Water Budgets :D

• Created by: Iskall
• Created on: 25-09-18 19:38
What is a water budget? (definition)
A water budget is the annual balance between precipitation, evapotranspiration and runoff.
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What is the formula for a water budget?
P = E + R ± S P is precipitation E is evapotranspiration R is runoff S represents changes in storage over a period of time, usually one year.
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What do water budgets on a national or regional scale indicate?
The amount of water that is available for human use (for agriculture, domestic consumption etc.)
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What do water budgets on a local scale inform about and who is it useful for?
At a local scale, water budgets can inform about available soil water. This is valuable to users such as farmers who can use it to identify when irrigation might be required and how much.
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What is available soil water?
Available soil water is the amount of water that can be stored in the soil and is available for growing crops.
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What is a river regime?
A river regime is the annual variation in the discharge or flow of a river at a particular point, and is usually measured in cumecs.
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What are the variable factors that influence the character of a river regime?
1. The size of the river and where discharge measurements are taken along its course. 2. The amount, seasonality and intensity of the precipitation. 3. The temperatures, with possible meltwater and high rates of evaporation in summer. 4. The geology
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What does a typical water budget graph look like? (A picture would help like but I am not paying to use a ******* flash card website)
A. Precipitation > potential evapotranspiration. B. Potential evapotranspiration > precipitation C. Soil moisture store is now used up D. There is a deficiency of soil water as the store is used up and potential evapotranspiration > precipitation E.
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How does a storm hydrograph differ from a river regime?
Whereas river regimes are usually graphed over the period of a year, storm hydrographs show discharge changes over a short period of time, often no more than a few days.
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What two things does a storm hydrograph plot?
The occurrence of a short period of rain (maybe a heavy shower or storm) over a drainage basin. Subsequent discharge of the river.
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In a storm hydrograph, once the rainfall starts and the discharge beings to rise; what is this known as?
The rising limb
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Why is peak discharge reached some time after the peak rainfall?
The water takes time to move over and through the ground to reach the river.
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What is the time interval between peak rainfall and peak discharge known as?
The lag time
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What is a falling or recessional limb?
Once the input of rainwater into the river starts to decrease, so does the discharge.
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Once the input of rainwater into the river starts to decrease, so does the discharge, what is this known as?
The falling or recessional limb
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What a 'flashy' hydrographs?
When hydrographs have very steep limbs, especially rising limbs, a high peak discharge and a short time lag.
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What are 'flat' or 'delayed' hydrographs?
Hydrographs with gently inclined limbs, a low peak discharge and a long lag time.
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What effects does urbanisation have on hydrological processes in a storm hydrograph?
Construction work Bare soil replaced by concrete and tarmac High density of buildings Drains and sewers Urban rivers channalised Bridges
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How does construction work affect the hydrological process in relation to a storm hydrograph?
Construction work leads to the removal of the vegetation cover. This exposes the soil and increases overland flow.
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How does bare soil being replaced by concrete and tarmac affect the hydrological process in relation to a storm hydrograph?
Bare soil is eventually replaced by a covering of concrete and tarmac, both of which are impermeable and increase surface runoff.
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How does the high density of buildings affect the hydrological process in relation to a storm hydrograph?
The high density of buildings means that rain falls on roofs and is then swiftly fed into drains by gutters and pipes.
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How do drains and sewers affect the hydrological process in relation to a storm hydrograph?
Drains and sewers reduce the distance and time rainwater travels before reaching a stream or river channel.
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How do channelised urban rivers affect the hydrological process in relation to a storm hydrograph?
Urban rivers are often chhannelised with embankments to guard against flooding. When floods occur, they can be more devastating.
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How do bridges affect the hydrological process in relation to a storm hydrograph?
Bridges can restrain the discharge of floodwaters and act as local dams, this prompting upstream floods.
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What is the list of physical factors affecting the shapes of 'flashy' and 'flat' storm hydrographs?
Weather/climate Rock type Soils Relief Basin size Shape Drainage density Vegetation Pre-existing(antecedent) conditions Human activity
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How does weather/climate affect a 'flashy' river?
Intense storm that exceeds the infiltration capacity of the soil. Rapid snowmelt as temperatures suddenly rise above zero. Low evaporation rates due to low temperatures.
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How does weather/climate affect a 'flat' river?
Steady rainfall that is less than the infiltration capacity of the soil. Slow snowmelt as temperatures gradually rise above zero. High evaporation rates due to high temperatures.
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How does rock type affect a 'flashy' river?
Impermeable rocks, such as granite, which restrict percolation and encourage rapid surface runoff.
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How does rock type affect a 'flat' river?
Permeable rocks, such as limestone, which allow percolation and so limit rapid surface runoff.
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How does soil affect a 'flashy' river?
Low infiltration rate, such as clay soils (0-4mm/h)
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How does soil affect a 'flat' river?
High infiltration rate, such as sandy soils (3-12mm/h)
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How does relief affect a 'flashy' river?
High, steep slopes that promote surface runoff.
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How does relief affect a 'flat' river?
Low, gentle slopes that allow infiltration and percolation.
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How does basin size affect a 'flashy' river?
Small basins tend to have more flashy hydrographs.
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How does basin size affect a 'flat' river?
Larger basins have more delayed hydrographs; it takes time for water to reach gauging stations.
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How does basin shape affect a 'flashy' river?
Circular basins have shorter lag times
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How does basin shape affect a 'flat' river?
Elongated basins tend to have delayed or attenuated hydrographs.
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How does drainage density affect a 'flashy' river?
High drainage density means more streams and rivers per unit area, so water will move quickly to the measuring point.
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How does drainage density affect a 'flat' river?
Low drainage density means few streams and rivers per unit area, so water is more likely to enter the ground and move slowly through the basin.
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How does vegetation affect a 'flashy' river?
Bare/low density, deciduous in winter, means low levels of interception and more rapid movement through the system.
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How does vegetation affect a 'flat' river?
Dense, deciduous in summer, means high levels of interception and a slower passage through the system; more water lost to evaporation from vegetation surfaces.
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How do pre-existing (antecedent) conditions affect 'flashy' rivers?
Basin already wet from previous rain, water table high, soil saturated so low infiltration/percolation.
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How do pre-existing (antecedent) conditions affect 'flat' rivers?
Basin dry, low water table, unsaturated soils, so high infiltration/percolation.
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How does human activity affect 'flashy' rivers?
Urbanisation producing impermeable concrete and tarmac surfaces. Deforestation reduces interception. Arable land, downslope ploughing.
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How does human activity affect 'flat' rivers?
Low population density, few artificial impermeable surfaces. Reforestation increases interception. Pastoral, moorland and forested land.
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Why have planners become important players in managing the impacts of urbanisation on the flood risk?
Many towns and cities are naturally prone to flooding because of their locations. Numbers of people who live in urban places and who therefore need protection. Huge amount of money invested in urban property.
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What actions foes flood risk management involve?
Strengthening the embankments of streams and rivers... Putting in place flood emergency procedures. Steering urban development away from high-risk areas such as floodplains.
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Other cards in this set

Card 2

Front

P = E + R ± S P is precipitation E is evapotranspiration R is runoff S represents changes in storage over a period of time, usually one year.

Back

What is the formula for a water budget?

Card 3

Front

The amount of water that is available for human use (for agriculture, domestic consumption etc.)

Card 4

Front

At a local scale, water budgets can inform about available soil water. This is valuable to users such as farmers who can use it to identify when irrigation might be required and how much.

Card 5

Front

Available soil water is the amount of water that can be stored in the soil and is available for growing crops.