The Silver Dragon
(sometimes called "The Black Dragon")
The Qiantang River Tidal
Bore
A
Mr. Incredible! Earthcache
An earthcache for the world's largest tidal
bore.
The Qiantang River and Hangzhou Bay are known for the world's
largest tidal bore, which is up to 9 meters (30 ft) high, and
travels at up to 40 km per hour (25 miles an hour). The ocean tide
(from the East China Sea) rushing into the river from the bay
causes a bore usually from 1.5 – 4.6 m ( 5 - 15 ft)
high, which sweeps past Hangzhou and menaces shipping in the
harbor. It is so dangerous that, until recently, no one attempting
to surf it (until recently...) has managed to remain upright for
more than 11 seconds. In September 2008, a group of American
surfers convinced the Chinese government to allow them to surf a
section of the river. Personal watercraft were used to safely
transport the surfers in and out of the tidal bore. The
surfers rode the Silver Dragon for
more than an hour and for more than 7 miles!
"Ripping the Tidal Bore" (surfing the
Silver Dragon)
WHAT IS A TIDAL BORE?
A tidal bore is the term used to describe the phenomenon of the
leading wave of a rising/ incoming tide as it rushes up a river or
a narrow inlet from a larger bay (think of a funnel). It is a
dramatic sight that is the more dramatic the greater the funnel
effect, i.e., the greater the size of the bay and the smaller/
narrower the river/ inlet. If the difference between the two is
great, then not only will the incoming wave be high (in Hangzhou,
China and in certain other parts of the world where the "funnel" is
exaggerated, surfers sometimes ride the tidal bore, though not
without risk to life and limb), the water level will rise
significantly, and can remain at this height for a half-hour or
more. The Hangzhou Bay and the Qiantang River are ideal
compoenents for a tidal bore!
The largest, or most forceful, tidal bores
occur during fall tides, when the sun, moon and earth all line up
(in any order), thus increasing the gravitational pull on the
earth. This occurs during a new moon or during a full moon. The
tidal bore is at its weakest at neap tides (aka neaps), when the
sun and moon are separated by 90 degrees (during the first-quarter
or third-quarter moon), for the gravitational pull from the one
tends to cancel the pull from the other. Hangzhou has a
festival each September to celebrate the huge Silver
Dragon.
From a
Hangzhou tourist website -
"This is one of nature’s
most unusual features: an inland wave far from the sea or the
ocean. A wave that comes up the river against the
current. A wave that the inhabitants of Qiantang have both feared
and admired for 2,000 years. The Silver Dragon
– or Chinese tidal bore – is not a wave that is easily
tamed or understood. The phenomenon arises from the meeting of the
incoming tide and the river’s outgoing current. The wave
invades the estuary and comes up the river, filling it with a
swirling wave. It has long brought destruction. With amazing
power, the wave breaks dams and spreads turbid salt water into the
fields. Famines have been frequent. The very votive population has
begged its forgiveness, offered sacrifices, or shot arrows in its
direction. Adopting transient aesthetic shapes, the tidal
bore curls, tacks, accelerates, rolls, and defies all predictions.
It thunders like a storm, jumps out when least expected, and draws
the admiration of scientists. Today, dams and gigantic walls
attempt to contain its undiminished power, and a festival honouring
the spirits of the sea illustrates the renewed peace with the
phenomenon."
Video of the Black Dragon (filmed before the surfing
video)
To Claim this Earthcache:
You will need to email me, Mr.
Incredible!, with the answers to the questions in
RED:
1. Go online to the Shanghai
Tide Chart
2. Find the time of high tide in Shanghai. You will
need to add 50 minutes for the Silver Dragon tidal
bore to reach Hangzhou. (What time was high
tide?)
3. Did you see a bore wave? If so, estimate its height.
If no visible wave, what did you see? (What time did you see
the tidal bore?)
4. Estimate the speed of the bore. Measure the distance
between two fixed points in meters using your GPSr and time the
bore wave using the timer on your watch or mobile phone in seconds.
Speed = distance divided by time. S=D/T Your answer will be
in meters per second (m/s). (What was the speed of
the Silver Dragon?)
4. Take a picture of
yourself (and your GPSr) with the Qiantang River in the background
and post it with your log entry. Extra points will be
given for having the Silver Dragon in
the background. (But I understand that timing could be
tricky!)
ALTERNATE LOGGING
RULES:
The tidal bore phenomenon is
not the same during the whole year. If the Silver Dragon does
not appear, and you did your best to be at the right place at the
right time, please follow these alternate rules.
1. Estimate the width of the river at the cache location.
(Email this to me through my profile page.)
2. Take a picture of
yourself (and your GPSr) with the Qiantang River in the background
and post it with your log entry.
3. Turn
and face the city, name the two "celestial" bodies the large new
buildings closest to you represent.
The Silver
Dragon
Downtown Hangzhou has undergone some upgrades,
be sure and check out the New City Civic Center.
Mr. Incredible! is a
Platinum EarthCache Master