Page 227 - NS-2 Textbook

222 NAUTICAL SCIENCES

3-foot bore that travels 21 miles inland. The Petitcodiac rectly exposed to the storm waves of the North Sea, re-
River in Nova Scotia, Canada, has a bore wave 5 feet high claims land from the sea, and creates a coastal highway
that travels 50 miles inland. system that connects many previously isolated islands in
Dangerous tidal Cllrrellts occur in places where there southern Holland ...
are big inlets with narro"\v entrances. This occurs with
some fjords (long narrow inlets from the sea) in Green-
land, Nonvay, Alaska, and Chile. Currents rushing past
at 8 or 10 knots make it much too dangerous for boats CRITICAL THINKING
and ships to attempt passage during much of the day.
Tidal currents surge at speeds up to 10 knots through 1. Identify the major ocean current patterns that exist off
the U.S. eastern and western coasts and describe the
channels in the Great Barrier Reef northeast of Australia.
effects that these currents have on the water and air
The meeting of tidal currents and winds of the Atlantic
Ocean and the North Sea in the Pentland Firth between temperatures along the coasts.
2. Research the current state of efforts to generate elec-
northern Scotland and the Orkney Islands creates a bore
trical power from the ocean tides. Do you think this is
sometimes 10 feet high.
Many sailors have lost their lives in the Pentland a valid method of helping to deal with the energy cri-
sis world\vide?
Firth bore (called the Swelkie by local Scots) since the
days of the Vikings. The firth is said to be halmted by
the ghosts of the drowned, who howl and call out with
the strong northwest winds to sailors passing by on dark Study Guide Questions
winter nights.
1. Who is the founder of modern U.S. Navy oceanog-
raphy?
TIDAL ENERGY 2. What is unique about the cooling and freezing of
water?
Tidal energy is one of the oldest forms of energy used by
3. How does the ability of water to store heat make life
humans. A tidal mill built in the Deben estllary (a wide
possible on Earth?
part of a river where it joins the sea) in Great Britain was 4. A. What are the four main elements in seawater?
mentioned in records as early as 1170 and is still in oper-
B. What is the percentage of salt in open ocean
ation. Creative engineering has resulted in a large num-
water?
ber of schemes that make the tides a reliable source of 5. A. What are the saltiest bodies of water in the world
energy.
ocean?
Tidal energy requires large capital investments, but
B. In landlocked lakes?
once built, tidal power installations may last much 6. How did the ocean water get salty?
longer (with small maintenance costs) than thermal or 7. Describe the hydrologic cycle.
nuclear power stations. Favorable tidal conditions for
8. What two minerals are extracted from seawater on a
such power plants exist at many locations in France, and
conunercial basis?
in Brazill Argentina, Australia, India, Korea, Canada,
9. A. What is the freezing point of seawater?
China, Russia, and some other countries. The French
B. What is the constant temperature of water in the
built the world's most highly successful tidal plant near deep sea?
SI. Malo at the mouth of the Rance River estuary. A dam
10. What determines the color of water (as seen by the
containing turbines spans the estuary. As the tides rise
human eye)?
and fall, they spin turbines that drive banks of genera- 11. VVhat is the most comnlon cause of ocean waves?
tors. The idea is simple: dam in a basin, which fills with
12. Upon what three things does wind-generated wave
the incoming tide, then, at low tide, release the water
height depend?
through sluice gates (regulated-flow channels or gates) 13. What are the parts of a wave?
so it can spin turbines and generate electricity.
14. What are the three kinds of breakers, and what deter-
The Dutch have worked for centuries reclaiming
mines each?
land from the sea with dikes and pumps. Their biggest 15. A. Why are surf and swell so important to amphibi-
project was the enclosure of the Zuyder Zee. Another
OllS operations?
was the Delta Estuary Plan across estuaries of the Rhine,
B. What is meant by "critical" height of surf?
Meuse, and ScheIdt Rivers, completed in 1978. One part 16. A. What water actions reshape coastal landforms?
of this system generates electricity by tidal flow. At the
B. What is such action called?
same time, the project creates freshwater lakes for recre-
17. What is the main type of structure built to protect
ation, reduces and protects the amount of shoreline di-
harbors from the sea called?