Key Stage 3 · Year 8 · Geography · 2 minutes
A river's journey: source to sea
Erosion upstream, transportation all the way, deposition downstream.
Key terms
- erosion
- The wearing away of rock by a river.
- transportation
- The carrying of eroded material downstream by the river.
- deposition
- When a river drops the material it carries because the water slows down.
- meander
- A big bend in a river's middle course, eroded on the outside and deposited on the inside.
- ox-bow lake
- A curved lake left behind when a river cuts straight through the neck of a meander.
- floodplain
- The flat land beside a river in its lower course that is covered when the river floods.
- estuary
- The wide mouth of a river where it meets the tide and the sea.
Transcript
High on the slopes of Cross Fell, in the North Pennines, the River Tees begins as a trickle. Eighty-five miles later, it flows into the North Sea. So what happens to a river on its journey?
Every river does three jobs. Erosion, wearing away rock. Transportation, carrying that material downstream. And deposition, dropping it when the water slows down.
In the upper course, the land is high and steep. Fast-flowing water erodes downwards into the riverbed, carving a narrow, V-shaped valley.
At High Force, the Tees plunges about twenty metres over a band of hard rock called the Whin Sill. The softer rock underneath erodes faster, so the waterfall slowly retreats upstream, leaving a gorge.
In the middle course, the valley widens and the land gets flatter. The river swings from side to side in big bends called meanders. Fast water erodes the outside of each bend, while slow water deposits sand on the inside.
Over time, the bends grow loopier, until only a narrow neck of land is left. In a flood, the river cuts straight through, and the old loop is left behind as an ox-bow lake.
In the lower course, near Yarm and Stockton, the Tees is wide and deep, winding across a flat floodplain. When it floods, the water spreads out, slows down, and deposits fine mud called silt.
Finally, at Teesmouth, the river meets the tide in a wide estuary. Its mudflats, like Seal Sands, are home to seals and thousands of wading birds.
So, the upper course is steep, with V-shaped valleys and waterfalls, where erosion wins. The middle course has meanders. And the lower course has floodplains, ox-bow lakes, and lots of deposition.
Sources
Every fact in the video, and where it comes from.
- 1en.wikipedia.org/wiki/River_Tees
- The River Tees rises on the eastern slopes of Cross Fell in the North Pennines.
- The Tees is about 85 miles (137 km) long and flows east into the North Sea at Teesmouth.
- Order along the river: Cross Fell source, Cauldron Snout, High Force, Middleton-in-Teesdale, Barnard Castle, Darlington, Yarm, Stockton-on-Tees, Middlesbrough, Teesmouth.
- 2en.wikipedia.org/wiki/High_Force
- High Force falls about 21 m over the Whin Sill, a hard igneous (dolerite) layer above softer limestone/sandstone; undercutting makes the fall retreat upstream, leaving a gorge.
- 3en.wikipedia.org/wiki/Yarm
- Yarm's old town lies inside a loop (meander) of the River Tees.
- 4publications.naturalengland.org.uk/file/4692529982472192
- Seal Sands at Teesmouth is one of the largest intertidal mudflats on the north-east coast, with harbour and grey seals and tens of thousands of wading birds in winter.
- 5bbc.co.uk/bitesize/guides/z3bx6sg/revision/3
- Ox-bow lakes form when a meander neck is cut through (often during a flood) and the old loop is sealed off by deposition.
Image and sound credits
- “High Force 3 (1151669367)” by Tony Hisgett from Birmingham, UK, CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)
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