Rivers Summary

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What is a drainage basin?

A drainage basin is an area of land drained by a river and its tributaries. ✓

Define these key words:

Watershed- the edge of a drainage basin. ✓

Confluence- a point in a river were one or more small rivers meet the main channel of the river. ✓

Tributary- a small river that runs into a larger river/ main channel of the river. ✓

Source- the start of a river. ✓

Mouth- the point in a river were the river meets the sea or lake. ✓

What is erosion?

Erosion is when rock is worn away by stones, air, water and other natural agents. ✓

What is transportation?

There are many different types of transportation within a river. The bedload are huge rocks that are too heavy for the river to transport through suspension. When rocks and stones are rolled along the bottom of the river, it is called traction. When small stones are bounced along the river bed it is called saltation. When small grains of sand and mud are carried along in the rivers flow it is called suspension and when dissolved minerals are carried along within the river it is called solution. ✓

What is an ox-bow lake?

AN ox-bow lake begins as a big meander, slowly over time as the meander becomes larger and more loopy as a result of the erosion on the outer bank which forms deposition which is carried to the inner bank. Eventually, the deposition will become so vast and the meander so large, the river takes a short cut and instead of going all the way around the meander, it cuts through as a straight line, leaving the meander behind as a separate lake. ✓

What is a meander?

A meander begins as a small bend in the river. As the water flows towards the meander, the current takes the main water flow to the outer bank of the meander. Over time the outer bank begins to erode as and all the deposition is deposited onto the inner bank of the meander. The meander then begins larger and ore loopy over time. ✓

Why do floods occur?

Floods occur for many reasons however factors that increase flood risk are, hard dry soil which has been dried out meaning no water can be absorbed into the ground, highly saturated soil which is so full of water that it can not absorb any more. Impermeable soil which has materials such as slate within it, meaning that water is not easily absorbed. Another flood risk factor is land surrounded by steep landscapes, as all the water will run down the hills at such speed that it has no time to absorb, also when many trees in an area are cut down there is no vegetation to absorb water. Another flood risk factor is when you build housing in a drainage basin because there is a high risk of flooding as a lot of the area in a drainage basin are flood plains. ✓

Boscastle Flood

The Boscastle flood in 2004 was a result of a tributary of 3 rivers, the Jordan, Paradise and Valency overflowing. Also huge amounts of rainfall fell, around 89mm in an hour, Boscastle received the amount of rain you would averagely get in a month, in 3 days. Furthermore, the ground in Boscastle was already saturated from previous rainfall meaning water could not be absorbed into the ground. Additionally, Boscastle is situated in a steep drainage basin meaning the drainage basin acted as a funnel, directing all the water down steep hills to Boscastle and no water could be absorbed when the water was running down the hills as it was travelling at such speed.. As well as that, the river channels in Boscastle are very thin meaning that the river banks burst very easily as the vast amount of water pouring into Boscastle had no were to go.

What is a waterfall?

A waterfall is a cascade of water falling from height, which is formed when a river is forced over a steep ledge. The ledge is called the overhang and is made of resistant rock meaning it is tough and hard for the river to erode. When the water falls over the overhang it dives into the plunge pool which is a bowl of water as it has been eroded over time by the force of the waterfall. The side of the waterfall is called the undercut, this is rock is less resistant and therefore is eroded by the waterfall over time.