Hydrosphere Flashcards
River erosion.
4 processes cause erosion in a river:
- attrition, when boulders, rocks and pebbles crash into each other and bits break off, making them rounder and smaller in size.
- corrasion, the wearing away of the river bed and the banks by the river’s load. this is the primary method of erosion.
- hydraulic action, the sheer force of the river hitting against the banks compresses air into the cracks of the rocks and particles break off.
- corrosion, dissolving of minerals in rocks by the river water.
The formation of a v-shaped valley.
a river flows downhill quickly and erodes the landscape vertically. the river cuts a deep gash into the landscape using hydraulic action, corrosion and corrasion. hydraulic action is the sheer force of the river hitting against the banks and compresses air into the cracks of the rocks and particles break off; corrosion is the dissolving of minerals in rocks by the river water: corrasion is the wearing away of the river bed and banks by the river’s load hitting against them. as the river erodes downwards, the sides of the valley are exposed to freeze-thaw weathering. this process loosens rocks and they fall into the river. this helps to produce steep valley sides. the rocks which have fallen into the river assist the process of corrasion which leads to further erosion.. the river transports rocks downstream. the process of attrition helps to break rocks down and they become smaller and rounder. the river channel becomes wider and deeper creating a v-shaped valley between interlocking spurs.
The formation of a waterfall.
the river flows over bands of less resistant and resistant rocks. the less resistant rocks are quickly worn away due to differential erosion. the river erodes in three main ways: hydraulic action when the sheer force of the water gets into cracks and breaks down the rock; corrasion when the river bed and banks are eroded by the load hitting against them; corrosion when the river water dissolves minerals from the rocks and washes them away. the river undercuts the harder rock leaving an overhang which becomes unsupported and collapses into the plunge pool below. after the overhang falls, some of the rocks are swirled around by the river and this helps to form a deep plunge pool below the waterfall. the plunge-pool is also deepened during times of high discharge when hydraulic action is most powerful. the waterfall is moved upstream, the process continues and a steep-sided gorge is cut into the back of the hillside.
The formation of a meander.
in a straight river channel, pools and riffles will develop as water twists and turn around obstructions such as large boulders. this results in areas of slower and faster water movement. pools are areas of deep water and greater erosion. riffles are areas of shallow water created by the deposition of coarse sediment. once pools and riffles have developed, the river flows from side to side in a winding course. a corkscrew-like flow of water called a helicoidal flow moves material from the outside of one meander bend and deposits it on the next bend. water moving faster has more energy to erode. this occurs on the outside bend and forms a river cliff. the river erodes the outside bend by hydraulic action, corrasion and corrosion. hydraulic action is when the sheer force of the water gets into cracks and breaks down the rock. corrosion is when the chemicals in the river water dissolve minerals on the rock and wash them away. corrasion when the river bed and banks are eroded by the load hitting against them. water moves more slowly on the inside of the bend and the river deposits some load, forming a gently sloping river beach. 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.
The formation of an oxbow lake.
the river is meandering across the valley and erodes laterally. most water is directed towards the outside bend, there is also reduced friction and increased velocity. the fast flowing water erodes the outside bends using hydraulic action when the sheer force of the water gets into small cracks and breaks down the rock, corrosion when the river water dissolves minerals from the rocks and washes them away and corrasion when the river banks are less eroded by the load hitting against them. there is less water on the inside bend, an increase in friction and decrease in velocity. as the river has less energy, it deposits material so its course is changing. over time, continual erosion and deposition narrows the neck of the meander. often during a flood the river will cut through the neck of the meander. the river continue on its straighter path and the meander is abandoned. the fastest current will now be flowing in the centre of the river channel and deposition is more likely to occur beside the banks. new deposition seals off the ends and the cut-off becomes and oxbow lake that will eventually dry up, except during periods of very heavy rainfall.
Drainage basin.
inputs:
the main input to the drainage basin is through precipitation so this input can vary depending on the type of precipitation eg rain, snow, sleet; how long the precipitation lasts and how intense the precipitation is.
storage:
stored water is held within the drainage basin system in lakes/lochs, this is known as surface storage.
water can also be stored by being absorbed by soils and stored by trees, this is known as interception.
- the amount of water that can be stored as groundwater depending on the rock type underlying the soil. if the rock is porous then water can be stored in the rocks/ underground.
- human activity can also interrupt the flow of water and can be dammed by HEP to create reservoirs to produce electricity or store fresh water. furthermore, forestry plantations in a catchment area will store more water.
transfers/flows:
- water transfers through tributaries and rivers known as surface runoff and the amount will depend on how many tributaries there are and how big the catchment area is.
- water can transfer by infiltrating through the soil and transfer through the soil known as through-flow and this is dependent on how porous the soil is.
- water can percolate through rock this is known as infiltration and there will be more infiltration if the rock is permeable. when water transfers through the rock this is known as groundwater flow.
- during periods of heavy rainfall the soil and sub-soil may become saturated resulting in an increase in surface run-off.
- sub rock may be impermeable meaning it contributes to increased groundwater flow.
output:
- evapotranspiration is the combined return of water into the atmosphere by evaporation and transpiration. Evaporation is the water loss from the ground or water surfaces driven by the heat energy from the sun. transpiration is water loss from vegetation. the hotter the temperatures then the more evapotranspiration there will be.
- river channel/course will eventually take the water from the drainage basin system out towards a sea or lake.
Factors affecting hydrographs.
area (basin size),
large basins receive more precipitation than small and therefore have a larger
runoff.
the larger size means a longer lag time as water has a longer distance to travel to reach the trunk river.
shape,
the elongated basin will produce a lower peak flow and longer lag time than a circular one of the same size.
slope,
the steeper the slopes, the faster the water flows overland and into rivers, making the rising limb steeper.
if the land is more gently sloping water flows over it more slowly and is, therefore, more likely to infiltrate soil- throughflow is slower than overland flow so the resulting rising limb will be less steep.
rock type,
permeable rocks mean rapid infiltration and little overland flow therefore shallow rising limb, less channel-fill and a longer lag time.
impermeable rocks mean faster channel-fill, steeper rising limb and a shorter lag time
