Water Resources - Lecture notes week 10 PDF

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10/3/2016

Chapter 6

Water Res our eso urcces

Lea Learnin rnin rningg Obje Objecti cti ctive ve vess • Describe the origin of Earth’s waters, report the quantity of water that exists today, and list the locations of Earth’s freshwater supply. • Illustrate the hydrologic cycle with a simple sketch and label it with definitions for each water pathway. • Construct the water-budget equation, define each of the components, and explain its use • Discuss water storage in lakes and wetlands and describe some large water projects involving hydroelectric power production. • Describe groundwater and define the elements of the groundwater environment. • Evaluate the U.S. water budget and identify critical aspects of present and future freshwater supplies.

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Water on Earth • Water on earth is thought to have formed from icy comets and hydrogen and oxygen-laden debris during the formation of Earth • Water has been observed to be abundant throughout the Universe • Water migrates from Earth’s interior to the surface through the process of outgassing. Outgassing is visible in volcanic eruptions and in geothermal areas with geysers, hot springs, and fumaroles • The condensation of outgassed water vapor in Earth’s early atmosphere was responsible for the formation of the first oceans and lakes • Hydrology is the science of water and its global circulation, distribution, and properties – focusing on water at or below Earth’s surface

Outgassing

Figure 6.1

Source: digital means.co

Water on Earth • Worldwide Equilibrium • Water in Earth’s hydrosphere maintains a steady-state equilibrium • Within an overall balance the H2O stored in glaciers and ice sheets periodically changes with climate, leading to global changes in sea level • Eustacy: changes in global sea level caused by changes in the volume of water in the oceans • During cooler global climatic conditions water is held in high latitude and high altitude ice sheets, lowering sea level. The situation is reversed during warm climatic periods • Sea-level changes specifically caused by glacial ice melt are known as glacio-eustatic

Source: http://static.skepticalscience.com/pics/gbr_changes.jpg

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Water on Earth • Distribution of Earth’s Water Today • Covers 71% of Earth’s surface by area • Land dominates the northern hemisphere and water dominates the southern hemisphere

Figure 6.2

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The distribution of Earth’s water between liquid/frozen, fresh/saline, surface/underground is shown below

Figure 6.3

Source: digital

The Hydrologic Cycle • The cycling of water in all its forms through the atmosphere, hydrosphere, biosphere, and lithosphere • Divided into 3 primary components: atmosphere, surface, and subsurface • The residence time for a water molecule will vary within different components of the cycle

Source: digital means.co.uk

Figure 6.4

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The Hydrologic Cycle • Water in the Atmosphere • Contributions to atmospheric moisture come from oceanic evaporation and terrestrial evapotranspiration • Advection transports atmospheric water within the atmosphere • Precipitation, in liquid and solid form, release water back towards Earth’s surface

Figure 6.4

The Hydrologic Cycle • Water at the Surface • Water upon reaching terrestrial surfaces will either flow overland or soak into the soil • Descriptors of surface flow: • Interception: occurs when precipitation lands on vegetation or other ground cover • Stem flow: occurs when water drains across plant leaves and down their stems • Throughfall: precipitation that falls directly to the ground

• Infiltration or infiltration: occurs when water penetrates into the soil surface • Overland flow: occurs when the ground is impermeable or the soil has reached its full water holding capacity • Streamflow: channelized flow of water

Figure 6.5

Source: digital means.co.uk

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The Hydrologic Cycle • Water in the Subsurface • Water moves downward into the soil or rock by percolation into the soil-moisture zone, which contains water that is accessible to plant roots – depending on the soil texture • 76% of precipitation infiltrates the subsurface. 85% of the infiltrated water returns to the atmosphere through evapotranspiration • Gravitational water: water that percolates into deeper groundwater after the saturation of soil • Zone of saturation: underground layer where subsurface pore spaces are filled by water • Water table: the top of the zone of saturation • Base flow: portion of streamflow that originates from groundwater

Figure 6.5

Source: digital means.co.uk

Water Budgets and Resource Analysis • Water budget: an accounting system for an area of Earth’s surface balancing inputs from precipitation and outputs from evapotranspiration and surface runoff • Soil-moisture acts as a store of water that eventually end up in ground water, evapotranspiration, or surface runoff

• Surpluses occur when inputs exceed outputs and vice versa for deficits

• Components of the Water Budget • Precipitation • Moisture supply to Earth’s surface in all its forms, such as rain, sleet, snow, or hail.

