134 DEPARTMENT OF THE NAVAL SERVICE 



6 GEORGE V, A. 1916 



the bay. Hence tLe local streams flowing directly into the bay could not have caused 

 the largest lowering of density observed during the whole summer. 



(2) On July 10 a much lower reading was obtained outside Gabriola pass, in 

 the open strait, than that obtained inside. The tide was then flowing east through 

 the pass. This change could therefore only be produced from some source on the 

 opposite side of the strait, i.e., the Fraser river. 



(3) The greatest fluctuation was observed about the end of June, when the 

 water was highest in the Eraser river. Preceding fluctuations were smaller, succeed- 

 ing fluctuations gradually diminished, corresponding to the gradually diminishing 

 volume of water poured out by the Fraser river. 



Fresh water, being less dense, tends to remain at the surface in calm weather, 

 and we consider that the variations in density which we have observed at the Station 

 are caused by large bodies of relatively fresh water travelling directly across the 

 strait from the Fraser river (this does not necessarily mean a noticeably rapid 

 movement). Actual observations off the Sand Heads lightship in calm weather show 

 that with flood tide the Fraser river water is taken in a strong current to the north- 

 ward, but when the ebb starts it is carried more towards Gabriola pass, Cowichan 

 gap and southward, hence under favourable conditions it is readily conceivable 

 that occasionally bodies of surface water may reach Departure bay comparatively 

 unchanged. With high winds and heavy seas the mixture of fresh water with the 

 deeper salt water naturally takes place more readily and rapidly, while strong cur- 

 rents travelling north or south in the strait would also prevent the fresher water 

 from reaching Departure bay. Since even during the summer months one or more 

 of these disturbing factors is usually in evidence the readings are as a whole nearer 

 the maximum observed than the minimum. 



Our conclusions with regard to Departure bay are strengthened by the short 

 series of readings made in Howe sound and in Vancouver harbour (August 19). 

 The former were attributable to the fresh water poured into Howe sound by the 

 Squamish river, since had the Fraser river been responsible similar small figures 

 should have been obtained for Vancouver harbour. With these results may be com- 

 pared those for Alberni canal and Barkley sound, which are quite similar and 

 similarly explained, since large bodies of fresh water flow into the canal at the head, 

 at Uchucklesit, and elsewhere, and, while higher values were obtained for the middle 

 of the sound, they were still lower than those for normal ocean salinity. 



These results indicate that from every large inlet along the coast a similar 

 result may be expected. 



Readings taken later than those here recorded show that with the autumn rains 

 and the consequent large increase in flow of the local streams, the effect of these on. 

 the surface water becomes strongly predominant. To quote a single instance: 



A narrow neck of land terminating in Jack point, separates the flat at the mouth 

 of the Nanaimo river from Northumberland channel. A row-boat passage is cut 

 through this neck about a mile from the point. On the east side, this passage opens 

 into what is called a lagoon although a large portion of it never dries, and this 

 lagoon is directly connected even at low-tide with Northumberland channel by two 

 passages, one of which is quite near the east entrance of the boat passage. On 

 October 19, after heavy rains, a current from the Nanaimo river passed out into 

 the strait in such a way that there was a distinct margin visible, running north- 

 easterly from Jack point, separating it from the surface waters of Northumberland 

 channel. A sample taken just within the current and about a quarter of a mile 

 from Jack point gave a density reading of 1-0129, while a sample taken but a few 

 yards away, outside of the margin of the current, had a density of 1-0216, and on 

 the other hand a sample taken off MacKay point, Newcastle island, about 2i miles 

 away but in line with the current, had a density of 1-0164. The water in the lagoon 



