Tidal_PAD_V1_Sec4.pdf - Snohomish County PUD

Snohomish County PUD –Pre-Application Document
4 – Existing Environment
4.3.1.4 San Juan Channel
San Juan Channel is one of the three primary passageways from the Strait of Juan de Fuca to the
Strait of Georgia. The channel is 21 km long and constricts overall from north to south, reaching
its narrowest point (1200 m) at the approximate midway point (Polagye et al. 2007).
The
maximum surface current velocity has been calculated to be 2.6 m/s, based on data obtained from a
nearby station (NOAA 2007a). The Coast Pilot (NOAA 2007) reports severe rip and eddy currents
occur in the southern portion of the San Juan Channel.
Table 4-5. San Juan Channel site parameters (Polagye et al. 2007)
Site
Channel Width
Average Depth (MLLW reference)
Deepest Point
Average Cross-sectional Area
Maximum Surface Current
1200 m
63 m
135 m
76,450 m
2.6 m/s
2
4.3.1.5 Deception Pass
Approximately 3.2 km in length, Deception Pass separates Whidbey and Fidalgo islands. The
channel becomes increasingly narrow as it approaches its middle, reaching a minimum width of
approximately 350 m south of Pass Island (Polagye et al. 2007). The decreased cross-sectional
area causes an increase in velocity by a factor of five compared to the eastern and western portions
of the channel and produces strong eddies along the shoreline. Current velocities within the pass
have been reported in excess of 4.4 m/s (8 knots) (NOAA 2007a).
Table 4-6. Deception site parameters (Polagye et al. 2007)
Site
Channel Width
150 m
Average Depth (MLLW reference)
30 m
Deepest Point
40 m
Average Cross-sectional Area 4,760 m 2
Maximum Surface Current
4.4 m/s
4-22 January 31, 2008