Precipitation in North America – the water supply Figure 6.6

Source: digital means.co.uk

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Water Budgets and Resource Analysis • Components of the Water Budget (Continued) • Evapotranspiration • Measurement: Evaporation pan or by a lysimeter • Actual Evapotranspiration (AE): The actual water moisture demand at a given location, which results in the transfer of water into the atmosphere from evaporation and transpiration • Potential Evapotranspiration (PE): the amount of water that could evaporate and transpire under ideal moisture conditions if adequate precipitation and soil moisture conditions were present • A moisture deficit exists when PE cannot be satisfied by precipitation inputs, soil moisture storage, or additional inputs of water by irrigation

Potential evapotranspiration for the United States and Canada – the water demand Figure 6.7

Source: digital means.co.uk

Water Budgets and Resource Analysis • Components of the Water Budget (Continued) • Soil Moisture • In the water budget, the volume of water in the soil-moisture zone that is accessible to plant roots is soil-moisture storage (S). • There are 3 categories of soil-moisture: • Gravitational water: water surplus in the soil body after soil becomes saturated during a precipitation event • Capillary water: soil water that resists the pull of gravity due to hydrogen bonds between the water molecules and between water molecules and soil. • Field capacity: portion of capillary water that is available for plants after drainage • Hygroscopic water: water that is inaccessible to plants due to tight binding to soil particles • Wilting point: point where only hygroscopic water remains leading to the wilting of plants

Figure 6.8

Source: digital means.co.uk

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Water Budgets and Resource Analysis • The Water-Budget Equation • For any location, the water inputs are equal to the water outputs plus or minus the change in water storage.

Figure 6.9

Source: digital means.co.uk

Water Budgets and Resource Analysis • Drought: The Water Deficit • General definition: An extended period of dry conditions caused by lower precipitation and often higher temperatures. • Definitions of drought vary by the application of the term. Meteorologists emphasize dry weather conditions, farmers emphasize soil-moisture shortages/surpluses, hydrologists emphasize snowpack size, streamflows, reservoir and groundwater levels. • Drought is a natural and recurrent feature of climate. Global climate change may increase future aridity

Figure 6.12

Source: digital means

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Surface Water Resources

Figure 6.13

Surface Water Resources • Snow and Ice • The largest amount of surface freshwater on Earth is stored in glaciers, permafrost, and polar ice (see Figure 6.3) • Seasonal melting of glaciers and the annual snowpack in temperate regions feeds streamflow, contributing to water supplies • Glaciers are a form of water storage, but are threatened by climate change. For example, on the world’s largest and highest plateau, the Tibetan Plateau, which is important as the source of rivers whose watersheds support almost half of the world’s population

Source: Wikipedia

Source: http://bit.ly/2cRvwhh

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Surface Water Resources • Rivers and Lakes • Rivers are fed by surface runoff and base flow, while lakes are fed by precipitation, streamflow, and groundwater • The world’s largest lake by volume is Lake Baikal in Siberia, Russia • Saline lakes and salty inland seas exist in areas of interior river drainage with no outlet to the ocean, such as Great Salt Lake (Utah), Salton Sea (California), Aral Sea (Uzbekistan, Kazakhstan), Dead Sea (Israel, Jordan)

Lake Baikal

Figure GN 6.2

Figure GN 6.1

Surface Water Resources •

Rivers and Lakes •

Aral Sea •

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Located in Kazakhstan and Uzbekistan Once the world 4th largest lake (by area) – 20,600 sq. mi Lost 90% of its volume since 1960 due to river diversion for Soviet irrigation projects Fisheries collapsed in 1982 In the surrounding areas the climate has become more continental, growing season has reduced, and dust storms are experienced 90 days/year

