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(Waddell et al. 2001). When tidal currents are sufficient to transport fine sand as bedload, 

 some fine materials may be winnowed leaving a lag deposit of sands and shells too large for 

 transport. Semi-diurnal tidal currents at the NLDS appear to be strong enough to rework 

 unconsolidated surface sediments through this process until surface sediments have a lag 

 deposit of sand or shells. However, fine surface sediments are also bound by biological 

 activity and may be remarkably resistant to erosion while the organisms are alive. 



The result of the surface sediment winnowing process includes six characteristics in 

 REMOTS® images: shell lag, winnowed surfaces, disturbed amphipod tube mats, physical 

 boundary roughness, and sand-over-mud stratigraphy. There are three potential causes for 

 surface disturbance of tube mats: 1) predator foraging; 2) microbial decomposition 

 following the abandonment of the tubes; and 3) disturbance from either trawling or a 

 temporary increase in near-bottom turbulence or current velocity. When tubes are 

 abandoned they are much more susceptible to physical transport by currents. 



Surface sediment reworking at NLDS appears to be limited to winnowing of fines 

 accumulated during the summer in areas where shell lag armors the surface. The shell lag 

 may form in the fall and winter during periodic storms, then again be covered with tube mats 

 that bind finer sediments in the spring and summer. This seasonal response is observed to 

 be consistent between reference areas and disposal areas, and results in a cyclic fluctuation 

 between seafloor surfaces covered with muddy tubes to surfaces with clean shell and fine 

 sand. This seasonal cycle may open opportunities for settlement of recolonizing benthic 

 organisms and explain their patchy distribution at reference areas. Any deposition of fresh 

 dredged material will begin to be exposed to this cycle and will eventually acquire tubes or 

 attached organisms depending on grain size. In general, there is evidence of fall-winter 

 winnowing in many areas of NLDS and spring-summer deposition of finer materials. As 

 shown by the long-term stability of mounds at the site (see above), this cycle does not appear 

 to result in any significant net loss or gain of sediment. 



4.2 Seawolf Disposal Mound 



The Seawolf Mound was developed during the 1995-1996 dredging season 

 (September-May). Disposal of maintenance work (material dredged within an authorized 

 depth) and new work (material dredged to a newly authorized depth) resulted in a total 

 estimated disposal volume of 877,512 in of sediments. 



The first portion of the project included an approximate barge volume of 306,000 m 

 of UDM originating primarily from the New London Naval Submarine Base and the Thames 

 River navigational channel and 800 m' of UDM from the Mystic River. These materials 

 were placed at the "Navy" buoy prior to capping operations (Figure 1-3). Following the 

 placement of UDM, an estimated barge volume of 556,000 m' of CDM dredged from the 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



