26 



U. S. COAST AND GEODETIC SURVEY 



figuration of the harbor, and the currents observed during the later 

 surveys may actually differ from those of earlier surveys. Many of 

 the small irregularities, however, may be the result of accidental con- 

 ditions prevailing at the time of the observations. Only in a few 

 instances did the observations at any station cover more than two 

 days, and in many cases the period was one day or less. There was 

 therefore no opportunity to average out any accidental errors that 

 might have resulted from special conditions prevailing on the day or 

 days on which the observations were made. 



The tidal currents have access to Boston Harbor through two main 

 channels, President Roads and Nantasket Roads. In general the 

 times of the current phases do not differ greatly in different parts of 

 the harbor. The slack before flood occurs near or soon after the time 

 of low water and the strength of flood from three to four hours later. 



Fig. 12.— TYPICAL CURRENT CURVES FOR STATIONS D46. W13, AND W16 



The slack before ebb occurs near the time of high water and the 

 strength of ebb from three to four hours later. 



The Narrows.— The Narrows (see fig. 7) is a channel leading into 

 Boston Harbor from the southeastward, with Lovell Island on the 

 northeast and Georges Island and Gallups Island on the southwest. 

 In this locality the main flood and ebb streams appear to flow westerly 

 and easterly, passing between Georges Island on the south and Lovell 

 and Gallups Islands on the north. In that part of the Narrows 

 lying between Lovell and Gallups Islands the currents appear to be 

 somewhat irregular, as indicated by the observations made at the 

 single station D46 in the year 1848.^ Tliis is illustrated in Figure 12, 

 in which a typical curve prepared from the current observations of 

 1848 at station D46 is compared with corresponding curves for sta- 

 tion W13 between Lovell and Georges Islands and for station W16 

 at the entrance to President Roads. It should be kept in mind. 



