3Mean Annual Precipitation The distribution of precipitation in different parts of the earth is certainly not even. Lack of precipitation, either regularly or seasonally, is the source of enormous human suffering. The amount of precipitation a particular area receives largely dictates the nature of vegetation and animals there. Such human suffering is prevalent in northern Africa where this map shows that less than 25 cm (10 inches) of rain falls per year.
4Windward flanks of mountains wet; leeward side (rain shadow) dry Mt. Waialeale, Hawaii: windward side gets 460 in/yr, leeward side (a few miles away) gets 18 in/yrWhen rain falls is important (during growing season)Varies seasonally
5Part 2: Major Water Compartments Or, where is water distributed?
6Interactions of water with soil. Groundwater, after ice, is the 2nd largest reservoir of fresh waterInfiltration - Process of water percolating through the soil and into fractures and permeable rocks.Zone of Aeration - Upper soil layers that hold both air and water.Zone of Saturation - Lower soil layers where all spaces are filled with water.Water Table is at the top of the Zone of SaturationPrecipitation that does not run off or evaporate percolates through the soil in a process called infiltration. This water interacts with the soil, first adsorbing nutrients and then later releasing them to plant roots, microorganisms or soil at deeper depths. Water that infiltrates soil can be a source for ground water. The zone of saturation is often the source of water for wells. The top of the zone of saturation is called the water table.
7GroundwaterAquifer – porous, permeable rock or sediment that transmits groundwater freelyMay be confined or unconfined (next slide)Aquitard/aquiclude – layers of rock or sediment that hinder/prevent water movementRecharge zones - areas where surface waters filter into an aquiferAquifers are porous underground layers that contain water. Besides water, aquifers typically contain porous layers of sand, gravel and rock lying below the water table. In cases where aquifers are used to supply water, they typically are closer to the surface of the earth and near areas where the water is required.The components of an aquifer include an aquitard (confining layers that keep water from moving further into the earth) and the water bearing porous zone. In cases where the aquifer is confined above as well as below, the water bearing zone rises above the land surface. Wells drilled into the aquifer will likely flow freely from natural pressure. This is termed an artesian well. Sometimes artesian wells occur naturally.The recharge zone is where water infiltrates into an aquifer. Recharge rates are often very slow. Currently, humans are removing ground water from aquifers faster than the aquifer can be recharged resulting in a net loss of groundwater.
8Confined aquifer Unconfined aquifer Recharge area unsaturated material In unconfined aquifers, the ground water only partially fills the aquifer and the upper surface of the ground water (the water table) is free to rise and decline. A confined aquifer is sandwiched between layers of impermeable materials such as clay which impede the movement of water into and out of the aquifer.
9WellsA hole bored into the zone of saturation for the purpose of extracting water (for this chapter, anyway)Drawdown – decrease in water table as water is withdrawn from by a wellAmount depends on the aquifer & how “hard” the well is pumpedDecreases with distance from wellCone of depression – a conical depression; the 3-D result of drawdown by a pumped wellThink of drinking a milkshake using a straw
14Rivers, Lakes and Streams Precipitation that does not evaporate or infiltrate into the ground runs off the surface, back toward the sea.Best measure of water volume carried by a river is discharge (the amount of water that passes a fixed point in a given amount of time)Amazon is the largest; Mississippi is 6thLakes – 100 times the water of rivers, but most in a few large onesGreat Lakes, Lake Baikal (Siberia), Great Rift Lakes (Africa)Other, smaller compartments of water include rivers, lakes, streams, wetlands and the atmosphere. The length of time water typically stays in a compartment is called its residence time. A water molecule has a residence time of approximately 3000 years in the ocean. In a living organism the residence time is about a week. In saline or fresh groundwater, the residence time can be as high as thousands of years depending on depth and other factors. Water in aquifers with long residence times can be made permanently unusable if pollutants are carried in from above since there is little turnover. Water in such aquifers is, for all practical purposes, non-renewable.
15Wetlands Bogs, swamps, marshes Play a vital role in hydrologic cycle Lush plant growth stabilizes soil and retards surface runoff, allowing more aquifer infiltration.Also tend to filter pollutants from water.Disturbance (including urban development) reduces natural water-absorbing capacity, resulting in floods and erosion in wet periods, and less water flow the rest of the year.
