Editing OR/16/036 Development of the BGS unsaturated zone model

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where ''Thickness<sub>USZ</sub>,<sub>i</sub>'' is the thickness of USZ at cell ''i'' (Figure 1); ''V<sub>USZ</sub>,<sub>i</sub>'' (m year<sup>-1</sup>) is the nitrate-transport velocity in the unsaturated zone; ''q<sub>i</sub>'' (m year<sup>-1</sup>) is groundwater recharge at cell ''i''; ''Rf<sub>aquifer</sub>'' (-) is the retardation factor determined in the calibration procedure, and; ''Sr<sub>aquifer</sub>'' (-) is the specific retention for the rock. The specific retention represents how much water remains in the rock after it is drained by gravity, and is the difference between porosity and specific yield. Model calibration is described in [[OR/16/036 Development of the BGS unsaturated zone model #Estimating annual nitrate concentrations in groundwater    |Estimating annual nitrate concentrations in groundwater]].
 
where ''Thickness<sub>USZ</sub>,<sub>i</sub>'' is the thickness of USZ at cell ''i'' (Figure 1); ''V<sub>USZ</sub>,<sub>i</sub>'' (m year<sup>-1</sup>) is the nitrate-transport velocity in the unsaturated zone; ''q<sub>i</sub>'' (m year<sup>-1</sup>) is groundwater recharge at cell ''i''; ''Rf<sub>aquifer</sub>'' (-) is the retardation factor determined in the calibration procedure, and; ''Sr<sub>aquifer</sub>'' (-) is the specific retention for the rock. The specific retention represents how much water remains in the rock after it is drained by gravity, and is the difference between porosity and specific yield. Model calibration is described in [[OR/16/036 Development of the BGS unsaturated zone model #Estimating annual nitrate concentrations in groundwater    |Estimating annual nitrate concentrations in groundwater]].
  
Recharge can be modelled and aquifer property data, such as porosity and specific yield are available for major and minor aquifers from Allen et al. (1997)<ref name="Allen 1997"></ref> and Jones et al. (2000)<ref name="Jones 2000">JONES, H K, MORRIS, B L, CHENEY, C S, BREWERTON, L J, MERRIN, P D, LEWIS, M A, MACDONALD, A M, COLEBY, L M, TALBOT, J C, MCKENZIE, A A, BIRD, M J, CUNNINGHAM, J, and ROBINSON, V K. 2000. The physical properties of minor aquifers in England and Wales. ''British Geological Survey Technical Report WD/00/4, Environment Agency R&D Publication 68''.</ref>. However these specific yields have been estimated for the saturated zone and assume that the aquifer remains fully saturated. These may not adequately represent conditions in the unsaturated zone.
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Recharge can be modelled and aquifer property data, such as porosity and specific yield are available for major and minor aquifers from Allen et al. (1997)<ref name="Allen 1997">ALLEN, D J, BREWERTON, L J, COLEBY, L M, GIBBS, B R, LEWIS, M A, MACDONALD, A M, WAGSTAFF, S J, and WILLIAMS, A T. 1997. The physical properties of major aquifers in England and Wales. ''British Geological Survey Technical Report WD/97/34, Environment Agency R&D Publication 8. British Geological Survey Technical Report WD/97/34, Environment Agency R&D Publication 8.''</ref> and Jones et al. (2000)<ref name="Jones 2000">JONES, H K, MORRIS, B L, CHENEY, C S, BREWERTON, L J, MERRIN, P D, LEWIS, M A, MACDONALD, A M, COLEBY, L M, TALBOT, J C, MCKENZIE, A A, BIRD, M J, CUNNINGHAM, J, and ROBINSON, V K. 2000. The physical properties of minor aquifers in England and Wales. ''British Geological Survey Technical Report WD/00/4, Environment Agency R&D Publication 68''.</ref>. However these specific yields have been estimated for the saturated zone and assume that the aquifer remains fully saturated. These may not adequately represent conditions in the unsaturated zone.
  
 
===Estimating nitrate transport velocity and dilution in the saturated zone===
 
===Estimating nitrate transport velocity and dilution in the saturated zone===

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