Page 289 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 9 Water resources 253
Mackenzie River basin
West Siberian Lowland
Hudson Bay Lowland
Manicougan
Reservoir
Lake Superior Lake Huron
Lake Ontario Lake Erie
Lake Michigan
Mississippi River basin
Lake Guri
Amazon River basin
Lake Volta
Congo River basin
Bratsk Reservoir
Lake Baikal
Pantanal
Lake Nasser
Lake Tanganyika
Lake Kariba
0 1500 3000 KILOMETRES
MAJOR RIVERS Yearly average discharge
high low
Lake Kariba, Zambia/Zimbabwe 181 Bratsk Reservoir, Russia 169 Lake Nasser, Egypt/Sudan 157 Lake Volta, Ghana 150 Manicougan Reservoir, Canada 142 Lake Guri, Venezuela 135
Major Freshwater Volume in Lakes km3
Lake Baikal, Russia Lake Tanganyika Lake Superior Lake Michigan Lake Huron Lake Ontario Lake Erie
22 000 18 750 12 500
4920 3545 1640
485
▲Figure 9.13 The world’s major rivers, lakes, and wetlands. earth’s largest streamflow volumes occur within and adjacent to the tropics, reflecting the continual rainfall associated with the intertropical Convergence Zone (iTCZ). regions of lower streamflow coincide with earth’s subtropical deserts, rain-shadow areas, and continental interiors, particularly in asia. [adapted from William e. Mcnulty, national geographic Society, based on data from USgS; World Wildlife Fund; State Hydrological institute, russia; University of kassel Center for environmental Systems research, germany.]
Surface Water Resources
Water distribution over Earth’s surface is uneven over space and time. Because humans require a steady water supply, we increasingly rely on large-scale management projects intended to redistribute water resources either geographically, by moving water from one place to another, or through time, by stor- ing water until it is needed. In this way, deficits are
reduced, surpluses are held for later release, and water availability is improved to satisfy natural and human demands.
The freshwater on Earth’s surface is found pri- marily in snow and ice, rivers, lakes, and wetlands. Surface water is also stored in reservoirs, artificial lakes formed by dams on rivers (review Figure 9.3, page 244). Figure 9.13 shows the world’s major rivers, lakes, reser- voirs, and wetlands, all discussed in this section.
Major Freshwater Area in Wetlands km2
Major Volume in Reservoirs km3
West Siberian Lowland Amazon River basin Hudson Bay Lowland Congo River basin Mackenzie River basin Pantanal Mississippi River basin
2 745 000 1 738 000 374 000 189 000 166 000 138 000 108 000
Georeport 9.2 How Is Water Measured?
in Canada, hydrologists measure streamflow in metres per second (m·s−1). However, there are great variations in measurement in other places. Most hydrologists in the United States use cubic feet per second (ft3 · s−1). For large-scale
assessments, water managers in the eastern United States use millions of gallons per day (MgD), billions of gallons per day (BgD), or billions of litres per day (BlD). in the western United States, where irrigated agriculture is so important, total annual streamflows are frequently measured in acre-feet per year. One acre-foot is an acre of water, 1 ft deep, equivalent to 325872 gal (1234 m3,
or 1233429 l, or 43560 ft3). an acre is an area that is equal to 0.4047 hectares. For global measurements, 1 km3 = 1 billion m3; 1000 m3 = 264200 gal = 0.81 acre-feet. For smaller measures, 1 m3 = 1000 l.