EQ1 5.3 WATER BUDGETS AND RIVER SYSTEMS Flashcards
what is the water budget
there is usually a natural rhythm that balances out times of surplus with times of deficit.
what is the best place to observe and measure the water budget
a drainage basin because factors within the basin control the amount of water available at any givern time
what is water surplus
precipitation is greater than evapotranspiration
what is soil moisture utilisation
soil moisture starts to be used up by plants
what is soil moisture deficit
evapotranspiration is greater than precipitation and any previously available moisture has been used (in soil moisture utilisation)
soil moisture recharge
recharge occurs when water is replaced after a drier period
field capacity
the maximum amount of water soil can hold
what inputs affect the water budget
precipitation, water diversion into the area, groundwater flow,surface flow, surface runoff
what outputs affect the water budget
evapotranspiration,water diversion out of the area,groundwater flow, surface water flow, surface runoff, , industrial or residential use
what is a river regime
the annual pattern of of discharge
what is a simple river regime
river experiences a period of seasonally high discharge followed by low discharge- typical of rivers that rely on glacial melt water or seasonal storms
what is a complex river regime
when larger rivers cross various relief or climactic zones eg. mississippi or are subject to human factors
what is a storm hydrograph
a hydrograph is a graph showing the discharge of a river at a given point over a period of time.
what does a hydrograph show
how a river responds to a particular storm
what is the rising limb
water makes its way down valley sides and into the river, the discharge increases (rising limb)
what is the lagtime
the gap between the peak rainfall and peak discharge is called the lagtime
what is the water budget
The balance between water being evaporated from the oceans and precipitated onto the land
what is fossil water
non-renewable, untouched, ancient freshwater stores
where can we find fossil water
beneath deserts and in polar areas
what is the impact of new technology on fossil water
New technology is now allowing us to access more of this water. For example, the extension of oil drilling technology and the use of satellite imagery can increase use of these fossil aquifers.
what is another examples of a non-renewable store of water
The cryosphere (glaciers and ice caps) is another non-renewable store as it continues to melt.
polar hydrology
The Polar area is also referred to as the cryosphere (ice-sheets and glaciers).
There is very little vegetation due to low temperature and limited light, so the ability for plants to grow is reduced.
polar hydrology in winter
During the winter, the ground, lakes and rivers are frozen in the cryosphere. Winter snow and ice mean that 85% of solar radiation is reflected.
Permafrost is soil that is permanently frozen.
polar hydrology in summer
In the spring and summer frozen water thaws in the cryosphere causing rapid surface runoff, resulting in increased evaporation.
As ice and soils thaw, biogenic gases (gases produced by or used by organisms e.g. methane) are released into the atmosphere.
tropical hydrology
In the tropical rainforest, there is little seasonal variation due to the consistent temperature, high rainfall and consistent sunlight.
There is a high density of vegetation that collects the majority of precipitation.
Around 50% of the precipitation is returned via evapotranspiration.
Rainforests are able to generate their own water cycle due to convectional rainfall.
Convectional rainfall is when the forest floor is warm and so the air on the surface heats up and expands. This air rises and condenses, forming rain clouds.
tropical rainfall deforested
Deforestation reduces evapotranspiration which in turn reduces precipitation levels and water supply as less water is being put back into the cycle via plants. It instead will have to flow through streams and rivers, taking longer to cycle through.
Vegetation is crucial for the area’s convectional rainfall.
Rainfall is essential for all rainforest life, so severe deforestation would have devastating knock-on effects on the rest of the ecosystem.
rainfall in tropics
The tropics receive a high concentration of solar radiation so there is a lot of ocean evaporation, resulting in high rainfall.
where does the yukon river flow through
it flows through alaska
what are the weather conditions in alaska
Conditions in Alaska are highly variable across the seasons. In the winter, conditions are near polar, but temperatures soar in the summer.
what climates does the yukon river flow through
different types of climates including the tundra and mountain
In winter, precipitation is frozen how does this affect the flow
This causes the Yukon’s flow to be low.
In summer, there is precipitation that does not freeze and also snowmelt of the winter’s precipitation. how does this affect flow
this causes the Yukon’s flow to be high
is there human influence on the river yukon
As the area is a largely natural landscape, there is very little human influence on the river’s flow.
what is the climate like in the amazon
The Amazon River flows through the Amazon rainforest where the climate is tropical.
