PhD: Sediment mobility in Himalayan rivers recorded by seismic monitoring with implications for flood risk under a changing climate via FindAPhD

University of Edinburgh

Edinburgh, UK 🇬🇧

About the Project

Summary

Big Himalayan rivers cause major floods when their channels switch course. This project will use seismic monitoring to determine the thresholds for this process and consider implications for flood risk.

Project background

The large rivers draining the Himalaya are prone to abrupt switching of their channel courses as they exit the mountain front and enter the Gangetic Plains. This has major implications for flood early warning systems and future land-use planning. This project will work with colleagues in Nepal and India to install a network of seismic monitors next to the Karnali and Kosi rivers in order to monitor the onset of mobility of coarse bedload (mainly cobbles). This will build on expertise we have through ongoing research monitoring bedload movement in the Glen Feshie in the Cairngorms, and initial fieldwork will accompany researchers in this field site to understand the technique. The two field sites in the Himalaya will be installed at the start of the project with local community members employed to maintain and download data. The data will then be analysed using the time series of power spectra of seismic frequencies in order to characterise the signal from water flow, environmental noises and bedload movement. These data will then be compared to the river level data from the gauging stations in order to assess the threshold value of river level that initiates bedload motion, and hence increases the likelihood of channel switching. This information will then be shared with the two NGOs with whom we are partnering (Practical Action Nepal and ICIMOD), who will integrate the information into flood early warning systems and DRR strategies in the regions. Looking into the future, the information from this project will enable forecasts to be made of changing flood risk in response to climatic changes in the region. 

Research questions

What is the water discharge at which rivers flowing out of the Himalaya mobilise coarse bedload sediment such as gravels and cobbles? 

Can the onset of coarse bedload mobility be integrated into flood early warning systems? 

What are the implications of future climate change scenarios on flood risk through channel switching in these regions? 

Methodology

The methodological development for this project has been developed during an earlier PhD project and NERC grant to work on the River Feshie in the Cairngorms where we have installed seven geophones with data loggers alongside the river. The data has then been processed in order to generate time series of the spectrum of seismic frequencies. These are then being compared to independent methods for assessing grain movements such as acoustic data. Bedload migration generates a different frequency relative to water turbulence which generates the strongest signal in these settings. These methodologies will be used directly for this project in Nepal. Currently, the monitoring sites use a geophone and datalogger charged by a large battery. For the purposes of this project, we have built low cost dataloggers that are smaller and can be installed more easily. The sensors will be installed in the first field season and be maintained through local colleagues that work with the NGOs Practical Action and ICIMOD. Additionally, during the first season, the grain size distributions will be studied across the rivers using trenches and drone surveys. Data from the monitoring stations will either be downloaded directly and sent to Edinburgh, or may be telemetred directly depending on wifi or network access. Before the first field season in November, there will be training sessions at the Glen Feshie field site. During the second half of the first year, the student will analyse the data and start to analyse satellite data in order to understand the frequency and history of channel avulsion and migration in these settings. The critical period will be during the monsoon (July to September) when we would expect the signal to record bedload movement. These data will be analysed with a further field season in the autumn of the second year. By spring of the second year, teh student will prepare preliminary results to be presented at EGU inAPril and AGU in December at the beginning of the third year.

Training

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. Additional training in the installation of the monitoring stations and the configuration of the stations relative to the expected signal will be achieved at the Feshie site before leaving for the first field season. Statistical analysis of the data generated from the data loggers will be carried out using R and supervised by M. Naylor. Courses on the use of google earth engine and on any necessary coding will be available within the School. 

Requirements

This project requires an enthusiastic geoscientist with a geophysical, geological or geographical background with an interest in rivers, sediment transport, flooding and flood risk. They will have good computing and quantitative skills, and be prepared to spend significant time in the field where logistics can be difficult, and where the differences in culture and climate can be challenging.  


References

Dingle, E.H., Creed, M.J., Sinclair, H.D., Gautam, D., Gourmelen, N., Borthwick, A.G.L. and Attal, M., 2020. Dynamic flood topographies in the Terai region of Nepal. Earth Surface Processes and Landforms, 45(13), pp.3092-3102.
Dingle, E.H., Sinclair, H.D., Venditti, J.G., Attal, M., Kinnaird, T.C., Creed, M., Quick, L., Nittrouer, J.A. and Gautam, D., 2020. Sediment dynamics across gravel-sand transitions: Implications for river stability and floodplain recycling. Geology, 48(5), pp.468-472.
Burtin, A., Bollinger, L., Vergne, J., Cattin, R. and Nábělek, J.L., 2008. Spectral analysis of seismic noise induced by rivers: A new tool to monitor spatiotemporal changes in stream hydrodynamics. Journal of Geophysical Research: Solid Earth, 113(B5).
Burtin, A., Hovius, N. and Turowski, J.M., 2016. Seismic monitoring of torrential and fluvial processes. Earth Surface Dynamics, 4(2), pp.285-307.
Dingle, E.H., Attal, M. and Sinclair, H.D., 2017. Abrasion-set limits on Himalayan gravel flux. Nature, 544(7651), pp.471-474.


POSITION TYPE

ORGANIZATION TYPE

EXPERIENCE-LEVEL