Water budgets and river systems Flashcards
What is a water budget? (definition)
A water budget is the annual balance between precipitation, evapotranspiration and runoff.
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.
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.)
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.
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.
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.
What are the variable factors that influence the character of a river regime?
- The size of the river and where discharge measurements are taken along its course.
- The amount, seasonality and intensity of the precipitation.
- The temperatures, with possible meltwater and high rates of evaporation in summer.
- The geology and soils, particularly their permeability and porosity; groundwater noted in permeable rocks is gradually released into the river as base flow.
- The type of vegetation cover: wetlands can hold water and release it slowly into the river.
- Human activities aimed at regulating a river’s discharge.
What does a typical water budget graph look like? (A picture would help like but I am not paying to use a fucking 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. Precipitation > potential evapotranspiration.
F. Soil water store is full, field capacity has been reached.
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.
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.
In a storm hydrograph, once the rainfall starts and the discharge beings to rise; what is this known as?
The rising limb
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.
What is the time interval between peak rainfall and peak discharge known as?
The lag time
What is a falling or recessional limb?
Once the input of rainwater into the river starts to decrease, so does the discharge.
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
What a ‘flashy’ hydrographs?
When hydrographs have very steep limbs, especially rising limbs, a high peak discharge and a short time lag.
What are ‘flat’ or ‘delayed’ hydrographs?
Hydrographs with gently inclined limbs, a low peak discharge and a long lag time.
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