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Surface Water Resources • Rivers and Lakes (Continued) • Lakes Warm with Climate Change • Increased air temperatures are affecting lakes throughout the world in the following ways: • Some lake levels are rising in response to melting glacial ice • Some lake levels are falling due to drought and high evaporation rates • Some waters at the warm surfaces of lakes fail to mix with cooler, nutrient rich waters from down below. Lakes affected by this issue include Lake Tahoe (California-Nevada) border and Lake Tanganyika in East Africa

Lake Tahoe: ecology impacted by changes in lake water temperatures

Source: Wikipedia

Surface Water Resources • Rivers and Lakes (Continued) • Hydroelectric Power • Human-made lakes are generally called reservoirs. Dams built across rivers cause surface water reservoirs to form upstream • Reservoirs are used for water-supply storage, hydroelectric power generation, and water-supply storage • Hydropower provides about 20% of the world’s electricity and about 7% of the US electricity supply • Issues that have been associated with hydroelectric power projects include: changes to a river’s ecology, inundation of culturally significant sites , movement of people (voluntary or forced), risk of structural failure (especially due to tectonic activity)

Source: USGS

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Surface Water Resources • Rivers and Lakes (Continued) • Hydroelectric Power • The largest hydroelectric power project in the world is the Three Gorges Dam in China

Figure 6.14

Surface Water Resources • Rivers and Lakes (Continued) • Water Transfer Projects • Transfer of water over long distances in pipelines/aqueducts is important in dry regions as most dependable water is far away from population centers. • The California State Water Project (SWP) is the nation’s most extensive water storage and delivery system. It includes dams, reservoirs, canals, pumping stations, and power plants that provide water for over 25 million people and 750,000 acres of farmland. • The Great Man-Made River in Libya is the largest water transfer project in the world moving water from the Nubian Sandstone Aquifer in the Sahara desert to cities along the Libyan coast.

Pipes for the Great ManMade Rover project in Libya, North Africa

Source: Wikipedia

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Surface Water Resources • Rivers and Lakes (Continued) • Wetlands • A wetland is an area that is permanently or seasonally saturated with water and characterized by vegetation adapted to hydric soils. • The water found in wetlands can be freshwater or saltwater. • Marshes, swamps, bogs, and peatlands are types of freshwater wetlands that occur worldwide along river channels and lakeshores, in surface depressions, and in the cool, lowland, high-latitude land regions. • Large wetlands are sources of freshwater and recharge groundwater. • As rivers flow over their banks, wetlands absorb and spread the floodwaters.

Gulf Coast Salt Marsh, Florida

Source: https://soils.ifas.ufl.edu/wetlandextension/types/gulfcoastmar sh.htm

Groundwater Resources • Although groundwater lies below the surface, under the soil-moisture zone and beyond the reach of plant roots, its an important part of the hydrologic cycle. • Groundwater is the largest potential freshwater source on Earth. • It is a volume similar to 70 times all the freshwater lakes in the world. • Groundwater is not an independent source of water: It is tied to surface supplies for recharge through pores in soil and rock.

Figure 6.15

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Groundwater Resources • Where groundwater pollution does occurs, it threatens water quality. • Overconsumption is another problem, depleting groundwater volume in quantities beyond natural replenishment rates and thus threatening global food security. • About 50% of the U.S. population derives a portion of its freshwater from groundwater sources. • In some states, such as Nebraska, groundwater supplies 85% of water needs, with that figure as high as 100% in rural areas. • Between 1950 and 2000, annual groundwater withdrawal in the United States and Canada increased more than 150%.

Pivot irrigation using groundwater

Source: USDA

Groundwater Resources • The Groundwater Environment • Precipitation is the main source of groundwater, percolating downward as gravitational water from the soil-moisture zone. • Water moves through the zone of aeration, where soil and rock are not saturated • Water then accumulates in the zone of saturation, until soil pore spaces are filled with water. • Bounded at the bottom by an impermeable layer of rock that obstructs further downward movement of water • The slope of the water table, which generally follows the contours of the land surface, driving groundwater movement toward areas of lower elevation and lower pressure .

