CHINA has many good reasons not to build the $5.2 billion Xiaonanhai dam on the Yangzi river in Chongqing. The site, on a gentle slope that moves water along only slowly, is not ideal for generating hydropower. The fertile soil makes it one of China’s most productive regions, so it is densely populated with farmers reaping good harvests. And the dam (see map), which would produce only 10% of the electricity of the Three Gorges project downstream, could destroy a rare fish preserve, threatening several endangered species including the Yangzi sturgeon.

Yet it does not matter how strong the case may be against Xiaonanhai, because the battle against a hydropower scheme in China is usually lost before it is fought. The political economy of dam-building is rigged. Though the Chinese authorities have made much progress in evaluating the social and environmental impact of dams, the emphasis is still on building them, even when mitigating the damage would be hard. Critics have called it the “hydro-industrial complex”: China has armies of water engineers (including Hu Jintao, the former president) and at least 300 gigawatts of untapped hydroelectric potential. China’s total generating capacity in 2012 was 1,145GW, of which 758GW came from coal-burning plants.

An important motive for China to pursue hydropower is, ironically, the environment. China desperately needs to expand its energy supply while reducing its dependence on carbon-based fuels, especially coal. The government wants 15% of power consumption to come from clean or renewable sources by 2020, up from 9% now. Hydropower is essential for achieving that goal, as is nuclear power. “Hydro, including large hydro in China, is seen as green,” says Darrin Magee, an expert on Chinese dams at Hobart and William Smith Colleges in New York state.

There is also a political reason why large hydro schemes continue to go ahead. Dambuilders and local governments have almost unlimited power to plan and approve projects, whereas environmental officials have almost no power to stop them.

Heavy on the levees

The problems begin with the planning for China’s rivers, which are divided into fiefs by the state-owned power companies that build dams in much the same way as the Corps of Engineers and the Bureau of Reclamation divided up American rivers in the early 20th century. Though the staff of the water-resources ministry in Beijing know a lot about the environment, they have no say. “Big hydro projects are designed and approved by everybody but the ministry of water resources,” says Mr Magee.

Local governments, meanwhile, view dams as enticing economic development projects. The dambuilders, which have special privileges to borrow, put up the financing. The extra electricity supports industrial expansion and brings in revenues. Local officials are promoted for meeting economic performance targets and some collude for personal gain with the dambuilders. Because of the decentralised nature of the industry, local officials try to include dams in their plans. Once they have done so, they can expect the environmental impact assessments that follow to be a formality—if only because the consultants who undertake them are paid by the hydropower companies.

Environmental officials who have not been financially captured by the dambuilding economy find themselves as scarce as some of the fish they are charged to protect. Environmental activists, meanwhile, can request access to public records and demand public hearings, both required by law. But they say that these avenues are barred when they are most needed—on controversial projects that face vocal opposition. For example, the authorities have rejected requests for public records on Xiaonanhai and they have not granted a public hearing.

If environmental regulators and activists want any hope of halting a project, they must go outside normal bureaucratic channels to lobby powerful Politburo members or the national media. Although that may not always work, it did in 2004, when Wen Jiabao, then prime minister, halted construction of a cascade of 13 dams on the Nu River in south-west China in order to protect the environment. Even then some work on the projects still proceeded. Meanwhile, smaller schemes race ahead unchecked. Promoted by dambuilders and local governments, nearly 100 smaller hydroelectric projects in the Nu river region went forward without needing permission from higher up. Some began before they had even received the final approval.

China’s new leaders in recent months have signalled that they want yet more dams, approving several ambitious new projects, including what would be the highest dam in the world, on the Dadu river. After Mr Wen stepped down from his posts in the party and the government, the dams on the Nu river that he blocked received the go-ahead again.

Chinese leaders have for millennia sought to tame the country’s great rivers, which have sustained and destroyed countless lives with cycles of abundance, famine and floods. Indeed their legitimacy as rulers has long been linked to their ability to do so. The Communist Party has built thousands of large dams since 1949. China is also the world’s leading builder of big dams abroad; International Rivers, a pressure group, says that Chinese companies and financiers are involved in about 300 dam projects in 66 countries.

The most controversial emblem of Chinese hydropower is the Three Gorges dam, the largest in the world with a capacity of 22.5GW. In contrast, America’s Hoover Dam has less than one-tenth of that capacity. Many critics within China felt that the Three Gorges was too big and too dangerous to build. They predicted that silt would collect in its reservoir, threatening the stability of the dam and lessening its capacity to produce power. They warned that the dam’s vast reservoir, which would submerge the homes of more than 1m people, would become polluted and alter the flow and ecology of the Yangzi river. They also feared that the dam could cause earthquakes, as it sits on two major fault-lines.

Damn the consequences

In the end, though, political power trumped scientific argument. Nearly one-third of China’s legislature either abstained or voted against the Three Gorges dam in 1992, in what remains the most vocal opposition the rubber-stamp body has ever registered against a proposal from China’s leaders. But Li Peng, then prime minister, had trained as a hydroelectric engineer and was determined to build the dam. (His daughter, Li Xiaolin, is head of a publicly listed arm of one of the five big state-owned power companies.)

Today authorities acknowledge that many of the predictions about the Three Gorges dam have come true. This has led to them proposing mitigation strategies, including building more dams upstream, such as Xiaonanhai, to slow the accumulation of silt. The state has also passed numerous laws and regulations in an attempt to balance dam construction with the protection of China’s rivers.

The Xiaonanhai dam, though, suggests that they are treading the same old path. First put forward in 1990, it was in recent years pushed hard by Bo Xilai, a member of China’s Politburo who was sacked as Chongqing’s party chief in March 2012 and tried last month. The dam, nevertheless, had its official groundbreaking ceremony just days after his downfall. China Three Gorges Corp, which is in charge of this section of the Yangzi river, has begun minor preparatory work on the dam; residents have been approached about resettlement; and last year Chongqing officials listed Xiaonanhai as a “major project” for 2013, making its construction almost a certainty, regardless of the environmental impact assessment when it comes.

Environmental activists are left to accept that hydropower will continue to transform all the big rivers of China. They argue that Xiaonanhai is not a “smart” dam even from the perspective of the power companies. For a large dam, it will not produce much electricity. And it is not ideally positioned to alleviate the silt build-up in the Three Gorges reservoir downstream—in part because so many other planned dams farther upstream will do the job, instead.

Guo Qiaoyu of The Nature Conservancy, an American environmental group, argues that Chongqing would do better to increase the power-generating capacity of existing dam projects in the region. A planned cascade of 12 dams along the lower Jinsha river nearby will produce almost 30 times as much electricity as the Xiaonanhai dam. About 90 other significant dams are planned in the region.

Fan Xiao, a Chinese environmental scholar and activist, argues that the dam will also destroy prime farmland that Chongqing needs to feed its 32m people. In a letter in 2011 to national leaders he called the area around Xiaonanhai “the most productive…concentration of arable land along the banks of the Yangzi river”.

Indeed, Liao Rengang, a farmer of tomatoes, cucumbers and peppers beside the Yangzi, says he earned more than 130,000 yuan ($21,000) last year. But Mr Liao says he will not bother fighting the dam: “If they want to take the land they can, because they are the state,” he says. “It’s not up to us.”