In the attractive Atlantic coast city of Savannah, where the river of the same name meets the ocean, we visited the US Army Corps of Engineers (USACE), famous worldwide for its work on dams and levees. USACE is the main builder of dams in the United States.
One hundred years ago, the United States was already building more – and bigger – dams than any other nation. The country manipulated its rivers to maximise human gains but, in the process, ignored other life forms such as fish, aquatic plants and microorganisms, not to mention the forests, wetlands, lakes, grasslands and animals that depend on the rivers. As Philip Fradkin writes of the Colorado River in A River No More: the Colorado River and the West, “A great river passing through arid lands has been wrung dry by man.”
Yet today, the US government, USACE, energy companies, conservation groups and the public all agree about the need to protect the rivers and each is doing its bit to help rescue river ecosystems. Few people in the United States now deny the true value of the rivers; it is recognised that only free-flowing rivers can ensure biodiverse, natural ecosystems, of which humanity is a part.
The International Commission of Large Dams defines any dam higher than 15 metres as “large”. In China, there are 22,000 such dams – 46% of the global total and more than any other country. The United States has 6,575. Major dam-building projects, which can easily cost tens of billions of yuan, have played a significant role in China’s GDP growth.
There is a clear difference between Chinese and US attitudes towards rivers. In the United States, canoeing, fishing and hunting are popular outdoor sports; in China they are either a way to earn a living or hobbies for the rich.
Outdoor sports associations have played a crucial role in the recovery of US rivers. Fans of these pastimes will not stand by and watch the rivers being tamed, or the forests falling silent. Nature lovers are loyal partners of The Nature Conservancy (TNC) and have a lasting enthusiasm for the cause – along with plenty of good ideas. For the majority of US citizens today, the ecological value of rivers is much higher than their use for energy generation. Perhaps it is this that has ultimately allowed the rivers to be saved.
The Savannah marks the border between the American states of South Carolina and Georgia. In a river basin stretching over 17,000 square kilometres, there is a wide range of ecosystems, supporting almost 100 rare animal and plant species and providing habitats for more than 100 species of fish; indeed, this stretch of water is home to more fish varieties than any other in the south-eastern United States.
Suddenly Megan, our TNC guide, stops the car – she has seen several people pointing cameras at a pool in the river. An alligator is casually observing the people on the bank. It suddenly leaps out of the water, revealing its full length, and then falls back down, leaving only the top of its head exposed.
This is my closest encounter with a wild alligator but afterwards, as we follow the river upstream, we frequently come across them in the marshes and pools. Amazingly, birds and ducks float only two or three metres away from them, seemingly oblivious to the danger.
The Savannah River’s ecosystem was also once in danger.
USACE experts tell us that, sixty years ago, they built three dams on the Savannah. The Hartwell, Richard B Russell and J Strom Thurmond were constructed upstream of Augusta, in order to generate electricity, prevent floods, provide reservoirs for recreation and tourism and supply water. But the dams dealt a grave blow to the integrity of the ecosystem, altering seasonal fluctuations in the river’s flow and threatening the continued existence of crabs, oysters, shrimp and unique fish species. The dams also limited the growth of broadleaf trees on the floodplains, which further affected water quality and reduced survival rates among the fish, mammals and birds reliant on the river water and floodplain forests. Moreover, the dams prevented fish from returning to breeding grounds, forcing them to spawn elsewhere and causing populations to shrink.
In a bid to improve management of the Savannah River, in March 2004 USACE adopted a TNC strategy for operating the dams. The plan restored and increased the number of spawning grounds for fish, while periods of low flow improved growth of broadleaf trees and increased fish reproduction and survival rates. As more water was released, seeds of broadleaf trees and other plants were disseminated and nutrient levels in riverside soil recovered, providing habitats for birds and giving highly endangered animals and plants, such as alligators and floodplain vegetation, another chance at survival.
USACE was applauded for its actions. A good environmental image is crucial for any US firm or organisation and, with public encouragement, USACE is increasing its efforts to restore river ecosystems.
According to USACE hydrologist Stan Simpson, the organisation carefully plans the river’s flow in order to meet the changing needs of the fish; software provided by TNC calculates how much water to release according to the time of year and weather. In the process, USACE has discovered that it used to release the water too quickly for fish to pass through the dam. The team implanted tracking chips into a number of fish and found none were making it back to the river mouth. Where had they gone? Had they turned back? And would they use the shallows in front of dams as new spawning grounds?
“We analysed the relationship between water temperature and flow rates,” says Simpson. “Water from the base of the reservoir, tens of metres deep, can be too cold, and the fish don’t like it. Similarly, they don’t like it if you release the water at the wrong time. Some fish swim near the surface of the water, but trout swim near the bottom; you can’t just release water because you need to give the trout a channel they can use. They are very sensitive to the environment.”
He tells us that the previous winter USACE implanted tracking chips, costing US$250 (1,707 yuan) a piece, into 30 fish to observe how dry years affect their mating patterns. This was done in winter because the chips have he least impact on the fish at that time.
Simpson adds that the role of dams in human life cannot be ignored when planning the river’s flow. “We also need to take into account the dams need for water for electricity generation,” he says. “We need to find a balance between forestry, agriculture, fish, electricity generation, and urban water supply.”
Simulating the natural water flow needed by the fish is no easy task. Hundreds of scientists took two years to produce a plan for dams to release water in waves over different seasons – a plan that is adjusted annually according to the weather, air temperature and changes in water quantity.
According to a TNC freshwater and river conservation expert, the acceptance of these conservation ideas and river restoration methods has prompted USACE into becoming more active in developing response plans. It has launched research programmes on a range of energy sources, including coal, nuclear and wind, to help it make better decisions about the most appropriate type of power to use and reduce the impact of hydropower on the rivers.
The Savannah’s future now looks brighter. But what about the prospects of saving China’s rivers? TNC’s expert argues that the Yangtze River’s situation is more complex than that of the Savannah and achieving the same aims will be more difficult. But, if all parties work together to improve dam management, she says there is still hope that bit by bit, stretch by stretch, China’s rivers can be revived.
Zhang Kejia is a reporter for China Youth Daily
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