430 and 320 minutes in Inner Bay and 372 and 

 382 minutes in Outer Bay. 



Third, the constriction causes the times of 

 high and low slack waters in Inner Bay to lag 

 behind those of Outer Bay. The tide tables 

 (U.S. Coast and Geodetic Survey, 1965) list 

 high and low waters in Inner Bay as 21 and 88 

 minutes behind those of Outer Bay. These lag 

 times are approximate and depend on the height 

 of the tide in question. For example, ona neap 

 tide (3-4 m. range) at Traitors Cove the times 

 of high and low water were both 40 to 50 

 minutes later in Inner Bay than in Outer Bay. 

 On spring tides (5-6 m. range) the times of 

 high and low slack waters were 50 to 70 and 

 90 to 120 minutes later in Inner Bay than in 

 Outer Bay. These data, which were provided by 

 personnel of the Bureau of Commercial Fish- 

 eries Biological FieldStationat Traitors Cove, 

 also show that the duration of the ebb becomes 

 greater as the tidal range increases. 



Fourth, the constriction creates ex- 

 ceptionally strong tidal currents that affect the 

 distribution of bottom sediments in its vicinity. 

 Jay Quast (Auke Bay Biological Laboratory), 

 who made a series of scuba dives in the area 

 near the constriction in Outer Bay in April 

 1964, found that the floor of the constriction 

 was bare rock and was free of sediments and 

 debris, probably because of tidal currents. He 

 noted a depression floored with bare rock and 

 large boulders at the foot of the falls in Outer 

 Bay; the bottom graded into flat cobbles, gravel, 

 and finally sand at greater distances from the 

 constriction. The steep rock shore across from 

 the constriction has undercut ledges pre- 

 sumably cut by currents of the ebb tide. Fig- 

 ure 13 is a sketch of Quast's observations of 

 the bottonn sediments and topography. 



SURFACE CURRENTS 



Between 1964 and 1965. drifts of 70 surface 

 drogues were followed under various condi- 

 tions of wind and tide to determine the general 

 patterns of surface currents. The times and 

 positions of these drogues were used to calcu- 

 late current velocities. Because the positions 

 of the drogues were not determined precisely, 

 the calculated velocities are probably accurate 

 to about 20 percent- -probably adequate when 

 one considers the highly variable nature ofthe 

 surface currents. Most of the data are from 

 observations of 1-m. drogues, although a few 

 observations were nnade with 35-cm. drogues 

 very near shore. Therefore, the observations 

 generally represent currents in the top 1 m. of 

 water. 



Because the surface currents obviously de- 

 pended on tidal condition, I present the patterns 



for ebb and flood tides (figs. 14 and 15). In 

 preparing the figures, I compensated for the 

 effects of wind by reducing the apparent velocity 

 of the currents by about 20 percent when the 

 wind and tide were in the same direction, and 

 increasing the velocity by about 20 percent 

 when the wind opposed the tide. 



Currents in both bays of Traitors Cove were 

 predominantly seaward during the ebb tide and 

 landward during the flood tide. Minor exceptions 

 were eddies formed near shore in the lee of 

 land projections during both tides. In Outer 

 Bay, currents were weaker than in Inner Bay 

 and occasionally appeared more dependent on 

 wind than on tide. In both bays, currents near 

 high and low stages of the tide were generally 

 weak (less than 5 cm. /sec), variable, and de- 

 pendent on winds. 



At the head of Inner Bay, currents during 

 the flood tide had speeds less than 1 5 cm. /sec. 

 and were normally directed up-inlet; in con- 

 trast, during the ebb tide currents were directed 

 down-inlet and had speeds of 20 to a maximum 

 of 27 cm. /sec. During both tides currents ap- 

 peared to be strongest on the southern shore. 

 Three or more eddies appeared during the 

 ebb along the north shore of Inner Bay. 



Pronounced gyres formed at the foot of Inner 

 Bay during the flood tide and at the head of 

 Outer Bay during the ebb. These gyres rotated 

 counterclockwise; nnaximunn velocities were 

 20 to 40 cm. /sec. Flow through the constric- 

 tion was turbulent and, although not measured, 

 was very fast. 



During flood tide, currents in Outer Bay 

 were generally landward and their speeds 

 were 10 to 25 cm. /sec; during the ebb, cur- 

 rents were variable in direction and weaker. 

 One series of drogues followed irregular and 

 rotating paths. Another series released during 

 an ebb tide moved landward rather than sea- 

 ward because of an up-channel wind--the 

 current was too weak to overcome the effect 

 of the wind. 



SOME EFFECTS OF THE SURFACE 

 CURRENTS 



At the head of Inner Bay the surface water 

 is slowly backed up the river during flood tide 

 and released rapidly • during ebb tide. This 

 motion has several important consequences on 

 the oceanography of the estuary. 



First, the fresh-water layer on the surface 

 flowed seaward rapidly during the ebb tide and 

 caused surface salinity to be lower at the tinne 

 of low tide than at high tide (figs. 6, 7, and 9). 

 This situation was not apparent in August 

 during the period of very low runoff (fig. 8). 



12 



