Operation of the Drainage Basin as an Open System Flashcards
Catchment
The area of land drained by a river and it’s tributaries
Watershed
The highland which divides and separates waters to flowing rivers
Condensation
The change from a gas to a liquid, such as when water vapour changes into water droplets
Dew point
The temperature at which dew forms; it is a measure of atmospheric moisture
Convectional Rainfall
Often associated with intense thunderstorms, which occur widely in areas with ground heating such as the Tropics and continental interiors
Cyclonic Rainfall
A period of sustained, moderately intensive rain; it is associated with the passage of depressions
Orographic Rainfall
Concentrated on the windward slopes and summits of mountains
Interception loss
This is water retained by plant surfaces and later evaporated or absorbed by the vegetation and transpired
Throughfall
This is when the rainfall persists or is relatively intense, and the water drops from the leaves, twigs, needles etc
Stem Flow
This is when the water trickles along twigs and branches and then down the trunk
Infiltration
The movement of water from the ground surface into soil
Infiltration Capacity
The maximum rate at which rain can be absorbed by soil
Surface run-off
The movement of water that is unconfined by a channel across the surface of the ground. Also known as overland flow
Percolation
The transfer of water from the surface or from the soil into the bedrock beneath
Saturated Overland Flow
The upward movement of the water table into the evaporation zone
Evapotranspiration
The combined effects of evaporation and transpiration
Channel flow
The flow of water in streams or rivers
Channel Storage
The storage of water in streams or rivers
Potential Evapotranspiration
The water loss that would occur if there was an unlimited supply of water in the soil for use by vegetation
Deforestation
The cutting down and removal of all or most of the trees in a forested area
Afforestation
The planting of trees in an area that has not been forested in recent times
Drainage basin
The area of land drained by a river and its tributaries
Drainage Basin
The area of land drained by a river and it’s tributaries
Inputs of drainage basin
Precipitation
Impacts of inputs on drainage basin depend on:
The amount of precipitation The type of precipitation Seasonality Intensity of precipitation Variability
Secular variability
Long term variability, result of climate change trends
Periodic variability
Happens in annual, seasonal, monthly, diurnal context
Stochastic Variability
Results from random factors, such as the localisation of a thunderstorm within a basin
Interception
Process by which water is stored in the vegetation, 3 main components - interception loss, through fall and stem flow.
Factors affecting interception loss
- point of storm, more interception loss at start and following dry period
- type of tree: coniferous tree greater, as dense needles.
- seasonality in deciduous forests: summer/winter
- wind speeds: decrease, intercepted water dislodged, and increases evaporation
- intensity & duration of rainfall - amount of rainfall increases, less water intercepted as tree canopies become saturated
- agricultural crops- more interception with more dense crop
Factors affecting infiltration
- decreases with time during a period of rainfall as a constant low level is reached
- Antecedent soil moisture, wet soils, less infiltration as already saturated
- Soil texture, level of porosity
- Type, amount and seasonal changes in vegetation. More vegetation = more infiltration
- Nature of soil surface, compact promotes overland flow
- Slope angle, steep = more runoff, flat = infiltration
Throughflow
The lateral transfer of water down slope through soil via natural pipes and percolines.
Percolines
Lines of concentrated water flow between soil horizons to the river channel
Fluxes in drainage basin
Interception, Infiltration
Flows and transfers in drainage basin
- Overland flow/surface runoff
- Throughflow
- Percolation
- Saturated overland flow
- Channel flow
Outputs of drainage basin
Evaporation, transpiration
Factors affecting Evaporation rate
- Climatic factors; temperature, hours of sunshine, humidity and windspeed. Temperature most important.
- size of water body
- depth of water
- water quality
- type of vegetation cover
- colour of water surface
Factors affecting transpiration rate
- Time of year
- type and amount of vegetation cover
- degree and availability of moisture in the atmosphere
- length of growing season
Physical factors affecting the drainage basin system
- Climate
- Soils
- Geology
- Relief
- Vegetation
Human factors affecting the drainage basin
- River management: Building dams/reservoirs, reduces flows. Abstracting water for domestic and industrial use, reduces flow. Abstracting groundwater for irrigation, reduces the water table.
- Deforestation: reduces evapotranspiration, increases infiltration and surface runoff
- Changing land use - AGRICULTURE: soils compacted by livestock, increased surface runoff. soils aerated by ploughing, increased infiltration as soils loosened
- Changing land use - URBANISATION: changing to urban land surfaces, increased surface runoff and less infiltration and percolation. Drains move rainfall to rivers and streams faster, increased chance of flooding.
Components of drainage basin mostly affected by humans
- evaporation & evapotranspiration
- interception
- infiltration
- groundwater
- surface runoff
