hydrology

• suggest reasons for the shape of a storm hydrograph when it

  • Land use such as urban areas where infiltration is low and runoff high
  • Soils and rock type – impermeable soils (clay) and impervious rocks(granite, basalt)
  • Drainage basin shape – round basins lead to rapid concentration of flowto the main channel
  • Drainage basin density – greater drainage density leads to more rapidflow to main channel
  • Gradient influences rate of runoff
  • Antecedent moisture
  • Lack of vegetation
• compare the characteristic of two storm hydrographs

  • Both rise and fall
  • Both have a single peak
  • A has a steeper rising limb than B
  • A has a higher peak discharge than B
  • A has a shorter lag time than B (peak is earlier)
  • A has a steeper recession (falling) limb than B
  • A starts lower
  • A starts earlier
• Describe the process of base flow in the drainage basin system:

  Base flow is the:

  • Flow of water below the water table (groundwater flow)
  • Towards the river channel
  • Its a result of water percolating through the soil and bedrock from thesurface
  • A relatively constant/slow flow compared to surface flow
• Briefly explain how the porosity and permeability of soils affect infiltration:


  Porosity: the ability of soils to absorb moisture.

  Permeability: the ability of soils to transmit moisturePermeability is most closely related to infiltration.

  "Both clay and sand may be porous but only sand with interconnected pore spaces would be permeable leading to infiltration."
• 1. Explain how waterfalls are formed:


  • Water spills over a sudden change of gradient, often over the edge of a plateau
  • Change of gradient is often caused by a resistant rock overlying a less resistant rock/caused by faulting
  • Rock is undercut by the falling water (plunge pool)
  • Explanation of processes of hydraulic action, cavitation and abrasion
  • Collapse of overhanging strata
  • This leads to a retreat of the waterfall back upstream
• Explain how an oxbow lake may have formed:


  • Initial development of a meandering channel (helicoidal flow); development – with the thalweg swinging towards the outside bend
  • Undercutting the outside bends; development – with evidence of processes
  • Curvature increasing/reduces width of neck
  • River cuts through; at times of high flow/floods
  • Deposition occurs in the cut off; over time becomes permanent with vegetation growth
• Explain two reasons why some extreme rainfall events do not result in river flooding:


  • Time of the year coinciding with land use change is also relevant such as when there are crops in the soil or the ground is bare or deciduous trees that have shed their leaves.
  • Management of the rivers (hard engineering) may also stop flooding following intense rainfall.
• Explain the latitudinal variation in solar radiation reflected by clouds:


  • the peak over the equator
  • the dips about 25 °N and 30 °S
  • the low values at the poles
  • the rise in mid-latitudes.
  • The amount of incoming radiation and the cloud cover at the equator as a result of intense heating and convectional uplift and less cloud cover in areas controlled by the descending limb of the Hadley cell.
  • The rise in the mid-latitudes also reflects the rising limb of the Ferrel cell with the high pressure at the poles being reflected in generally clear skies.