Factors and process of groundwater movement

Groundwater moves slowly through the pores and fractures of rock and soil from areas of high hydraulic head to areas of low hydraulic head.

Factors affecting groundwater movement

1. Porosity and permeability: interconnected pores and fractures allow flow; clay has high porosity but low permeability.
2. Grain size and sorting: coarse, well-sorted material gives high flow.
3. Hydraulic gradient: greater slope of the water table or piezometric surface gives faster flow.
4. Geological structure: joints, faults, folds, dip and bedding control direction of flow.
5. Fluid properties: viscosity and temperature (warm water moves faster).
6. Recharge and discharge: rainfall, river seepage and pumping change the head.
7. Topography and vegetation.
8. Presence of impermeable layers forming barriers or confining beds.

Process of movement

1. Rain or snow melt infiltrates through the zone of aeration (vadose zone) to the saturated zone (recharge).
2. Water joins the water table and flows under gravity and pressure along the hydraulic gradient.
3. Flow is laminar and obeys Darcy's law, $v = K\,i$.
4. Flow is from recharge areas (highlands) to discharge areas (springs, rivers, lakes, wells, sea).
5. Rates are very slow, from a few cm per day in fine sand to metres per day in gravel.