I am a fluvial geomorphologist with interests in the interaction between geomorphology adn ecology, particularly salmonids, but also trees (wood in rivers) and riparian habitats. I also research on river restoration, sediment transport and morphodynamics. I use a range of approaches from field, flume to numerical modelling.
This study aims to address the gap in the Natural Flood Management (NFM) evidence base concerning... more This study aims to address the gap in the Natural Flood Management (NFM) evidence base concerning its implementation potential in groundwater-dominated catchments. We generated a typology of 198 chalk catchments using redundancy analysis and hierarchical clustering. Three catchment typologies were identified: (1) large catchments, (2) headwater catchments with permeable soils, and (3) catchments with impermeable soils and surfaces (urban and suburban land uses). The literature suggests that natural flood management application is most effective for catchments <20 km2, reducing the likelihood of significant flood mitigation in large catchments. The relatively lower proportion of surface runoff and higher recharge in permeable catchments diminishes natural flood management’s likely efficacy. Impermeable catchments are most suited to natural flood management due to a wide variety of flow pathways, making the full suite of natural flood management interventions applicable. Detailed g...
The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload t... more The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the shape and location of each grain relative to surrounding grains and the bed surface. We present the first complete suite of three-dimensional (3-D) grain geometry parameters for 1055 water-worked grains, and use these to parameterize a new 3-D grain entrainment model and hence estimate τc. The 3-D data were collected using X-ray computed tomography scanning of sediment samples extracted from a prototype scale flume experiment. We find that (1) parameters including pivot angle and proportional grain exposure do not vary systematically with relative grain size; (2) τc is primarily controlled by grain protrusion, not pivot angle; and (3) larger grains experience larger forces as a result of projecting higher into the flow profile, producing equal mobil...
A restatement of the natural science evidence concerning catchment-based "natural" floo... more A restatement of the natural science evidence concerning catchment-based "natural" flood management in the United Kingdom
... 105 NJ Clifford, MC Acreman and DJ Booker 8 Uncertainty Surrounding the Ecological Targets an... more ... 105 NJ Clifford, MC Acreman and DJ Booker 8 Uncertainty Surrounding the Ecological Targets and Response of River and Stream Restoration 139 ... 209 BL Rhoads, MH Garcia, J. Rodriguez, F. Bombardelli, J. Abad and M. Daniels ...
1.1 The Quantifiable Continuum of Uncertainty. Notice that once uncertainties are acknowledged as... more 1.1 The Quantifiable Continuum of Uncertainty. Notice that once uncertainties are acknowledged as unquantified uncertainties, increased knowledge about the uncertainties will determine their position on the continuum.. .. .. 11 1.2 Typology for sources and degree of uncertainty. Adapted from Van Asselt's (2000) proposed typology for uncertainties in integrated assessment.. .. 12 1.3 Some potential relationships between knowledge and uncertainty through time. Contrary to the argument of the positivist, no unique inverse relationship between uncertainty and knowledge exists. See Section ref{TYPOLOGYSEC 15 1.6 Five Philosophical Attitudes Towards Uncertainty. The Venn diagram is meant to illustrate the overlap between contemporary attitudes towards uncertainty. Note that ignoring uncertainty, shares no overlap with contemporary attitudes towards uncertainty.. 1.8 Cope With Uncertainty Strategy. The reductionist view of coping with individual sources of uncertainty. The end result of this strategy is always to cope with uncertainty. In terms of river management and restoration applications, applying the precautionary principle allows decisions to be made in the face of uncertainty and adaptive management allows iterative 2.1 Premise of Reducible Ignorance in Embracing Uncertainty Framework Context. The limited knowledge within the restoration community about uncertainties is highlighted here as reducible ignorance, which could be reduced through further research and education. The grayed out areas are the linkages to the rest of the 'embracing uncertainty' framework (see Figure 1.
This study aims to address the gap in the Natural Flood Management (NFM) evidence base concerning... more This study aims to address the gap in the Natural Flood Management (NFM) evidence base concerning its implementation potential in groundwater-dominated catchments. We generated a typology of 198 chalk catchments using redundancy analysis and hierarchical clustering. Three catchment typologies were identified: (1) large catchments, (2) headwater catchments with permeable soils, and (3) catchments with impermeable soils and surfaces (urban and suburban land uses). The literature suggests that natural flood management application is most effective for catchments <20 km2, reducing the likelihood of significant flood mitigation in large catchments. The relatively lower proportion of surface runoff and higher recharge in permeable catchments diminishes natural flood management’s likely efficacy. Impermeable catchments are most suited to natural flood management due to a wide variety of flow pathways, making the full suite of natural flood management interventions applicable. Detailed g...
The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload t... more The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the shape and location of each grain relative to surrounding grains and the bed surface. We present the first complete suite of three-dimensional (3-D) grain geometry parameters for 1055 water-worked grains, and use these to parameterize a new 3-D grain entrainment model and hence estimate τc. The 3-D data were collected using X-ray computed tomography scanning of sediment samples extracted from a prototype scale flume experiment. We find that (1) parameters including pivot angle and proportional grain exposure do not vary systematically with relative grain size; (2) τc is primarily controlled by grain protrusion, not pivot angle; and (3) larger grains experience larger forces as a result of projecting higher into the flow profile, producing equal mobil...
A restatement of the natural science evidence concerning catchment-based "natural" floo... more A restatement of the natural science evidence concerning catchment-based "natural" flood management in the United Kingdom
... 105 NJ Clifford, MC Acreman and DJ Booker 8 Uncertainty Surrounding the Ecological Targets an... more ... 105 NJ Clifford, MC Acreman and DJ Booker 8 Uncertainty Surrounding the Ecological Targets and Response of River and Stream Restoration 139 ... 209 BL Rhoads, MH Garcia, J. Rodriguez, F. Bombardelli, J. Abad and M. Daniels ...
1.1 The Quantifiable Continuum of Uncertainty. Notice that once uncertainties are acknowledged as... more 1.1 The Quantifiable Continuum of Uncertainty. Notice that once uncertainties are acknowledged as unquantified uncertainties, increased knowledge about the uncertainties will determine their position on the continuum.. .. .. 11 1.2 Typology for sources and degree of uncertainty. Adapted from Van Asselt's (2000) proposed typology for uncertainties in integrated assessment.. .. 12 1.3 Some potential relationships between knowledge and uncertainty through time. Contrary to the argument of the positivist, no unique inverse relationship between uncertainty and knowledge exists. See Section ref{TYPOLOGYSEC 15 1.6 Five Philosophical Attitudes Towards Uncertainty. The Venn diagram is meant to illustrate the overlap between contemporary attitudes towards uncertainty. Note that ignoring uncertainty, shares no overlap with contemporary attitudes towards uncertainty.. 1.8 Cope With Uncertainty Strategy. The reductionist view of coping with individual sources of uncertainty. The end result of this strategy is always to cope with uncertainty. In terms of river management and restoration applications, applying the precautionary principle allows decisions to be made in the face of uncertainty and adaptive management allows iterative 2.1 Premise of Reducible Ignorance in Embracing Uncertainty Framework Context. The limited knowledge within the restoration community about uncertainties is highlighted here as reducible ignorance, which could be reduced through further research and education. The grayed out areas are the linkages to the rest of the 'embracing uncertainty' framework (see Figure 1.
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