Where Has All the Water Gone?
Evaporation and transpiration return liquid water to the water vapor state as part of the Earth's hydrologic cycle.Copyright 2007 Mtwoews, Wikimedia Commons http://commons.wikimedia.org/wiki/File:Surface_water_cycle.svg
Students learn about the Earth's water cycle, especially about evaporation. Once a dam is constructed, its reservoir becomes a part of the region's natural hydrologic cycle by receiving precipitation, storing runoff water and evaporating water. Although almost impossible to see, and not as familiar to most people as precipitation, evaporation plays a critical role in the hydrologic cycle, and is especially of interest to engineers designing new dams and reservoirs, such as those that Splash Engineering is designing for Thirsty County.
Engineers must consider evaporation in the design and operation of dams. Evaporation is an important factor in the site selection and operation of dams, as it can cause serious water loss, especially in hot, dry environments. Ideal reservoir locations are deep, narrow canyons that provide large storage with minimal exposed surface area, which minimizes the potential for water loss due to evaporation. Typically, engineers and hydrologists use computer models and spreadsheets to estimate a reservoir's water "budget," which takes into account the effects of evaporation on its storage.
After this lesson, students should be able to:
- Define precipitation, evaporation and transpiration.
- Grasp the important role of evaporation in the hydrologic (water) cycle.
- Describe how evaporation affects the reservoir behind a dam and why engineers must consider evaporation in their designs of dams.