22nd December 2016 by Dr Matthew O'Hare, Freshwater Ecologist at Centre for Ecology and Hydology
Our recent publication, 50 for the Future, lists 50 things that we believe should happen in Scotland over the next 50 years to benefit both people and wildlife. In this week's 50 for the Future article, Dr Matthew O'Hare, a Freshwater Ecologist at the Centre for Ecology and Hydrology in Edinburgh, explains how rivers have been changed over the last two centuries and discusses the need to restore them to a more natural state.
Water never really wants to travel in a straight line if it can help it. Turn on your kitchen tap, watch the water flow down and it will curl round itself, the subtle differences in forces creating spiralling patterns. That’s how water flows down rivers too. The patterns etch onto the landscape, becoming more pronounced, reinforced slowly year after year and then, quickly exaggerated or dissipated by floods. Those processes produce a wealth of channel forms; in Scotland we see step-pool sequences, meanders with associated riffle-pool sequences and long runs and glides, point bars, side bars and mid-channel islands. This dynamic variety of form provides the physical habitat template for many species. Unique assemblages of vegetation are found in the riparian zones of our rivers and the instream habitat complexity is directly related to the ability of these systems to support fish and invertebrate life.
Anyone out for a riverside walk in Scotland might well wonder if there is a need to rehabilitate our rivers, are they not natural already? Well, in many cases they are, Scotland’s steep hills give such energy to its rivers that attempts by man to channelize or engineer them are literally swept away. But there have been changes to our rivers, mainly through hard graft and industry. Many of the changes began 200 years ago when the enlightment encouraged men to improve the world around them. They dug straight channels from meandering rivers throughout Aberdeenshire, the Borders and elsewhere turning wetlands into good agricultural land. Travel through the Tweed valley, for example, and the roads you go on lie along the valley floors, near the rivers. Two hundred years ago you would have travelled across the high ground for the valley bottoms were impassable in many places; now the land is drained, the river disconnected from its floodplains and rivers moved out of the way. So what we see, what we are familiar with, what looks wild is often highly modified. It is also not surprising that for many there is a very human reluctance to change rivers back to what they consider less desirable forms.
Although we have gained much from containing our rivers we have lost much too. And not all changes were well thought through. The focus of most flood defence and channelization is to speed water past vulnerable areas but that strategy literally passes the problem downstream in the form of sediment load and flood water. In a related article you can read about what happens to our floodplains when they are divorced from their rivers, as part of this process.
Much river engineering work and hydrological flood risk work was done in the past with little understanding of how those changes might effect river processes. Why is this? Well even today there is a lingering disconnect between engineers, hydrologists, ecologists and those that understand sediment movement - the fluvial geomorphologists. This has also led to some major mistakes in the USA for example, meanders have been ‘reinstated’ where they were entirely inappropriate for the river type and this has led to serious channel failures.
Its an easy mistake to make but is also easy to fix. One focuses on reinstating the right processes rather than specific channel forms. River restoration is a relatively new undertaking and we are still learning how to do it right. There are many potential pitfalls; understanding how re-naturalisation operates in systems subject to other stresses, applying the correct fluvial processes to the right river styles and balancing humans needs for rivers to provide many services.
As river restoration is a relatively new technique there are limits to our knowledge base, but within Scotland one of our strengths is learning from others to avoid, or put right, past mistakes. In the next 50 years, we will see a shift in river management towards a more holistic and cost effective approach, one which is rooted in science and driven by our desire to improve our landscape. It has the potential to bring significant benefits for wildlife, flood alleviation and buffer our systems against climate change. I look forward to seeing it happen.
Let us know your thoughts by emailing email@example.com or Tweet @ScotWildlife using #50fortheFuture.
Matthew O'Hare is a Freshwater Ecologist at the Centre for Ecology and Hydrology.
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