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Indian Arm-Burrard Inlet

Physical Description

Length: ~50 km
Maximum Depth: 220 m
Major Basins: one main deep basin
Sill Depth: shallow (15m to 25 m) and 15 km long sill region through Burrard Inlet/Vancouver Harbour

Map and Section

Runoff

Pickard (1961) lists Indian Arm as a low runoff fjord having only small rivers and streams. De Young and Pond (1988) report that the average annual freshwater flow into Indian Arm is about 42 m3 s-1 of which about half is discharged by the Buntzen power plant. The Indian River which is located at the head of the inlet is a relatively small river and contributes about 12 m3 s-1. The Seymour and Capilano Rivers are also significant sources of freshwater that discharge 15.9 m3 s-1 and 19.8 m3 s-1 respectively into Burrard Inlet. Gilmartin (1962) describes the flow of freshwater into Indian Arm as having a bimodal cycle: a late spring to early summer peak caused by melt waters and a fall to winter peak caused by direct runoff from rainfall and regulated flow from the Buntzen power plant.   

Deep Water Renewal Process

De Young and Pond (1988) have studied the deep water renewal process and describe the intrusions of denser water into Indian Arm as quasi-periodic. In the years when renewals take place, they occur late in the year coincident with the timing of the highest density at 100m depth in the Strait of Georgia. Given the long and shallow sill region in Burrard Inlet, the spring-neap variations in tidal mixing over the constricted sill control the timing of the inflows of denser waters into Indian Arm. The reduced mixing during neap tides in combination with periods of low run off permit dense waters from outside to traverse the sill in Burrard Inlet with comparatively small reduction in density. During spring tides or periods of high run off the dense water from outside is vigorously mixed and its density sufficiently reduced to prevent deep water renewal in Indian Arm. 

Time Series of Deep Water Properties

Temperature
  • large amplitude temperature variations (~3 C) and saw-tooth renewal cycle: low deep water temperatures at time of renewal follow by slow and prolonged (several years) warming. 
  • ~1.5 C increase in the cold water phase of the renewal cycle: in the first half of the time series deep water temperatures after renewal were in the 6 to 6.5 C range; after the 1980's deep water temperatures after renewal were in the 7.5 to 8 C range. 
  • warmest deep water temperature observed in 1999, more than 1C higher than any previous observation. relatively sparsely sampled and time series has many  multi-year gaps

Salinity
  • there are many multi-year gaps in this time series
  • saw-tooth renewal cycle: relatively high deep water salinity at time of renewal followed by one to 3 year decay in salinity.
  • no trend apparent

Dissolved Oxygen
  • very large amplitude dissolved oxygen variations (0 to 4.5 ml/l): high deep water dissolved oxygen at time of renewal follow by rapid decay to near zero concentrations.
  • very low dissolved concentrations at times
  • no trend apparent