Page 489 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Environmental Effects of Dams on the Nu River in China
In the United States, the razing of dams and restoration of rivers has become a multibillion dollar industry, discussed in Focus Study 15.1 in this chapter. However, in China the trend is quite different. There, and in certain other countries, dam build- ing and hydropower development con- tinue in order to meet increasing energy demands. In 2013, the Chinese govern- ment announced plans to build a series of large dams on the nu River—Southeast Asia’s longest free-flowing watercourse.
The nu River, known as the Salween in Thailand and Myanmar, flows from the mountains of Tibet, through the yunnan province of southwestern China, and into the Andaman Sea (Figure gn 15.1). The river’s headwaters lie adjacent to those of the Mekong and yangtze Rivers within the Three Parallel Rivers World Heritage Site, famed for its biological diversity.
The upper water-
shed is home to peo-
ple from 13 ethnic
groups, many relying
on subsistence farm- ingasawayoflife
(Figure gn 15.2). The
Chinese government
is proposing to re-
locate some 60 000
people from these
communities to make
way for the reservoirs
that are part of the hydropower develop- ment. In some areas, the relocation has already begun as dam sites are being prepared for construction.
Interruptions to Water and Sediment Flows Rivers move both water and sedi- ment, a process that builds fertile soils
▲Figure GN 15.2 Locals crossing
a suspension bridge spanning the
Nu River, Yunnan, China. [Redlink/Corbis.]
of large reservoirs along fault lines) is not new, the proposed dams on the nu River have prompted scientists to take a fresh look at this phenomenon. The mass of a large reservoir creates pressure that forces water into cracks and fissures in the ground beneath, increasing instability and possibly lubricating fault zones. Seis- mic events induced by large reservoirs may damage the dams that impound them, increasing the risk of catastrophic flooding in the event of dam failure.
First proposed almost 10 years ago, the nu River dams were delayed in light of environmental concerns, primary among which were the high numbers of sensitive species in the watershed and the potential earthquake hazard. However, development along the river has been underway since 2006 in preparation for dam construction.
China already suffers from poor air quality owing to industrial pollution; as power demand increases, the govern- ment continues to develop hydropower on its rivers despite the environmental risks. This chapter examines stream and river systems—their natural processes and the role of humans in altering them.
geosystems now online go to Chapter 15 on the MasteringGeography website (www .masteringgeography.com) for more on the downstream effects of dams on river systems. For a recent study on the im- pacts of small dams in southwestern China, see www.agu.org/news/press/pr_ archives/2013/2013-22.shtml.
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▲Figure GN 15.1 Map of the Nu/Salween River system, Southeast Asia.
Nu/Salween River drainage basin
on valley floors and in the flat- lands where rivers meet the sea. Dams interrupt this pro- cess, starving downstream areas of sediment and nutri- ents that naturally replenish farmland in the cycle of annual spring floods. Farmers in the nu River’s lower reaches stand to suffer soil degradation and crop losses if the dams move forward as planned.
Sediment is also critical for maintaining stream habitat, as well as coastal wetlands near the river’s mouth. When sediment is trapped behind a dam, exces- sive erosion often results down- stream, leading to degradation of banks and the riverbed. Al- terations to water and sediment movement also have detrimen- tal effects on fisheries, which are critical food resources for popu- lations in the downstream por- tions of the river system.
Induced Seismicity Scientists have warned that reservoirs may be connected to earth- quake activity in tectoni- cally active southwest China. Although the idea of “reser- voir-induced seismicity” (earth- quakes induced by the location
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