River Bore
A tidal bore, also known as the bore is a tidal phenomenon in which the highest incoming tides form a wave (or waves) of water that travels up a river or confined bay against the path of the river or bay’s current. The word “bore” is derived through Old English from the Old Norse word Bara meaning “ wave” or “swell”.
A bore occurs in some places worldwide, generally in areas with larger tidal range and where incoming tides are passed into a shallow narrowing of a river of the lake through a broad bay.
The funnel-like shape not only increases the tidal range but also decreases the duration of the flood tide where the flood appears as an immediate increase in a water level. A tidal bore always occurs during the flood tide and never occurs during an ebb tide.
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Qiantang River Tidal Bore
Qiantang River tidal bore, also known as the silver dragon tidal bore, is the world’s largest tidal bore. It is a river in east china and runs from Hangzhou bay on China’s eastern coast. The Qiantang River tidal bore is a famous scenic spot of the Qiantang River.
Generally around August 15, the Lunar calendar is the best time to observe the silver dragon tidal bores. Driving this time, this largest tidal bore can be several meters. Before the sea tide appeared, a white ting dot appeared in the distance, which transformed into a silver thread in a blink of an eye. Later, the white line rolled to the sea as it was accompanied by waves of dull thunder.
In ancient Hangzhou, Phoenix mountain, the Jianggan area was the best place to watch the Qiantang River tidal bore. Due to the transformation of geographical location from the Ming dynasty, Haining, Hanguan was the first resort to observe the silver dragon tidal bore, so it was also called "Haining Tidal Bore".
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Petitcodiac River Tidal Bore
The Petitcodiac River tidal bore - retrograde wave moving upstream over the downstream wavers. It occurs twice a day and comes from the world’s largest tide in the Bay of fundy. The first European mention of the Petitcodiac river tidal bore by the British Lieutenant Colonel George Scott on 17 November 1758.
The Petitcodiac River tidal bore ranges from 1 to 2 m (3.3 - 6.6 ft) in height, with a speed from 5 to 15 km/h. Peter Fisher in 1825, observed that the noise of the bore is heard at a great distance, and animals instantly take to the highland and manifest visible signs of terror if near it. Before the causeway, the value of the Petitcodiac river tidal bore was compared with the tidal bores of Qiantang, Hooghly, and Amazon river. The bore reached heights from about 5 to 75 cm after the causeway was built.
Bay of Fundy Tidal Bore
The Bay of Fundy tidal bore is the bay found between the Canadian province or territories of New Brunswick and Nova Scotia, with a small part touching the US state of Maine. The bay of fundy tidal bore has an extremely high tidal range. The name is derived from the French word Fendu meaning “split”.
The tidal range in the Bay of Fundyis around 16 m ( 52 ft). Some tides are higher than others, depending on the position of the moon, the sun, and other atmospheric conditions. Tides in the Bay of Fundy are semi-annual, meaning they have two highs and two lows on each day with about 6 hours and 13 minutes between each high and low tides.
As per the Guinness Book of World records, the World’s highest tides are found in the Bay of Fundy, where the mean spring range in the Minas basin is 14.5 meters (47.6 feet). The largest tide on record in the Bay was 21.6 meters ( 70.9 ft) in 1869.
Pororoca Surfing
The Pororoca is a tidal bore, with waves up to 4 m (13 ft) high that travels as much as 800 km ( 500 mi) inland upstream on the Amazon river and other adjacent rivers. The word “ porocca” is driven from the indigenous tulip language where it could translate into “great roar”. The Pororoca tidal bores occur at the mouth of the river where its water meets the Atlantic ocean.
The Pororoca river waves have become popular with surfers. However, pororoca surfing is especially dangerous as water contains a significant amount of debris from the shores of the river ( often entire trees) along with the dangerous fauna.
Did You Know?
Tidal bore can occur every day, like the tidal bore of the Batang River in Malaysia, known as benak.
Tidal bore, like the porocca, occurs during spring tides.
The bore is the fastest and highest in some of the small rivers like Salmon River in Truro, the St. Croix and Kennetcook river in the Minas Basin, and the Maccan river and River Hebert in the Cumberland basin.
The second highest tides in the World is Severn Estuary-after the Bay of Fundy in Canada and the highest in Europe.
There are around 60 tidal bores around the Globe.
The World's highest tidal bore occurs along the Qiantang River in Hangzhou,China, where tides reach upto 30 feet and travel at upto 40 kilometers per hour.
FAQs on Tidal Bore
1. What is a tidal bore in geography?
A tidal bore is a remarkable geographical phenomenon where the leading edge of an incoming tide forms a wave, or series of waves, that travels up a river or narrow bay against the river's natural current. It essentially appears as a wall of water moving upstream. This occurs only when specific conditions, such as a large tidal range and a funnel-shaped, shallow river mouth, are met.
2. What are the key effects of a tidal bore on a river's ecosystem and human activities?
Tidal bores have both positive and negative effects. They can be destructive but also beneficial for the river environment.
- Negative Effects: Powerful bores can cause soil erosion along river banks, damage ships and docks, and pose a danger to navigation and life.
- Positive Effects: They help in aerating the water, cleaning debris from riverbanks, preventing water stagnation, and transporting nutrients from the sea upstream, which can enrich the ecosystem.
3. Which river in India is famous for its tidal bore?
The Hooghly River, a distributary of the Ganga River in West Bengal, is famous for having the highest tidal bore in India. This phenomenon, locally known as 'Baan', is crucial for the Kolkata Port as it helps in clearing out silt and allows larger ships to navigate further inland during high tide.
4. Where is the world's largest and most powerful tidal bore located?
The world's largest tidal bore occurs on the Qiantang River in China. Known as the "Silver Dragon," this tidal bore can reach heights of up to 9 metres (30 feet) and travel at speeds of up to 40 km/h. It is a major tourist attraction, especially during the autumn season when it is at its most powerful.
5. How is a tidal bore different from a tsunami?
While both are powerful waves, a tidal bore and a tsunami have completely different origins and characteristics.
- Origin: A tidal bore is a predictable tidal event caused by the gravitational pull of the moon and sun. A tsunami is an unpredictable event caused by large-scale geological disturbances like underwater earthquakes or volcanic eruptions.
- Frequency: Tidal bores occur regularly with the tides (daily or semi-daily). Tsunamis are rare and isolated events.
- Nature: A tidal bore is a single wave or a small series of waves travelling up a river, whereas a tsunami is a series of extremely long waves affecting a vast coastline.
6. Why are some tidal bores popular for surfing?
Some tidal bores are popular for surfing because they create a long, continuous, and unbroken wave that can be ridden for several kilometres. This offers a unique and much longer ride compared to typical ocean waves that break quickly. Famous tidal bores for surfing include the Pororoca on the Amazon River in Brazil and the Severn Bore in the UK.
7. Why don't all rivers that meet the sea have a tidal bore?
Tidal bores are rare because they require a very specific combination of conditions that most rivers do not have. The key requirements are:
- A large tidal range at the river mouth, typically more than 6 metres between high and low tide.
- A funnel-shaped estuary that narrows and becomes shallower as it moves inland, which concentrates the tidal energy.
- A low volume of river discharge that doesn't overpower the incoming tide.
