Lecture 6

    Cards (16)

    • water inputs equal water outputs plus or minus changes in water storage in a catchment
    • precipitation is measured with gauges and radar/micro wave (radar more accurate but microwave higher resolution)
    • global data from radar and microwave satellites but must be validated with ground data
      • NASA Global precipitation measurement mission
      • 6 km pixels
      • can get precipitation every 30 minutes
      • misses the high intensity events (need rain gauges for that)
    • soil water content is measured by loss of weight of a soil sample when heated (to 105 degrees C over 24 hours)
    • indirect methods for mapping soil surface moisture content include using airborne or satellite based radar
    • groundwater monitored by changing levels in wells and volume derived from estimates of the bedrock's effective porosity (e.g. chalk aquifers)
    • infiltration
      whether falling liquid precipitation infiltrates or runs off depends on:
      • rainfall rate
      • soil permeability which depends on: soil porosity; degree of soil saturation; whether ground is frozen
    • infiltration-excess overland flow
      precipitation falling at too fast a rate to be able to percolate/drain into the soil
    • saturation-excess overland flow
      soil already full of water (saturated) and thus no more space to accommodate inputs
    • flood return period:
      • used to determine how often floods occur
      • uses the record of each year's biggest flow
      • quite sensitive to the length of the timeseries
    • urban catchments have peakier ('flashier') discharges with shorter lag times
    • rural areas:
      • water interception (more vegetation)
      • water infiltrates into the soil/groundwater
      • water therefore takes longer to reach water courses
    • atmometer
      measures evaporation by monitoring loss of water from a porous surface
    • lysimeter
      measures potential evapotranspiration (PE) by monitoring weight of an isolated vegetated area of soil with an unlimited water supply
    • equation for river discharge
      Q = A x V
      discharge = area x velocity
    • current-meter discharge measurements are made by determining the discharge in each subsection of a channel cross-section and summing the subsection discharges to obtain a total discharge
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