Chapter 6, Unnumbered Figure 1, Page 204

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Groundwater Resources • The Groundwater Environment (Continued) • Aquifers and Wells • An aquifer is a subsurface layer of permeable rock or unconsolidated materials (silt, sand, or gravels) through which groundwater can flow in amounts adequate for wells and springs. • An unconfined aquifer has a permeable layer above, which allows water to pass through, and an impermeable one beneath. • A confined aquifer is bounded above and below by impermeable layers of rock or unconsolidated materials. • The solid, impermeable layer that forms such a boundary is known as an aquiclude.

Groundwater Resources • The Groundwater Environment (Continued) • Groundwater at the Surface • Springs are common in karst environments, in which water dissolves rock (primarily limestone) by chemical processes and flows underground. • Hot springs are common in volcanic environments where water is heated underground before emerging under pressure at the surface. • Streamflow supplements groundwater during periods of water surplus.

Hot Creek. A hot spring in Yellowstone National Park, WY

Source: USGS

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Groundwater Resources • Overuse of Groundwater • As water is pumped from a well, the surrounding water table within an unconfined aquifer might experience drawdown, or become lowered. • Drawdown occurs if the pumping rate exceeds the replenishment flow of water into the aquifer or the horizontal flow around the well. • Resultant lowering of a water table around the well is a cone of depression.

Source: http://www.kgs.ku.edu/HighPlains/atlas/depletion.gif

Groundwater Resources • Overuse of Groundwater • Groundwater Mining of the High Plains Aquifer • The utilization of aquifers beyond their flow and recharge capacities is known as groundwater mining. • Groundwater mining is of special concern for the massive High Plains Aquifer, North America’s largest known aquifer system. • The High Plains Aquifer underlies a 174,000 square mile area shared by eight states and extending from southern South Dakota to Texas.

Figure 6.17

Figure 6.17

Figure 6.16

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Groundwater Resources • Overuse of Groundwater • Groundwater Mining of the High Plains Aquifer • Also known as the Ogallala Aquifer, it is composed mainly of sand and gravel, with some silt and clay deposits. • Heavy mining of this groundwater for irrigation intensified after World War II. The High Plains Aquifer now irrigates about 1/5 of all U.S. cropland and the aquifer supplies drinking water for nearly 2 million people. • The overall effect of groundwater withdrawals has been a drop in the water table of more than 100 ft. in most of the region. • Rising water levels occurred in Nebraska and in areas of Texas due to recharge from surface irrigation and downward percolation from canals and reservoirs. • Water accumulation in the High Plains Aquifer occurred over millions of years, and recharge today is extremely slow. • The USGS estimates that recovery of the aquifer would take at least 1000 years if groundwater mining stopped today.

Figure 6.18

Groundwater Resources • Overuse of Groundwater • Aquifer Compaction and Collapse • A possible effect of removing water from an aquifer is that the ground will lose internal support and collapse as a result. • If the water is removed through over pumping, air infiltrates the pores. Air is readily compressible, and the tremendous weight of overlying rock may compact or crush the aquifer. • The result is land subsidence, a settling or sinking of earth materials on the surface, resulting in building foundations, changes in surface drainage, and sinkholes. • Land subsidence due to aquifer depletion has occurred in places such as: The San Joaquin Valley (CA) and Mexico City

USGS scientist in 1977 using a utility pole to demonstrate where a farmer would have been standing in 1925, 1955 after land subsidence in the San Joaquin Valley.

Source: https://www.revealnews.org/

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Groundwater Resources • Overuse of Groundwater • Desalination • In areas with declining groundwater reserves, desalination of seawater is an important method for obtaining freshwater. • Desalination processes remove organic compounds, debris, and salinity from seawater. • The volume of freshwater produced by desalination worldwide is projected to nearly double between 2010 and 2020. • Approximately 50% of all desalination plants are in the Middle East. In the United States, especially in Florida and along the coast of southern California, desalination use is slowly increasing. • Drawbacks to desalination include the expense and the disposal of concentrated salts

Source: http://macaulay.cuny.edu/eportfolios/tomkiewi czs10/files/2010/03/desalunit.jpg

Groundwater Resources • Pollution of Groundwater • Whereas pollution in surfa...