Britain’s rivers are under the spotlight because of an untreated sewage crisis, and the pendulum of floods and droughts that are the hallmark of a warming world. But hidden within these policy debates is a pervasive and under reported issue: quite simply, people have forgotten what a natural river even looks like.
This is important because it underpins attitudes towards the kind of rivers people expect to live with, and therefore constrains the changes to rivers that people will be willing to accept. Scientific evidence says radically different looking rivers are needed in order to accommodate larger, more frequent floods and droughts, to deliver increases in biodiversity, and to store more carbon.
Why have we forgotten what our natural rivers look like? In the UK and most other developed economies, the network of streams and rivers have been managed, and physically altered in some cases, for more than 1,000 years to support more farms and later more industry.
It is no wonder most people do not realize that the rivers they grew up with, fish in, swim in, or simply walk along are nothing like the natural ecosystems they once were. History and culture has evolved around modified river systems.
In Britain, for instance, 1,000 years of change has meant 97% of rivers are fragmented by barriers like weirs. Things accelerated after World War I with 36% of the river network of England and Wales, some 35,500 km, subject to major modifications. And these are only the documented changes—much more was routinely maintained such as the annual removal of silt or vegetation.
In the early 1990s, I visited every flood defense office in England and Wales as part of a study asking how much sediment is removed from rivers, how expensive it was and why we were doing it. It became clear that it was costly and in many cases it was done simply because “that is what happens on October 15″—and woe betide you if you were late because the locals expected it. This expectation of river cleansing is still apparent today in calls to dredge rivers after a major flood or sometimes to push gravel back into them.
There has been some increase in river restoration (or “re-wiggling”) with more than 2,500 km restored in the UK since the early 1990s. However, this represents less than 3% of the highly damaged river network and much more needs to be done. Though the sewage crisis dominates headlines in the UK, the physical modification of rivers matters too.
Physical form of a river
The “look” of a river isn’t just aesthetics—things like the number and shape of channels, gravel shoals and sandbanks, or the presence of vegetation or an eroding riverbank all affect how it acts as an ecosystem.
More complex and “messy” rivers tend to store and slow down the flows of water, sediments and nutrients. This creates a better habitat for plants and animals. It also means these rivers don’t strip as many nutrients from the surrounding landscape, and are able to store more carbon in the form of living and dead plants (as peat, for example). Messy rivers release water slowly like a sponge, protecting against both floods and droughts.
That said, modified rivers can…
Read More: We have forgotten what a ‘natural’ river even looks like