The fieldwork started with a lot of preparation work: several days of planning to define what data were most important to collect and relevant points to collect them. I had to analyse the hydrography, topography, and geology maps of the region, in addition to discovering the paths (roads) that I could access in the area. Then I had to prepare the final details: book the transport vehicle, the accommodation and separate the field equipment (GPS, camera, maps, tape measure, waders and first aid kit). With everything ready, the day arrived: I finally visited my study area in the Scottish Highlands! I spent five days walking on the rivers of the Carron catchment in the Scottish Highlands, along with my supervisor, Rebecca, and the iCONN manager, Jenny. A team that helped me a lot on the field!
Starting the fieldwork: discussing plans using a map with Rebecca
We mainly collected data on sediment size and riverbed sediment cover. My main (and, virtually, only!) equipment was my phone – with a camera, GPS and a note-taking app.
Main field equipment: a phone
Visiting this place and seeing my object of study (the Carron catchment) was a great pleasure. It helped me to understand fluvial processes and to imagine factors that can affect them. I have been simulating sediment transport in the Carron river network with numerical modelling. I am studying what controls sediment accumulation in some river sections – called alluvial reaches – and the absence of sediment in other sections – called bedrock reaches.
A bedrock reach in a small and confined gorge
An alluvial reach with the famous Highland Cow!
The Carron catchment drains an area of 300 km2. The main river is about 44 km long, but the entire river network is around 144 km. If you try to walk along these rivers, you will see that the scenery changes a lot! It ranges from flat valleys with meanders and calm water, to rapids, rocky gorges and waterfalls. The sediment sizes vary from sand to boulders over one meter in diameter.
Glencalvie Falls. We saw a salmon trying to jump upstream of this 6 meter high waterfall!
This field trip was one of the most memorable moments of my PhD journey. In addition to collecting data and better understanding my study area, it was great to visit this beautiful place in the Scottish Highlands, especially with the early autumnal colours.
Cute mushroom hiding near the river
After fieldwork, I had to process the collected data. I calculated the grain size distribution of more than 200 photos and the average sediment cover of around 40 reaches. I used a program called PebbleCounts (Purinton and Bookhagen, 2019) to estimate the grain sizes automatically.
Example of a photo to measure grain size of river bars. The white card (85 x 64 mm) in the centre was used as a scale
The same photo after processed by PebbleCounts. It measured the size of 284 pebbles in 3 minutes! There are errors, but the pebble selection is good overall.
I’ve been simulating sediment transport in the Carron river system for months now. My simulations are just a simplified representation of what I saw in the field. That’s the most exciting part of going to the field: I could see the real fluvial system that I’ve been studying, with all the complex factors and interactions that affect sediment transport. Now I can continue with the simulations but I am aware of how well the simulations are representing reality.
Carron river: a mixed bedrock and alluvial system
References:
Purinton, B. and Bookhagen, B.: Introducing PebbleCounts: a grain-sizing tool for photo surveys of dynamic gravel-bed rivers, Earth Surf. Dynam., 7, 859–877, https://doi.org/10.5194/esurf-7-859-2019, 2019.
