劉宇涵

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.? ? ? ? ? ? ? ? ? ? ? ? ? ?■

為何要為數(shù)千條河流修復(fù)彎道

英國的霍布格倫布爾峽谷與斯溫代爾河在坎布里亞湖區(qū)交匯，從這里往下便是一個懸谷。盡管條件極為不利，人們也已在此耕種了幾個世紀(jì)。如今，在當(dāng)?shù)刂挥幸患肄r(nóng)場還在經(jīng)營。破敗不堪的建筑和47公里長、綿延至山路最高處的石墻，見證了那個年代十幾戶人家在這蠻荒之地艱難謀生的日子。

夏日，人們會來溫潤的谷底收割草料。嚴(yán)冬時，懸谷兩側(cè)的陡峭巖坡上寒風(fēng)徹骨、大雪覆蓋，全然不能放牧，人們便用制成的干草喂羊。兩百年前或者更早，人們將原本彎曲的河道修直，以便河水能加速流過谷底，使草場變干。

這種控水之戰(zhàn)在英國屢見不鮮，這是因為種植范圍擴大了，土地所有者一直努力使河流變直變窄，將其控制在它們所屬的河床內(nèi)，以此最大程度地增加可耕種的土地面積。但是，河流卻不愿筆直前行，流淌在像這樣平坦懸谷里的河流尤其如此。河流百折千回乃天性使然，那些急彎河曲隨時間在大地上變遷。

曲折的水道優(yōu)點良多：水流流速較慢;從池塘到礫石河床和急流，野生動植物棲息地更為多樣，急流會提高水中的含氧量;會形成彎道和水塘，河流中的沉積物存留于此，而不會沖走，從而水質(zhì)得以提升;景色也更美。此外，還有一個越發(fā)突出的優(yōu)點是，曲折的水道使水流徘徊在上游的時間更長，從而減少了下游發(fā)生洪澇災(zāi)害的風(fēng)險。

農(nóng)業(yè)耕作已經(jīng)日漸衰微，榨取這塊土地的最后一點生產(chǎn)力不再緊要，河流管理者便開始重視其他方面。于是，在斯溫代爾和其他地區(qū)正在形成一種新的趨勢：英國正在復(fù)原河流原本的彎道并鼓勵恢復(fù)全國千萬條河道的河曲。

為此，最簡單、也最難預(yù)測的辦法是在修直的河床上端設(shè)障堵截，讓河水取道自流。此法在同樣位于坎布里亞湖區(qū)的恩納代爾河上施行，大獲成功?？紤]到要保護斯溫代爾的農(nóng)田，地貌學(xué)家先估算出了河流最可能的自然流徑，用挖掘機挖通河道，幫助河水流向山谷的最低處——正好流入干草甸一側(cè)。

從生態(tài)學(xué)的角度來說，這類做法可以使河床延長，也更健康。就在挖掘工作結(jié)束后的幾個月里，斯溫代爾自然形成了嶄新的礫石河床，鮭魚也開始在河床上產(chǎn)卵。在河流兩岸、懸谷兩側(cè)的山坡上展開大規(guī)模的植樹計劃，可保持水土穩(wěn)定，進一步阻止沉積物流失，增加碳儲量，這樣不僅能提高土壤肥力，還能吸收大氣中的部分二氧化碳，有助于應(yīng)對氣候變化。

然而，要實現(xiàn)這一切，未必能一帆風(fēng)順。湖區(qū)屬于世界文化遺產(chǎn)，保存景觀的農(nóng)耕文化特性責(zé)無旁貸。沿襲古老耕種方式的農(nóng)民在獲知祖先開辟的河道有誤時并不總能理解，也不去做本該做的事。

然而，像在斯溫代爾實施的這種項目或許能給農(nóng)民啟發(fā)，幫助他們換個角度來看待自己的土地。自英國脫歐后，歐盟寬松的共同農(nóng)業(yè)政策似乎正被一種更為緊縮的新補貼政策取代。新政策規(guī)定，補貼將與環(huán)境服務(wù)措施等方面掛鉤。“這些地區(qū)的多數(shù)農(nóng)民承認(rèn)，要想在這些邊緣高地謀生其實并非易事?！奔贰げ祭拐f道。布利斯在斯溫代爾以北約10公里的勞瑟農(nóng)場務(wù)農(nóng)，該農(nóng)場占地3500英畝。

目前，勞瑟農(nóng)場正在向順乎天然的耕種模式轉(zhuǎn)型。和其他許多農(nóng)場一樣，勞瑟農(nóng)場也有一條順直型河渠橫貫而過。幾個月以來，布利斯先生及其團隊一直致力于引導(dǎo)河水恢復(fù)自然的曲流——河道蜿蜒的痕跡在這片土地上仍然可見。該農(nóng)場的目標(biāo)就是養(yǎng)殖一群規(guī)模比以往小得多的純種長角牛，共120頭，運營成本更低，還能受益于土地更富饒、生態(tài)更健康的“荒野農(nóng)場”——以及一條貫穿整個農(nóng)場的蜿蜒河流。? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?□

（譯者單位：華中農(nóng)業(yè)大學(xué)）

1 wiggle波浪形線，波紋線。在本文指河流的曲線。? 2 against all the odds盡管困難重重。? 3 pass關(guān)隘;山路。? 4 hay（用作飼料或覆蓋物的）干草。

5 oxbow 呈U字形彎曲的。? 6 salience顯著，突出。? 7 imperative緊要事情。? 8 take hold確立地位。? 9 kink（繩線、管道等直線物體上的）扭結(jié)，彎。

10 geomorphologist地貌學(xué)家。? 11 plain sailing一帆風(fēng)順。? 12 onus義務(wù)，負擔(dān)。

13 marginal（常指位于沙漠或荒野邊緣的土地）貧瘠的。? 14 transect橫切。? 15 pedi-gree優(yōu)良品種的;純種的。