I am a NERC funded PhD student in the School of GeoSciences at Edinburgh University, where I am part of the Land Surface Dynamics group. I am fascinated by the way in which sediment is generated, transported and deposited across and eventually out of active mountain ranges. I am also keen to explore how we can consider and apply our knowledge about these processes in a more practical and risk based approach.
My PhD research concerns the dynamics of rivers on exiting the Himalayan mountains as they enter the Indo-Gangetic Plain, with a specific focus on tributaries of the Ganges or Ganga River in northern India and southern Nepal. Many of the rivers of the Ganga Plains are prone to abrupt switching of channel courses causing devastating floods over some of the most densely populated regions on the globe. Despite this, our understanding of the factors that control the dynamics of these river systems downstream of the mountain front is surprisingly limited. Furthermore, understanding how sensitive these rivers are to longer term projected climate change and more immediate anthropogenic pressures remains unclear.
i) Subsidence control on river morphology and grain size
In the first part of my PhD, I developed a new basin-scale approach to quantifying floodplain and channel topography using a swath-based method that identifies areas where channels are super-elevated (e.g. the east Ganga Plain) or entrenched (e.g. the west Ganga Plain) relative to their adjacent floodplain (Dingle et al., 2016). The probable controls on these observations were explored through an analysis of basin subsidence rates, sediment grain size data and sediment supply from the main river systems that traverse the Plain.
ii) Where does all the gravel go? Controls on gravel flux and the gravel-sand transition
In this part of my PhD I have examined how the amount of coarse sediment (or ‘gravel’) exported into the foreland basin varies across rivers discharging in the Ganga Plain. The amount of coarse sediment exported could directly influence the morphology of these systems, as the entirety of this coarser sediment fraction is retained within the Plain upstream of the gravel-sand transition (where the river bed changes from gravel-domianted to sand-dominated). As part of my PhD, I have mapped the position of the gravel-sand transition in the major tributaries of the Ganga River at distances of only ~20-40 km downstream of the mountain front! From rivers draining the highest mountains in the world, we see little more than sand-sized particles being exported into the Ganga Plain – why is this?
iii) To 10Be or not to 10Be?
Our current understanding of the total sediment flux into the Ganga foreland basin is based principally on suspended sediment data from gauging station networks, but the spatial coverage of these data is restricted. Advances in detrital cosmogenic radionuclide (CRN) analysis have allowed 10Be concentrations to be measured in modern river sediments, allowing approximation of average erosion rates from the source catchments over timescales of thousands of years. The concentrations of these radionuclide data give an indication of how sediment flux delivered to the foreland basin varies spatially between the major river systems that drain the Himalaya. In the final part of my PhD I will be analysing a series of Holocene and modern river sediments to test both the short and long-term variability in 10Be concentrations against existing 10Be concentrations and dated river terraces which can be related to extreme geomorphic events or periods of varying monsoon intensity.
I am also very grateful for the financial support I have received, in particular to help with two fieldtrips during October 2014 and Feb/March 2015 from the International Association of Sedimentologists, British Society for Geomorphology, Natural Environment Research Council and Edinburgh University Clan of Toronto.