SOME OBSERVATIONS OF TURBIDITY IN BRITISH COLUMBIA INLETS1

Abstract

Measurements have been made by a light scattering method of the optical turbidity of the waters in some typical British Columbia inlets with depths to 700 m. (The optical turbidity here used is the extinction coefficient or fractional reduction in light intensity per meter length due to scattering.) The major contribution to the turbidity in the large inlets is the minerogenic material brought in by rivers. Therefore those inlets with rivers originating in glaciers exhibit the highest turbidity values and there is a marked seasonal variation. In the surface layers, values recorded for turbidity range from 0.2 m−1 in winter to 35m−1 in summer with a marked decrease from head to mouth of the inlet. The main body of water in an inlet is usually fairly uniform in turbidity at 0.1 to 2m−1. (For comparison, double distilled water has a turbidity of 0.024m−1 for light of wavelength 5460 a in air.) Particle sizes average about 20µ diameter in summer and 8µ in winter, with little material less than 2µ in diameter. An increase in turbidity near the bottom is common and may be due to tidal currents but evidence suggests that turbidity currents originating at the inlet head may be common and contribute to the bottom water turbidity.