# 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).
