Hydrology

Hydrology

What is a drainage basin?
1. Open system
  1. Inputs and Outputs but also the movement within the system
  2. Area changes characteristics
    1. For example, a drainage basin in america would have high evaporation and low physical output to the see
Inputs and outputs of a drainage basin
1. INPUTS
  1. Precipitation
    1. rain
    2. snow
    3. Hail
    4. Condensation
      1. Vapour to liquid
      2. Due to the cooling of the vapour
        Hills
        The cloud rises up the hill, cools and falls (Rain shadow on the other side
        Convectional Rain
        often occurs near the equator
        The heat causes the air to rise and condense very quickly- Thunderstorms occur
        Frontal
        Cold air meets hot air
        Warm air is less dense so rises, condenses and falls as rain
      3. Occurs on surfaces (ground)
        Attaches itself to dust particles
2. OUTPUTS
  1. River discharge
  2. Evaporation
  3. Transpiration
    1. plants
  4. inter basin transfer
    1. When rocks allow water to flow through them, transferring the water to another basin
    2. Man made:- Locks, canals
    3. Common example: Escarpment where the dip encourages the movement of water underground
  5. Evapotranspiration
    1. Easy pathway for moisture to return to the atmosphere
what is the water balance?
1. Shows the equilibrium in the drainage basin: Between outputs and Inputs
  1. in England: Input exceeds Output
  2. P = Q + E
    1. P= precipitation
    2. Q= runoff
    3. E= evapotranspiration
Processes and Stores
1. Soil stores
  1. essential for our food.
  2. highly variable becoming completely saturated after prolonged rain and dryed out within weeks with little rain. Farmers often try to alter the soil storage to suit crops needs. Drainage can reduce excess moisture and irrigation tops up soil moisture defiencies
  3. depends on several factors such as soil depth, soil texture, soil structure and land use management practises.
  4. Field capacity: the natural amount of water that the soil can hold.
2. Ground water stores
  1. in permeable rocks
  2. large stores of ground water are called aquifers and the surface of this underground water is the water table. This moves up and down depending on the level of water. If water is extracted, the water table goes down.
3. Surface storage
  1. any body of water from a puddle to a lake.
Human affect
1. Human activity can modify the storage. eg. terracing, a deliberate design in order to improve the water balance.
2. Deforestation- Reduces the amount of water that is held above land in the trees.(reduces stores)
Storm Hydrographs
1. What affects the shape?
  1. Lag time. This is the time it takes for water to move through the systems and stores of a basin
2. a graph that shows discharge and rainfall in a drainage basin
3. Rain fall is the bar graph, Discharge is the line.
Flooding
1. Causes
  1. Fluvial flooding: these are caused by a long period of rainfall over a large area or because of rapid melting of snow or ice.
  2. Flash flooding: This is caused by excessive and localised rainfall that accumulates in low-lying areas when the soil becomes too saturated and cannot absorb any more water.
  3. Groundwater flooding: This is caused when the water table rises too much and causes overland flow, this type can last for days or weeks
  4. Dam Failure: The release of huge amounts of water caused by design failure or ageing construction materials. can also be caused by earthquakes or landslides.
2. Impacts
  1. environment destroyed
  2. Economy loss
  3. Loss of lives
  4. Loss of homes and businesses
  5. Spread of disease
3. Stategies
  1. Effectiveness?
    1. soft engineering tends to be cheaper, and works WITH nature, rather than against it.
    2. Hard engineering needs to be replaced and often gets damaged. Not only this but it is often referred to as an eyesore.
  2. Hard engineering
    1. Flood walls and embarkments
    2. River channelisation (EG. MISSISSIPPI)
    3. Dams and reservoirs
  3. Soft engineering
    1. Afforestation
    2. Provision of wetlands
    3. Land-use management

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