Page 84 - (DK) Ocean - The Definitive Visual Guide

82 TIDES AND WAVES

ATLANTIC OCEAN NORTHEAST ATLANTIC OCEAN EAST PACIFIC OCEAN NORTHEAST Four times a day, strong movements
of water occur through the Golden
Needles Overfalls Garofalo Whirlpool Yellow Bluff Gate—twice flowing into the bay on
the flood tide and twice flowing out
FEATURES FEATURES Tide Rip on the ebb tide. These currents can
Tidal race and overfalls Tidal race, small reach a speed of up to 5 mph (8 km/h)
whirlpools, and overfalls FEATURES
TIMING during spring tides. Inside the bay, the
Four times daily TIMING Tide rip, standing waves,
Four times daily and eddies pattern of currents becomes more
complex, as they either split (during
TIMING
Twice daily the flood tide) or converge (during
LOCATION Needles Channel, northwestern coast of LOCATION Strait of Messina, between the northeast the ebb tide) from different parts of
the Isle of Wight, England, UK coast of Sicily and Calabria in mainland Italy the bay. The currents are also modified
LOCATION San Francisco Bay, California, US
by the varying depth of the water
The Needles Channel is a 5-mile- The Strait of Messina separates the around the shoreline, by the shoreline’s
(7-km-) long stretch of water between “toe” of Italy from the Mediterranean A tide rip is a stretch of rough, shape, and by subsurface obstructions.
a line of chalk sea stacks on one side island of Sicily. It varies in width from turbulent water caused by a tidal At Yellow Bluff, disturbances to the sea
(the Needles) and an underwater reef 2 to 10 miles (3 to 16 km) and is the current converging with, or flowing surface are most noticeable during the
on the other. This stretch of water site of numerous complex currents across, another current. Thus it differs ebb tide, when the tidal streams are
is affected by short, breaking waves and small whirlpools that vary over from a tidal race, which occurs where converging, and are characterized by
(overfalls) at the time of the maximum the tidal cycle and hamper navigation a tidal stream of water accelerates such phenomena as extremely rough,
ebb or flood tide. If the wind is through the Strait. In Italy, the small through a narrow opening in a coast. fast-moving water, standing waves,
blowing in the opposite direction of whirlpools that form are called garofali, An example of a tide rip occurs and eddies. The spot is popular with
the tidal stream, these overfalls are but in the English-speaking world, the at a place called Yellow Bluff in San extreme kayakers, who challenge
greatly exacerbated, producing an whole system of tidal disturbances is Francisco Bay, not far from the bay’s themselves against the strong currents
extremely rough sea. known as the Garofalo Whirlpool. entrance, the famous Golden Gate. and surf on the standing waves.

One of the world’s most famous tidal liters) of seawater to rush through the
PACIFIC OCEAN NORTHEAST HUMAN IMPACT
races occurs at the Skookumchuck gap, creating turbulence and some
Skookumchuck Narrows on British Columbia’s small whirlpools. On the flood tide, SURF-KAYAKING
Sunshine Coast, not far from when water is flowing into the Sechelt
Narrows Tidal Race Vancouver (Skookum is a native Inlet (but not the ebb tide, when it
American word for “strong” and chuck flows out), the tidal stream across an
FEATURES Tidal race,
small whirlpools, and means “water”). Four times a day, outcrop of bedrock in the channel
standing wave on there is a strong tidal rush of water creates a large standing wave—a
flood tide through this 1,000-ft- (300-m-) wide mound of breaking water that remains
TIMING Four times daily; channel, which connects two inlets stationary at a particular spot on the
flood tide twice daily into the coast—the Sechelt and Jervis surface. At its peak, the flow rate is
inlets. A 10-ft (3-m) difference in sea about 4.75 million gallons (18 million
LOCATION Skookumchuck Narrows, British Columbia, level between low and high tide causes liters) per second, and current velocities
Canada
some 167 billion gallons (760 billion can reach 20 mph (32 km/h).

Skookumchuck Narrows is a
popular destination for enthusiasts
of extreme surf-kayaking. The
standing wave that arises there
is up to 8 ft (2.5 m) high and 23 ft
(7 m) wide and is regarded as
one of the world’s great white-
water kayaking locations. When
surf-kayaking, the object is to stay
in the wave as long as possible,
which requires strength and skill.

INTRODUCTION POWERFUL RAPIDS

Here, water is flowing right to left,
from the Sechelt Inlet into Jervis Inlet.
Six hours later, it flows back in the
opposite direction.