Groundwater

Groundwater: subsurface water that saturates sediments and rocks

• meters to kilometers below the surface

1. Unsaturated zone: unsaturated region where pores are mostly filled with air

2. Saturated zone: pores mostly filled with water

3. Water tale: boundary between saturated and unsaturated zones

Recharge: the process the replenishes the groundwater

• precipitation

• river or lake (infiltration)

• or groundwater from another reservoir

Porosity and Permeability

Porosity: void spaces between grains and amount of water sediment can hold, a higher porosity means that there is more space for water to be stored

• well sorted = 30% pore space

• pooly sorted = 15% pore space

• sediment rock with cement material = minimal

Sandstone/Sediment: 10-40% porosity, the sand grains have large spaces

Granity/Igneous: < 1% porosity, tightly packed with little space once magma cooled

Permeability: te connectedness of pore spaces and the ability to pass water

• high porosity + high permeability = hydraulic conductivity = K

  • at what rate will water be able to flow through a material

Hydraulic Gradient

1. Formula: hA-hB/l = change in h/l

   • gradient always moves from high to low

   • the steeper the channel = the higher the energy = the faster the flow = the higher the gradient

Groundwater Storage

Aquifer: a body of sediment/permeable rock that contains usable water

1. Unconfined: aquifers directly connected to seepage from the land surface (direct from surface to subsurface)

   • water level = water table level

2. Confined: not directly connected to surface, has impermeable layers above and below, gets water from another region where water is unconfined

   • water level = recharge water table level (potentiometric)

   • artisean well = water shoots out of well, no pump needed

3. Perched: island of aquifer that is unconfined

Aquifer Properties

Good aquifers: have sediment sands and gravels (sandstones)

• clay has a high porosity but a low permeability (poor aquifer)

• sandstone has moderate porosity and high permeability

Water can also flow from large cracks in rock

• ie. mountains with igneous rock (that are very low porosity and low permeability) will have large cracks which allows water