end of Kalgin Island, and at the mouths of Knik and
in water level response to the tides. The tidal range var-
Turnagain Arms (NOS 1994, Nelson 1995). All of
ies greatly depending on location, as shown in Figure
Turnagain Arm experiences very strong currents, and
20. From north to south the mean water level fluctua-
the tide often comes in as a tidal bore with a wave
tion varies from 3.47 m (11.4 ft) at Kennedy Entrance to
height of up to 1.8 m (6 ft) (NOS 1994).
7.89 m (25.9 ft) at Anchorage. The greatest tidal ranges
The extreme tidal changes that occur in Cook Inlet
occur during spring tides, when the mean ranges are
are exceeded in magnitude only by those occurring in
exceeded by more than 1.5 m (5 ft). Extreme tidal
the Bay of Fundy in eastern Canada. The phenomenon
ranges at the upper ends of Knik and Turnagain Arms
is mainly due to resonance. That is, the Inlet water's
are as high as 12 m (39.4 ft) (Rappeport 1982, Nelson
natural period of oscillation closely matches that of the
1995). Large east-to-west tidal differences are caused
astronomical tides (Raney 1993, Pearce et al. 1999). The
by the Coriolis effect, which produces higher tide lev-
tides are semi-diurnal in that there are two high and two
els along the eastern shoreline. For example, the mean
low tides of unequal height (a "diurnal inequality") in
tidal range is 3.84 m (12.6 ft) at Oil Bay and 4.79 m
each lunar day of 24 hours and 50 minutes. From the
(15.7 ft) at Homer, which are equal in latitude but on
entrance to the head of the Inlet, there is a 4.5-hour lag
opposite sides of the Inlet.
58
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