Putting the Wiggles1 Back in Rivers 复原曲流

刘宇涵

Why thousands of waterways are having their curves restored

Beneath the junction where Hobgrumble Gill meets Swindale Beck in the Lake District of Cumbria is a suspended valley that has been farmed， against all the odds2， for centuries. Today just one active farm remains. Crumbling buildings and 47km of stone walls that climb right up to the highest hill passes3 bear witness to a time when ten or more families would have eked a living from this inhospitable land.

The wet valley floor is mown in the summer to provide hay4 for sheep in the winter months， when steep and rocky flanks of the valley are too cold and snowy for grazing. At some point， 200 years ago or perhaps more， the river was straightened in an effort to speed up the movement of water through the valley and to dry out the hay meadows.

This kind of battle to control water was repeated across Britain， as farming expanded and landowners consistently sought to keep rivers on the straight and narrow， inside their riverbeds where they belonged， and thus maximise the land area available for cultivation. But rivers， particularly ones that travel through flat valleys like this one， do not want to run straight. Their natural inclination is to wander back and forth in oxbow5 bends that shift across the land over time.

Meandering waterways have many virtues. They are slower; they have a greater diversity of wildlife habitats from ponds to gravel beds and rapids which draw more oxygen into the water; they boost water quality， by creating elbows and pools where sediment flowing down the river gets trapped rather than washing off the land; they are prettier. And—a matter of increasing salience6—their water spends more time upstream， reducing the risk of floods downstream.

Now that farming has receded， and squeezing the last unit of production out of this land is no longer an imperative7， these other considerations are gaining weight among those who manage rivers. As a result， a new trend is taking hold8， in Swindale and elsewhere： Britain is putting the kinks9 and wiggles back into its rivers. Across the country， thousands of waterways are being encouraged to take a wander.

The simplest but least predictable approach to re-wiggling a river is to block the upper end of its straightened bed and let the water find its own way. This was done at Ennerdale， also in Cumbria， with great success. In Swindale， there was farmland to consider so geomorphologists10 estimated the rivers most likely natural path， which diggers then scraped out helping the water find its way to the valleys lowest point—conveniently off to the side of the haymeadows.

The result of all this is a longer and healthier riverbed， ecologically speaking. Within months of the diggers moving out of Swindale， new gravel beds had formed organically and salmon were using them to spawn. A vast tree-planting programme on the banks of the beck and up the sides of the valley should also stabilise the land， further hold back sediment and increase the amount of carbon stored， which both enriches the soil and sucks some of the carbon dioxide out of the atmosphere， helping combat climate change.

It is not all plain sailing11. The Lake District is a World Heritage site， which puts an onus12 on preserving the cultural identity of the landscape as a farmed one. Farmers who follow ancient farming practices do not always appreciate being told that the rivers their forefathers created are the wrong shape and dont do the jobs they need to do.

Nonetheless， projects like the one under way in Swindale may help inspire farmers to think differently about their land. After Brexit， the EUs comfortable Common Agricultural Policy looks like being replaced with a new， less generous subsidy regime， in which payments will be tied to， among other practices， the provision of environmental services. “Most farmers in these areas will admit that its hard to make money in these marginal13 upland areas，” says Jim Bliss， who helps farm the 3，500-acre Lowther estate some 10km north of Swindale.

Lowther estate is in the process of shifting to the nature side. Like many others， it is transected14 by a straight river channel. But for some months now， Mr Bliss and his team have been nudging the water this way and that， encouraging it to go back to its natural winding course， whose trace can still be seen on the landscape. The goal is to have a much smaller， pedigree15 herd of 120 longhorn cattle that cost less to maintain and benefit from a richer， healthier “wildland farm”. And a wiggly river running through it all.                           ■

为何要为数千条河流修复弯道

英国的霍布格伦布尔峡谷与斯温代尔河在坎布里亚湖区交汇，从这里往下便是一个悬谷。尽管条件极为不利，人们也已在此耕种了几个世纪。如今，在当地只有一家農场还在经营。破败不堪的建筑和47公里长、绵延至山路最高处的石墙，见证了那个年代十几户人家在这蛮荒之地艰难谋生的日子。

