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Chapter 7: Human Alterations to Riparian Areas
Water Withdrawal
- Water withdrawals can be from surface and ground water.
- Benefits from water withdrawal include: water for municipal, industry and irrigation uses.
- Withdrawals of surface water can impact ground water and vice versa.
- By withdrawing surface water, recharge to ground water can decrease.
- Ground water withdrawal can increase transmission losses of surface water (page 9, chapter 3).
- Both activities can lead to an increase in the depth to ground water.
- Increase in the depth to ground water, as a result of water withdrawal, can put stress and eventually cause mortality of native riparian vegetation. This also helps the invasion of exotic and drought tolerant species.
- Surface and ground water withdrawals are one of the reasons for many perennial streams and rivers in the western United States changing into intermittent and ephemeral systems.
- The main surface water conveyance system in Arizona is called Central Arizona Project (CAP).
- In this system 1.5 million acre-feet of water are removed yearly from the Colorado River and used primarily in the Phoenix and Tucson metropolitan areas.
- This water is transferred over 336 miles of canals, tunnels, siphons and pipelines and raised up 2,900 feet with 14 pumping stations.
Figure 7.6. Aerial photo of a canal of the Central Arizona Project (CAP) that transports water from the Colorado River to the Phoenix area.
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