Year 10 River Landscapes 11.

Physical When water enters cracks in rocks and freezes it expands by 10%.When this process is repeated the rock may be slowly broken up.

ChemicalRainwater contains weak acids which react with certain types of rocks such as limestone

BiologicalThis is when plants and animals cause the rock to break up.

Hydraulic Action

This is the pressure of the water being pushed against the banks and bed of the river.

Air may also be pushed into cracks in rocks and this may cause the rocks to be broken up and eroded.

Corrasion

When the river banks are eroded by the load the river is carrying.

Any rocks or pebbles in the river may be thrown against the banks of the river causing it to be eroded

Corrosion

When dissolved acids in the water can wear the rocks in the river away.

Very evident on limestone rock

Attrition

When the rocks carried by the river knock into each other and will continually break up and become smaller.

They chip away at each other until smooth rounded pebbles are formed

2. 3.

4.

Mass Movement

Soil Creep

This is the slowest downhill movement of soil.

Gravity will pull the water that is contained in the soil down the slope

The soil will move downhill with the water

Can add to the load of sediment in the river

Slumping

Common on river bank. Large areas of river bank may move through rotational slipping. Very common on clay river banks;

During dry weather the clay dries out and cracks. When it rains the water runs into the cracks and causes the soil to become wet and it may slump.

5.

6.7.

There are many changes to the river between the source and mouth

Year 10 River Landscapes 2

Storm Hydrographs

You must know and be able to use the following terms;

• Peak rainfall

• Lag time

• Peak discharge

• Rising limb

• Falling limb

• Base level

8.

9. Features of Erosion

10.

Features of Deposition 11.

The floodplain is the low, flat area either side of a river channel in it’s middle and lower course

When a river has more water than it can carry it floods the surrounding land.

This means the load carried by the river is deposited

The deposited sediment means the land around the river becomes very fertile and is often used as rich farmland

12. Features of Erosion and Deposition

13.

Year 10 River Landscapes 314

A long period of hot dry weather makes the solid very hard so that water cannot soak in when it rains. Therefore it runs off the surface into the river

Dams may burst which will cause excess water in river channels and flooding of large areas

River beds that have become silted up (mud and rocks line the base of the river making it shallower) make he channel smaller and more likely to flood.

If there are large amounts of rain day after day, the water will saturate the ground and flow more quickly into the river

During a thunderstorm, the rain droplets are so large and fall so quickly that there is no time for the water to sink into the ground. Water runs very quickly into the river and causes flooding

If vegetation has been removed, then there is less interception (rain collected by vegetation that doesn’t reach the ground) and water will move to the river more quickly

P = Physical

H = Human

Steep valley slopes make rainwater run off rapidly into the river channel

The building of towns on a floodplain ieurbanisation add storm drains which allow water to move into the river at a greater speed and so make flooding more likely. Tarmac and concrete adds to this as they don’t allow infiltration.

Physical and Human causes of flooding15

16

Advantages and disadvantages of hard and soft management17