Hydrosphere

Question 1

Formation of a V-shaped valley

Answer 1

1. Rivers flow quickly down the mountainside and erode the landscape vertically, creating steep valley sides that are shaped like a letter V.
2. The valley sides are then attacked by weathering processes, such as freeze-thaw and biological weathering.
3. The weakened valley sides eventually collapse or move down slope due to processes such as slumping or soil creep.
4. The force of the water and the grinding rocks and stones cut down into the river bed to carve out a V-shaped valley between interlocking spurs.
5. Interlocking spurs are areas of more resistant rock left behind because the river erodes softer rock quicker.
6. Hydraulic action, corrasion and corrosion further erodes the valley sides and the characteristic V shape is created over time.
7. Eventually, the valley becomes deeper and wider.

Question 2

Formation of a waterfall

Answer 2

1. Hydraulic action of fast flowing water compresses air into the river bank causing materials to be dislodged.
2. The force of the water throws bedload against the banks, causing erosion through abrasion.
3. Solution also occurs when soluble rocks react with acids in the water, further weakening the banks.
4. Differential erosion takes place over bands of more and less resistant rock.
5. Some types of rocks (shale, for example) wear away more easily than others (such as sandstone or limestone).
6. The river wears away the weak rock and travels across the surface of stronger rocks. These more resistant rocks become the capstones to waterfalls.
7. Undercutting causes an overhang of the hard rock.
8. Over time the hard rock is unsupported and collapses due to gravity into the plunge pool.
9. Attrition can occur where the rocks in the plunge pool hit off each other, eroding them further.
10. Over time, the waterfall retreats upstream.
    * The height and number of waterfalls along a stream or river depends upon the type of rocks that are being eroded by the water.

Question 3

Formation of a meander

Answer 3

1. Water twists and turns around stones and other obstructions resulting in areas of slower and faster water flow.
2. Water moving faster has more energy to erode. This occurs on the outside of the bend and forms a river cliff.
3. The river erodes the outside bends through corrasion, corrosion and hydraulic action.
4. Water moves slowly on the inside of the bend and the river deposits some load, forming a river beach/slip-off slope.
   * Meanders are mostly found in the middle and lower courses of a river.

Question 4

Formation of an oxbow lake

Answer 4

1. After a long period of continual erosion, the meander in a river becomes very curved and deposition narrows the neck of the meander.
2. Eventually the river cuts through the neck during a flood, cutting off the meander and forming an oxbow lake.
3. The river continues on its straighter path and the meander is abandoned.
4. The fastest current will now be flowing in the centre of the river channel and deposition is more likely to occur beside the banks.
5. New deposition seals off the ends, and the cut-off becomes an oxbow lake that will eventually dry up.

Question 5

What is a drainage basin?

Answer 5

• A drainage basin is the area from which one river and its tributaries receives water from above and below the ground.
• A drainage basin is an example of an open system because it is open to inputs from outside, such as precipitation, and is responsible for outputs out of the system, such as output of water into the sea and evaporation of water into the atmosphere.

Question 6

Drainage basin input

Answer 6

Precipitation, mainly in the form of rainfall and snow, with the amount and duration having an impact on the level of water in the system.

Question 7

Drainage basin storage

Answer 7

Water is stored:
* On the surface in lakes and rivers
* Underground in the groundwater store through the processes of infiltration and percolation.
* In leaves and roots of vegetation with water also seeping into the ground by interception.
* As soil moisture in the upper layers or deeper down in rock stores such as the water table.

Question 8

Drainage basin transfer

Answer 8

Water is transferred through:
* Overland flow - transfers water through the basin either as sheetwash, across the surface, or in tiny channels called rills.
* Throughflow - transfers water beneath the surface. Water moves through upper soil layers towards the river, with the much slower groundwater flow taking longer to enter the river.
* Movement of clouds bearing moisture by the process of advection.
* Water that has been intercepted by foliage, either directly as throughfall, or by running down branches and stems via stemflow.

Question 9

Drainage bain output

Answer 9

• The most typical output of a drainage basin is surface runoff into the seas or oceans.
• Some water can also be lost to direct evaporation.

Question 10

Factors affecting storm hydrographs

Answer 10

1. Large drainage basins catch more precipitation so have a higher peak discharge compared to smaller basins.
2. Smaller basins generally have shorter lag times because precipitation does not have as far to travel.
3. Drainage basins with steep sides tend to have shorter lag times than shallower basins. This is because water flows more quickly on the steep slopes down to the river.
4. Basins that have many streams (high drainage density) drain more quickly so have a shorter lag time.
5. If the drainage basin is already saturated, then surface runoff increases due to the reduction in infiltration. Rainwater enters the river quicker, reducing lag times, as surface runoff is faster than baseflow or through flow.
6. If the rock type within the river basin is impermeable surface runoff will be higher, throughflow and infiltration will also be reduced meaning a reduction in lag time and an increase in peak discharge. Areas that have been urbanised result in an increase in the use of impermeable building materials.
7. Heavy storms with high precipitation result in more water entering the drainage basin which results in a higher discharge.