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# 2:4.2 Shallow Aquifer

The water balance for the shallow aquifer is:

$$aq\_{sh,i}=aq\_{sh,i-1}+w\_{rchrg,sh}-Q\_{gw}-w\_{revap}-w\_{seep}-w\_{pump,sh}$$                                                      2:4.2.1

where $$aq\_{sh,i}$$ is the amount of water stored in the shallow aquifer on day $$i$$ (mm H$$*2$$O), $$aq*{sh,i-1}$$ is the amount of water stored in the shallow aquifer on day $$i-1$$ (mm H$$*2$$O), $$w*{rchrg,sh}$$ is the amount of recharge entering the shallow aquifer on day $$i$$ (mm H$$*2$$O), $$Q*{gw}$$ is the groundwater flow, or base flow, into the main channel on day $$i$$ (mm H$$*2$$O),  $$w*{revap}$$ is the amount of water moving into the soil zone in response to water deficiencies on day $$i$$ (mm H$$*2$$O), $$w*{seep}$$ is seepage from the shallow aquifer to the deep aquifer on day $$i$$ (mm H$$*2$$O) and $$w*{pump,sh}$$ is the amount of water removed from the shallow aquifer by pumping on day $$i$$ (mm H$$\_2$$O).