Groundwater Chapter 10

Hydrosphere The water on or in Earth’s crust makes up the hydrosphere “hydro” = Greek term for water 97% of hydrosphere is in the oceans Only 3% is freshwater 90% in polar ice caps & glaciers Almost all rest is in groundwater All the rivers, streams and lakes on Earth’s surface represent only a small fraction of earth’s liquid freshwater.

Precipitation The ultimate source of all water on Earth comes from the atmospheric release of evaporated seawater Evaporation introduces water into the atmosphere in the form of invisible water vapor and visible clouds. Brings atmospheric moisture back to Earth’s surface Rain, Sleet, Snow etc.

Precipitation cont… Some falls directly into oceans… some falls on the land where a small portion becomes runoff and is returned to the oceans through rivers and streams. Much of it percolates into the ground and becomes groundwater through the process of infiltration. Infiltration – the precipitation that falls on land soaks into the ground Eventually water gets back to the surface through springs Finally travels to oceans

Groundwater Storage and movement - When water infiltrates the ground it does so at different rates according to the subsurface material it is passing through. - This is because subsurface materials are not totally solid but contain openings called pores which allow water to pass through (gravity, adhesion, cohesion, surface tension and capillary action all contribute to this movement) Porosity: the percentage of pore space in a material. Permeability: The ability of a material to allow water to pass through it. Examples of materials with high porosity/permeability: (coarse grained materials with relatively high flow velocities-up to 1m/h) sand, gravel, sandstone, limestone and fractured bedrock Examples of materials with low porosity/permeability: (fine grained materials with low flow velocity- m/y) Silt, clay and shale. ***Clay is so impermeable that a clay lined depression will hold water. (Used to line artificial ponds and landfills)

The Zone of Saturation The area below Earth’s surface where groundwater completely fills all the pores The upper boundary of the ZoS (the very top/surface plane) is the water table. (Strictly speaking, only water in the zone of saturation is called groundwater.) Zone of Saturation

Zone of Aeration Zone above the water table NOT Groundwater Materials are moist due to gravitational water but pores contain mostly air. The materials just above the water table are nearly saturated with capillary water that is drawn upward into the ZOA.

Groundwater Movement Groundwater flows downhill due to gravity and follows the topography/slope of the land above it. The flow velocity primarily depends on the slope but permeability is also a major factor. Aquifers – permeable underground layer through which groundwater flows relatively easily Wells tap into aquifers to supply homes with H20 Aquicludes – impermeable layers that block the flow of water.

Groundwater Movement cont… Draw Diagram from pg. 243 ****Add this: In stream valleys the water table is near the surface (a few meters deep). In swampy/marshy areas it is almost at the surface. On hills/mtns it can be 10s to 100s of meters deep.