Senior Lecturer in Physical Geography

Contact Details

• Tel: 0116 252 3850
• Email: dmp6@le.ac.uk
• Fax: 0116 252 3854
• Office: Bennett Building F44

Research Interests

My research interests are in Fluvial Geomorphology with particular focus on the sediment transport dynamics of alluvial rivers.  Rivers are active agents of erosion and deposition, and as such an understanding of how they move sediment is needed to tackle problems pertaining to channel instability, flood management, sustainable gravel extraction, reservoir sedimentation, river restoration and ecosystem quality.

Much of my work concerns dryland fluvial systems and is based on monitoring sediment transport processes in sand- and gravel-bed rivers at field sites in SW USA and southern Israel.  I also conduct laboratory-based research into the fundamental physics of sediment entrainment and transport.  A current focus of my research is understanding the control exerted by bed surface structure on the movement of sediment from the bed.

Recent and ongoing projects

Bed material transport in dryland fluvial systems 

Despite the infrequence of floods in semi-arid regions, it has long been recognised that dryland rivers are effective agents of erosion and sedimentation and are associated with many of the world’s most pressing problems of river management.  The aim of this research programme is to develop a better understand the dynamics of sediment transport in semi-arid and arid fluvial systems.  Research conducted in southern Israel in collaboration with Ian Reid (Loughborogh University, UK) and John Larronne (Ben Gurion University, Israel) is concerned with sediment transport in gravel-bed rivers.  Sediment transfers in sand-bed rivers have been studied as part of a wider project concerning sediment delivery by water in semi-arid catchments undertaken with Tony Parsons (Sheffield University), John Wainwright (Durham University) and Richard Brazier (Bristol University) in SE Arizona.

Reach-scale channel morphology and sedimentology of upland gravel-bed rivers in dryland environments

The aim of this project is to characterise the reach-scale morphology of gravel-bed rivers in semi-arid environments and to seek genetic explanations for the distinct channel morphologies that we identify.  Research conducted in the northern Negev, Israel provides important insights concerning the adjustment of river channel morphology under conditions of high sediment supply.

Roughness properties of alluvial river banks

Little is known about the roughness characteristics of river banks, even though recent research suggests that the form roughness generated by the irregular topography of a river bank can be a major component of the total flow resistance and bank shear stress with important consequences for the determination of stage-discharge relationships and for modelling bank erosion.  In this study, the technique of terrestrial laser scanning is used to derive high resolution digital elevation models (DEMs) of river bank microtopography.  The DEMs are analysed to provide multi-scale estimates of roughness and how roughness properties change over time as the banks erode. 

Characterisation of river bed surface structure (CHORUS)

New research in conjunction with Nick Tate of Leicester University, Steve Rice and Ian Reid of Loughborough University and Jo Wood of City University seeks a better understanding of how bed surface structure controls the movement of sediment in gravel-bed rivers.  The approach is to quantify the changing properties of gravel surfaces and their influence on flow and sediment transport in a series of experiments using a laboratory flume. The goal of the experimental program is to obtain a suite of simultaneous and detailed measurements of flow velocity, bedload movement and surface grain size and structure at a temporal resolution commensurate with time scales of bed adjustment.  Through a better understanding of bed-surface characteristics and the nature of the fluid/sediment interactions that control their development, we will improve our ability to predict sediment transport rates in river systems.

External Activities

Member of the British Sedimentological Research Group

PhD Students

David Ackerley: Bed surface structures in gravel-bed rivers.

Most recent publications

Powell, D.M., Larrone, JB, Reid, I and Barzilai, R. (2012). The bed morphology of upland single-thread channels in semi-arid environments: evidence of repeating bedforms and their wider implications for gravel-bed rivers. Earth Surface Processes and Landforms. DOI: 10.1002/esp.3199.

Wainwright J, Parsons AJ, Müller, EN, Brazier, RE and Powell, D.M. (2010). Standing proud: a response to ‘Soil-erosion models: where do we really stand?’ by Smith et al. Earth Surface Processes and Landforms, 35, 1349–1356. DOI: 10.1002/esp.2047.

Powell D.M. 2009. Dryland rivers: Processes and forms. In Geomorphology of Desert Environments, Parsons AJ, Abrahams AD (Eds). Springer Science+Business Media BV: Berlin; 333-373.

Full list of publications