Modern civilization is filled with artificial re-creations
of nature. People decorate houses with artificial Christmas
trees, wear artificial hair, play games on artificial
grass and build zoo cages with artificial rocks. Scientists
have even developed artificial
One of mankind's oddest re-creations of nature is the
artificial ocean shore, also known as the wave pool.
These popular water park attractions are sanitized, regimented
revisions of the wild, organic surfs created by nature. In
wave pools, the water is chlorinated, the beach is concrete
and the waves arrive like clockwork, once every few minutes.
In this edition of HowStuffWorks,
we'll peek behind the scenes of Thunder Bay, the main
attraction at Wet 'n Wild Emerald Pointe in Greensboro,
NC. As we'll see, it takes a lot of sophisticated,
powerful equipment to keep the waves rolling all day long. But
the basic idea is very simple.
Making Waves In the ocean, most waves
are created by the wind. The rushing air pushes some water
molecules together, producing a swell of water -- a
disturbance in the ocean's surface -- at a particular
point. These molecules push on the molecules next to them,
which push on the molecules next to them and so on. In this
way, the disturbance is passed along the surface of the ocean,
while the individual water molecules stay in roughly the same
There are a number of ways to replicate this type of wave
action. All you need is a basin of water and some means of
creating a periodic disturbance. You could use a strong blast
of air along the surface, a rotating paddle wheel (like the
ones used on steamboats) or an oscillating plunger. Basically,
you push on the water at one point and this energy
travels outward, through the surrounding water. This is the
same thing that happens when you drop a rock into a pond.
The wave generator at Emerald
Pointe's Splash Island uses pressurized air to
Emerald Pointe features a wave pool of this sort at Splash
Island, a swimming area for younger kids. In this pool, gentle
ripples spread out from the deeper end, just under a volcano
structure, and wash up on the small beach.
The machinery that generates this effect is very simple. In
a pump room below the pool, a high-speed fan blows air
into a wide metal pipe, which leads to an exhaust port
at the base of the volcano. In the middle of this pipe, there
is a butterfly valve, a wide disc with a swiveling
metal axis rod. When the rod is swiveled one way, the disc
rests horizontally in the pipe, blocking the air flow. When
the rod is swiveled the other way, the disc moves to a
vertical position so the air can pass.
A hydraulic piston swivels the rod back and forth at
regular intervals, allowing short bursts of pressurized air to
flow up to the exhaust port. These air blasts blow on the
water at the base of the volcano, generating the flowing
here to watch a video of an air-powered wave
generator in action.
small waves is fairly simple with this sort of system, but
it's a lot harder to form large, surfable waves. You would
need an absurdly intense blast of air or a large, awfully
strong plunger. Such devices would likely be inefficient,
cumbersome and dangerous, so they wouldn't make for
particularly good water park attractions. Instead, water parks
use water-pumping wave systems. In the next couple of
sections, we'll see how this sort of wave pool works.
Just Add Water In the last section, we
looked at an extremely simple wave pool. In this design, short
bursts of pressurized air apply force to a relatively stable
pool of water. This creates little waves, which extend outward
along the surface of the water.
A larger wave pool system works differently. Instead of
pushing on the water with air or a paddle, the wave machine
dumps a huge volume of water into the deep end of the pool.
The surge in water travels all the way to beach; the water
level in the pool balances out again. Since water is
fairly heavy, it pushes very hard to find its own level. If
you dump more water in, you increase the size and strength of
is a lot of powerful equipment involved in this process, but
the idea is pretty simple. The wave pool has five basic parts:
A water-pumping system
A water-collection reservoir
A series of release valves at the bottom of the
A giant, slanted swimming pool
A return canal, leading from the beach area to
the pumping system
Robert Bochenski, the maintenance manager at Emerald
Pointe, compares this sort of wave pool to a giant toilet. The
pump system draws water from the return canal into the
collection reservoir in the same way that a toilet draws water
from the water line into its tank. When the water level in the
reservoir is high enough, the system opens up the release
valves at the bottom of the reservoir. This is like flushing a
toilet: It dumps all of the collected water into the pool,
creating the wave.
In this system, the water is constantly circulating.
It moves from the deep end of the pool, out to the canal,
around to the pumping system and back into the deep end of the
pool. The return canal is fenced off so swimmers will never be
exposed to the pumping mechanism.
The return canal at Thunder Bay Click
here to watch as waves rush toward the return canal.
As they flow around the corner, they create a small
are any number of ways to configure the wave-generating system
in this setup. In the next section, we'll look at the specific
machinery used at Emerald Pointe's Thunder Bay.
On a busy day,
thousands and thousands of people will take a dip in the
Thunder Bay wave pool, and even the cleanest among them
leave a certain amount of dirt and oil behind. To keep
the water sanitary, Emerald Pointe keeps a
filtering system going 24 hours a day.
The Thunder Bay wave pool uses six massive filters,
located just behind the wave generator. A powerful pump
sucks water in from the canal, sends it through the
filter system and shoots clean water back out. The
collected dirty water is pumped to the city sewer
line almost a mile away.
