Overview

Project Highlights:

  • Conduct experimental research into fundamental processes of sediment transport using state-of the art equipment;
  • apply the results to help improve our understanding of stream restoration;
  • opportunities to engage with catchment managers and to use knowledge in applied contexts.

Fine-grained sediment (FGS) comprising material < 2 mm is an important component of natural fluvial systems, influencing a range of hydraulic and geomorphological processes and contributing to ecosystem form and function1. In recent decades, however, land use intensification and change has significantly increased the supply of FGS to many streams and rivers2,3 with deleterious effects on water quality, riverine ecology and the provision of ecosystem services (Figure 1). The effects reflect issues of both sediment quantity and quality and are therefore wide ranging, impacting on all life stages of fish, macro-invertebrate populations and macrophyte communities3,4.

Under the EU’s Water Framework Directive, UK surface waters have to attain good ecological status by 2027. Attempts to mitigate the ecological impacts of FGS in lotic environments have focused on soil and water conservation though the development of community-based erosion control initiatives as exemplified by DEFRA’s Catchment Sensitive Farming5 and Water Friendly Farming6 programmes. Although rarely stated explicitly, the ultimate aim of such initiatives is to reduce the flux of sediment to watercourses, thereby facilitating a process of passive stream restoration whereby water quality and riverine ecology gradually improve as FGS stored within channel systems are evacuated downstream. However, our understanding of the potential timescales and trajectories of channel restoration is severely constrained by a lack of knowledge concerning processes of FGS transport in alluvial systems. For example, current relations developed to predict the transport rates of sand-gravel mixtures7 fail to predict sand transport accurately when it is present in the interstices of coarser gravel frameworks and further work is needed to improve model predictions of the depths to which FGS may be eroded from gravel substrates8.

The aim of this project is to develop our understanding of FGS transport dynamics in fluvial systems with a focus on understanding the behaviour of surficial and interstitial fines under conditions of reduced sediment supply. This information will be combined with existing knowledge to develop a conceptual framework for understanding potential channel responses to soil and water conservation measures currently being introduced to mitigate the adverse effects of FGS on water quality and riverine ecology.

 

Fine-grained sediment pollution in the Eye Brook, Leicestershire. Photo by Ros Nicholls.

Methodology

Experiments on the erosion of FGS from a gravel-bed will be conducted in a 10 m long, 0.3 m wide laboratory flume located in the Geography Department at Loughborough University. Four sets of experiments will be conducted to study the erosion of surficial and interstitial FGS from both mobile and immobile gravel substrates. The precise experimental designs will be informed by existing theoretical frameworks9,10 and conditions typical of sediment-impacted streams as exemplified by the catchment of the River Welland, Leicestershire6. Key variables such as bed surface elevation, bed composition, near bed flow field and sediment transport rate will be quantified using laser scanning, bed photography, particle image/acoustic doppler velocimetry and by sampling the flume outflow respectively. The conceptual framework for understanding potential channel responses to reductions in FGS supply will be developed in association with scientists engaged in the Water Friendly Farming (WFF) Programme of the Allerton Trust, Leicestershire6.

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to the student's projects and themes. In addition to this, students will receive project specific training in techniques of laser scanning, the generation of high resolution digital elevation models and flow characterisation using particle image/acoustic doppler velocimetry. Additional training will also be given to support ancillary techniques e.g. sediment sampling and grain size analysis.

Timeline

Year 1: Research Design Phase: Complete literature review on the dynamics of FGS in streams and rivers; reconnaissance field trip to the Water Friendly Farming project of the Allerton Trust; design of flume experiments; training in laboratory techniques; pilot studies.

Year 2: Data collection phase: Conduct flume experiments and preliminary data analyses.

Year 3: Data analysis and writing-up phase. Complete data analyses; further visits to the Allerton Trust; write up thesis.

Partners and collaboration (including CASE)

The project represents a collaborative research initiative between Dr. Mark Powell and Professor Stephen Rice of the Universities of Leicester and Loughborough respectively. In addition, the project is undertaken in association with Professor Chris Stoate, a lead scientist in the Water Friendly Farming Project of the Game and Wildlife Conservation Trust’s Allerton Trust. Powell and Rice are fluvial geomorphologists, with considerable expertise in monitoring sediment transport processes and their effects on bed sedimentology in both field and flume environments. Stoate has considerable knowledge of farming and farm management practices and the implementation of soil and water conservation measures therein.

Further Details

The project would suite a candidate with a strong background in Physical Geography/Earth Science or a related discipline. Interests and/or experience of process-based modelling of fluvial systems and/or flume experimentation would be an advantage. Potential applicants are invited to contact Dr. Mark Powell (dmp6@le.ac.uk; 0116 2523850).