Hydrosphere

Question 1

Formation of a Meander

Answer 1

1. Pools and Riffles develop as water twists and turns around obstacles leading to slower (pools) and faster (riffles) water movements.
2. Pools are areas of deep water and greater erosion. Riffles are areas of shallow water created by the deposition of course sediment.
3. One pools and riffles have been developed the river flows from side to side in a winding course.
4. A corkscrew-like flow of water called helicoidal flow moves materials from the outside of one meander to the inside of the next bend.
5. Water moving faster has more energy to erode. This occurs on the outside bend of the river and forms a steep river cliff.
6. The river uses hydraulic action (sheer force of the water gets into small cracks and breaks down rock), abrasion (load hitting off banks and bed) and corrosion (slightly acidic water dissolving material and washing it away) to erode outside bends.
7. Water moves slowly in the inside bend and the river deposits some load, forming a gentle sloping river beach.
8. Continuous erosion on the outer bank and deposition on the inner bank forms a meander in the river which will migrate downstream and change shape over time.
9. Named example - River Severn meander at Caersus.

Question 2

Formation of a V-Shaped Valley

Answer 2

1. Rivers begin high up in the mountains so they flow quickly downhill eroding the landscape vertically.
2. The river cuts a deep notch down into the landscape using hydraulic action, when the sheer force of the river gets into small cracks and breaks down the sides of the river valley. Abrasion also takes place which is when the river bed and banks are eroded by the load hitting against them.
3. Another type of erosion is corrosion when the acidic river water dissolves minerals from the rocks and washes them away.
4. As the river erodes downwards the sides of the valley are exposed to freeze-thaw weathering which is when water enters cracks in upland rocks and freezes at night expanding by 9%. Continuous freezing and thawing puts pressure on surrounding rocks until small pieces of rock break off. This loosens the rocks and steepens the valley with some rocks falling in the river.
5. The rocks that fall into the river assist the process of abrasion and leads to further erosion downstream.
6. The river transports the rocks downstream. and the channel becomes wider and deeper creating a v-shaped valley between interlocking spurs which is the hill that a river meanders around. When viewed from downstream the river seems to be locked together.
7. Named example - River Severn.

Question 3

Formation of a Waterfall

Answer 3

1. The river flows are bands of less resistant (softer) and resistent (harder) rocks.
2. The less resistent rock is more quickly worn away due to differential erosion.
3. The river erodes the rock in three main ways:
   - Hydraulic action -when the sheer force of the water gets into small cracks and breaks down the rock.
   - Abrasion - when the the river bed and banks are erided by the load constantly hitting off them.
   - Corrosion - when the acidic river water dissolves minerals from the rocks and washes them away.
4. The river undercuts the harder rock leaving an overhang which becomes unsupported and collapses into the plunge pool (pool found at the bottom of the waterfall created by hydraulic action and the abrasion of the plunging water).
5. After the overhang falls, some of the rocks are swirled around the river and this helps to form a deep plunge pool below the waterfall. The plunge pool is also deepend in times of high discharge when hydraulic action is most powerful.
6. The waterfall is moved upstream, the process continues and a steep sided gorge is cut back into the hillside.
7. Named example - High Force, River Tees.

Question 4

Formation of an Ox-bow Lake

Answer 4

1. The river erodes laterally as is meanders across the valley.
2. Most water is directed to the outside bend, there is also reduced friction and increased velocity.
3. The fast flowing water erodes the outside bends using hydraulic action when the sheer force of the water gets into cracks in the rocks pushing all the air out creating a small explosion which breaks the rocks apart, corrosion when the acidic river dissolves the rocks minerals and washes them downstream and abrasion when the load of the river hits off the bed and banks breaking the rocks down.
4. There is less water on the inside bend, an increase in friction and a decrease in velocity. As the river has less energy it deposits the material so its course changes.
5. Over time continued erosion and deposition narrows the neck of the meander.
6. Often during times of high discharge the river will cut through the neck of the meander.
7. The river continues on its straightened path and the meander in abandoned.
8. The fastest current will now be flowing in the centre of the river channel and deposition is more likely to occur beside the banks.
9. New deposition seals off the ends and the cut off becomes an ox-bow lake that will eventually dry up exept during periods of heavy rainfall.
10. Named example - Cuckmere Haven, Sussex, England.

Question 5

Reasons for Hydrographs

Answer 5

• Area, shape, slope
• Large basins recieve more precipitation than small basins, resulting in larger run off.
• The shape of the basin affects run off. The wider the shape the greater the run off and channel flow.
• Channel flow will be faster on a steep slope compared to a gently sloping area.
• Rock type
• Permeable rocks let water pass through them and may be porus (chalk) and pervious (limestone) which lets water sink through. These rocks allow rapid infiltration and little surface drainage.
• Impermeable rocks (granite) are water tight. They do not let water pass through. This creates a rapid surface run off and a high density.
• Soil type
• This influences the rate of infiltration and the speed of through flow.
• The depth of the soil and the porosity (does it let water pass through) are important.
• Infiltration is greater on thick soils and less on thin soils.
• Clay soil, impermeable, rapid surface run off, encourages flooding.
• Sandy soil, permeable, slow surface run off, discourages flooding.
• Land use - urbanisation
• Concrete and tarmac form impermeable surfaces.
• Heavy rainfall and rapid run off can quickly exceed the capacity for guttering and drains to cope causing flooding in towns and cities.
• Land use - afforestation
• Areas of forest are able to reduce the jmpact of heavy rainfall due to interception by the canopy and the soaking properties of tree roots. This delays surface run off.
• Where there are areas of deforestation run off is very fast.
• Drainage density
• This is lower on permeable rocks and soils.
• Lots of streams allow rapid run off.
• Lower density means fewer streams to channel water flow.
• Storage capacity
• Large streams have a larger capacity to channel flow.
• Small streams have a small capacity.

Question 6

Hydrological Cycle

Answer 6

1. Bodies of water are heated and evaporated by energy from the sun. This is a change from liquid to gas (water vapour).
2. Water is lost to the atmosphere through transpiration which is water loss from plants through leaf pores.
3. Clouds are moved inland by winds (advection).
4. As water vapour cools it condenses and forms clouds. When these clouds are big enough they produce precipitation (any moisture eg. rain, sleet, snow).
5. The rainwater can be intercepted by vegetation or can be stored in lakes etc.
6. If the rainwater falls on an impermeable surface it will run over the surface to the nearest body of water as surface run off.
7. If rainwater lands on soil it will sink in called infiltration. Water moves through the soil due to gravity called through-flow.
8. Sometimes it will sink deeper into the rocks below the soil known as percolation. It can then flow through the rocks as ground water flow. Alternatively it will be stored in rocks as groundwater storage.