Sounding out the river: a new system for monitoring bedload mobilisation and transport

The mobilisation and transport of coarse sediment, referred to as bedload, has a profound impact on the evolution of mountain rivers, the surrounding basins they feed, and the communities that live within their catchments. However, we have few effective methods to routinely monitor bedload transport in near real-time because it is such a high energy and erosive environment under peak flow conditions. Hence, bedload monitoring can be considered a missing component of real-time environmental monitoring.

In 'Sounding Out the River' we take advantage of low cost seismic sensor systems that have become available because of the rise of technology such as the Raspberry Pi computer and the ease to which these systems can be telemetered. We will demonstrate this system for monitoring the mobilisation and transport of bedload along the River Feshie in Scotland, which is catchment already monitored for a range of scientific projects. In order to ensure that the system is useful, usable and used we will co-produce the design with a range of stakeholders including SEPA, CEH, Practical Action Nepal and cbec eco-engineering UK Ltd.

Beyond this proposal, we will then be able to address a range of environmental challenges, for example:

- In Nepal the supply of coarse bedload to the mountain front has resulted in successive channel avulsion events on the Kosi River. This has caused the displacement of vulnerable people and the deposition of gravels across agricultural land has devastated communities. Through near real-time monitoring of bedload transport, we can better understand the dynamics of such systems and have the potential to develop early warning.

- When rivers carry bedload, their erosive capacity increases; and when the bedload is deposited the beds become armoured. This poses a clear challenge for managing critical infrastructure.

- Forecasting of flood hazard requires knowledge of the shape of the river bed. However, when flood waters mobilise the bedload, the shape of the bed changes which poses a problem for flood modelling. Our near-real time monitoring system has the potential to inform where and when we would expect flood models to start breaking down.

- Bedload transport is an important process that cascades in the wake of other hazards, such as the monsoonal mobilisation of coarse sediment derived landslides triggered by the 2015 Nepal earthquake. It is often the case that these secondary processes (bedload transport) do not receive the same attention as the primary hazard (earthquake induced landsliding) because the uncertainty is often described as cascading, implying growing uncertainty. We believe that through the effective use of the monitoring proposed in this project, we have an opportunity to constrain the uncertainty and manage this cascading hazard.

Having discussed the technology with a range of stakeholders prior to and/or during the preparation of the current proposal, we are confident of achieving tangible impact in several modes including (i) Better planning for Disaster Risk Reduction (ii) Establishment of an Early Warning system for associated flood risk in near real time, (iii) Better-informed regulatory decision making, (iv) An augmented routine monitoring system, and (v) Improved design of river restoration projects. Below, we highlight quotes from our partners letters of support to elaborate on these potential impacts from their perspective.

Scottish Environment Protection Agency (SEPA) identify the potential of our anticipated findings to inform several core operations: "we believe that there may be scope for using the technology to establish a network of bedload monitoring points across Scottish rivers for routine monitoring purposes. There is also potential for application of the technology on specific rivers for specific projects where understanding of bedload transport would help to inform regulatory decision making or aid in the design of river restoration projects."

cbec eco engineering identify the potential to "augment our existing practices": "We are interested in the potential for the seismic sensor system to monitor the transient sediment transport response of sites after a restoration intervention on a river has been undertaken, and to allow us to quantify uncertainty in bedload processes for sediment transport models. This will allow us to better design river management solutions in systems with high bedload transport rates".

Practical Action, Nepal highlight the potential application for Disaster Risk Reduction in developing countries: "Our collaborations with your colleagues in Edinburgh on a GCRF grant highlighted the importance of sediment transport, and its impact on modifying the rivers ability to hold the flood waters. We are therefore enthusiastic to hear that you are developing new methods which would allow us to monitor both the transport of the gravel bed, as well as monitor the water levels. It is clear that some of the worst floods in the Terai occur when river channels change their course through erosion and re-deposition of the sand and gravel. In fact, many of the communities recognise the difference between the beneficial floods that inundate their fields, bringing nutrients and irrigation versus the negative impact when coarse sand and gravel is deposited over the fields and other parts are eroded away.

"While we recognise that you are initiating the development of the monitoring techniques on rivers near to you in Scotland, we hope that you will be able to bring these techniques to the benefit of our communities in Nepal."

Beyond these organisations, there are also benefits for the communities living with catchments where bedload erosion, transport and deposition are important processes. For example, the recent SEPA report "Gravel Deposits and Flood Risk to Agricultural Land" highlights the role that bedload erosion and deposition had in the Ballater community during the 2015 floods and on agricultural land near the confluence of the Tay and the Tummel. Our monitoring system will help constrain uncertainties around bedload process and the fate of bedload.