Summary

This project seeks to improve our understanding of environmental controls on the dispersal of flood waters, and the formation and the geomorphological and sedimentary characteristics of fluvial crevasse splays. Advances in the field will contribute to understanding of landscape evolution, to prediction of floodplain deposits, and to interpretations of environmental change from the stratigraphic record.

• Opportunity to undertake field-based sedimentological data collection including digital landscape data form on modern floodplains.
• Lab-based flume-tank experiments of crevasse processes in scaled rural and urban floodplains, and/or numerical modelling of sedimentary processes and products.
• Assess distribution of pollutants in modern floodplains, and effectiveness of floodbasins designed to reduce flood risk.
• Attend international conferences in Europe, the US and elsewhere.
• Opportunities for career development (academia, internships, industry and beyond)

Background

Crevasse splays are lenticular sediment accumulations deposited by river floods that breach channel levees and inundate floodplains. These landforms and their deposits are prominent features of riverine landscapes and of the sedimentary record of fluvial successions. In present-day coastal areas and subsiding waterlogged alluvial plains, crevasse-splay formation is a primary agent of land building and predicting where their inception takes place is key for forecasting landscape evolution. On cultivated floodplains, crevasse channels can cause undesired sand and particulate (e.g., microplastics, pollen of invasive species) accumulation, rendering agricultural soils sterile or polluted. Yet in dryland settings, splays associated with repeated flood events provide a lifeline to agriculture where they drain into arid floodbasins.

In ancient subsurface fluvial successions, sand-prone crevasse-splay deposits typically form significant porous components of buried alluvial successions. Geological characterization is required to predict sedimentary heterogeneity and fluid-flow properties of such porous geological media. They are targets for heat exploitation in subsurface geothermal reservoirs, and therefore are important for associated clean, sustainable energy generation. They are potential repositories for the safe, short-term underground storage of hydrogen that can later be used as a fuel source. They are suitable as long-term underground repositories for carbon dioxide used in carbon capture and storage (CCS) schemes.

It is therefore important to improve our ability to predict the likelihood of occurrence, size and lithology of crevasse splays – both in modern rivers and in subsurface fluvial successions. However, crevasse splays and associated drainage networks of crevasse channels are highly variable with regards to their geomorphology, hydrology and internal sedimentary characteristics; their likelihood of development varies considerably between rivers and across environmental settings. It is recognized that this variability arises because of the complex interplay of factors. For example, crevasse-splay sedimentation is governed by the climate of river floodplains and catchments, through climatic controls on modes and rates of water and sediment delivery, floodplain drainage state, water-discharge regime, and floodplain vegetation. In addition, catchment controls are determined by the physiography and size of drainage areas and associated river systems, for example because of their effect on the volume and concentration of suspended sediment of splay-forming floods.

Aim and objectives

The overall aim of the PhD project is to improve our understanding of the controls on crevasse-splay formation, evolution and abandonment, and of how these translate to landforms and deposits. This will be achieved through an interdisciplinary study, conducted using multiple lines of investigation, whose balance can be tailored to the interests of the appointed research student.

Specific research objectives are as follows: (i) to quantify the influence of controlling factors (e.g., river hydrology, floodplain physiography) on crevasse-splay genesis, evolution and characteristics; and (ii) to design physical experiments to monitor crevasse events and dispersal patterns in the laboratory using scaled rural and urban landscapes.

Methodology

The research will seek to integrate results from several of the following study approaches: (i) laboratory-based flume experiments to investigate controls on crevasse-channel development and the morphology of resultant splay deposits using different floodplain configurations; (ii) field-based data acquisition and analysis from ancient (outcrop) or Quaternary (surface or shallow-subsurface) overbank successions; (iii) numerical modelling of overbank sedimentation for prediction of stratigraphic architecture in splay deposits; and (iv) analyses of remote-sensing datasets (satellite images, LiDAR data) of flood events to validate models. The appointed research student will be able to focus on study methods of interest to them.

Figure: Modern crevasse splays and crevasse-splay deposits in the rock record.

Potential for high-impact outcome

A major outcome of this project will be the development of physical and numerical models of flood water inundation in different floodplain environments. This will improve our understanding of the dispersal patterns of particulates and pollutants in rural and urban landscape, which will support mitigation strategies of a range of stakeholders. Results have implications for the prediction of fluvial landform response to currently on-going environmental change. From an applied standpoint, the method to be developed will aid the lithological characterization of subsurface fluvial splay successions that can inform appraisal of long-term carbon sequestration sites. The appointed candidate will be expected to publish the results of their research in leading research journals. The project supervisors each have long track histories of internationally recognized research publications in this field.