Chapter 7.3 (cont.) surface water Glen Canyon Dam was completed in 1963 designed to generate hydropower and create a reservoir to supply water to Arizona, California, Nevada, and Mexico through first two decades, dam operated to maximize hydropower environmental impact study in late 1980s showed that the dam had seriously damaged the downstream ecology of the Colorado River in 1996, Secretary of the Interior Bruce Babbit issued new rules that established minimum and maximum water-release rates designed to enhance ecological and recreational values of the river

dam impacts large dams have an enormous social impact, leading to the displacement of people and the drowning of ecosystems valuable freshwater habitats are lost implications often extend beyond river wetlands that are filled by occasional floods no longer receive water, leading to loss of habitat for waterfowl fish attempting to swim upriver to spawn often have problems with fish ladders

problems in estuaries estuaries are among the most productive ecosystems on Earth rich breeding grounds for many species of fish, shellfish, and waterfowl as a rivers flow is diverted for irrigation, less fresh water enters and flushes the estuary leads to increased salt concentration which affects the estuary’s ecology San Francisco Bay has lost 60% of the freshwater that once flowed into it, leading to profound species loss and an increase in the presence of invasive species

groundwater the Ogallala aquifer supplies irrigation water to 10.4 million acres to the High Plains (about 20% of the irrigation water in the U.S) water referred to as “fossil water” because the aquifer was mostly recharged at the end of the last ice age as a result, the withdrawal rate exceeds the aquifers capacity, leading the water table to lower 6 feet per year falling water table has impact on surface water wetlands dry up, leading to loss of habitat and other ecological implications about 75% of the water in aquifers is like the Ogallala—it will take centuries to recharge known as nonrenewable groundwater

land subsidence as water table drops, water filling spaces in cavities no longer provides support for soil above gradual settling leads to land subsidence rate of sinking may be 6-12 inches per year San Joaquin Valley in California has settled as much as 29 feet due to groundwater removal causes foundations, roads, and pipes to crack another kind of land subsidence, a sinkhole, may develop suddenly and dramatically saltwater intrusion also results from dropping water tables

Chapter 7.4 Water Stewardship: Public Policy Changes hydrologic cycle provides enough freshwater to meet all human needs however, water is not distributed evenly results in persistent scarcity in many parts of the world expanding populations create an ever- increasing demand for additional water for irrigation, industry, and municipal use

obtaining more water What are the possibilities of meeting these existing needs and growing demands in a sustainable way? 4 options: 1. capture more of the runoff water 2. gain better access to existing aquifers 3. desalt seawater 4. conserve present supplies by using less water

1. capture more runoff 260 new dams are built around the world each year (down from 1000 per year in the mid 1900s) despite ecological issues, dams provide flood control, water storage, and hydropower dam problems in the U.S., many dams have been dismantled or are being considered for removal

2. tapping more groundwater already, more than 2 billion people depend on groundwater supplies renewable groundwater is becoming increasingly polluted by fertilizers, pesticides, animal wastes, and industrial chemicals

3. desalting seawater with increasing water demands, there is a new emphasis on desalination two technologies are used: microfiltration (reverse osmosis) forces seawater through a fine membrane filter that removes salt distillation often use waste heat to evaporate water, then recondense the purified water vapor costs of building and maintaining plants (even when using waste heat) are considerable in best case, desalinized water costs $2 per 1000 gallons (2-4x what most in the U.S. pay)