Going with the flow …


I’ve written before about my enthusiasm for Leonardo da Vinci as an exemplar of the fertility of bringing artistic sensibilities to science and vice versa (see “Imagined but not imaginary”).   A small exhibition at the Laing Gallery in Newcastle with ten of his drawings from the Royal Collection on display gave me an opportunity to indulge my passion, particularly as it included one drawing that is pertinent to the subject of this blog.

It is an intriguing story because it brings Leonardo together with some of the most notorious names in Renaissance Italy: Cesare Borgia and Niccolo Machiavelli.   It was at the court of Cesare Borgia that Leonardo crossed paths with Machiavelli, then the Florentine ambassador, and was later employed by the government of Florence on a grand engineering scheme.

The scheme – which truly deserves the adjective “Machiavellian” – involved diverting the River Arno downstream of Florence in order to deprive their rivals, the Pisans, of the water supply they needed to survive a siege.   Later in the same year, he was also commissioned to design a canal to help convey Florentine trade goods to the Mediterranean. The diagram above is one of the maps he drew as part of his preliminary survey of the river and shows the River Arno flowing from left to right.

What is interesting is his depiction of the damage caused by the river at two points on the bank below the weir. The impression from the map is of an artificial embankment on the right bank of the river which is being eroded by the force of the river as it emerges from the weir and then again a short distance downstream as the current describes an arc within the river channel. Called in to advise on “hard engineering”, he deftly points out the folly of working against nature.  Like many of Leonardo’s grand ideas, the diversion of the Arno never got passed the planning stages. Ironically, his plans to alter the Tuscan landscape were confounded by changes in the political landscape: the defeat of Pisa by conventional military means and, ultimately, the defeat of Florence and Machiavelli’s fall from power.

I would have noted this drawing and have moved on were it not for an article I had read the same morning in the Independent on Sunday, describing the UK Government’s belated conversion to the importance of soft engineering in the aftermath of the winter floods. Increased spending on flood defence is also a key feature of today’s budget and, whilst a large part of this will, I am sure, be directed towards old-fashioned hard engineering (and, indeed, this will be necessary to protect some towns), I am glad to see that, 500 years after Leonardo, its limitations are finally being recognised by politicians.


More about floods …

And no sooner than I had uploaded the previous post, lo, my prophecy was proved correct.  Eric Pickles’ rant about the Environment Agency at the weekend betrayed such fundamental ignorance that one commentator (a Professor of Water Engineering, no less) suggested that Pickles would be “more use as a sandbag”.

The words of Liddell-Grainger and Pickles lead me back to a book I read last year, called “Nudge”.  Nudge theory is the idea that people can be persuaded to make right decisions by simple changes in how choices are presented to them.  It was touted as a way of reconciling a libertarian political outlook with responsible government, by-passing the “Nanny State” in the process.   Interestingly, the authors of Nudge, Richard Thaler and Cass Sunstein, both economists from the University of Chicago, pick out the environment as one area of government where “nudge” may be able to play a significant role.

Part of the reason Thaler and Sunstein were looking at the environment in this book was their perception that much environmental management adopted a “command-and-control” approach to regulation that did not fit with their own libertarian outlook.  Were there, they wondered, opportunities to encourage people and businesses to make more enlightened choices?   They give some examples of where this might be the case.  However, Rabbi Julia Neuberger, who chaired a House of Lords inquiry into “nudge” was more pessimistic.  In many cases a “push” or a “shove” is needed, not just a gentle “nudge”.

