2 Case History: Long Island GW pollution: a serious problem on the western end of the island since beginning of 20th centuryGW below Nassau County is tremendous, yet intensive pumping causing as much as 15 m decline in water levelSalt water intrusion due to decline in water levelUrbanization triggered more serious water pollution: urban runoff, sewage and fertilizers, road salt, industrial and other wastes, landfills
3 Global Water Cycle Cyclic nature Global movement of water between different water storage compartmentsGlobal distributionAbundance not a problemDistribution in space and over time a problemSupply vs. use a problem
4 Global Water Cycle Water’s vertical movement Upflow: Evaporation, transpirationDownflow: Precipitation and infiltrationWater’s horizontal movementSurface runoffShallow subsurface flowGroundwater flow
6 Surface Water (1) Surface runoff Drainage network Drainage basin or watershedDrainage divideStream order and size of drainage basin
7 Surface Water (2) Sediment yield in surface runoff Geological factors: Type and structure of soils and rocksTopographic factors: Relief and slope gradientClimatic factors: Type, intensity, duration, and distribution of precipitationVegetation factors: Type, size, and distributionLand-use practice factors
8 Groundwater (1) Groundwater (GW) profile Vadose zone (unsaturated zone, zone of aeration)Zone of saturationWater table: The boundary of the above two zonesPerched water table: Local water table above a regional water table
9 Groundwater (2)Aquifer: A unit capable of supplying water at an economically useful rateAquitard or aquiclude: A confining layer or unit restricting and retarding GW flowUnconfined aquifer: no overlying confining layerConfined aquifer: with an overlying aquitard layerPerched aquifer: local zone of saturation above a regional water table
11 Groundwater (4) GW recharge and discharge Recharge zone: Area where water infiltrates downward from surface to GWDischarge zone: Area where GW is removed from an aquifer, such as spring, well, river, etc.Influent stream: above the water table, recharge water to GW, may be intermittentEffluent stream: perennial stream with the addition of GW when precipitation is low
12 Groundwater (5)GW pressure surface: Generally declining from source along the flow from recharge area to discharge areaArtesian well: Water self-rising above the land surface in a confined aquiferCone of depression: Drawdown cone of GW in a well
13 Groundwater Movement (1) Hydraulic gradient: The gradient of water table, generally following the topographic gradientHydraulic conductivity: Ability of rock materials to allow water to move through (m3/day/m2)Porosity: Percentage of void (empty) space in sediment or rock to store waterPermeability: Measuring the interconnection of pores in a rock material
15 Groundwater Use and Supply (1) Available GW estimated above the total flow of the Mississippi during the last 200 yearsGW as primary drinking water source for ~50% of the U.S. populationGW overdraft problems (extraction rate exceeding recharging rate) in many parts of the country, particularly some states in the Great Plains regionEstimated 5% of GW depleted, but water level declined more than 15 m (50 ft) in some areas
17 Interactions b/w SW and GW Overdraft of GW: Leads to lower water levels of streams, lakes, reservoirs, etc.Overuse of SW: Yields lower discharge rates of GWEffluent stream (in GW discharge zone): Tends to be perennialInfluent stream (in GW recharge zone above the water table): Often intermittent or ephemeralSpecial linkage area: Sinkholes and cavern systems in the karst terrains
18 Water Use (1)Offstream use: Removal or diversion from its SW or GW sources temporarily, e.g., irrigation, thermoelectric, industrial useConsumptive use: Type of offstream use of water without intermediate return to the SW or GW, such as transpiration and human useInstream use: Navigation, fish and wildlife, recreational uses
19 Water Use (2) In major urban areas Overwithdrawal of groundwater Overuse of local surface waterThreats of local urban landfills to the water supply, e.g., Long Island, NYWater import issues and problems: What is distance to transport? How much water available? From where? Conflicts with other areas, litigations, and long-range planning
20 Trends in Water Use (1) Based on the data from 1950–1995 SW use far greater than GW useThe rate of water use decreased and leveled off since 1980Irrigation and thermoelectric are major consumptive fresh water useLess fresh water use since 1980 due to new tech and water recycling
22 Water ConservationEngineering technology and structure (canals): Regulating irrigation and reducing evaporationBetter technologies in power plants and other industries: Less use of water due to improved efficiencyIncreased water reuse and recycling
23 Water Management (1) Needs for water management Increasing demand for water use (population and economic development)Water supply problems in semiarid and arid regionsWater supply problems in megacities of humid regionsWater traded as a commodity: Capital, market, and regulations?
24 Water Management (2) Aspects to be considered: Leopold philosophy Natural environmental factors: Geologic, geographic, and climaticHuman environmental factors: Economic, social, and politicalStrategiesMore SW use in wet years, more GW use in dry yearsReuse and recycle water on regular basis as well as in emergencies
25 Management of the Colorado River (1) Managing the waterWater appropriation to 7 states in the U.S. and to MexicoLocal needs vs. regional needs (Colorado River compact of 1922)The U.S. vs. Mexico (Treaty w/ Mexico in 1944)Human use vs. needs of lands (1974 Salinity Control Act)
26 Management of the Colorado River (2) Managing the riverDam constructionImpact on flood frequencyImpact on sediment distribution, particularly downstreamImpact on wildlife habitatsControlled and planned floods
27 Water and EcosystemsEcosystems: changes in response to climate, nutrient input, soils and hydrologyGeneral tendency: Increased human use of water, increased degradation of natural ecosystemsOverall reconciliation between multiple water usesWater resources development (dams, reservoirs, canals) and associated impact on surface water environmentReconciling the uses of water: Agriculture, industry, urbanization, and recreationProtection of wetlands and water resources
28 Emerging Global Water Shortage Isolated shortage of water: indication of a global pattern of water shortageDepleted water resources: over-drafted aquifers, dried lakes (Aral Sea), troubled streams (Colorado and Yellow River not reaching seas some years)Polluted limited water resources due to development and increased wastesDemands for water resources tripled as population more than doubled last 50 yrs and growing fast next 50 yrsGlobal warming: causing more problems
29 Applied and Critical Thinking Topics In your area, which type of water source (SW or GW) is more important? Why?If we change the ways we use water, what would be the impact on the global water cycle?Is the global hydrologic cycle a closed system or an open system?Which continent will have a great impact on its water resources from global warming?
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