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Groundwater Chapter 11: 

Groundwater Chapter 11

Importance of groundwater: 

Importance of groundwater Groundwater is water found in sediment, plus narrow fractures in bedrock Groundwater is the largest reservoir of fresh water available to humans

Slide3: 

Distribution of Groundwater

Fresh water of the Hydrosphere: 

Fresh water of the Hydrosphere

The water table: 

The water table Water table is the upper limit of saturation Variations in the water table Depth is highly variable Varies seasonally and from year to year Shape is usually similar to surface topography

Factors influencing movement of groundwater: 

Factors influencing movement of groundwater Permeability, aquitards, and aquifers Permeability – the ability of a material to transmit a fluid Aquitard – an impermeable layer that hinders water movement (such as clay) Aquifer – permeable rock strata or sediment that transmits groundwater freely (such as sands and gravels)

Springs may result from a perched water table: 

Springs may result from a perched water table

Features associated with groundwater: 

Features associated with groundwater Hot springs Water is 6-9oC warmer than the mean annual air temperature of the locality The water for most hot springs is heated by cooling of igneous rock

Distribution of hot springs and geysers in the United States: 

Distribution of hot springs and geysers in the United States

Slide11: 

Glenwood Hot Springs

Slide12: 

Mt Princeton Hot Springs

Features associated with groundwater: 

Features associated with groundwater Geysers Intermittent hot springs Water erupts with great force Occur where extensive underground chambers exist within hot igneous rock Groundwater heats, expands, changes to steam, and erupts

Slide14: 

Evolution of a geyser eruption

Slide15: 

Old Faithful geyser in Yellowstone Natl Park

Slide16: 

Yellowstone Geyser erupting

Slide17: 

Yellowstone Geyser Pool prior to eruption

Slide18: 

Aquifer Model for the Front Range

Slide19: 

Location of Ogallala Aquifer

Features associated with groundwater: 

Features associated with groundwater Wells To ensure a continuous supply of water, a well must penetrate below the water table Pumping of wells can cause Drawdown (lowering) of the water table Cone of depression in the water table

Formation of a cone of depression in the water table: 

Formation of a cone of depression in the water table

Problems associated with groundwater withdrawal: 

Problems associated with groundwater withdrawal Treating groundwater as a nonrenewable resource In many places water available to recharge aquifer is less than amount being withdrawn Subsidence Ground sinks when water is pumped from wells faster than natural recharge replaces it

Problems associated with groundwater withdrawal: 

Problems associated with groundwater withdrawal Saltwater contamination Groundwater withdrawal causes saltwater to be drawn into wells, contaminating supply Primarily a problem in coastal areas

Saltwater contamination due to excessive well pumping: 

Saltwater contamination due to excessive well pumping

Groundwater contamination: 

Groundwater contamination Common source is sewage Extremely permeable aquifers, such as gravel, have such large pores that groundwater may travel long distances without being cleaned Sewage usually becomes purified as it passes through a few dozen meters of an aquifer composed of sand or permeable sandstone

Slide26: 

Contamination of water well by Septic System

Slide27: 

Fast flow contaminates well

Geologic work of groundwater: 

Geologic work of groundwater Caverns Most caverns are created by acidic groundwater dissolving soluble rock at or just below the surface in the zone of saturation

Geologic work of groundwater: 

Geologic work of groundwater Groundwater dissolves rock Groundwater is often mildly acidic Contains weak carbonic acid Forms when rainwater dissolves carbon dioxide from the air and from decaying plants Carbonic acid reacts with calcite in limestone to form calcium bicarbonate, a soluble material

Geologic work of groundwater: 

Geologic work of groundwater Caverns Features found within caverns Composed of dripstone (travertine) Calcite deposited as dripping water evaporates Collectively, they are called speleothems Includes stalactites (hanging from the ceiling) and stalagmites (form on the floor of a cavern)

Speleothems in Carlsbad Caverns National Park: 

Speleothems in Carlsbad Caverns National Park

“Soda straws” in Carlsbad Caverns National Park: 

“Soda straws” in Carlsbad Caverns National Park

Geologic work of groundwater: 

Geologic work of groundwater Karst topography Landscapes that have been shaped by the dissolving power of groundwater Some common features include Irregular terrain Sinkhole or sinks (formed by groundwater slowly dissolving the bedrock often accompanied by collapse) Striking lack of surface drainage (streams)

Slide34: 

Stream incision, cave development and karst topography

Slide35: 

Development of a Sinkhole

Slide36: 

Sinkholes in Florida

Slide37: 

Sinkholes in Urban Settings

End of Chapter 11: 

End of Chapter 11

Slide39: 

Hydraulic head and urban water supplies