Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 11 Fresh Water of the Continents Visualizing Physical Geography by Alan Strahler and Zeeya Merali

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter Overview The Hydrologic Cycle Revisited Ground Water Surface Water Stream Flows and Floods Lakes Surface Water as a Natural Resource

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Hydrologic Cycle Revisited The hydrologic cycle traces the paths of water through the oceans, atmosphere, and land

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Hydrologic Cycle Revisited Precipitation may infiltrate, run off, evaporate/transpire Infiltration: absorption and downward movement of precipitation into the soil and regolith Runoff: flow of water from continents to oceans through stream flow and ground-water flow

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ground Water Ground water: subsurface water in the saturated zone that moves under the force of gravity Water table: upper limit of the body of ground water; marks the boundary between the saturated and unsaturated zones Percolation: flow of water through the soil by gravity

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ground Water The Water Table Water table rises: Water percolates through unsaturated zone High precipitation Water table falls: Water seeps into lakes, streams, marshes During droughts Aquifer: layer of rock or sediment that contains abundant freely flowing ground water In an artesian well, water under pressure flows freely from the well Aquiclude: impervious rock layer

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ground Water Hot Springs and Geysers Hot rock heats ground water Heated water emerges as hot springs or geysers Mineral deposits build up around hot springs

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ground Water Limestone Solution by Ground Water Carbonic acid: weak acid produced when carbon dioxide dissolves in water Carbonic acid erodes limestone at or below the surface Karst: landscape or topography dominated by surface features of limestone solution and underlain by a limestone cavern system

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ground Water Limestone Solution by Ground Water Karst landscape is characterized by sinkholes, caverns, limestone towers, no surface streams

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Ground Water Ground Water Management Problems Rapid withdrawal of ground water Cone of depression: lowering of the water table in a cone shape, around a well Drawdown: difference in height between the cone tip and the original water table Subsidence of land Contamination of wells by pollutants Saltwater contamination

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water Overland Flow and Stream Flow Overland flow: runoff that flows downslope in broad sheets Sheet flow: continuous thin film of overland flow Streamflow: water runs in a channel Stream: long, narrow body of flowing water moving along a channel to lower levels under the force of gravity

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water Overland Flow and Stream Flow Characteristics of stream flow: Water slowed by friction with channel walls and bed Velocity is greatest in the middle and top of the stream The steeper the gradient, the faster the flow Discharge: volume of the stream, cubic meters/second Q=AV=constant Q: discharge A: cross-sectional area V: velocity

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water Overland Flow and Stream Flow Discharge of major rivers in the U.S.

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water Drainage Systems Drainage System: a branched network of stream channels and adjacent slopes converging to a single channel at the outlet Drainage divides separate drainage basins or watersheds

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Freshwater Resources Surface Water Water is used for domestic, agricultural, and industrial use, in differing proportions around the world

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water Freshwater Resources Drinkable water is scarce in some regions Conflicts over water arise in many parts of the world

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Stream Flows and Floods Urban areas affect the flow of streams: Urban surfaces often impervious to water  water cannot infiltrate  overland flow increases  flooding may increase Less infiltration  less groundwater recharge  decrease in base flow to stream channels In dry periods, stream discharges lower in urban areas In wet periods, greater chance of flooding Storm sewers carry storm runoff quickly to streams  reduces lag times, increase peak discharges A hydrograph plots discharge of a stream over time

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Stream Flows and Floods Chattahoochee River hydrograph

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Stream Flows and Floods River Floods Floodplain: a broad belt of low, flat ground bordering a river channel that floods regularly

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Lakes Lake: body of standing water that is enclosed on all sides by land Includes ponds, marshes, swamps Lakes receive water from streams, overland flow, ground water Lakes may lose water at an outlet; also by evaporation Lakes are sources of water, food, power, beauty Created by tectonic processes, landslides, glacial processes, artificially with dams Lakes eventually disappear by drainage, sedimentation, climate change and evaporation

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Lakes Saline Lakes and Salt Flats A lake with no surface outlet will be saline (salty) Streams bring dissolved salts into the lake; evaporation removes pure water: salts remain behind Salinity may reach a point where salts precipitate as solids Salt flats/dry lakes form when there is high evaporation, little inflow to the basin The Aral sea is drying up because water from the streams that feed it has been diverted

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water as a Natural Resource Surface water used for : Agriculture Industry Domestic water supplies Hydroelectric power Travel Surface water supplies are limited: about 20 times as much groundwater is available as water in freshwater lakes

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Surface Water as a Natural Resource Pollution of Surface water Sources of water pollution: industrial plants, untreated sewage, salts and fertilizers in suburban areas, fertilizers and livestock waste, mining operations, releases from nuclear facilities. Pollutants: Chemical compounds Fertilizers, sewage Acid mine drainage Toxic metals Bacteria and viruses Thermal pollution Eutrophication: excessive growth of algae and other related organisms in a stream or lake as a result of the input of large amounts of nutrient ions, especially phosphate and nitrate