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The oceanography of Chatham Sound, British Columbia Trites, Ronald Wilmot

Abstract

A detailed analysis of data taken on an oceanographic survey of Chatham Sound in the spring and summer of 1948 is presented. The primary purpose of the survey was to determine, if possible, whether there was any obvious characteristic of the water in the region which could be correlated with the known migration of salmon to the spawning grounds up the Nass and Skeena Rivers. The path taken by the fresh water between the river mouths and the more open waters of Dixon Entrance and Hecate Strait is shown to depend on the volume of fresh water discharged from the rivers. The rivers reach their peak discharge in late May or early June and during this period the amount of fresh water in the sound is 3 - 4 times the average. The effect of tides on the distribution of properties is also discussed. Anchor stations occupied for periods varying from 10 - 40 hours indicates that as a rule there is a good correlation between tidal, salinity, and temperature cycles. Dynamic calculations giving velocities, volume and fresh water transports have been made. During normal river discharge conditions, the agreement with the observed velocities, and fresh water discharge determined from gauge readings, suggests that even in these coastal waters there is an approximate balance between the horizontal pressure gradients and the coriolis force associated, with the motion. Stations at the mouth of Portland Inlet exhibit an apparent balance at all times which suggests that transverse inertial and fractional forces are slight compared with the transverse pressure gradient and coriolis force. Evidence of a variation in geopotential slope as the result of tidal variation is proposed. The relatively large tidal amplitudes together with the wide and rapid fluctuations in river discharges make it exceedingly difficult to obtain reliable synoptic observations over the entire Sound.

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