Nudge may work where individual choice is significant but the issues underlying the current problems associated with flooding and severe weather will only be solved by collective action.  And this is the problem for Conservative politicians: they argue against big government and for reducing the government spending but flood defence requires massive investment and co-ordinated action across several branches of the public service.   It will also – whisper this quietly – require “red tape” if developers and businesses are to be warned off inappropriate use of flood plains.   The aftermath of Hurricane Katrina is a grim warning of the dangers of ideology overriding common sense in flood defence management (see “Black Swan #2: McEcology and Steve Earle”)

But there is a bright side: I recall my visit last year to a flood alleviation scheme in east London masquerading as a “country park” (see “Things we’ve forgotten to remember”).  This was not high grade habitat but it was a vital green lung for local inhabitants and, once or twice a year, it provided flood relief for the surrounding area.   Interventions to prevent flooding can have wider societal benefits, but it does need to take place in a planning framework where experts from different disciplines can work together and, in some cases, over-ride short term and purely financial interests.   That’s the challenge that the Conservatives have to face over the coming months as flood waters recede and the usual bickering about public spending takes centre stage again.

The River Ehen in January

Fieldwork in January is always a mixed blessing.  On the one hand, you get a break from the tedium of office- and lab-based activities that dominate the ecologist’s winter agenda.  On the other hand, there is the weather.   It is only when the water is freezing and the wind is blowing that you realise just how reliant we are on our fingers.   At each site I have to pick stones from the riverbed, then manipulate forceps to collect fragments of the different organisms present, and finally write some legible notes in my field book.

A year or so ago, I found a partial solution in the form of a box of veterinarian’s disposable gloves which extend right up my arm.   A cyclist’s reflective ankle band then holds the top of the glove in place while I plunge my arm into the river.   This means that I don’t need to remove outer layers of clothing before plunging my arm into the water, though the thin plastic of the gloves offers no insulation to my hand itself.

The second problem we face is that we are wholly at the mercy of the river flow.   Life is easier now than in the past because you can get real-time readings of flow from the Environment Agency’s website.   The knack is to translate the number that you read on the web page into a meaningful indication of risk. After visiting the Ehen for over a year, and comparing what I see with the hydrographs, I now know that a flow of about 100 MLD (mega-litres per day) means that the water comes no higher than my calves whilst 500 MLD is the limit for safe working.  And today’s hydrograph reads … 500 MLD.

So here’s my question: if the river is flowing so fast that I can only just stand up, and if there have been a series of spates over the past couple of weeks, what is this going to do to all the algae that live on the stones at the bottom of the river?   The answer will surprise everyone but me.  The reason I am not surprised is that I am the one trying to stand up in the river and one of the problems I face is that the rocks beneath my feet are slippery with algae (remember “healthy streams are slippery streams …”?).

We’re using a device called a “Benthotorch” to measure the quantity of algae on the river bed.  This is a portable fluorimeter, calibrated to measure the amount of chlorophyll on a given area of stone.   The more algae there are on the stones the greater the concentration of chlorophyll that we record.  When I collated all the evidence we’ve patiently collected over the past year, it becomes clear that there to be much more algae in the winter than in the summer.   Substantially more.   What is going on?


Maria using a benthotorch to measure chlorophyll concentrations on stones from the River Ehen, February 2013.

The summer values are, perhaps, the easier to explain: on most of our visits here during the summer we  noticed lots of tiny midge larvae on the stone surfaces (see “A very hungry chironomid …“).   These were munching their way through the algae and, in turn, were being eaten by larger invertebrates and fish.   The low chlorophyll measurements, in other words, are a result of natural process in a healthy ecosystem.   The larger quantities we find in the winter can partially be explained by the same mechanism: the cold weather means that the bugs are not so active, meaning that algae tend to accumulate rather than being converted into midge larvae.


Variation in chlorophyll concentrations on stones in the upper River Ehen.   Bars are the average values of five replicate measurements from each of four sites.   No data were collected in December 2012 or January 2013.

But if I have trouble keeping my feet in the fast current of the River Ehen, how come those algae that do accumulate are not washed away?   Some of the algae will be removed by the current.   Sand and gravel carried by the stream will abrade the surface of the stones and, at high velocities, the stones themselves will be rolled downstream.  Yet it is easy to over-estimate the effect of the stream itself.   The stream bed generates a huge amount of friction which slows the flow of water in the centimetre or so closest to the bottom to almost zero.   The physics befuddle me but better brains than mine have worked out that life in this “boundary zone” can carry on whilst those of us who set out to study it are struggling to keep our feet.