Windward 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/yr When rain falls is important (during growing season) Varies seasonally
Part 2: Major Water Compartments Or, where is water distributed?
Groundwater, after ice, is the 2nd largest reservoir of fresh water –Infiltration - 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 Saturation Interactions of water with soil.
Groundwater Aquifer – porous, permeable rock or sediment that transmits groundwater freely May be confined or unconfined (next slide) Aquitard/aquiclude – layers of rock or sediment that hinder/prevent water movement Recharge zones - areas where surface waters filter into an aquifer
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. Unconfined aquiferConfined aquifer saturated material unsaturated material Recharge area
Wells A 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for the purpose of extracting water (for this chapter, anyway) Drawdown – decrease in water table as water is withdrawn from by a well Amount depends on the aquifer & how “hard” the well is pumped Decreases with distance from well Cone of depression – a conical depression; the 3-D result of drawdown by a pumped well Think of drinking a milkshake using a straw
Artesian water Pressure causes groundwater to rise above the level of the aquifer Does not mean a well drilled into such an aquifer will flow freely
The concept used in everyday life
Rivers, 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 6 th Lakes – 100 times the water of rivers, but most in a few large ones Great Lakes, Lake Baikal (Siberia), Great Rift Lakes (Africa)
Wetlands 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.
The 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.
Part 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.
Part 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 supply Widespread water shortages are predicted by 2025.
Depleting 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 rapidly Withdrawing 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.
Karst & sinkholes A 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 caverns If formed too near the surface, roof collapses, making sinkholes
Some days just ain’t good
The Wink Sink Formed in 1980 near the town of Wink, Texas In the middle of an oil field Believed to be result of dissolution of subsurface salt related to field activities Diameter 350 ft Another formed about a mile away in 2003 (about 900 ft dia.)
Sink 1 Sink 2
Saltwater intrusion Occurs along coastlines where overuse of freshwater reservoirs draws the water table low enough to allow saltwater to intrude Hard to undo
Ways to Increase Water Supplies Building Dams, Canals and Reservoirs –Dams are controversial in terms of environmental costs, justice, price mechanisms and water policy, sedimentation, evaporative losses, etc. –Lake Lanier, Allatoona, etc. Cloud Seeding –Condensation Nuclei – shooting salt particles into moisture-rich clouds (actually use silver salts) –Hasn’t been very effective in past, but is being re- evaluated now
Towing Icebergs –Cost Desalination –Separate fresh water from salts in sea water –Most common methods are distillation and reverse osmosis. Three to four times more expensive than most other sources.
Part 5: Water Management and Conservation Watershed management Sound farming and forestry practices Wetlands conservation Domestic conservation Water reclamation and recycling Water rights
Domestic 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 showering