1Groundwater and Water ResourcesGlobal water resource availability Patterns in use of water resourcesGetting surface water into the groundPorosity and Permeability – Aquifers and AquitardsWater table and springs1pgEffects of pumping from wells – cone of depressionEffects of overuse of groundwaterRedistribution and overuse of surface waterWater pollutionSome solutions to supply problems2Vital Water Graphics – United Nationshttp://www.unep.org/vitalwater/3Vital Water Graphics – United Nationshttp://www.unep.org/vitalwater/Irrigation is the largest use of groundwater. It also is one of the top two uses of surface water. Worldwide, agriculture uses about 75% of global water consumption and industry 20% Fig. 12.17 Understanding Earth4Infiltration Origin of Groundwater Rainwater may enter the ground through infiltration or flow across the surface as runoff. Surface slope, type of surface material, and vegetation are among the factors which influence the relative amounts of infiltration and runoff.5Next: infiltration and rising water table.MOVFig. 15-2 Geology 2ndedition - ChernicoffPorosity -amount of space that may contain water – most pore space is in the form of spaces between sediment particles or fracturesPermeability6Permeability -ability of water to flow through a material –related to the amount, size, and inter-connectedness of the poresFig. 12.7 Understanding Earth(a) has the greatest porosity and permeability(e) has the least2Water tableFig. 12.8 Understanding Earth7 8Relationship between water table, groundwater flow, and topography in an unconfined aquiferFig. 15-8 Geology 2ndedition - ChernicoffCone of depression around a pumping well The overall shape of the cone depends upon the characteristics of the aquifer material, the amount of recharge, and the amount of pumping. Pumping more water from the well can deepen and widen the cone of depression over time. Note that the steepness of the cone is exaggerated in this illustration.9Fig. 12.13 Understanding EarthOveruse of groundwater depresses the water table and can change the direction of groundwater flow. Water also can flow underground from wetlands toward the area of lowered water table, possibly causing the wetlands to go dry.10Fig. 15-18 Geology 2ndedition - ChernicoffGroundwater use exceeds recharge in much of the U.S. and many other places around the world11Fig. 10.13 Keller, Environmental GeologySubsidence Overuse of groundwater can cause aquifer sediments to compact and the ground surface to subside (sink)12Cracks related to uneven sinking of the ground surface at Edwards Air Force Base, California Fig. 12.14 Understanding EarthFig. 11-8 NAGT lab manualnext: San Joaquin subsidence.MOV313Subsidence around Santa Clara, California - change in land surface elevation from 1934 to 1967Fig. 11-8 NAGT lab manualChange of water level in well (graph) and subsidence (table) in San Jose California from 1912 to 1967Figs. 16-12 & 16-13 NAGT lab manual1415Saltwater intrusion in coastal areas Overuse of fresh groundwater may result in salt water reaching wells.Fig. 12.15 Understanding EarthIn many places, much of the water in the ground has been there for a very long time. Some of this water is left over from a time when the local climate was wetter than today. When this very old or “fossil” water is used, it is may not be replaced by modern-day recharge. Use of such water sometimes is called “water mining” since the resource is limited and may eventually run out just like when mineral resources are mined.16Vital Water Graphics – United Nations http://www.unep.org/vitalwater/17Center-pivot irrigation in a desert region, Saudi Arabia, January 1990The water being extracted to irrigate these fields entered deep aquifers at a time when the climate was much wetter than it is today. The amount of this “fossil” water is limited, and eventually the wells may go dry. Center-pivot irrigation and the use of fossil water is not unique to Saudi Arabia. Water left behind by ancient wetter climates is being used in many parts of the world.image from NASAIrrigated agriculture in a desert, Southern California and Northwestern Mexico August 1985Agricultural field patterns stand out in contrast to the natural desert landscape. Two rivers the ColoradoNorthPacific OceanOveruse of water also occurs with our limited supplies of surface waterSan Diego18rivers, the Colorado and the Gila, are the major sources of water for this arid region. Because of water use for agriculture and other activities, the Colorado River usually goes dry before it reaches the ocean.NASAColorado RiverSalton Sea4Shrinking of Mono Lake -Water diverted to supply the growing population of Los Angeles resulted in a 45 foot drop in lake level between 1941 and 1989. (Note the exposed shoreline surrounding the lake.) This put at risk an entire ecosystem that draws millions of birds to Mono Lake each year. An agreement was finally reached that put limits on the water diversions and stabilized the lake level.NASA photo (October, 1985)19Owens Lake, California (dry) Before an aqueduct was built to divert water from the Owens River to the city of Los Angeles, Owens Lake (center) was about 18 miles (29 km) long and nearly 10 miles (16 km) wide. The dry20lakebed is now the single largest source of PM-10 dust (a form of air pollution) in the United States. Owens lake is located south of Mono Lake.NASA photo (May 1991)21Shrinking lakes are a global problemVital Water Graphics – United Nationshttp://www.unep.org/vitalwater/Another problem: water quality…Some sources of groundwater (and surface water) contamination22Fig. 12.22 Understanding EarthPossible solutions to groundwater supply issues• Conservation – find ways to use less• Enhance recharge to replenish aquifers23• Greater storage of surface water – e.g. new and bigger dams & reservoirs• Find new sources – e.g. desalination, importation from other areas,reclaimed waterRecharge basin - Long Island, New YorkOne possible solution to shortages of groundwater is to increase infiltration.Fig. 15-24 Geology 2ndedition -Chernicoff245Fig. 10.16 Keller, Environmental GeologyIn California, the places with the most water are different than the places of greatest water use. To accommodate this, a great deal of water is transported via canals and pipelines.25Canal photo from: USGS WRIR 03-4091http://water.usgs.gov/pubs/wri/wri034091/DesalinationOther sources of water also can