GROUNDWATER TRANSPORT

GROUNDWATER TRANSPORT - is the flow of water in the saturated underground layer. Just like on the surface, the water can be accumulated on top of an impervious layer underground. In that case the water that comes from the top with the infiltration and percolation processes accumulates and reaches saturation concentrations. Once all the pores between the soil particles are filled there is an alternative for the water either to keep accumulating and increasing the height of the water table under the ground or to start moving horizontally to areas with lower saturated water head. All this is very similar to the processes on top of the surface, except that instead of a free flow of water in case of groundwater we are dealing with motion of moisture in the porous media. The rate of this flow is considerably slower and defined by horizontal hydraulic conductivity. This rate is very much dependent on the soil type and can vary by several orders of magnitude.

As with surface water transport, strictly speaking groundwater flow is not a process to consider within the framework of a unit model. It is driven by spatial gradients, whereas in the unit model, all spatial characteristics, are assumed to be uniform over the whole modelled area. Therefore we will look at this process in more detail when describing the spatial implementation of the model. At this point we simply provide a function that will remove a certain proportion of the available groundwater to keep it close to a steady state.

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