Storage

• groundwater storage: groundwater level/table rises after rainfall event, saturating part of unsaturated zone and storing water in soil

  • depend on soil type
• specific storage (Sw mm): volume of water in soil per unit area

  • increased by infiltration
  • decreased by evaporation
• storativity/storage coefficient (mu): ratio between change in specific storage and change in groundwater level

  • smaller than porosity
• $mu =$$delta(Sw)/delta(h)$

  • Sw (mm) = specific storage
  • h (mm) = groundwater level
• field capacity: wetness of upper soil layer when soil has lost its surplus of water to groundwater after wet period
• groundwater level measured using piezometer or groundwater tube
• storativity not constant, depends on groundwater level and past weather
• surface water can store water which results in more gradual discharge towards catchment outlet

  • rivers including floodplains
  • natural lakes
  • man-made lakes
  • retention basins
  • reservoirs
• density of fresh snow is eight times smaller than water

  • 100 cm snow = 12.5 cm water
• density of old/wet snow is 50% of density of water
• snow density calculated using snow water equivalent (SWE) and change in snow pack height
• $mu (snow density) =$$delta(SWE)/delta(h)$

  • SWE = snow water equivalent
  • h = snow pack height
• snow accumulation leads to low groundwater levels and low discharges due to hampered infiltration and percolation
• rain-on-snow events are often destructive due to liquid precipitation accelerating snowmelt