during dredging and overflow probably did not produce any significant adverse environmental effect upon eggs, larvae, juveniles and adult forms of estuarine-dependent fish and shellfish species.