When the levee breaks: crevasse-splay evolution, geomorphology and sedimentary record

A PhD studentship to be run under the auspices of the Fluvial Research Group (FRG) in the School of Earth and Environment at the University of Leeds – https://frg.leeds.ac.uk/

Summary

This project seeks to improve our understanding of environmental controls on the formation and on the geomorphological and sedimentary characteristics of fluvial crevasse splays. Advances in the field will contribute to both fundamental and applied science, for example to predictions of landscape evolution, to the characterization of subsurface clastic successions, and to interpretations of environmental change from the stratigraphic record.

  • Opportunity to undertake field-based sedimentological data collection combined with lab-based flume-tank experiments and/or numerical modelling of sedimentary processes and products.
  • Join an integrated research group, with linkage to international research associates and industry.
  • Attend international conferences in Europe, the US and elsewhere.
  • Project sits alongside linked research as part of a larger programme.
  • Opportunities for career development (academia, internships, industry and beyond).
Modern crevasse splays and crevasse-splay deposits in the rock record.

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. Deposits of fluvial splays have considerable environmental and applied importance.

In present-day coastal areas and subsiding waterlogged alluvial plains, for example, 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 accumulation, rendering agricultural soils sterile. Yet in dryland settings, splays associated with repeated flood events provide a lifeline to agriculture where they drain into arid floodbasins. Elsewhere, the deposits of crevasse splays act as sites for the concentration of naturally occurring hazardous materials such as arsenic and uranium, else can concentrate anthropogenic contaminants such as microplastics and biochemical pollutants.

In ancient subsurface fluvial successions, sand-prone crevasse-splay deposits typically form significant porous components of alluvial aquifers and reservoir successions. Geological characterization is required to predict sedimentary heterogeneity and fluid-flow properties of such porous geological media. Crevasse-splay deposits in subsurface fluvial sedimentary successions have considerable economic significance. They form connectors that link together larger channelized fluvial sand bodies and are therefore important in dictating subsurface aquifer and reservoir connectivity. They act as hosts for minerals such as uranium. They are important conduits for contaminant dispersion. 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. They are potential long-term deep underground repositories for nuclear waste.

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 geological factors. For example, tectonics, base-level and hinterland controls on river grade drive accommodation generation, which in turn regulates the preservation of overbank deposits and influences the development of gradient advantages that trigger levee crevasses. Crevasse-splay sedimentation is also 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. Moreover, downstream controls on crevasse-splay formation and characteristics operate in lower fluvial reaches, because of marine processes – like tide and backwater effects – that influence river morphodynamics.

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 variable landforms and sedimentary deposits. This will be achieved through an interdisciplinary study, conducted using multiple lines of investigation, whose balance can be tailored to the specific 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; (ii) to generate outputs that serve as predictive tools and as guides to geological interpretation, for use in fundamental and applied geosciences (e.g., qualitative facies models, quantitative empirical characterization); (iii) to demonstrate the applied benefits of the research through case studies in environmental or subsurface geoscience.

Methodology

The research will seek to integrate results from several of the following study approaches: (i) analyses of remote-sensing datasets (satellite images, LiDAR data) of several modern rivers, conducted with consideration of river and catchment characteristics (hydrology, climate, vegetation, etc.); (ii) meta-analysis of published literature datasets on the Quaternary and ancient sedimentary record of crevasse-splay deposits; (iii) field-based data acquisition and analysis from ancient (outcrop) or Quaternary (surface or shallow-subsurface) overbank successions; (iv) laboratory-based flume experiments to investigate controls on crevasse-channel development and the morphology of resultant splay deposits; (v) numerical modelling of overbank sedimentation for prediction of stratigraphic architecture in splay deposits. The appointed research student will be able to focus on study methods of interest to them.

As part of the project, there will be scope for assessing the value of the fundamental findings for predictive purposes, in contexts of applied subsurface geology or environmental change.

Potential for high-impact outcome

A major outcome of this project will be the development of predictive facies and sequence stratigraphic models, which will improve our understanding of factors controlling the evolution and resultant sedimentary architecture of fluvial splays. Results have implications for the prediction of fluvial and floodbasin 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 form important reservoirs, groundwater aquifers and sites currently being considered for long-term carbon sequestration. Past and on-going research on similar topics to this, and also undertaken at Leeds, have been funded by NERC to address their mission aims. The appointed candidate will be expected to publish the results of their research in leading pure and applied research journals such as Nature Geoscience, Geology, Sedimentology, Journal of Sedimentary Research and Basin Research. The project supervisors each have long track histories of internationally recognized research publications in this field.

Eligibility

Applicants should have a BSc degree (or equivalent) in geology, geology-geography, earth sciences, geophysics or a similar discipline. An MSc or MGeol in sedimentology or geoscience (or similar) is desirable. Skills in field-based geological data collection and field sedimentology and stratigraphy are desirable. Experience of using GIS software would be useful, though is not essential.

Training

The project will likely involve field-based data collection over a series of field seasons. Training in field-based sedimentology data acquisition techniques will be provided. There will be opportunities for the appointed applicant to spend time working closely with our chosen project partner, Petrotechnical Data Systems (PDS), and one or more of our partner companies. Training will be provided in advanced concepts and techniques in clastic sedimentology and stratigraphy, in approaches to basin analysis, and in non-marine sequence stratigraphy. The nature of this research project will enable the appointed applicant to consider a future career in either academia or industry. The successful applicant will join a team of 30+ academic staff, PDRAs and PhD research students who collectively form the Sedimentology Group, which is based at Leeds but additionally benefits from a world-wide network of research associates. The group has been undertaking world-leading sedimentary research for 30 years and is supported by a large consortium of sponsor companies.

CASE Partner

The proposal has been agreed as a “Partnership Project” (a CASE project) with Petrotechnical Data Systems (PDS) Ltd, who design and deliver innovative software technologies, R&D and consulting services to the Exploration and Production Industry. The project aligns with an existing collaboration between Leeds and PDS to develop innovative geological database technologies for better characterization of subsurface sedimentary successions.