Groundwater occupies pores or open space within Earth materials Porosity = measure of the % of total volume of a material occupied by open space (pores) Depends on (for example): abundance and distribution of fractures shape and size of openings in sediments, packing of grains, cementation, etc.

Low Porosity < 5 % High Porosity > 15 % Mud Unconsolidated sediment 20 to 50 % Mud high porosity Low Porosity < 5 % High Porosity > 15 % Figure 19.2

Permeability = ability to transmit fluids Depends on: total porosity interconnections between openings Figure 19.4

Water Table Contact between unsaturated and saturated Figure 19.6 Capillary Fringe- water lifted up by tension against pull of gravity

can be some distance from the surface 100 to 200 m Figure 19.6 Water saturated Water saturated Arid region can be some distance from the surface 100 to 200 m lakes and rivers provide water to the ground Humid region groundwater can be very near the surface lakes and rivers directly connected to the

Gravity drives the flow of groundwater moves to lower elevation along curved paths Figure 19.9

Hydraulic head – elevation and pressure at the water table pressure = 0 so hydraulic head = elevation or slope of the water table Figure 19.11