Summary: Ppt Lec 5 - Groundwater Recharge

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• 1 The driver of hydrogeological systems

• 1.1 Definition of groundwater recharge

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• What parts of the soil can be defined as the unsaturated zone and how can it also be called?

  
  Net infiltration in a topography-driven groundwater flow system will occur across topographically elevated areas where often a substantial unsaturated zone (also called Vadose Zone) occurs.
  The water that reaches the water table from below the root zone through the vadose zone is classically indicated as the ‘recharge’ of the groundwater system.

• Name 6 fluxes of water flow that occur in the soil. Think about the interaction with plants, air, water and soil particles.

  Puddling/overland flow (runoff)
  Infiltration
  Redistribution
  Percolation/capillarity
  Storage/uptake by roots/evaporation
  Drainage/seepage

• 2 How to measure groundwater recharge?

• Name 7 techniques to measure GW recharge in the unsaturated (vadose) zone (3 techniques) and deeper aquifers (4 techniques).

  Unsaturated zone:
  - Lysimeter
  - Chloride mass balance
  - 'Historical' tracers
  
  Deeper aquifers:         
  
  - Water Table Fluctuations
  - Environmental Tracers (groundwater age dating)
  - Temperature-depth profiles- Darcinian Principles

• 2.1 Unsaturated zone

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• What's a different term for unsaturated zone recharge?

  Infiltration

• What does a lysimeter measure to estimate recharge in the soil? What are downsides of the lysimeter?

  It weighs volume of a representative soil. 
  
  Lysimeters are based upon a direct measurement
  of the mass balance of a volume of representative
  soil. Weighing this volume and a record of in and
  outflows are the primary data collected.
  
  Downsides are that it is a pointmeasure of the drainage just below the rootzone, no lateral flow is recorded, it's expensive, needs maintenance. 

• There's a multi-compartment sampler, what do you think it would do?

  Check lecture

• Explain the Chloride Mass Balance and for which zone it is used. Use the terms precipitation and recharge to the aforementioned zone.

  
  Continuous supply of Cl in the atmosphere,
  hence precipitation contains a more or less
  constant concentration of Cl.
  
  
  Thus, measurements of P and Cl in P, and Cl
  in the deep vadose zone or just below the
  water table should give fair estimates of D.
  
  Used for measuring recharge in the vadose zone. 

• What are downsides about using the CMB technique to measure recharge to the vadose zone?

  
  Main issues with CMB recharge estimates are
  sources/sinks of Cl along the pathway from
  surface to water table.
  
  
  CMB equation shows that elevated Cuz is
  associated with low recharge, and vice versa.
  Since low Cl concentrations are increasingly
  more difficult to measure for relatively large
  recharge. CMB only works well up to recharge
  rates of ~300 mm/y.

• What's the formulas used for CMB to measure recharge to the vadose zone? Use both the drainage and precipitation fluxes for this formula.

  See fig

• Give an example of how CMB is used to make a map of recharge in Nebraska, USA.

  
  Assuming a Cl concentration for P, and doing further GIS
  based interpolation, a detailed map of groundwater recharge
  can be produced using CMB as a method.