Changing landscapes of the UK: rivers

What is deposition

This is when a river loses energy and it drops off the material it is carrying

What are the factors leading to deposition

• shallow water

• At the end of the rivers journey

• When the volume of water decreases

What is drainage basin

This is an area of land around the river that is drained by the river and its tributaries

What is a watershed

This is an area of high land forming the edge of a river basin

What is the source of a tuber

This is where the river begins

What is the mouth of a river

This is where the river ends and meets the sea

What is a confluence

This is a point where two rivers meet

What is a tributary

This is a small river that joins a larger river

What is a river channel

This is where the river flows

What is the long profile of a river

This is a line representing a river from its source to its mouth

What is the upper course of a river

This is where the river starts and is usually an upland area. The river channel is narrow and shallow here and the load here is large because it hasn’t been broken down by erosion

What is the mid course of a river

This is where the gradient becomes less steep and the river channel gets deeper and wider as the bed and banks are deeper

What is the lower course of a river

This is the final course of the river where the land is a lot flatter. The rivers load is fine sediment as erosion has broken down the rocks

Describe erosion at the upper course of river

As the river flows downhill there is increase in vertical erosion. The channel is shallow and narrow because there isn’t a lot of water here

Describe erosion in the middle course of a river

As the river flows into the middle course there is some vertical erosion but more lateral erosion this makes the channel wider and deeper

Describe erosion in the Lower course of a river

This is a lot less erosion only some lateral erosion. The river is at its widest and deepest

What is a waterfall

This is a sudden drop along the river course. It forms when there are horizontal bands of hard rock over soft rock

Describe the formation of a waterfall

• the soft rock is eroded quicker than the hard rock and thus creates a step

• As erosion continues the hard rock is undercut forming an under hang

• The action of abrasion and hydraulic action creates a plunge pool

• The plunge pool gets bigger increasing the size of the overhang until the hard rock is no longer supported and it collapses

• This process continues and the waterfall retreats upstream

• A steep sided valley is left where the waterfall once was this is called a gorge

What is a meander

This is a curve or bend in a rivers course

Describe the formation of meanders

• meanders are formed by erosion and deposition

• The force of the faster flowing water erodes the outside bend undercutting thee bank and forming a steep river cliff

• The water is shallower and flows more slowly on the inside bend

• Sand and gravel are deposited on the inside bend to form a slip off slope

• Deposition takes place here because the river has less energy

• As meander erodes the outside bend the bends get wider

• Lateral erosion widens valley floor

What is an oxbow lake

U-shaped body of water that forms when a river's meander, or bend, is cut off from the rest of the river

How are oxbow lakes formed

• erosion makes the neck of a meander narrow

• The meanders move closer together

• When there is a flood the river cuts across the neck taking a new shorter route

• Deposition will cut off the original meander leaving a horseshoe shaped oxbow lake

What is a floodplain

This is an area of land which is covered in water when the river bursts its banks

How are floodplains formed

• they are formed due to erosion and deposition

• Erosion removes any interlocking spurs creating a wide flat area on either side of the river

• During a flood material carried by the river is deposited

• Over time the height of the floodplain increases as material is deposited on either side of the river

What are levees

These are naturally raised river banks found on the side of a river and are prone to flooding

How are levees formed

levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs

how do levees affect rivers

• sediment that has been eroded further upstream is transported downstream

• When a flood occurs the river loses energy. Yhe largest material is deposited first at the side of the river banks and smaller material further away

• After many floods the sediment builds up to increase the height of the river banks meaning that the channel can carry more water and flooding is less likely to occur

What is an estuary

This is where the river meets the sea

What is flooding

Flooding occurs when a river breaks its banks and overflows the surrounding land

What are the causes of flooding

• prolonged rainfall

• Heavy rainfall

• Relief: steep valley is more likely to flood than a flatter valley cause the rainfall will run off into the river more quickly

• Geology: permeable rocks allow water to pass through pores

• Vegetation: trees and plants absorb water known as interception

What is an hydrograph

This shows how a river responds to a period of rainfall

What is peak discharge

Maximum amount of water held in a river channel

What is peak rainfall

Maximum amount of rainfall

What is lag time

This is the time between peak discharge and peak rainfall

What is the rising limb

This shows the increase in discharge on an hydrograph

What is the falling limb

This shows the return of discharge to base flow on an hydrograph

What is base flow

The normal discharge of a river

What factors affect lag time

• geology: if the rock are impermeable the lag time is shorter

• Soil type: clay soils do not drain easily so they increase lag time

• Slope: steeper slopes lead to rapid water transfer and shorter lag times

• Vegetation: no vegetation means the water runs off quicker therefore it would have a short lag time

• Antecedent conditions: wet conditions before a storm cause the ground to be saturated which speeds up over land flow and shortens lag times

What are hard engineering strategies for flood

• damns

• River straightening and dredging

• Embankments

Describe dams

• can be used to produce electricity by passing water through a turbine

• They can attract tourists

• Very expensive to build

• Habitats are flooded leading to rotting vegetation

Describe river straightening and dredging

• river straightening speeds up the water so high volumes of water can pass through

• Dredging makes the river deeper so it can hold more water

• More water can be held in the channel

• Dredging needs to be done frequently

• Speeding up the river leads to floods downstream

Describe embankments

• this involves raising the banks of rivers so it can hold more water

• Cheap with one off cost

• Allow for flood water to be held in a river

• Looks unnatural

• Can increase flood risk downstream

what are soft engineering strategies for floods

• flood warnings

• Floodplain planing

Describe floods warning

• People have time to try and protect their property

• People have time to evacuate areas

• Flash floods may happen too quickly for any warning to be effective

• They do not stop flooding

describe floodplain planing

• More expensive buildings are further away from the river

• Less damage is caused leading to fewer insurance claims

• Not always possible to change existing land users

Why does river discharge change along the course of a river

Why does river velocity increase downstream

• tributaries join the main channel so there’s more water in the river

• Channel becomes a more efficient shape so there’s less friction