DENSITY AND TEMPERATURE COASTAL WATERS 135 



SESSIONAL PAPER No. 38a 



showed a density of 1-0207, almost as high as that in Northumberland channel 

 (1 -01216), but the water on the Nanaimo river side of the boat passage was only 

 1-0014. The temperature was not materially different in the different cases. It 

 was just about low slack water at the time the readings Avere taken and there was 

 about a foot of water in the boat passage. 



It will require much investigation to find out at all definitely the relative value 

 of the influence exerted by the local streams and of the Fraser river in various 

 localities at different times of the year. While we are of the opinion that during 

 the summer months the larger portion of the variation in surface density is due to 

 the Fraser river water, even in Departure bay, we have not sufiicient data at present 

 to offer any opinion concerning conditions during the remainder of the year. 



From the figures in Appendix B it would appear that the coastal waters between 

 Vancouver island and the mainland can be divided roughly into three large areas: 

 (i) north of Seymour narrows and the Yucultas; (ii) between these and the chain 

 of islands extending southeast from Gabriola island and forming the southern limit 

 to the strait of Georgia; (iii) southwest and south of this boundary. It will be 

 seen from the map that the second section is a relatively closed area. Of these 

 areas (i) and (iii) have an average density distinctly higher than (ii). In the first 

 area the value increases as the open waters of Queen Charlotte sound are approached. 

 In the third area a similar result is noticeable as Haro strait and the strait of Juan 

 de Fuca are neared. The figures indicate an average for (i) and (iii) of the order 

 1-021 to 1.0'2'2, and for (ii), 1-018 to 1-019. The difference is due to the addition 

 of fresh water at different points already referred to. 



The variations of temperature readings can be attributed to: (i) the influence 

 of fresh water (Howe sound) ; (ii) influence of ocean waters (cf. the lowering of 

 temperature on nearing Queen Charlotte sound, Haro strait, Barkley sound, etc.; ; 

 (iii) special effects produced in shallow waters (indicated by readings at the station, 

 and true for all similar bays) attributable to the influence of air temperatures and 

 shown by the comparison of air and water temperatures on the curves in fig. 1. In 

 the series of readings taken in Departure bay and shown in fig. 1 generally a rise 

 in density is accompanied by a fall in temperature, indicating very frequently, 

 admixture of surface water with water from a lower depth. 



These readings both of density and temperature refer only to surface water. The 

 type of variation with depth is shown in fig. 2. It was possible to take but one set 

 of readings of this nature during the time the other readings tabulated were taken, 

 all of the others being taken later. These readings, quoted in Appendix C, give a 

 chance for comparison of water from the deeper part of the strait with that from 

 the shallower bays and channels. They show plainly that the main portion of the 

 variation in both density and temperature occurs in the five fathoms nearest the 

 surface. Below this there is a very slight gradual increase with the depth until 50 

 fathoms, after which there appears to be little or no variation down to 100 fathoms, 

 the greatest depth at which samples were taken. Below 50 fathoms there seems to be 

 little difference in either density or temperature in different localities in readings 

 taken at or near the same time. The set of readings taken in Departure bay on 

 October 14, after heavy rains had swelled the local streams, that taken in the open 

 strait, east of Breakwater island, on October 26, and that taken at Sand heads on 

 October 2, show the sudden change from water of low density at the surface to water 

 of greater density 5 fathoms down. 



For any one set of readings the curve is not quite regular, due to cross currents, 

 irregularity of bottom, etc., but it is quite possible, if a number of sets could be taken 

 during a period of settled weather, that the average would give a fairly regular curve. 

 Even the curve made from the average of those here recorded gives one which is quite 

 satisfactory. A very much extended series of readings is required for any definite 

 statements in the matter. 