16The Atmosphere - Among the smallest water reservoirs Contains 0.001% of total water supply.Has the most rapid turnover rate.Provides a mechanism for distributing fresh water over landmasses and replenishing terrestrial reservoirs.
17Part 3: Water Availability and Use Clean, fresh water is requisite for human survival.Renewable water supplies consist of surface runoff and shallow ground water. These supplies are most plentiful in the Tropics.Picture to the left shows a ditch being used to divert water for irrigation of crops. Water rights for such activities have long been a source of tension and conflict.Water availability and quality has always been a primary concern for human survival. Humans require about a gallon of water per person per day. Clean water is not only an important input directly into humans, but it is also necessary for the production of food, for carrying out industrial processes, and for removing wastes from contact with humans. The city of Seattle, for instance, spends hundreds of millions of dollars per year to provide high-quality water to the region. In addition, many hundreds of millions of dollars per year more or spent to purify water that has been used in order to assure that discharge of wastewater does not degrade the quality of other water bodies (for example, Lake Washington and the Puget Sound).
18Part 4: Freshwater Shortages About 25% of the world's people lack adequate, clean drinking water and about 50% lack adequate sanitation.Water stress - water consumption exceeds by >20% the available, renewable water supplyWidespread water shortages are predicted by 2025.Shortages of fresh water required by humans are just as much a shortage of high-quality water as they are of water itself. One of the important rituals that surrounds life in many of the poorer countries of the world is the daily or more than daily visit to the water supply. In some cases, these trips are to a contaminated water source. It is relatively rare (>2/3's of world's households retrieve water from outside the home) that water is acquired simply by opening a valve for most people in the world.Today, 45 countries (mostly in Africa and the Middle East) cannot meet the minimum essential water requirements of their citizens. In fact less available water often costs more, and sanitation levels decline when water is expensive. An estimated 1.1 billion people lack access to an adequate supply of drinking water and 2.4 billion lack acceptable sanitation. Globally, water supplies are abundant, but (along with capital resources) water is an unevenly distributed resource.
19Depleting Groundwater Groundwater provides nearly 40% of the fresh water for agricultural and domestic use in the United States. In many areas in the U.S., groundwater is being withdrawn from aquifers faster than natural recharge can replace it.Ogallala Aquifer (large aquifer in the Central Plains) - water usage here is the similar to mining for a nonrenewable resource and the water resource is being depleted rapidlyWithdrawing large amounts of groundwater in a small area causes porous formations to collapse, resulting in subsidence.San Joaquin Valley, California - ground surface sinking is occurring due to excessive groundwater pumping.Groundwater provides about 40% of the fresh water supply for agricultural and domestic consumption in the U.S., with about half of all Americans in about 95% of people living in rural areas getting their water supply from groundwater. Problems of the supply of ground water follow a familiar story. The very first people to drill a well typically have no problem with groundwater supply. As more and more people use a particular source of groundwater, and as each person increases their individual consumption by irrigating their lawn, filling their swimming pools, watching cars, and other uses, the consumption can exceed the recharge of groundwater. This can occur on a small or large scale. For instance, the Ogallala aquifer underlies eight relatively dry States from Texas to North Dakota. Use of water from the Ogallala aquifer greatly exceeds the recharge of water into the aquifer over much of its area. As the water table drops, wells that previously produced water dry up, and of course, the response is to drill wells deeper and deeper. When the bearing of load from groundwater is released land can also subside above the aquifer. For instance, in the San Joaquin Valley in California land surfaces have sunk as much as 10 m over last few decades because of excessive groundwater pumping. In many cases, large scale utilization of groundwater is more like mining an irreplaceable mineral that using a renewable resource because of the very slow replacement of groundwater by recharge.
20Karst & sinkholesA type of topography developed in areas underlain by limestone (usually)Limestone is dissolved by carbon dioxide-rich waters (from the atmosphere & decaying organics in the subsurface)Creates cavernsIf formed too near the surface, roof collapses, making sinkholes
23The Wink Sink Formed in 1980 near the town of Wink, Texas In the middle of an oil fieldBelieved to be result of dissolution of subsurface salt related to field activitiesDiameter 350 ftAnother formed about a mile away in 2003 (about 900 ft dia.)
