Explain Orographic rainfall
- Warm moist air rises over a barrier such as a mountain
- As it rises the air cools and condenses due to cooler temperatures
- It rains on the high ground which results in a rain shadow down the slope
Explain is Cyclonic rainfall?
- Warm air rises over cool air as it is less dense
- The vapour condenses and leads to rain
- Cumulus clouds are formed
Explain Conventional rainfall?
- Warm air rises, as it rises it cools due to lower temperatures
- As it cools it condenses and rains
- The cool air then descends and is replaced by warm air (continuing the cycle)
Describe the best conditions for interception and infiltration
- Coniferous forest
- non-intense rainfall
- small waterbed
- little to no wind
- flat slope
- thin soil
Describe the worst conditions for interception rates and infiltration
- deforested
- intense rainfall
- saturated soil
- windy
- steep slope
Describe the best conditions for percolation and groundwater flow
- sandy soil
- structured soil
- pervious /permeable rock
- near water storage
What affects Evapotranspiration rates and how?
- Temperature, high temperatures increase the rate of photosynthesis which releases water vapour
- Wind, wind reduces relative humidity which increases rates of transpiration
- Vegetation cover, more vegetation more plants transpiring
- Soil moisture content determines the volume of water available for transpiration
What is channel flow?
Water that has collected to flow in a rivulet, stream in a river and is another output from the drainage basin system
Name the human disruptions in the drainage basin
- Cloud seeding
- Dam construction
- Urbanisation
- Farming
- Groundwater extraction
What is water budget?
the natural balance between inputs and outputs in a given river area. Formula used is P=Q+E±S where P=Percipitation Q=channel discharge E=evepotranspiration and S=change in store
What units are used to measure the river discharge?
Cumecs (m^2s^-1)
What factors affect a river regime?
- Size of the river
- Volume, pattern and intensity of precipitation
- Temperatures and seasonality
- Geology and groundwater soils
- Amount and type of vegetation around the soil
- Human activity (e.g. dams)
Describe a simple river regime
- Rivers experience a period of seasonally high discharge followed by low discharge
- This is typical of rivers where inputs depend on glacial meltwater, snowmelt or seasonal storms (e.g. monsoons)
- Rivers with temperate climates which rise in mountainous regions where summer snowmelt occurs tend to be like this
Describe a complex regime
- Large rivers which cross several different relief and climatic zones and therefore experience the effects of different seasonal climatic event, (E.g. Mississippi or Ganges)
- Human factors contribute to the complexity such as damming rivers for energy or irrigation
What physical factors contribute to a “flashy” hydrograph?
-Weather/Climate: storms, soil exceeding infiltration capacities, rapid snowmelt or prolonged rainfall
-Rock type: Impermeable which restrict percolation and encourage rapid runoff
-Soil type: Clay soils are low in porosity and grains swell when water is absorbed, this means the soil saturates quickly
-Drainage basin: small basins fill quicker, circular basins are equidistant
-Vegetation: Less vegetation increases runoff and decreases lag time
Antecedent conditions: Pre-saturated soil, high water table, low infiltration and percolation due to saturation of the soild
