Freshwater - Drainage basins Flashcards
What is a drainage basin?
Area that is drained by a river and its tributaries. They have inputs and outputs so they’re open systems
What are examples of inputs and outputs in a drainage basin?
Inputs:
Precipitation
Outputs:
Leakage
Run-off
Evapo-transpiration (evaporation and transpiration)
What are examples of storage in a drainage basin?
Vegetation
Surface
Soil moisture
Ground water
Channel storage
Aquifers
Cryosphere
What are examples of flows in a drainage basin?
Interception
Channel precipitation
Throughflow
Overland flow
Base flow
Evaporation
Transpiration
What is precipitation?
Transfer of moisture to the earth’s surface from the atmosphere e.g hail, snow, rain, sleet, dew
What is interception?
Capture of rain by vegetation cover that prevents direct contact of rain with soil. If retaining capacity of leaves is exceeded, rain will fall to the ground (throughflow). Some will go down branches and stems (stemflow) and some is stored in leaves and later evaporated`
What is evapotranspiration and potential evapotranspiration?
Evapotranspiration is the combined loss of water from vegetation and water surfaces to the atmosphere
Potential evapotranspiration is the rate of water loss from an area if there was water was unlimited
What is infiltration and what is infiltration capacity?
Process by which water sinks into the ground
Capacity refers to amount of moisture soil can hold
What is throughflow?
Water moving in the soil laterally following natural pipes, percolines, or between horizons
What is overland run-off?
Occurs when precipitation intensity exceeds infiltration rate or when infiltration capacity is reached and soil becomes saturated so water moves on land
What is percolation?
Refers to the movement of water moving deep into the groundwater zone
What is baseflow?
The movement of ground water. For baseflow to occur, the water table must rise above the river level to provide hydraulic gradient needed for water movement
What is an aquifer and why are they important?
Rocks that hold water and are most important store of water as regulate the hydrological cycle and maintain river flow.
How does soil moisture vary?
Varies with the porosity, amount of pore spaces in the soil, and with permeability.
What is the cryosphere?
Largest store of freshwater and is stored in snow and ice
What is discharge?
Volume of water passing a certain point per unit time in cumecs (cubic metres per second)
What does the bradshaw model show?
Shows changes to channel characteristics over the course of a river
Water velocity, discharge, occupied channel width, water depth all increase as you move downstream and shows load particle size, channel bed roughness and gradient all decrease as you move downstream
What are the 4 main types of erosion?
Abrasion- wearing away of bed and bank by the load of the river
Attrition- Load of river wears away each other forming smaller, rounder particles
Hydraulic action- Force of air and water on the sides of river and in cracks
Solution/corrosion- removal of chemical ions, especially Ca, which causes dissolving of rocks
What are factors that affect erosion?
Load
Velocity and discharge
Gradient
Geology
pH
Human impact
What are the main types of transport?
Suspension- small particles held up by turbulent flow in river
Saltation- heavier particles bounce or bump along river bed
Solution- chemical load is dissolved in the water
Traction- heaviest material is dragged or rolled along the bed
Floatation- leaves and twigs are carried on the surface of the river
What does the capacity of a stream mean?
Refers to the largest amount of debris that a stream can carry
What does the competence of a stream mean?
The diameter of the largest particle that can be carried
What does critical erosion velocity mean?
Lowest velocity at which grains of a given size can be moved by a river
What is the Hjulstrom curve?
Hjulstrom curve explores the relationship between river capacity, competence and critical erosion velocity.
3 main features:
Smallest and largest particles require high velocities to lift them
HIgher velocities are required for entrainment than for transport
When velocity falls below a certain level particels are deposited
