Dams and Landslides

Geological risks and sediment problems with dam building in southwest China

(April 7, 2009) The following article was posted to the popular Science Times (Kexue shibao) website on Feb 20, 2009.

Upper Yangtze watershed: a geological disaster-prone region

A 2007 survey by the China Geological Survey Bureau concluded that southwest China, and particularly the upper Yangtze region, is one of China’s most geologically disaster-prone areas. Its geological disasters include earthquakes, landslides, mountain collapses, and rock-mud-flows. The survey identified as many as 21,000 geological disaster zones (excluding 12,000 new disaster zones created by the powerful Wenchuan earthquake on May 12, 2008). Of these, 12,678 are identified as landslides, 2,568 as mountain collapses, 2,756 as rock-mud-flows, 452 as land subsidences, and 2,858 as unstable slopes, which have killed 11,269 people and resulted in a direct economic loss of 23 billion yuan [US$3.3 billion]. As many as 1.45 million people are affected by these geological hazards, and 18 billion yuan [US$ 2.6 billion] worth of property is under threat.

A total of 91 recorded geological disasters – 73 landslides and mountain collapses, and 18 rock-mud-flows – were so serious that they blocked the upper reaches of the Yangtze River and its major tributaries in places, killing 9,200 people, destroying 1,611 hectares of farmland, and resulting in a direct economic loss of 170 million yuan [US$24.3 million].

  • On August 25, 1933, a devastating earthquake with a magnitude of 7.5 [on the Richter scale] struck the town of Diexi of Maoxian county in Sichuan province, killing 6,865 people, injuring 1,925 people, and destroying 5,780 houses. The Min River [a Yangtze tributary] was dammed for 45 days due to the massive landslides and rock-mud-flows caused by the quake. Finally the lake that had formed behind the dam burst through, forming waves as high as 60 metres, and destroying the Dujiangyan irrigation canals, 200 kilometres downstream.
  • In 1967, a huge landslide occurred along the Yalong River [a Yangtze tributary] at Tanggudong in Yajiang county of Sichuan province. The river was dammed for nine days. When the dam finally collapsed, the force of the water released caused damages hundreds of kilometres downstream along theYalong and the Yangtze; 435 houses were destroyed, 230 hectares of land was flooded, and eight bridges and three small hydropower stations were completely washed away.

Table 1. Fault belts and seismic activity in the Hengduan Mountain area (1)

Fault belts Length (Km) Average sliding speed (mm/year) Earthquakes occured (MS≥5) Earthquakes occured (MS≥7) Highest magnitude (MS)
Longmenshan 500 1.4~1.8 26 1 8
Songpan-Pingwu 5~10   35 4 7.5
Xianshuihe 300 16.0~17.4 >47 8 7.9
Anninghe 200 1.5~5.3 9 2 7.5
Zemuhe 150 3.5~4.9 5 1 7.5
Jinsha-Honghe >1100 16.0~20.0 >57 3 7.3
Langcang-Mekong >600   3   6.0
Nantinghe >180 3.0 12 1 7.2

Most hydro dams are being built on fault belts in southwest China

In China, the development of hydropower is highly concentrated in the southwest along great rivers, including: Jinsha (upper Yangtze), the Min, Dadu, and Yalong (Yangtze tributaries), as well as the Lancang-Mekong, Nu-Salween, and their tributaries. Most hydro dams planned or built along these rivers are on fault belts.

The Zipingpu dam on the Min River, for example, was built on a central fault belt  (known as the Yingxiu-Beichuan Fault) of the longer Longmenshan Fault Belt [See Table 1]. Zipingpu had been operating for just two years before the May 12th earthquake struck last year. The earthquake drastically changed the geological environment in the Zipingpu reservoir area. Hundreds of millions of cubic metres of materials produced by landslides and mountain collapses were deposited in the reservoir. This buildup of sediment not only threatens the safety of the dam project but is likely to shorten the useful life of the reservoir.

Apart from Zipingpu, hundreds of dams built on the Min, Tuo, Fu and Jialing rivers and their tributaries were seriously damaged by last year’s earthquake; 60 percent of the medium and small hydropower stations along these rivers are beyond repair.

In the Min basin alone, as many as 130 hydropower stations (excluding Zipingpu) were seriously damaged by last year’s earthquake. The Yingxiuwan, Taipingyi, Futang and Yuzixi hydro stations were nearly destroyed, resulting in a direct economic loss of 15.1 billion yuan [US$2.2 billion]. In all of Sichuan province, about 470 hydro dams (with a total generating capacity of 3,300 MW) were damaged; 85,377 electric poles or towers collapsed, and 31,969 kilometres of long distance power lines were broken.

In addition, dozens of high dams are newly-built or under construction on major fault belts in Sichuan and Yunnan provinces:

<!–[if !supportLists]–>§         <!–[endif]–>In Sichuan province, the Pubugou dam on the Dadu River [Yangtze tributary], with a dam height of 186 metres and a storage capacity of 5.39 billion cubic metres, is being built on the Xianshuihe Fault Belt, which criss-crosses the Dadu River. To make the situation worse, dozens more dams are under construction upstream and downstream of Pubugou.

