Log entry: environmental studies: earth science

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Chapter 11 Fresh Water of the Continents

Visualizing Physical Geography by Timothy Foresman & Alan Strahler

Chapter Overview

Fresh Water and the Hydrologic Cycle

Ground Water

Surface Water and Fluvial Systems

Lakes

Water as a Natural Resource

Fresh Water and the Hydrologic Cycle

Distribution of Fresh Water

Fresh water makes up only 2.5% of the Earth’s water.

Most fresh water is contained in glaciers and ground water.

What percentage of the

total water on Earth is in

freshwater lakes?

a. 0.0067%

b. 0.27%

c. 0.4%

d. 2.5%

Fresh Water and the Hydrologic Cycle

Distribution of Fresh Water

Ground water = The subsurface water in the saturated zone that can move as part of the hydrologic cycle.

Fresh Water and the Hydrologic Cycle

Movement of Fresh Water through the Hydrologic Cycle

How will a global temperature rise affect the hydrologic cycle?

Fresh Water and the Hydrologic Cycle

Movement of Fresh Water through the Hydrologic Cycle

Infiltration = Absorption and downward movement of precipitation into the soil and regolith.

Soil-water belt

Evapotranspiration

Fresh Water and the Hydrologic Cycle

Movement of Fresh Water through the Hydrologic Cycle

Runoff = Flow of water

leaving an area

through surface,

subsurface, or

groundwater flow.

Overland flow: surface runoff on ground surface

Overland flow moves sediment

Ground Water

Percolation: precipitation sinks into soil and flows down under force of gravity

Water table = The upper limit of the body of ground water, marking the boundary between the saturated and unsaturated zones.

Saturated zone: where water fills pore spaces

Ground Water

Aquifer = A layer of rock or sediment that contains abundant freely flowing ground water.

Water in the unsaturated zone percolates downward to the saturated zone of ground water.

Ground Water

Aquicludes: rock layers relatively impermeable to groundwater

Artesian well: self-flowing well due to confined water moving under influence of gravity

The Water Table

Ground water and the water table

Where water table is at or above surface, groundwater emerges by seeping into ponds, streams, lakes, marshes

The Water Table

Limestone Solution by Ground Water

Carbon dioxide dissolves in water and makes carbonic acid

Acid dissolves limestone

Cavern development

Stalactites

Stalagmite

Sinkholes

Karst topography results

The Water Table

Limestone Solution by Ground Water

Evolution of a karst landscape

The Water Table

Limestone Solution by Ground Water

Evolution of a karst landscape

The Water Table

Groundwater Use and Management

Groundwater withdrawal

Cone of depression

Drawdown

The Water Table

Groundwater Use and Management

Subsidence: land sinks when water is taken out

Pore space collapses due to soil pressure

Land subsidence mapping using satellite data

Santa Clara Valley, CA (seasonal water withdrawal)

Other western locations

The Water Table

Pollution of ground water

Groundwater contamination

Groundwater pollution from chemicals

Accidental

Intentional

Surface Water and Fluvial Systems

Drainage Systems

Overland flow: water travels on surface

Sheet flow: continuous thin film

Surface Water and Fluvial Systems

Drainage basins

Drainage system = A branched network of stream channels and adjacent land slopes that converge to a single channel at the outlet.

Drainage divides

Drainage basin (watershed)

Surface Water and Fluvial Systems

Drainage patterns

Dendritic pattern

Trellis pattern

Annular pattern

Radial pattern

Surface Water and Fluvial Systems

Stream Channels and Discharge

Stream: long, narrow flowing water body

Discharge (Q): volume per unit time thru cross section

Stream gradient: slope of stream

Stream velocity: shape & slope determine

Surface Water and Fluvial Systems

Stream discharge

Discharge within a drainage system

Surface Water and Fluvial Systems

Stream discharge: cross section & velocity determine

Pools and rapids

Base flow: water supplied to stream by groundwater

As the slope increases, the _______ of the stream is constant

and the _______ decreases.

a. velocity; area

b. area; velocity

c. area; discharge

d. discharge; area

Surface Water and Fluvial Systems

Discharge related to base flow and overland flow

Hydrograph: plot of stream discharge with time at given location

Surface Water and Fluvial Systems

Flooding: soil gets saturated, runoff fills streams & rivers; they overflow banks and into floodplain

Floodplains = A broad belt of low, flat ground bordering a river channel that floods regularly.

Surface Water and Fluvial Systems

Mississippi River Flood of 2011

NASA’s MODIS Imager satellite data

Note change in river during flood

May 6, 2010

May 6, 2011

Surface Water and Fluvial Systems

Mississippi River Flood of 2011

Millington, Tennessee (north of Memphis)

Other areas also affected

Surface Water and Fluvial Systems

Flood Stage: National Weather Service designates a particular water surface level as flood stage for a given river at a given place; water rising above this level inundates floodplain

National Weather Service does flood forecasting for U.S. and notifies public

Surface Water and Fluvial Systems

Flood profiles: graphical depiction of rainfall rate and stream discharge as a function of time during flood event; note lag time to peak flow after precipitation event

Flash floods: short lag time; small watershed w/ steep slopes

Surface Water and Fluvial Systems

Urbanization and flooding

Lakes

Lake = A body of standing water without an appreciable gradient or current

Receive water from streams, overland flow, and groundwater

Stores small quantities of water compared to other resources

Short-lived features: drain or become filled in

Lakes

Hydroelectric dam: artificial lake

Lakes

Water level of lakes & ponds is close to level of water in water table in moist climates

As climate changes, lake level can be affected

Water as a Natural Resource

Water Access and Supply

Dams: location-specific

Pipelines (California aqueduct)

Urban centers: wastewater recycling

Desalination (and effects on conservation)

Water as a Natural Resource

Pollution of Surface Water

Eutrophication: nutrients stimulate plant growth; decomposition of organic matter uses up oxygen and resulting low levels kill fish

Hypoxia: point at which organisms have lack of oxygen