hydrology

• evaporation

  liquid changes into water vapour, from puddles and streams. rate of evaporation increases in hot, dry and windy condition sand with larger soil surface area
• transpiration

  water is drawn up from the soil by the plant and leaves the plant as water vapour through tiny pores on the underside of the leaves known as stomata
• infiltration

  soaks/absorbs into soil
• percolation

  water downwards through soil into bedrock
• aquifer

  permeable rocks that contain water
• river regime

  studies responses of river to its environment
• storm hydrograph

  shows variation of river discharge over a short period of time
• drainage basin characteristics

  size and shape - small response quicker so smaller lag time, circular ones respond quicker than liner

  drainage density - lower causes longer lag time (less paths to take)

  soil porosity and permeability - impermeable surfaces cause more overland flow so greater peak flows

  rock type - impermeable rock causes reduced lag time and higher peak discharge

  slopes - steeper gradient means higher peak discharge and shorter lag time due to more overland flow

  land use - creation of impermeable surfaces or deforestation increases overland flow
• laminar flow

  glass-like effect

  appears clear and motionless

  particles move in parallel and at constant speed
• turbulent flow

  interacting swirls

  unpredictable

  direction and magnitude are constantly changing
• helicoidal flow

  due to centrifugal force

  forces water outwards as it rounds a bend

  hits back of river an thrown back towards main flow
• braided river channel features

  • divided by islands or eyots
  • islands are vegetated, whereas bars and not and unstable
  • easily erodible banks
  • highly variable discharge
  • steep gradient
  • when discharge and velocity decrease, sediment is plentiful an eyots form
  • with reduced discharge, river must split to go around the eyots
• how are meanders formed?

  pools and riffles cause thalweg to deflect

  where thalweg is fastest erosion occurs, and deposition where it is slowest

  overtime creating a pronounced bend in the river
• river cliffs

  steep side on outside bend of meander where erosion is strongest and downwards
• point bars

  deposits of sediment on the inside bend, where thalweg is slowest and rising
• oxbow lakes

  narrowing of the bend neck caused by erosion with the thalweg

  after flood event the neck is breached

  meander cut off with more deposition
• pools

  deep sections where erosion dominates

  (high velocity and dominant laminar flow)
• riffles

  shallower sections of the riverbed where sediment has been deposited

  (low velocity, turbulent flow)
• waterfalls

  • river spills over gradient change where more resistant rock is on top of less resistant rock
  • water undercuts rock by abrasion
  • plunge pool removes support for overhang so it collapse
  • causing upstream migration
• gorges

  deep, steep sided valley caused by waterfall retreat
• levees

  following a flood event where banks burst.

  increase friction reduces velocity so material is deposited around the banks
• deltas

  sediment is deposited where the river meets a standing body of water, due to a loss of energy

  needs : large sediment load / low tidal range / low energy environment / large continental shelf

  has three comments : topes, forest, bottomset

  arcuate - fan shaped

  cuspate - pointed like a tooth

  bird's foot - divides river into small distributaries
• climate influence on drainage basins

  • precipitation type and intensity
  • temperature
  • evaporation
  • transpiration
  • evapotranspiration
  • antecedent moisture
• bluff formation

  • on outside bend of meander where erosion dominates
  • water erodes lower section of river bank, causing upper section to become unsupported and therefore unstable
  • upper part breaks off, leaving high wall of a bluff
• flood prevention

  forecasting and wanring
• soft engineering

  • afforestation
  • flood diversion
  • floodplain and drainage basin management
  • river restoration
  • wetland and river bank conservation
• hard engineering - usually effective but causes more problems up/ downstream

  • dams
  • levees
  • channel straightening
  • reservoirs
  • diversion spillways