<!–[if !supportLists]–>§         <!–[endif]–>On the Yalong River [Yangtze tributary], the Jinping 1 and Jinping 2 dams, completed in December 2006 and November 2008, respectively, are situated in a geologically complicated zone where two fault belts – the Muli Fault Belt and Daocheng-Jianchuan Fault Belt come together. Based on historical records, several powerful earthquakes have occurred in the area within the last few hundred years. Yet more high dams and big reservoirs are planned and under construction in the Yalong valley, without any seismic risk assessments.

  • On the middle and lower reaches of the Jinsha River, a 13-dam cascade is  planned for below Shigu town in Yunnan province, on or near three major fault belts: Xiaojiang, Anninghe, and Luyejiang.
  • Upstream of the Tiger Leaping Gorge in Yunnan province, four large hydro dams: Xiangjiaba, Xiluodu, Baihetan and Wudongde, are part of an 8-dam cascade planned for the upper Jinsha River on two fault belts: Dongchuan-Songming and Mabian-Zhaotong.
  • On the Yangtze mainstream, four high dams are planned or already in operation within seismically-active zones containing at least three fault belts: Xiaojiang, Anninghe, and Luyejiang.  These dams are Shipeng (planned), Xiaonanhai (under construction), Three Gorges (nearly completed) and Gezhouba (completed).
  • On the Lancang [upper Mekong] river, a 13-dam cascade with a total storage capacity of 51.53 billion cubic metres is under construction in a seismically active area containing the Lancang fault belt.
  • On the Nu [upper Salween] river, a 13-dam cascade with a total generating capacity of 21,320 MW is planned in a seismically active area containing the Nu fault belt.

From a geological perspective, the design and scale of all these dams under construction makes them truly dangerous.  Concern is growing within China about the effects of so many dams in such geologically complicated areas. Many geologists admit that there is a lack of basic research and study of important geological issues in China, including active fault belts, seismic activity, and geological stresses. As an example, there has been no systematic study of the geotectonic conditions and main faults along the upper reaches of the Min River and the Longmenshan Fault Belt in particular. Such studies are needed to better understand how various factors affect change in geological stress before building so many high dams and deep reservoirs in southwest China.

The problem of sediment build-up in southwestern China’s rivers and reservoirs

Rivers in southwest China, particularly the upper Yangtze, face another serious problem: sediment build-up. Building cascades of high dams and deep reservoirs in rivers with heavy sediment loads not only poses a risk for the safe operation of reservoirs but increases the risk of floods in the upper end of the reservoirs. Once the process of sedimentation begins, a chain of events follow that is hard to deal with, as happened at the Sanmenxia dam on the Yellow River in the 1950s and 1960s – an experience from which tremendous lessons should be learned in China.

Rivers in the upper Yangtze basin all carry heavy sediment loads due to a combination of factors, such as geotectonic and geological conditions, rugged terrain, as well as land reclamation and deforestation. The Jinsha River, for example, is sending on average more than 500 million tonnes of silt to the Three Gorges reservoir every year (The highest recorded volume was 728 million tonnes in 1980).

The most serious sedimentation problem is found along a 1000-kilometre section of the Jinsha River between Shigu and Pingshan. Surveys have identified 700 landslides, nearly 300 rock-mud-flows, and more than 3 billion cubic metres of rockmass at risk of collapse. The situation is expected to become worse with increased mining activities, road construction, and dam building. Concern about the problem of sedimentation, with so many high dams and deep reservoirs proposed and built along this section of the river, is growing.

Attempting to block sediment by building more dams on both the main channels and tributaries is not a final solution even though it may hold sediment back for a short while. Doing so only transfers the sediment problem to upstream areas, leaving hidden problems for younger generations to deal with. When sediment builds up in the reservoirs, they can no longer perform their flood-control function, and a vicious cycle ensues.

Addressing geological risks and sedimentation with restructuring and conservancy

To deal with the twin problems of geological risk and sedimentation, a national energy strategy is needed to restructure the power sector and introduce energy saving policies to reduce energy consumption, protect the environment, and use land resources more wisely in developing the economy.

The planning of hydropower projects must change to consider national conditions and natural resources, and by dumping old approaches such as “development first, protection second” and “pollution first, management second.”

Decisions to build large multipurpose dams must be based on careful selection and scientific feasibility study. At the same time, existing reservoirs that were poorly built and are now dangerous should be strengthened and maintained; operation of some of the smaller dams should be suspended.

Reducing river pollution in the southwest and across the country needs more funding and technology. The development of energy-intensive enterprises should be curbed. And industries should be restructured in order to save energy, reduce emissions, and achieve sustainable socio-economic development.

To address unresolved problems with dam-related resettlement, tourism and ecological industries are needed to enhance the resettlers’capacity to improve their standard of living after resettlement. Increased citizens’ awareness about environmental protection is also needed.

Science Times and Yang Yong, Translated by Three Gorges Probe, April 7, 2009

The author, a geologist and river explorer, is currently deputy director of the Beijing-based China Foundation for Desertification Control under the State Forestry Bureau. (www.chinafdc.org)

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