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.
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