34 



BIOLOGICAL REPORT 31 



41 u N 



41 °30'N 



40 30' N 



73 30'W 73 W 72° 30'W 72° W 71° 30'W 71°W 70° 30'W 



Fig 3.5. The southern New England Bight From Spaulding and Gordon (1982). 



current speeds are many times higher than the av- 

 erage speeds within the central (20-30 cm/s), head 

 (<1 cm/s), or near the mouth (50 cm/s) of Buz- 

 zards Bay (Fig. 3.6). With less important conse- 

 quences, differences in tidal phase and amplitude 

 create strong currents through the Cape Cod Ca- 

 nal joining Buzzards Bay and Cape Cod Bay (Fig. 

 3.6). Mean tidal range in Cape Cod Bay is 2.8 m 

 and averages 1 .2 m in Buzzards Bay. The estimated 

 turnover time of water within Buzzards Bay is about 

 10 days ( Sumner etal. 1913; Moore 1963; Signell 

 1987). 



Tidal current is the most important factor influ- 

 encing sediment pattern, and two major currents 

 within the bay proper predominate during ebb and 

 flood tides. One current, running parallel to Naushon 

 Island and terminating near Woods Hole, reaches 

 0.6 to 0.8 knots; the second is about 1 1/2 km 

 wide and runs along the northwest shore of Buz- 

 zards Bay, with core velocities of about 0.6 knots. 

 Midbay surface currents are weak, generally less 

 than 0.4 or 0.5 knots, with no defined directional 

 flow (Fig. 3.6). Although currents running between 

 the islands do not extend far into the bay, they are 

 important to bottom sediments near the islands form- 

 ing sand protuberances into the bay The well-sorted 

 sediments found along the shore north of Woods 

 Hole result from strong currents in this area ( Moore 

 1963). The distribution and sorting patterns of 



shallow water sands are directly related to tidal cur- 

 rents, with accumulation of silts in deeper waters 

 the result of bathymetric entrapment and less dy- 

 namic current activity (Moore 1963). Wind is also 

 identified as a major factor in sediment composi- 

 tion because wind-driven wave activity creates high- 

 energy waves in shallow areas of the bay, eroding 

 areas unprotected by headlands. This erosion is in- 

 dicated by a general coarseness of sediments found 

 in these areas and the presence of greater accumu- 

 lations of fine sediments on the southwesterly than 

 on the northwesterly margins of harbors and coves 

 (Driscoll and Brandon 1973). 



Although tidal forcing is the dominant factor in 

 the circulation within Buzzards Bay, other param- 

 eters influence localized currents, especially in the 

 more restricted area near the head and the more 

 sheltered harbors and embayments ringing the bay. 

 Of the meteorological factors, local wind conditions 

 are the most significant; however, nonlocal winds 

 and atmospheric pressure are also important. Winds 

 in this region are generally northwesterly in winter 

 and southwesterly in summer, with local sea breezes 

 often augmenting the southwesterly influence dur- 

 ing summer months (Fig. 3.7). Major storms, how- 

 ever, often blow from the north or northeast, roughly 

 along the long axis of the bay. In addition, varia- 

 tions in nonlocal wind and atmospheric pressure can 

 lead to a rise and fall of average bay level. The 



