Fuluvial environments

• Percolation


  The movement of water from the soil into the underlying rock
• Rocks


  • Can store water either within the rock itself (porous), or within the cracks and joints they contain
  • This stored water is referred to as groundwater and it slowly makes its way into river channels as groundwater flow
• Water table

  The height of the groundwater level in rock
• Groundwater can maintain river flow even after weeks or months without rainfall
• Factors to measure river flow

  • Depth
  • Width
  • Velocity of river (m/set)
• Hydrograph


  A graph that plots the pattern of changing discharge at any point along a river over time
• Annual hydrograph


  Shows the variation in river discharge over a year
• Annual hydrographs can be averaged over 30 years or more to give the mean flow pattern
• The annual hydrograph illustrates the system's normal yearly flow pattern, sometimes called a river's regime
• Annual hydrograph


  • Graph showing average monthly discharge (cumecs) over a year
• Geology


  • Impermeable rock, eg. igneous rocks or slate which have few bedding planes are non-porous
• Soil


  • Clay rich soils have small pores, on baked/arid soils reduced infiltration capacity
  • Thin upland soil cannot absorb much moisture
  • Frozen soils impermeable
• Land use


  • Urbanised areas with impermeable surfaces
  • Deforested areas with only low-lying vegetation will provide less interception
• Drainage density


  • River has a high drainage density (high no. of tributaries) more rapid transfer of water to main channel
• Gradient


  • Steep gradient thin soils and gravity will speed up the rate of moisture transfers
• Shape of basin


  • Small basin = Flashy response
  • Wide basin usually higher drainage density so more rapid river response
• Type of precipitation


  • Heavy or prolonged rainfall will saturate sub surface stores more rapidly
• Antecedent amounts of rainfall in weeks prior

  Will result in partially or fully saturated soils
• Drought


  Can result in arid or baked soils
• Tide up rivers


  Can result in higher discharge
• Drainage Basin


  The area of land that gathers water for a river
• A drainage basin is an open system as it has inputs and outputs
• Inputs and outputs of a drainage basin

  • Inputs: Precipitation
  • Outputs: evaporation, transpiration (evapotranspiration)
• Stores in a drainage basin

  • Ground water, soil moisture, interception, surface store
• Transfers in a drainage basin


  • Infiltration, stem flow, percolation, throughflow, ground water flow, surface run-off
• Storm Hydrograph


  Shows short term variations in river discharge (over days). Allows investigation of relationship between rainfall events and discharge
• River regime


  The annual variation in the flow of a river
• Discharge


  The volume of water in a river passing any one point at a given time
• Lag Time


  The time between peak rainfall and peak discharge
• Base Flow


  The normal flow of the river