Water – Supply & Use

Groundwater

– Vadose zone (formerly known as the unsaturated zone)

– Zone of saturation or water table– Capillary fringe

– In general, water moves through the subsurface as a function of:

• Permeability – ability of a material to transmit fluid

• Porosity – percentage of void space in a material

• Be careful not to confuse these two terms!

Show flash animation: http://geomorph.geology.ufl.edu/~adamsp/Outgoing/Lectures2030/Animations/WaterTable.html

Aquifers

“zone of earth material capable of supplying groundwater at a useful rate from a well.”

Can be composed of gravel, sand, soil, fractured rock with sufficient pore space (sandstone, granite, metamorphics)

Example of Unconfined Aquifer

Aquifers

Confined Aquifer

Aquiclude or Aquitard forms a confining layer, due to much lower permeability – can hold water, but not transmit it fast enough to support well pumping.

Zone of Recharge – where precip. infiltrates the surface to enter the groundwater system (eventually, the aquifer)

Recharge can be natural or artificial.

Artesian conditions – pressurized water that emerges from surface to a level of the pressure surface.

Groundwater Pumping

Show flash animation: http://geomorph.geology.ufl.edu/~adamsp/Outgoing/Lectures2030/Animations/ConeDepress.html

Causes “discharge”, as opposed to recharge

Forms a cone of depression

Groundwater Movement

Hydraulic gradient – approx. the slope of the water table

Hydraulic conductivity – ability of a material to allow water to move through it – expressed as a velocity (m/day)

Porosity and Permeability

Groundwater Movement

D'Arcy's Law (black board example next lecture)Q = KIA

Q=discharge (Q)K= hydraulic conductivityI= hydraulic gradientA= cross-sectional area (confined aquifer)More complicated when unconfined because

h= thickness varies)

Henry Darcy

More Groundwater

Potentiometric Surface and Hydraulic Head

Driving force for groundwater movement is hydraulic head, usually the elevation of the potentiometric surface

Groundwater always moves from an area of higher head to one of lower head (i.e., from high potentiometric contours to lower contours)

Interaction of Groundwater and Surface Water

Influent streams (Losing)

Effluent streams (Gaining)

Springs