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Howe Sound

Physical Description

Length: 44 km
Maximum Depth: 285 m
Major Basins: one basin
Sill Depth: 73 m, located 18 km from the head, at Defence Islands

Map and Section

Runoff

Howe Sound is a high runoff fjord and receives more freshwater discharge than some of the longer and larger fjords (Bute and Knight). The Squamish River with an annual mean discharge of 300 m3s-1 is the principal source of runoff to this fjord. Discharging at the head of the fjord, the Squamish River and its tributaries account for approximately two-thirds of the estimated 460 m3s-1 total freshwater discharge to Howe Sound (Trites 1955). The watershed for the Squamish River and tributaries which totals about 3,600 km2, drains both interior snow and ice fields and lower elevation coastal  regions. Like Knight and Bute inlets the maximum discharge occurs during the summer as the interior and higher elevation snow and ice fields melt.  However, Howe Sound experiences a secondary and highly variable discharge maximum in the late fall because of precipitation falling mainly as rain. Minimum flows are in late winter and early spring when precipitation is mainly snow and is stored at the higher elevations.  

Deep Water Renewal Process

Bell (1973) examined the deep water renewal process  in Howe Sound using data collected from 1959 to 1973 and described the deep waters of Howe Sound as undergoing aperiodic  renewals.  Exchanges of the deepest water occur every 3 to 4 years, and the renewals occur in the winter coincident with the seasonal density maximum in the outside waters (Strait of Georgia) at sill depth. According to Bell (1973), the deepest renewals were also related to strong outflow winds (Squamish winds) associated with outbreaks of the cold air mass over the interior. Exchanges of the intermediate deep waters are more frequent and often occur in late spring and  appear at times to be triggered by the Squamish River freshet.

Time Series of Deep Water Properties

Temperature
  • relatively sparsely sampled and time series has many  multi-year gaps
  • ~1 C increase from mid 70's to present
  • no clear trend apparent  the first half of the time series.

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