This video lesson describes the effects of overuse on two major water resources in the U.S.: the depletion of the Ogallala Aquifer and the overdrawing of the Colorado River.
Depletion of Ground and Surface Waters
Water is incredibly important to us, but there is only a limited amount of it on Earth. However, the number of people on Earth is increasing every day. It would be nice to think that water is both evenly distributed on Earth and shared equally among everyone, but this is not the reality.
When too much water is drawn from one source, as is often the case, serious problems with human health and the environment can arise. Let's look at examples of how two major water resources have been affected in the U.S.: the depletion of the Ogallala Aquifer and the overdrawing of the Colorado River.
The Ogallala Aquifer
In another lesson, we learned that aquifers are underground water reservoirs that act like giant sponges. Water is removed from aquifers through wells for a variety of reasons, such as for drinking water and agricultural irrigation. They can hold large amounts of water and take a very long time to fill and refill. Aquifers are a major supply source to surface waters, releasing almost 500 billion gallons of water daily to surface water systems in the U.S. alone!
The world's largest aquifer, the Ogallala Aquifer, is found underneath the Great Plains of the United States. Before pumping of this aquifer began, it had a water-holding capacity of almost 900 cubic miles, was over 1200 feet deep at its thickest point, and spanned over 175,000 square miles in eight different states.
Before irrigation and pumping practices in this area began in the 1950s, the Great Plains area was actually quite dry. Droughts were frequent, and agriculture was very unproductive. However, since that time, the Ogallala Aquifer has become an important source of drinking water for approximately 2.3 million people, and over a quarter of the irrigated land in the U.S. is found in this area.
Depletion of the World's Largest Aquifer
The volume and extent of the aquifer has been greatly reduced because too much water has been removed too quickly. Since pumping of the aquifer began in the 1950s, the total water storage has been depleted by about 9%. The U.S. Geological Survey estimates that about a third of the cumulative depletion of the Ogallala Aquifer occurred from just 2001 to 2008. And, while in recent years there have been many efforts to conserve the aquifer, it will take more than our lifetimes for it to recharge to the volume and size that it once was.
The depletion of such a large water supply has led to issues for human health and economics. People have started to realize that the aquifer is not a renewable source, as the recent droughts in this part of the country have emphasized.
Water is essential to the productivity of the Great Plains area, and as water shortages become more common, livelihoods of farmers and ranchers will be impacted both by the cost and availability of water.
The Colorado River
The Colorado River is one of the grandest rivers on Earth. Beginning high in the Rocky Mountains and ending in the Gulf of California in Mexico, it is 1450 miles long and is the creator of the Grand Canyon. The Colorado River used to flow freely to the Gulf, providing necessary water, sediment, and nutrients to the delta there.
However, due to dams and overuse, the Colorado River often runs dry before reaching the Gulf. Today, it is used to irrigate 7% of the croplands in the U.S., provides drinking water for 20 million people, and fills all those glittering swimming pools and elaborate fountains in the Las Vegas desert. Other major cities, such as Phoenix, San Diego, and Los Angeles, also depend on water from the Colorado River.
Overdrawing the Grand River
The water of the Colorado River comes from snow melt high in the Rocky Mountains and, therefore, provides a limited supply. The extreme withdrawals and numerous dams along the river prevent it from traveling the way it would normally. The altered water flow threatens the agriculture that depends on it for irrigation, the people that depend on it for drinking water and hydroelectric power, and the ecosystems that depend on specific environmental conditions.
In 1922, the Colorado River Compact was signed by all seven of the states that the Colorado River runs through. This allocated a certain amount of water from the river to each state, though some states, like California, used more than they were allocated because other states, such as Utah, did not use their full amount. However, in 2003, California was forced to reduce its withdrawal from the river by about 15% over 15 years.
The quality of the river water has also been affected. Overdrawing surface waters leaves behind waters that are more saline, or have a higher salt concentration. Nutrient and toxin concentrations are also higher when surface waters are overdrawn, which leads to serious human health issues.
Aquifer depletion and overdrawing surface waters have negative economical and environmental impacts. The U.S. is home to the world's largest aquifer, the Ogallala Aquifer in the Great Plains, and one of the world's largest rivers, the Colorado River, which reaches all the way to Mexico. Each of these water resources supports natural ecosystems and provides irrigation for farm crops, drinking water, and other things, like electricity and recreation.
While there has been work to conserve these resources, much of the damage is irreversible. So much water has been removed from the Ogallala Aquifer that it can't recharge during our lifetime. The Colorado River used to reach the Gulf of Mexico with great fervor, but now often runs dry before it even makes it there. The future of these two important resources is uncertain, as is the livelihoods of the people, plants, and animals that depend on them.
Following this lesson, you'll be able to:
- Describe the importance of the Ogallala Aquifer and the Colorado River
- Identify how the Ogallala Aquifer is being depleted and explain the negative consequences of that depletion
- Summarize the Colorado River Compact
- Explain why the Colorado River no longer reaches the Gulf of Mexico like it once did and describe the negative consequences of its overuse