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A lake reborn

By Ruth Slavid
Wenying Lake is providing much-needed leisure facilities for the growing Chinese city of Datong – and also improving its ecosystems.

Creating an attractive leisure facility around an existing lake is a laudable thing to do, particularly in the centre of a city where such facilities are in short supply. This is what AECOM has done at Wenying Lake in the Chinese city of Datong in the region of Shanxi and for this it deserves praise. But what makes the project so much more interesting than ‘just’ an attractive piece of landscape is the history of the lake and the way in which its regeneration improves the way of life of Datong residents beyond the pleasure that they can derive from some relaxing evening strolls.

To appreciate what has been done at Datong it is necessary to understand what has happened there historically, both in geological terms and in the time frame of the last few decades. Wenying Lake sits on the alluvial plain of the Yu River. In wetter times, centuries ago, the climate was warm and humid and the plain was a large lake. As the climate became drier, only a few areas of wetland remained, including Wenying Lake.

In the 1970s, local authorities took steps to maintain this precious resource in the now extremely dry climate. They built a 10km-long dyke to retain the water, creating a reservoir with its edges raised between 1 and 3m above the surrounding ground, and between 2 and 4m above the water level. But this rather crude intervention was not enough. As Datong city continued to grow, abstraction of ground water led to the continuing shrinkage of the lake. This was exacerbated by the nature of the local industry – the city, which is on the edge of China’s loess plateau and near the border with Mongolia, lies within the country’s coal belt.

Salvation came at the start of this century, when the government decided to integrate reservoirs and river systems in the Taihang Mountains area, and channelled water from the Yellow River to refresh the watercourse. (This is part of a massive project in China to divert water from the Yellow River to drought-stricken areas, called the South-North Water Transfer Project. It is in addition to emergency measures that have been taken in drought crises, and is controversial. But for Wenying Lake, the results have definitely been positive). But the environment around the lake was also changing. Previously the city sat to one side of the lake, but with growth came a need for expansion and a new district was planned, to the east of the existing development, and with Wenying Lake at its heart. The aim was for the lake, no longer a nearby attraction but now an integral part of the city, to become a major site of leisure and revitalisation.

AECOM therefore, when appointed to design the project, had to look at both the restoration of the lake and at fitting it to cope with the changing circumstances. In its entry to the 2013 Landscape Institute Awards, in which the project was highly commended in the large projects category (pipped to the post by Singapore’s Gardens by the Bay), the AECOM team wrote, ‘The aim of the project was to restore the ecosystem through meticulous planning and design, bringing back to life its waters and natural habitats in order to revive Wenying Lake to is former beauty.’

The intention was twofold (and sometimes of course these aims can be opposed to each other): to provide a destination for leisure and to restore the eco-system. The task was made more complex by the fact that the lake had to continue to function as a reservoir and its storage capacity had to be guaranteed. It was seen as vital as well in regulating potential flooding in the region, and this was bound to increase with the new city construction and its concomitant growth in hard surfaces.

The leisure element was essential because, prior to this project, the city, which has a population of more than 1.5 million, had only two exhausted parks providing open space. The result is an area that residents use mostly for strolling and walking and where they enjoy the sight, unusual in this district, of a large body of water. In addition there is a growing interest in fishing and in bird watching.

None of this could happen though without an approach that could guarantee that there is a large, clean, relatively unpolluted body of water which is sustainable in terms both of environmental profile and of volume. AECOM has combined four approaches to achieve this.

Creation of a rain garden
The project includes a public square, designed to be the most heavily used area. As a result, there is a risk of pollution emanating from the square and potentially running into the lake. To prevent this, AECOM has created a series of rain gardens around the square, into which run-off will drain and which act as an absorbing and purifying element.

Sunken green space
AECOM has created a sunken green space on the western side of the lake to compensate for the increase in hard surfaces that has been caused by relatively intense development. This has as its function ‘to regulate and store the rainfall flood in the flood season, facilitate rain infiltration, and improve the potential for flood control and waterlogging of the surrounding land.’

Wetland purification
A large natural wetland was designed on the northern side of the lake, next to the northern embankment. Because of the embankment, this area has to be maintained by pumping water into it from the lake. This has a purifying effect, since the wetland cleans the water which is then pumped back into the lake to improve its water quality. Because the wetland sits between the embankment and the road, in a depressed area, it would be of relatively restricted amenity use, since visitors using this area would be unable to see the lake, the main purpose of their visit. Instead, it can be used as a holding area when water levels are high, ameliorating flooding and helping to maintain the level of the water in the lake at dryer times. The area has a variety of habitats, including a rain garden and a landscape planting pool. In addition to its role in regulating the water level and quality of the lake, it provides an additional habitat for wild fowl. And for pedestrians, walking on a path placed on the embankment, there is an increase in interest since they are seeing the lake on one side and on the other the wetland area, increasing their experience of being near water.

Planting, habitat and soils
Getting the planting and the soil right was essential to this project. The approach had to be appropriate for the dry climate and rapid evaporation in the region, as well as the fact that most of the planted areas would be prone to flooding at some time. The designers used large hybrid particles in the planting soil in order to increase water infiltration, and combined grass, shrubs and trees with the indigenous ground cover. Since most of the area is gently sloping down to water, the majority of the plants are suited to wetland.

Another important resource is a ‘bird island’ that has been constructed off the east embankment of the lake, which is more than 10 ha in size. Long ago, Wenying Lake was an important habitat which Siberian migratory birds used during their north-south journeys, and the aim is to re-establish this stopping point. No human access is allowed apart from scheduled maintenance, and the planting is intended to provide food for the migrants. A series of shoals and beach areas have been created around the island, to provide food and shelter for water fowl.

However good a habitat is created, its impact will be limited if it is isolated from its surroundings.

At Wenying Lake, the design team has recognised this, linking the lake to a green corridor in the grassland north and south of the lake, which in turn joins the forest park of Mapu Mountain to the north and the Shilihe Wetland (to the south of the Yu River) This layout defines the future development of Datong providing an environmental buffer to the extension of the city.

The approach has worked, with thousands of waterfowl using the bird island and surrounding area, including hundreds of swans.

These environmental results have been achieved alongside more conventional ‘parklike’ approaches, such as the creation of a sculpture garden around the main square. The result is a facility that would be welcome anywhere, but that in Datong, with its lack of public space, is twice as valuable.

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