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Saanich Inlet

Physical Description

Length: 24 km
Maximum Depth: 225m
Major Basins: one
Sill Depth: 70m, located at the mouth
Surface Area 65 km2

Map and Section

Saanich Plan View Depth Profile

Runoff

There are no major rivers discharging along the shores of Saanich Inlet as the total watershed area for Saanich Inlet is relatively small (~400 km2).  The mean annual discharge for the Goldstream River and Shawnigan Creek combined is less than  3 m3 s-1 (Drinnan et al 1995).  However, the Cowichan River, which discharges outside the inlet into Satellite Channel, is a significant source of freshwater (mean annual discharge ~ 50 m3 s-1) in the immediate vicinity of the inlet.  The local streams and the Cowichan River have the highest flow rates in the winter months and minimum during the drier summer months. Within the Georgia Basin, the Fraser River is by far the major source of freshwater.  The Fraser River flow is highly seasonal and unlike the Cowichan River its peak discharge occurs in late May and June as a result of the snowmelt in the interior of the province.

Deep Water Renewal Process

For most of the year the deep waters are devoid of dissolved oxygen or anoxic, and hydrogen sulphide (H2S) is often detected near the bottom.  In the late summer and early fall, the density of waters in Haro Strait and Satellite Channel are sufficiently high that some oxygenated waters spill into the deep basin of Saanich Inlet (Anderson and Devol 1973). The amount of renewal or replacement of the inlet deep waters varies from year to year. The details of the renewal process are controlled by the neap - spring variation in tidal mixing in the energetic tidal passages outside Saanich Inlet (Stucchi and Giovando 1984). During neap tides when tidal mixing is at a minimum, dense renewal water in Haro Strait is present at or above sill depth and able to traverse Satellite Channel and arrive at the mouth of Saanich Inlet with sufficiently high density to flow into the deep waters of the inlet. During spring tides, tidal mixing is strong and the depth of the renewal water is below that of the inlet's sill depth. Immediately after a renewal, the deep waters have low but detectable amounts of dissolved oxygen, but after a few months the deep waters return to anoxic conditions.

Time Series of Deep Water Properties

Temperature
  • the time series of deep water temperatures show an overall increase of about 1C since the 30's and an increase of 0.5C since the mid 70's.
  • no relationship with occurrence of El Nino

Salinity
  • no trend apparent
  • unusually low salinities in 1979-1980 coincident with cold temperatures in Strait of Georgia

Dissolved Oxygen
  • Dissolved oxygen usually absent (anoxic) or very low
  • Periods of very low dissolved oxygen e.g. late 70's and early 80's and late 90's