Let it All Out Thunder Bay is 84 feet (26 m)
across at the deep end, and it is more than 400 feet (122 m)
long. Overall, the pool holds about 2 million gallons (7.6
million L) of water, and the wave itself is 90,000 gallons
(341,000 L). To make a wave this big and get it to make its
way across the entire pool, you need some pretty heavy
The wave generator uses a 100-horsepower
pump, a 200-horsepower pump and a 300-horsepower pump. Each
pump has a motor at the
top, which spins a long drive shaft. The drive shaft extends
down through a pipe, to a propeller positioned 13 feet (4 m)
underwater. When the drive shaft spins, it rotates the
propeller, which drives water upward through the pipe (in the
same way a spinning fan drives air forward).
A wave pool,
just like any swimming pool, is constantly losing water.
Some of it evaporates into the air, some of it is
filtered out and a good bit is carried away in swimmers'
bathing suits (and on their bodies).
To keep the water level up in Thunder Bay, Emerald
Pointe has to constantly pump in new water. The park is
connected to the city water line, but most of the water
comes from several underground wells. The wells pump
water into the wave-pool canal as well as into other
feeder pools in the park. Installing the water wells
required a hefty initial investment, but it meant much
lower monthly water bills in the long run.
At the base level of the
pump, the pipe curves, runs horizontal for 6 feet (1.8 m),
then curves up and rises another 10 feet (3 m) before finally
opening into the water reservoir. In all, the pumps move the
water 29 feet (9 m)! At their standard speed, the pumps drive
about 40,000 gallons (150,000 L) of water per minute.
The water reservoir is broken up into eight connected
chambers, each with its own release valve. The
release valve has three major elements:
The valve seat - The opening that leads down to
The valve plate - A wide piece of metal that fits snugly
on top of the valve seat
Metal struts that pivot on a stationary steel
beam attached to the reservoir walls on one end and to the
valve plate on the other end
The hydraulic-cylinder piston, which is attached
to a metal beam running between the two struts
Since the metal struts pivot freely on the stationary steel
beam, you can swing the valve plate back and forth. The plate
is fairly heavy, so it naturally will swing over the valve
seat. This plugs up the reservoir so water can't escape. (A
rubber gasket around the valve seat keeps the valve
from leaking too much.)
When pressurized oil is directed to the hydraulic
cylinder, it moves the piston with a great deal of force. This
pushes out on the metal struts. The valve plate extends
outward, unplugging the water reservoir. The water drops
directly underneath the reservoir, into a curved passageway
leading to the pool. As it rushes into the pool, the water
ramps up a sort of reef in the concrete floor. This
focuses the flowing water so that it moves in a
good-sized, surfable wave.
One of the release valves at Thunder
here to watch a video of the valve
water pumps do most of the work in building up a wave, but the
hydraulic system is the crucial element that actually gets it
going. In the next section, we'll look at the simple but
ingenious mechanism that controls this system.
Oil and Water In the last section, we saw
that the wave generator's valves are opened by hydraulic
pistons. As with most any hydraulic
machine, these pistons are powered by a basic hydraulic
pump. The pump keeps a steady stream of pressurized oil
flowing into the system. Emerald Pointe actually uses
vegetable oil, rather than regular machine oil, since
there is some risk of the oil leaking into the wave pool.
The directional control valve that operates
the release gates at Thunder
In the wave generator, the oil flow is controlled by a
directional control valve. The valve is connected to
several hoses, leading to:
The hydraulic pump
A collection tank that feeds oil back into the
The cylinder pistons
If you were to cut
open one of the piston cylinders, you would see something like
You can see that the piston rod that extends outside the
cylinder is actually moved by a piston head inside the
cylinder. There is fluid on both sides of this piston head,
fed by two different hoses. If the force is greater on the
blue side, the piston will move to the left, and if it is
higher on the orange side, the piston will move to the right.
To change the direction of force, you stop pumping oil to one
side and start pumping it to the other. This sort of piston
cylinder is commonly called a hydraulic ram.
The directional control valve directs the flow to these
rams. It has a small spool that moves back and forth, blocking
some inlet and outlet ports and opening others. In this
animation, you can see the basic design of this sort of
When the spool is to the left, the high-pressure oil goes
to the left side of the cylinder, pushing the piston outward.
When the spool is to the right, it pushes the piston back in.
As the high-pressure oil pushes on one side, the low-pressure
oil on the other side is forced back into the oil tank.
The spool is moved back and forth by a simple solenoid
(an electromagnetic switch controlled by an electrical
current). The solenoid is controlled by an electrical
timer. Every two minutes, the timer activates the
solenoid so it pushes the pistons out for a few seconds and
then pulls them back in. This opens up all of the release
valves, creating a wave.
One of the most amazing things about this control system,
and the wave generator in general, is how durable it is. All
summer long, the Emerald Pointe crew starts the waves at the
crack of dawn and doesn't shut the system down until the park
closes in the evening. That's one tough work week!