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 7.4Water 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)