Chapter I 7 Underground Water Global distribution of

Chapter I 7 Underground Water

Global distribution of water • • • Oceans Glaciers Groundwater Lakes Atmosphere Rivers 97. 2% 2. 15% 0. 61% 0. 001% 0. 0001%

The Distribution of Water on Earth

The water cycle • The continuous movement of water on, above and below the earth’s surface is called the water cycle OR hydrologic cycle.

The water cycle • Processes: – Evaporation – Transpiration – Precipitation

Dry Period: Dam Streams bring in small amounts of water… and carry away small amounts. Wetlands

Wet Period: Dam Streams bring in large amounts of water… which is stored… and slowly released during dry periods. Wetlands

Average U. S. Annual Precipitation

Water • Atmospheric water: vapors • Surface water: rivers. Lakes, oceans • Subsurface water: groundwater

Distribution of underground water • 2 zones – Unsaturated zone: vadose zone – Saturated zone – Separated by Water Table

Underground materials • Underground materials may either contain water or they may be dry. • In order to contain water, they have to be porous and permeable.

Underground materials • Porosity: is a measure of the material ability to hold water. • Permeability: capacity of a material to transmit water.

Porosity varies with % Cement Sorting Fracturing

Porosity Varies with % Cement MORE POROUS Noncemented Sand LESS POROUS Cemented Sandstone

Porosity Varies with Sorting MORE POROUS Well Sorted Sand LESS POROUS Poorly Sorted Sand

$Porosity Varies with Fracturing MORE POROUS Fractured Shale LESS POROUS Unfractured Shale$

Porosity Varies with Fracturing MORE POROUS Fractured Shale LESS POROUS Unfractured Shale

Porosity and Permeability of Different Aquifer Types Type of Aquifer Porosity Permeability Gravel Coarse- to fine sand Fine-grained sand & silt Sandstone, mod. cemented Fractured Shale Metamorphic Rocks Unfractured Shale Very High Moderate Mod - Low Low Very High Mod - Low Low Very Low

Aquifers • Any geologic material which can yield water in significant amounts. • Aquifers must be porous and permeable. • Any geologic material which cannot hold and transmit water is called Aquiclude.

Types of aquifers • 2 types – Unconfined aquifer – Confined aquifer

• Unconfined aquifer: no confining layer on top of the saturated zone

Unconfined Aquifer Unsaturated Zone: Pores include both air and water Groundwater Table Saturated Zone: Pores filled with water

• Confined aquifer: the saturated zone is capped by a confining layer.

• Good aquifers include; – Unconsolidated deposits – Sandstone – Conglomerate – Jointed limestone

• Good aquicludes are; – Shales – Granite – Marble

Springs • A spring forms where underground water flows naturally onto the land surface. • A spring occurs when water table intersects the land surface.

Groundwater erosion and deposition • Depending on the chemical environment, water erodes the material over which it moves. • Later on the eroded material is deposited at another location.

Groundwater erosion and deposition • Erosional features: – Caves – Sinkholes – Karst topography

• Caves: underground chambers large enough for humans to enter into it. –Speleothems: calcite deposits formed by dripping water from cave ceiling.

Two types of speleothems: • Stalactites: pendants of calcite hanging from roof ceiling • Stalagmites: cone-shaped bodies of calcite formed on cave floor.

Mammoth Cave, KY

• Sinkholes: depressions formed by the collapse of a cave roof. • Karst topography: an area underlain by numerous caves and sinkholes.

Subsurface Features of a Karst Landscape

Dishman Lane collapse, Bowling Green Ky. Feb. 2002

Depositional features • Petrified wood • Geodes • Concretions

• Petrified wood: organic material is replaced by silica.

• Geodes: partly filled bodies of silica having crystals of quartz or calcite.

• Concretions: calcite or silica carried by groundwater can replace original material such as shells, bones or twigs.

High-temperature underground water • Hot springs: water temp. is higher than 37º C. – Water gains heat from hot igneous bodies – Water may also be heated through deep circulation.

• Geysers: type of hot spring that periodically erupts hot water (100º C) and steam. • Eruption may be regular as in Old Faithful geyser…. 79 mins. 45 -105 mins • Irregular eruptions are common. Ranging from days to weeks.

Water enters the ground by infiltration Hydrothermal Systems Hot Springs: form when heated groundwater reaches the surface Geysers: form where a Heated water begins to rise complicated plumbing system allows steam pressure to be built up, causing intermittent eruptions

• Hot water deposits: calcite deposited in the form of travertine.

Geothermal energy • Electric power can be generated from the hot water and steam from a hot spring. • San Francisco Geysers field. 2000 MW. Mostly used for room heating.

Water Contamination • Water is considered contaminated when it is harmful to human use. • Sources of water contamination: – Agricultural activities – Human wastes – Industrial effluents