hydrosphere Flashcards
waterfall
Waterfalls form where water rushes down steep hillsides in upland areas and erodes the rocks
Hydraulic action of fast flowing water compresses air into the river bank causing materials to be dislodged
The force of the water throws bedload against the banks, causing erosion through abrasion
Solution also occurs when soluble rocks react with acids in the water, further weakening the banks
Differential erosion takes place over bands of more and less resistant rock/where harder rock is overlaying softer rock/bands of hard/soft rock
Some types of rocks (shale, for example) wear away more easily than others (such as sandstone or limestone)
The river wears away the weak rock and travels across the surface of stronger rocks. These more resistant rocks become the capstones to waterfalls
Undercutting causes an overhang of the hard rock
Over time the hard rock is unsupported and collapses due to gravity into the plunge pool
Attrition can occur where the rocks in the plunge pool hit off each other, eroding them further
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
ox-bow lake
A meander is a bend, loop, turn, or winding in the channel of a river produced by a stream or river swinging from side to side as it flows across its floodplain or shifts its channel within a valley
Water twists and turns around stones and other obstructions resulting in areas of slower and faster water flow, with faster moving water having more energy to erode. This occurs on the outside of the bend and forms a river cliff
The river erodes the outside bends through corrasion, corrosion and hydraulic action
Water moves slowly on the inside of the bend and the river deposits some load, forming a river beach/slip-off slope
After a long period of continual erosion, the meander in a river becomes very curved and deposition narrows the neck of the meander
Eventually the river cuts through the neck during a flood, cutting off the meander and forming an oxbow lake, then the river continues 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 an oxbow lake that will eventually dry up
v-shaped valley
When a river flows down a hill in the upper course it has a lot of excess energy. This causes the river to erode vertically by corrasion and hydraulic action
As a small valley begins to form, weathering of the land beside the river weakens the exposed sides
Mass movement including soil creep also occurs when the soil is very saturated or due to gravity
All of this causes material to fall into the river which helps with further corrasion while other rock fragments collect beside the river and so make the slope at the bottom more gentle
drainage basin
Input:
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.
Storage:
Water is stored on the surface in lakes and rivers. Water can be stored underground in the groundwater store through the processes of infiltration and percolation.Water is stored in leaves and roots of vegetation with water also seeping into the ground by interception (ie, the storage of water on leaf and plant stems). Can be stored as soil moisture in the upper layers or deeper down in rock stores such as the water table.The amount of water stored will vary depending on the porosity of the soil and on the permeability of the rock.
Transfer:
The sum of all the water flowing over the drainage basin’s surface is called runoff. Runoff is made up of streamflow, which is flow through permanent river channels, and overland flow or surface runoff. Overland flow transfers water through the basin either as sheetwash, across the surface, or in tiny channels called rills. Beneath the surface, water is transferred via throughflow - the movement of water through the upper soil layers towards the river, with the much slower groundwater flow taking longer to enter the river. Transfer also occurs through the movement of clouds bearing moisture by the process of advection. Water that has been intercepted by foliage may also be transferred, either directly as throughfall, or by running down branches and stems via stemflow.
Output:
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. Moisture can be lost through plants withdrawing water from the soil via their roots
8 physical influences on hydrographs
Large drainage basins catch more precipitation so have a higher peak discharge compared to smaller basins. Smaller basins generally have shorter lag times because precipitation does not have as far to travel.
The shape of the drainage basin also affects runoff and discharge. Drainage basins that are more circular in shape lead to shorter lag times and a higher peak discharge than those that are long and thin because water has a shorter distance to travel to reach a river.
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.
Basins that have many streams (high drainage density) drain more quickly so have a shorter lag time.
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.
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.
If a drainage basin has a significant amount of vegetation this will have a significant effect on a storm hydrograph. Vegetation intercepts precipitation and slows the movement of water into river channels. This increases lag time.
Water is also lost due to evaporation and transpiration from the vegetation. This reduces the peak discharge of a river.
2 human influences on hydrographs
Drainage systems that have been created by humans lead to a short lag time and high peak discharge as water cannot evaporate or infiltrate into the soil.
Areas that have been urbanised result in an increase in the use of impermeable building materials. This means infiltration levels decrease and surface runoff increases. This leads to a short lag time and an increase in peak discharge.
