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Stream capture by headward

erosion, leaving a wind gap

The Maumee River basin. The

Maumee, flowing north-east, has broken into part of another river's

basin, capturing west-flowing

streams and forcing them to

reverse direction on entering it.

Stream captureFrom Wikipedia, the free encyclopedia

Stream capture, river capture, or stream piracy is a

geomorphological phenomenon occurring when a stream or river

drainage system or watershed is diverted from its own bed, and flows

instead down the bed of a neighbouring stream. This can happen for

several reasons, including:

Tectonic earth movements, where the slope of the land changes,

and the stream is tipped out of its former course

Natural damming, such as by a landslide or ice sheet

Erosion, either

Headward erosion of one stream valley upwards into

another, or

Lateral erosion of a meander through the higher ground

dividing the adjacent streams.

Within an area of karst topography, where streams may

sink , or flow underground (a sinking or losing stream) and

then reappear in a nearby stream valley

The additional water flowing down the capturing stream may accelerate

erosion and encourage the development of a canyon (gorge).

The now-dry valley of the original stream is known as a wind gap.

Contents

1 Capture mechanisms

1.1 Tectonic uplift

1.2 Glacial damming

1.3 Headward erosion

1.4 Karst

2 Effect on freshwater life

2.1 Australian freshwater fish

3 References

4 See also

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The River Thames as it passes

through the Goring Gap

Capture mechanisms

Tectonic uplift

Barmah Choke

About 25,000 years ago, an uplift of the plains near Moama first dammed the Murray River and then

forced it to take a new course. The new course dug its way through the so called Barmah Choke and

captured the lower course of the Goulburn River for 500km.

Barrier Range

The original course of the Murray River was to a mouth near Port Pirie where a large delta is still

visible protruding into the calm waters of Spencer Gulf. An uplift of the land blocked the river near

the southern end of the Flinders Ranges, and the river eventually found its way to a new mouth near

Lake Alexandrina.

Glacial damming

The River Thames in southern England originally entered the

North Sea near Ipswich. About 450,000 years ago, an ice

sheet expanding from the north pushed the course of the river

southwards, forcing the Thames to cut a new mouth where the

mouth of the River Blackwater, Essex now is, north of London. It later moved southwards again to its current

position as a result of cutting through the Chiltern Hills at

Goring-on-Thames, an event which created the Goring Gap.

Headward erosion

The Teays River, captured by the Ohio River.

The Rio Grande which before capture flowed into a closed basin, Lake Cabeza de Vaca, but after

capture flowed into the Gulf of Mexico.

The ancestral Niger River captured what is now the upper reaches of the Niger which once flowed

into an endorheic basin to the east northeast of Timbuktu.[1]

The River Stour, Kent, largely captured by the River Beult /ˈbɛlt/, River Teise /ˈtiːz/ and others.

The River Wey, in southern England, the western arm of which is the former upper waters of the

River Blackwater (River Loddon).

The River Rheidol in Wales which has captured the headwaters of other streams and now runs for

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part of its length in a deep gorge.

The River Lyd in Devon, England.

The Black River, in Kings County, Nova Scotia, Canada, captured by the Gaspereau River

Karst

The Donauversickerung (Danube Sink), currently developing in Germany, where a large portion of the upper parts of the Danube river sinks into the limestone bedrock, and resurfaces in the Aachtopf

spring, a tributary of the River Rhine.

Effect on freshwater life

River capture is a shaping force in the biogeography or distribution of many freshwater fish species.

Australian freshwater fish

Australia provides a particularly fascinating series of examples of freshwater fish species and distributions

resulting from river capture events. The formerly massive Great Dividing Range runs the length of the

eastern coastline of Australia and has isolated native freshwater fish populations east and west of the range

for millions of years. In the last two million years erosion has reduced the Great Dividing Range to a

critical point where west-to-east river capture events have been possible. A number of native fish species

that originated in the Murray-Darling river system to the west are (or were) found naturally occurring in a

number of coastal systems spanning almost the entire length of the range.

None of the river capture events that allowed native fish of the Murray-Darling system to cross into and

colonise these East Coast river systems seem to have formed permanent linkages. The colonising Murray-Darling fish in these East Coast river systems have therefore become isolated from their parent species, an

due to isolation, the founder effect, genetic drift and natural selection, have become separate species (see

allopatric speciation).

Examples include:

Golden perch (Dawson-Fitzroy river system, central Queensland).

Eel-tailed catfish (several rivers, northern New South Wales) (However, note recent genetic research

which now indicates eel-tailed catfish colonised east coast drainages in multiple colonisation events

relatively recently (by evolutionary standards) and may subsequently have colonised the Murray-

Darling system via an east-to-west river capture event, contrary to usual west-to-east capture events

listed here.)

Macquarie perch (Hawkesbury-Nepean rivers, Shoalhaven River, southern New South Wales).

River blackfish (multiple rivers, Victoria).

Murray cod, whose eastern species/subspecies are:

Eastern freshwater cod (Clarence River system, northern New South Wales. It was also found

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Wikimedia Commons has

media related to Stream

capture.

in the Richmond River system in New South Wales but that population is now extinct.)

Brisbane River cod (Brisbane River system, southern Queensland. That population is now

extinct, and its exact taxonomic status is not known.)

The Mary River cod (Mary River, southern/central Queensland.)

The mountain galaxias species complex (multiple rivers, southern Queensland, New South Wales,

Victoria).

Olive perchlet ( Ambassis agassizii), western carp gudgeon ( Hypseleotris klungzingeri), pygmy perch

( Nannoperca australis) and Australian smelt ( Retropinna semoni) also appear to have made crossings into

coastal systems, the last two species seemingly many times as they are found in most or all coastal streams

in south eastern Australia as well as the Murray-Darling system.

Unfortunately, with the exception of eastern freshwater cod and Mary River cod, it has not been widely

recognised that these coastal populations of Murray-Darling native fish are separate species and their

classifications have not been updated to reflect this. Many are threatened and two, the Richmond River cod

and the Brisbane River cod, have become extinct.

References

1. Tom L. McKnight; Darrel Hess (2005). "16, "The Fluvial Processes" ". Physical Geography: A Landscape

Appreciation (8th Edition ed.). Upper Saddle River, New Jersey: Pearson, Prentice Hall. p. 462. ISBN 0-13-

145139-1.

See also

Lake capture

Niger River

Misfit stream

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Categories: Rivers Biogeography Geomorphology Hydrology

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