27Ways to Increase Water Supplies Building Dams, Canals and ReservoirsDams are controversial in terms of environmental costs, justice, price mechanisms and water policy, sedimentation, evaporative losses, etc.Lake Lanier, Allatoona, etc.Cloud SeedingCondensation Nuclei – shooting salt particles into moisture-rich clouds (actually use silver salts)Hasn’t been very effective in past, but is being re-evaluated nowThere are ways to increase water supplies, but, at first glance, some may seem impractical. Building dams, canals and reservoirs is probably the most practical approach; yet, as large projects to produce these features have increased, more environmental and political problems with these approaches surface. We will talk about these problems next.Of course, the easiest and cheapest way to have more water is to use what we have more efficiently and use less.
28Separate fresh water from salts in sea water Towing IcebergsCostDesalinationSeparate fresh water from salts in sea waterMost common methods are distillation and reverse osmosis.Three to four times more expensive than most other sources.Perhaps, the first major dam controversy in the United States was associated with the damming of the Hetch Hetchy Valley to provide electricity and water to San Francisco. Remember the picture of John Muir and Teddy Roosevelt in the Yosemite Valley from Chapter 1. Missing from that picture was Gifford Pinchot who is considered to be the father of forestry in the U.S. Pinchot and Muir worked closely together to conserve and protect American natural resources until they went different ways regarding the Hetch Hetchy Dam. Pinchot wanted to see water and electricity made available to San Francisco. Muir favored preservation of the valley in its natural state. The growth of San Francisco and the American West largely dominated policy, and the Hetch Hetchy valley was flooded.Similarly, the water of the Colorado River backed up by the Glen Canyon Dam flooded a spectacular canyon and changed sediment deposition patterns downstream in the Grand Canyon.Throughout most of U.S. history, water policies have generally worked against conservation. In general, these are summarized geographically as:Eastern - Riparian Use RightsWestern - Prior Appropriation RightsIn most federal reclamation projects, customers have been charged only for the immediate costs of water delivery. For instance, review the Klamath reclamation project case study on page 233 of the text.
29Part 5: Water Management and Conservation Watershed managementSound farming and forestry practicesWetlands conservationDomestic conservationWater reclamation and recyclingWater rightsThe management and conservation of water is typically far more economical and environmentally acceptable than developing new sources of water supply. The practice of watershed (all the land drained by a river) management is becoming a universal way of providing high quality water to cities and other users of water while preserving the watersheds that produce that water. Retaining crop residue on fields reduces flooding and minimizes plowing and lessening forest cutting on steep slopes protects watersheds. Retaining vegetation and ground cover helps retard rainwater and lessens downstream flooding.In particular, the city of Seattle takes nearly all of its water from two sources, the Cedar River watershed and the Tolt watershed (both are east of Seattle). Access to these watersheds is restricted, and any management practices that take place within the watershed must do so considering that the first priority is production of high-quality water for the city of Seattle and the region. Since farming and forestry are practiced on large areas of land that produce water from runoff, maintaining vegetation and protecting soil from erosion not only protects the soil resource, but also insures the production of high quality water.In addition, the protection of wetlands aids in the production of high-quality water because of their filtering function. Wetlands sometimes also function as major sources of groundwater recharge. Conserving water wherever it is used means that less water must be provided. This means that marginal sources of water, economically and environmentally, need not be developed. Presently, Seattle has plans to reclaim and recycle waste water produced from its sewage treatment plants, not for human consumption directly, but to use this water for industrial processes and irrigation. Finally, the assignment of rights to the use of water must address water use goals.
30Domestic Conservation Estimates suggest we could save as much as half of current domestic water usage without great sacrifice or serious change in lifestyle.Largest domestic use is toilet flushing.Small volume of waste in large volume of water.Significant amounts of water can be reclaimed and recycled (purified sewage effluent)Amount of time showeringAs mentioned at the start of this part on water management and conservation, of the 3 R's (reduce, reuse and recycle), reduce is always the cheapest and easiest.