STATIONS 



OUTER BAY 

 6 7 



INNER BAY 

 8^6 



HIGH TIDE 



Figure 12. — Dissolved oxygen (ml./l.) of Outer and Inner Bays, Traitors Cove, Alaska, August 1963. (Time of surveys: 

 Outer Bay-- 1728- 1305 August 21. Inner Bay— low tide, 0945-1215 August 22; high tide, 1525-1710 August 22.) 



on low tide (after an ebb). On the October 

 survey, local runoff onboth tides was sufficient 

 to cause stratification in Inner Bay about half 

 a kilometer from the falls. 



The actionof the water flowing over the 55-m. 

 sill at the outer entrance of Outer Bay is dif- 

 ferent from that of the action of water at the 

 sill at the constriction. The 55-m. sill does 

 not cause strong turbulence but merely blocks 

 the entrance of water from Behm Canal into 

 Outer Bay at depths greater than 55 m. For 

 example, in April and August the 75-m. water 

 in Behm Canal was more saline and contained 

 less dissolved oxygen than water at the same 

 depth in Outer Bay. Being more saline and 

 hence more dense, the water at 75 m. in Behm 

 Canal cannot rise up and pass over the 55-m. 

 sill to enter Outer Bay. On the other hand, 

 Behm Canal water at depths of 55 m. or less 

 moves easily into Outer Bay. The density of 

 the deeper (greater than 55 m.) water of 

 Outer Bay is thus governed by the density of 

 the water at 55 m. in Behm Canal. If denser 

 water were to appear at or above the sill depth, 

 it would flow over the sill and replace the 

 bottom water of Outer Bay. 



The deep water of Outer Bay had general 

 seasonal trends in its properties. From April 

 to October the temperature of this water de- 

 creased, the salinity increased, and the con- 

 centration of dissolved oxygen decreased. (The 

 only exception to this pattern was salinity, 

 which was slightly less in October than August.) 



These trends in oceanographic properties 

 are results of wind-driven movements of 

 surface water along the coast. In winter, 

 southeasterly winds are strong and persistent. 



They force the coastal surface waters shore- 

 ward by Coriolis deflection and cause a down- 

 welling along the coast. In summer, the south- 

 east ■winds relax and may shift to northerly. 

 This change in wind relaxes the onshore trans- 

 port and may cause slight offshore transport 

 of surface waters. Reduced onshore transport 

 in turn allows a moderate upwelling of deep 

 waters. This upwelled water is cold, saline, 

 and low in oxygen, and gradually flows into the 

 coastal inlets at depth. It is the slow intrusion 

 of this water that causes the decrease in 

 temperature, increase in salinity, and decrease 

 in dissolved oxygen in Outer Bay from April to 

 October. The properties of the deep water of 

 Auke Bay near Juneau, Alaska, were attributed 

 to the inflow of water at depths for sinnilar 

 reasons (U.S. Federal Water Pollution Control 

 Administration, 1966), 



TIDAL EFFECTS 



In addition to its effect on circulation in the 

 estuary, the constriction influences the tidal 

 regime of Traitors Cove in four major ways. 

 First, the linnited capacity of the constriction 

 restricts the volume of water that can move 

 into and out of Inner Bay during a tidal cycle 

 and hence reduces the tidal range of Inner Bay 

 with respect to that of Outer Bay. The tide 

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

 list a mean tidal range of 3.44 m. in Inner 

 Bay and 4.11 m. in Outer Bay. 



Second, the constriction causes the ebb tide 

 in Inner Bay to last longer than the flood tide. 

 On our surveys the ebb and flood tides averaged 



11 



