How do we Measure That…

It was 9:55am and, scrolling through my emails, one particular message from Dr Andrew Black caught my attention: ‘Fieldwork Help Required Today’. It didn’t take me long to hit reply…

>1 m standing waves dowstream of Pony Bridge.

Two hours later Finlay and I were driving north on the A9 as quickly as legally possible in our tiny rental car, an ADCP (Acoustic Doppler Current Profiler) jammed in the back seats. The aim of our mission was to quantify the exceptionally high flows occurring on the River Feshie, caused by rapid melt of the snowpack (~40 mm rainfall equivalent) which fell 3 days earlier during Storm Deirdre. We followed the Spey into the Cairngorms. In some places its swirling water had overtopped the banks and here and there a couple of sheep could be seen standing marooned by floodwaters.

SEPA had estimated peak flows of 107 cumecs at their Feshie Bridge gauging station and, as we drove up into Glen Feshie, it became apparent that, if anything, their estimation was conservative. Murky water roared down the glen, tugging at vegetation and cutting into the river banks. We stood uneasily on the Pony Bridge, the standing waves downstream over a metre high! Upstream, fresh erosion could be seen on the high outside banks of the meander and, as we tied ropes to the ADCP, a tree shot past, borne along by the floodwaters.  Neither Finlay or I had ever attempted to gauge flows in conditions quite like this and soon found out first hand just how much power water has.

Big boat, little car.
Preparing the ADCP for launch.

The ADCP emits sound waves and utilises the doppler effect to capture the flow velocities throughout the water column and generate a profile of the river bed. The device must be dragged across the width of the river to obtain a reading and, equipped with several lengths of orange rope, we stationed ourselves on opposite banks. However, with the ADCP in the water, it very quickly became apparent that pulling it across in such high flows was going to be difficult and we hauled it in before it could be swept downstream. Slightly upstream, we found a wider section of river with lower flow velocities.

Ropes at the ready.

However, keeping the long ropes out of the water proved impossible and, once the river had hold of them, it wouldn’t let go! No matter how hard we pulled, the ropes stayed put and gradually slipped through our hands and further downstream! Eventually Finlay waved his arms… it was no use. I let go and, with a snap, the rope leapt from the bank and vanished downstream (it was thankfully tied to a tree on the other bank). At this stage we admitted defeat and packed up our kit. The SEPA gauge downstream at Feshie Bridge had recorded a peak flow of 141 cumecs.

High water under the bridge.


It was an opportunity missed and, in hindsight, there may have been other ways to get the data we were after. Although significantly less high tech, we could have played Poohsticks with twigs, timing their journey down a measured section of river to estimate water velocities across the channel. A river bed profile could then have been obtained another day in more benign conditions. However, now that river levels have fallen again, debris lines left behind by the flood could perhaps be mapped to reconstruct what was going on in the river that afternoon.

End of semester field visit – the re-watered River Garry (Perthshire)

The exams are all finished now, so what better than a field visit to revisit some of the key themes of the semester just passed?  More so when there’s the offer of a guided tour from Scottish & Southern Energy’s biologist Dr Alasdair Stephen, and a shining yellow thing in the sky all day long!

Struan Weir photo
Visiting Struan Weir – now mostly removed to once again permit fish to ascend the Garry above its confluence with the Errochty Water.

The focus for our day was the River Garry, which has been dry for most of the past 60 years thanks to a diversion of the upper river to supply water to Loch Errochty, for renewable power generation at Errochty Power station.  SSE concluded an agreement with the Scottish Environment Protection Agency (SEPA) and the Tay District Salmon Fishery Board to allow the new provision of environmental flows, commencing in autumn 2017.  We spent some time in class talking about in-stream habitat and ecosystems: the role of water depths, velocities and wetted perimeter.  The works allow SSE to put the demands of the Water Framework Directive into practice.

Calvine Falls Photo
Falls below Calvine. If you were a salmon, would you be able to jump that? At least now the fish get the chance – and observations show that salmon are indeed migrating beyond this natural barrier.

But the trip soon revealed that a lot more was required than ‘just’ hydraulic and ecological modelling.  Our discussion turned to questions of scientific evidence, stakeholder benefits, partnership working, people as much as policy, and balancing acts – how best to protect the local freshwater environment without causing unnecessary losses of generation water?

River Garry sediment downstream of intake
Heavily Modified! Sediment in the foreground has been excavated from the headpond above the Garry Intake, and is deposited adjacent to the river to allow sediment to be entrained in spates – providing a source of suitable bed sediment downstream.

A few photos here give a flavour of the day.  Many thanks, Alasdair, for sharing your knowledge, many experiences and insights.

Loch Garry Weir
Dry river bed at the outlet (east end) of Loch Garry. This is the next phase of the Garry restoration project, to provide a continuous environmental flow here.
Loch Garry inflow - east end
The flow of the Allt Coire Luidhearnaidh joins the Allt Dubhaig and normally flows west into Loch Garry. These watercourses will provide the water planned to re-water the upper Garry.
Sediment traps
Sediment traps on the Allt Coire Luidhearnaidh. Why?

Read more about the Garry re-watering here from:

Garry below Calvine: photo
River Garry downstream of Calvine. The bed is dominated by bedrock. Has it always been like that, or do we see here a result of sediment starvation?