Water Resources - Environmental Science - Lecture Slides, Slides of Environmental Science

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Chapter 15 Water Resources Docsity.com World Water Distribution • Total: 97% salt water 3% freshwater • Freshwater: 70% glaciers 29% aquifers 1% lakes, rivers, streams Docsity.com Watersheds of the world Docsity.com Groundwater Groundwater: water that is beneath the earth’s surface Water table: the upper level of water underground Aquifer: • underground formation that contains groundwater • made of materials like rock, sand, gravel with spaces in which the water can be held like a sponge • Water can be tapped from aquifers by wells for use by people; if used too much and too quickly, it can go dry • Groundwater can also become surface water when it comes up in a spring Docsity.com Aquifers • Confined aquifer = water-bearing, porous rocks are trapped between layers of less permeable substrate (i.e., clay) – Is under a lot of pressure – Wells that tap into confined aquifers are called artesian wells • Unconfined aquifer = no upper layer to confine it – Readily refilled by surface water that percolates down through permeable layers above it – definition of recharge area: any area where water infiltrates Earth’s surface and reaches aquifers Docsity.com Global Water Use: Agriculture Which countries have the highest percent of their water use dedicated to agriculture? Docsity.com Global Water Use: Industry Industrial uses – manufacturing, producing power (including reservoirs by dams), cooling of power plants Docsity.com Global Water Use: Industry How does water use compare in developing and developed countries? Which countries have more than 50% of their water used by industries? Docsity.com Water Use Calculator http://www.tampagov.net/dept Water/informa tion resources/Saving water/Water use calc ulator.asp ® Docsity.com What can you do to conserve water? Residential – how can you conserve water? • Awareness of water use and conscious decisions to reduce water use (shorter showers, turn off water when brushing teeth, etc.) • Low flow faucets, shower heads and toilets • Don’t use toilet as a waste basket • Run dishwasher and washing machine only when full • Fix leaky plumbing • Xeriscaping - landscaping using plants adapted to arid conditions • Water lawns at night, when evaporation is minimal • Don’t wash driveways and sidewalks with water Docsity.com • Do you think water is a renewable resource? • It is a renewable resource because it can be replenished by nature (water cycle) • However, if it is made unusable by pollution or used faster than nature can replenish it, then it is considered nonrenewable Docsity.com Much of our overuse is related to agriculture Today, 70% more water is withdrawn for irrigation than in 1960 – The amount of irrigated land has doubled – Crop yields can double Docsity.com Most irrigation is highly inefficient • Only 45% of water is absorbed by crops via “flood and furrow” irrigation • Over-irrigation leads to waterlogging, salinization, and lost farming income • Water for irrigation may be drawn from rivers or groundwater Docsity.com Gravity Flow (efficiency 60% and 80% with surge valves) Water usually comes from an aqueduct system or a nearby river. Drip Irrigation (efficiency 90-95%) Above- or below-ground pipes or tubes deliver water to individual plant roots. Center Pivot (efficiency 80% with low-pressure sprinkler and 90–95% with LEPA sprinkler) Water usually pumped from underground and sprayed from mobile boom with sprinklers. Docsity.com Case Study: The Aral Sea • Once the fourth-largest lake on Earth – It has lost more than 80% of its volume in just 45 years – The two rivers leading into the Aral Sea were diverted to irrigate cotton fields • Consequences of a shrinking sea – 60,000 fishing jobs are gone – Pesticide-laden dust from the lake bed is blown into the air – The cotton cannot bring back the region’s economy Docsity.com Case Study: Colorado River People have long diverted water to farm fields, homes, and cities The once mighty Colorado River has been extensively dammed and diverted Aqueducts carry water from the river to other places that need it Docsity.com The Colorado River is heavily diverted – What water is left after all the diversions comprises just a trickle into the Gulf of California • On some days, water does not reach the gulf – Diversion has drastically altered the river’s ecology Docsity.com Can we “make” more water to meet demands? Desalination is the process of removing salt from salt water – may be answer to providing more water to a growing human population It is expensive, requires fossil fuels, and produces concentrated salty water as a waste product Used in some places, such as Saudi Arabia, where water is scarce, but fuel for the process is abundant Docsity.com Managing the flow of water Dams – purposes: • flood control • hydroelectric power • creation of reservoirs for drinking water, irrigation and recreation Only a few major rivers remain undammed – In remote regions of Canada, Alaska, and Russia Docsity.com A typical dam New recreational Population opportunities Sediment displacement capture Crop irrigation and drinking ‘é 7 Risk of failure and water " catastrophic flooding Habitat alteration (upstream and downstream) 4). —— Lost recreational opportunities Generation of electricity Declining fisheries control Reduced downstream flow and disruption of flooding Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Docsity.com Benefits and drawbacks of dams • Benefits: – Power generation – Emission reduction – Crop irrigation – Drinking water – Flood control – Shipping – New recreational opportunities • Drawbacks: – Habitat alteration – Fisheries declines – Population displacement – Sediment capture – Disruption of flooding – Risk of failure – Lost recreational opportunities Docsity.com Some dams are being removed • Some people feel that the cost of dams outweighs their benefits – They are pushing to dismantle dams • Rivers with dismantled dams – Have restored riparian ecosystems – Reestablished fisheries – Revived river recreation • 500 dams have been removed in the U.S. – Property owners who opposed the removal change their minds once they see the healthy river Docsity.com Dikes and levees are built to control floods • Flooding is a normal, natural process – Floodwaters spread nutrient-rich sediments over large areas • Floods also do tremendous damage to property • Dikes and levees (long, raised mounds of earth) along the banks of rivers hold rising waters in channels – The U.S. Army Corps of Engineers has constructed thousands of miles of levees • Levees can make floods worse by forcing water to stay in channels and overflow Docsity.com Case Study: Louisiana Waterway for ships called the Gulf Outlet may have caused the storm surge to arrive at 2-3 times the speed it would have It provided a channel by which the storm surge more easily reach populated areas Docsity.com Aerial view of New Orleans after 17th St. Levee broke due to Hurricane Katrina This area is completely flooded Docsity.com Summary: Events in place that made effects of Hurricane Katrina worse • Existence of a city below sea level meant it was already vulnerable to flooding • Loss of wetlands reduced the storm buffer • Gulf Outlet served as a “hurricane highway” • Levees channeled water but then broke Docsity.com Drinking Water Treatment 3. Second filtration – layers of sand, gravel, coal used to filter remaining impurities Docsity.com Drinking Water Treatment 4. Chlorination – chlorine added to stop bacterial growth Docsity.com Drinking Water Treatment 5. Aeration – bubbling air through the water removes unwanted gases, improves odor and taste Docsity.com