Page 276 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

9
Water Resources
concepts
key learning
After reading the chapter, you should be able to:
• Describe the origin of earth’s waters, report the quantity of water that exists today, and list the locations of earth’s freshwater supply.
• Illustrate the hydrologic cycle with a simple sketch, and label it with definitions for each water pathway.
• Construct the water-budget equation, define each of the components, and explain its use.
• Discuss water storage in lakes and wetlands, and describe several large water projects involving hydroelectric power production.
• Describe the nature of groundwater, and define the elements of the groundwater environment.
• Evaluate the Canadian water budget, and identify critical aspects of present and future freshwater supplies.
The valley of Oued Todgha (Todgha
river) forms an oasis that supports palm plantations and other agriculture near the city of Tinghir in the desert of Morocco in northwest africa. The Todgha flows south- ward from the atlas Mountains—a range that extends across Morocco, algeria, and Tunisia, reaching elevations over 4000 m— carrying snowmelt runoff in surface and subsurface flows until finally disappearing permanently into the ground during most
of the year. Water in this arid region is a precious resource; extensive canal systems direct surface flows to irrigate fields, and pumping systems extract subsurface water for agriculture and other uses. Dissolved salts from farm fields now threaten ground- water quality throughout Morocco. This chapter examines earth’s water supply and distribution, and their importance for human populations. [ignacio Palacios/age fotostock.]