Guest blog - Fiona Bowles, Vice Chair RRC Board of Directors
Working as I do, in a catchment where we need to redress the usual nutrient and sediment overload and where fears of ‘over abstraction’ alternate with those about rivers being ’out of bank’, we need ‘multi benefit’ solutions. We work hard on reducing nutrient losses from farming but I don’t see so much action, or cash, around resolving the physical modification issues in rivers. I am sure that our catchment issues coincide with the estimated loss of 80% of riverside marshes, swamps, lakes, ponds and floodplain forest in N. America and Europe in the last 200 years. Apparently wetlands are still disappearing three times faster than forests globally (United Nations Climate Change report). Here in Poole Harbour, we may need 250 hectares of 'new’ wetlands as part of the solution to resolve nitrogen eutrophication in the estuary. Although we have gained support for small natural flood management schemes and locally Wessex Water is building constructed wetlands to protect some drinking water resources, these are still limited in extent.
So I was excited last year to hear about the 'Stage Zero’ work from the USA at the RRC conference. This approach aims to fully re-link water flow with its flood plain, effectively ‘rewilding’ it within natural depositional zones, bringing a wide range of benefits to flood resilience, water quality, biodiversity in general and fish populations in particular, through the re-creation of wetlands. https://vimeo.com/266399565 So it offers a multi-benefit solution which is sustainable, especially where beavers are available to do all the natural flood management maintenance. Some people found the jump from USA to overcrowded Europe too hard to imagine.
Then I got a copy of Ellen Wohl’s new book, 'Saving the Dammed’ to review. I can see that North Americans, despite their lower population density and shorter history of agricultural intensification, have managed to reduce many rivers to single channel ribbons too, drying up their rivers. Beavers were nearly extinct there by the end of the 19th century and have been extinct here for 400 years. Ellen describes a year in the life of beavers in a Colorado wetland and in doing so she neatly brings to life the natural science of rivers and their connectivity with floodplains and wetlands, from geological times to the present. Where beavers still exist, or have been re-introduced, the benefits that wetlands bring include; nutrient cycling, carbon and nitrogen storage, flow moderation and improving groundwater levels, biodiverse habitats. These are all described and referenced. Highly relevant here to me are the nitrogen budgets, wetlands can remove 80% of the nitrate load entering. This is supported by the Exeter University's findings in the Devon trial site where beaver created wetlands accumulated 100 tonnes of sediment, nearly 1 tonne of Nitrogen and over 15 tonnes of carbon. Carbon is more complex in that wetlands can give off methane when wet, but when wetlands are cycled by beavers to the stage of an organic rich meadow (now typically prized for agriculture), carbon storage can be more than in adjacent forest soils. The moderation of flow peaks is well described through the catastrophic effects in adjacent, none beaver, tributaries and the benefits of higher ground water tables where the spreading of flood water increases the hyporheic exchange. Wet floodplains reduce forest fires and in the USA, fisheries managers are advocating log jams, and beaver dams, in fisheries restoration.
So Ellen's book provides a highly readable review on just how much more we can gain by reconnecting our rivers and flood plains, and harnessing nature- ideally beavers-to achieve that goal of ‘restoring natural processes'. With physical modification still being the top cause of failure for English water bodies (EA 2019 data) and rural pollution a close second, we need to test 'Stage Zero’ concept. The National Trust have already led the way with their recent Mudpool Meadow scheme in Somerset. The questions remain about whether we can overcome the disparate land ownership and presence of infrastructure in flood plains elsewhere to deliver these benefits, with or without the help of those furry 'green engineers'.