夏日，人们会来温润的谷底收割草料。严冬时，悬谷两侧的陡峭岩坡上寒风彻骨、大雪覆盖，全然不能放牧，人们便用制成的干草喂羊。两百年前或者更早，人们将原本弯曲的河道修直，以便河水能加速流过谷底，使草场变干。

这种控水之战在英国屡见不鲜，这是因为种植范围扩大了，土地所有者一直努力使河流变直变窄，将其控制在它们所属的河床内，以此最大程度地增加可耕种的土地面积。但是，河流却不愿笔直前行，流淌在像这样平坦悬谷里的河流尤其如此。河流百折千回乃天性使然，那些急弯河曲随时间在大地上变迁。

曲折的水道优点良多：水流流速较慢;从池塘到砾石河床和急流，野生动植物栖息地更为多样，急流会提高水中的含氧量;会形成弯道和水塘，河流中的沉积物存留于此，而不会冲走，从而水质得以提升;景色也更美。此外，还有一个越发突出的优点是，曲折的水道使水流徘徊在上游的时间更长，从而减少了下游发生洪涝灾害的风险。

农业耕作已经日渐衰微，榨取这块土地的最后一点生产力不再紧要，河流管理者便开始重视其他方面。于是，在斯温代尔和其他地区正在形成一种新的趋势：英国正在复原河流原本的弯道并鼓励恢复全国千万条河道的河曲。

为此，最简单、也最难预测的办法是在修直的河床上端设障堵截，让河水取道自流。此法在同样位于坎布里亚湖区的恩纳代尔河上施行，大获成功。考虑到要保护斯温代尔的农田，地貌学家先估算出了河流最可能的自然流径，用挖掘机挖通河道，帮助河水流向山谷的最低处——正好流入干草甸一侧。

从生态学的角度来说，这类做法可以使河床延长，也更健康。就在挖掘工作结束后的几个月里，斯温代尔自然形成了崭新的砾石河床，鲑鱼也开始在河床上产卵。在河流两岸、悬谷两侧的山坡上展开大规模的植树计划，可保持水土稳定，进一步阻止沉积物流失，增加碳储量，这样不仅能提高土壤肥力，还能吸收大气中的部分二氧化碳，有助于应对气候变化。

然而，要实现这一切，未必能一帆风顺。湖区属于世界文化遗产，保存景观的农耕文化特性责无旁贷。沿袭古老耕种方式的农民在获知祖先开辟的河道有误时并不总能理解，也不去做本该做的事。

然而，像在斯温代尔实施的这种项目或许能给农民启发，帮助他们换个角度来看待自己的土地。自英国脱欧后，欧盟宽松的共同农业政策似乎正被一种更为紧缩的新补贴政策取代。新政策规定，补贴将与环境服务措施等方面挂钩。“这些地区的多数农民承认，要想在这些边缘高地谋生其实并非易事。”吉姆·布利斯说道。布利斯在斯温代尔以北约10公里的劳瑟农场务农，该农場占地3500英亩。

目前，劳瑟农场正在向顺乎天然的耕种模式转型。和其他许多农场一样，劳瑟农场也有一条顺直型河渠横贯而过。几个月以来，布利斯先生及其团队一直致力于引导河水恢复自然的曲流——河道蜿蜒的痕迹在这片土地上仍然可见。该农场的目标就是养殖一群规模比以往小得多的纯种长角牛，共120头，运营成本更低，还能受益于土地更富饶、生态更健康的“荒野农场”——以及一条贯穿整个农场的蜿蜒河流。                                           □

（译者单位：华中农业大学）

1 wiggle波浪形线，波纹线。在本文指河流的曲线。  2 against all the odds尽管困难重重。  3 pass关隘;山路。  4 hay（用作饲料或覆盖物的）干草。

5 oxbow 呈U字形弯曲的。  6 salience显著，突出。  7 imperative紧要事情。  8 take hold确立地位。  9 kink（绳线、管道等直线物体上的）扭结，弯。

10 geomorphologist地貌学家。  11 plain sailing一帆风顺。  12 onus义务，负担。

13 marginal（常指位于沙漠或荒野边缘的土地）贫瘠的。  14 transect横切。  15 pedi-gree优良品种的;纯种的。