Although the Amazon has a relatively consistent high temperature and rate of precipitation, there is some seasonal precipitation that leads to a lower river discharge.
The temperature and high biodiversity lead to very high levels of evapotranspiration.
seasonality in the amazon affecting flows
consistent temperatures and rainfall create a largely consistent river flow. Some lower rainfall in September and December leads to a lower river flow.
La Niña and El Niño years also produce changes in rainfall, which affects river discharge levels.
human influences affecting flows in the amazon
Deforestation affects interception, infiltration and surface runoff increasing the flow.
Large dams used by Brazilian cities for both hydroelectric power and irrigation can cause more discharge above the dam and a reduced flow below the dam.
the murray-darling river climate
The Murray-Darling is in Australia where the climate is seasonal sub-tropical.
Most of the Murray-Darling’s basin is in a rain shadow.
This means that the basin is surrounded by mountains that collect most of the region’s rain. This can cause periods of prolonged drought.
The tributaries to the north experience a monsoon climate, whilst the southern tributaries experience temperate climate.
There are wet (Aug-Nov) and dry (Jan-Apr) seasons that cause high and low river flows respectively.
seasonality in the murray-darling river
There is a high seasonal variability for the Murray-Darling’s discharge because of the clear wet and dry seasons.
The river is also impacted by the changes in rainfall patterns during La Niña and El Niño years.
La Niña brings cooler than normal sea surface temperatures and wetter weather to Australia.
El Niño brings the opposite; less rainfall.
human influence in the murray-darling river
Water is drawn from the Murray-Darling for use in Australia’s cities and also to irrigate farms.
The natural flow paths of the river have been altered for human access, which has led to loss of habitat for local animals and a decline in quality of water.
hydrographs
Hydrographs show how river discharges changes over time at a particular point in a river.
how does increased runoff affect a hydrograph
Increased runoff leads to a reduced lag time and greater discharge, producing a steep hydrograph because more water gets into the river channel quicker.
what is river discharge
River discharge is the volume of water flowing in a river each second and is measured in cumecs (m3/s).
peak discharge
maximum discharge in the period of time.
peak rainfall
maximum rainfall in the period of time.
lag time
the interval between peak rainfall and discharge.
rising limb
when the discharge is rising
falling limb
when the discharge is falling
how does permeable rock and soil affect the hydrograph
If the rock and soil is permeable (i.e. Limestone), precipitation will be able to infiltrate and percolate which lengthens the lag time and reduces the peak discharge.
how does impermeable rock and soil affect the hydrograph
Impermeable rocks and soils (i.e. clay) stop precipitation infiltrating so surface runoff increases. Lag time is reduced and peak discharge is increased in these circumstances.
how does saturated or frozen soil affect the hydrograph
If the soil is fully saturated or frozen by antecedent conditions, there will not be any infiltration leading to increased surface runoff, increasing the peak discharge.
how does the steepness of the land affect the lagtime
The steeper the catchment of the river basin, the quicker the water reaches the river which increases peak discharge and reduces lag time.
how does the level of vegetation affect the hydrograph
River catchments with high levels of vegetation will see high interception and evapotranspiration.
how does the tree roots affect the hydrograph
Tree roots help to promote infiltration and results in catchments with more vegetation having a lower surface runoff, and reduced peak discharge.
how does the shape of the catchment affect the hydrograph
The larger the catchment area of the river basin, the higher the peak discharge but the longer the lag time.
The more circular the catchment area shape, the shorter the lag time.
how does the drainage basin affect the hydrograph
Denser drainage networks transport water more efficiently, increasing the flow and peak discharge.
how does the land use affect the hydrograph
Areas that remain forested or as their natural habitat will see reduced peak discharge due to an increase in infiltration and interception of precipitation by vegetation.
There will be less interception in areas that have been deforested. This will increase the peak discharge.
Ploughing of agricultural land increases surface runoff. This causes lag time to reduce and peak discharge to increase.
how does the urbanisation affect the hydrograph
Urbanisation leads to an increase in the number of impermeable surfaces (tarmac, concrete and tiles).
Impermeable surfaces lead to a decrease in infiltration, an increase in surface runoff and ultimately a reduction in the lag time. A shorter lag time means a greater peak discharge.
how does the water management affect the hydrograph
Dams and reservoirs can be used to regulate the flow of the river by storing water and choosing when to release it downstream.
Abstraction of aquifers lowers groundwater levels and increases percolation and infiltration when rainfall happens.
