A new study by a team of researchers including Professor Rolf Aalto has suggested that 19th C. gold mining in California remains a major contamination risk as mercury-contaminated sediment is delivered to lowland areas every time there is a major flood.

'Frankenstorm' Sandy tracked directly over the Christina River Basin Critical Zone Observatory (CRB-CZO) giving scientists including Professor Rolf Aalto, the opportunity to document how landscapes respond to the extreme weather events that can account for the majority of landscape evolution.

Landscape and ecosystem dynamics

Large river dynamics

A fourth major LED theme is on river and catchment dynamics. Through NERC and NSF funding, studies of major river and floodplain systems, including the Rio Beni, Columbia, Jamuna, Mekong, Paraná, and Fly-Strickland, have been undertaken. Key outcomes include the first physics-based model to simulate meandering and braided river channels, leading to new insight into controls on large river morphodynamic diversity; and the first demonstration that fluvial carbon exports from Papua New Guinea exceed those from the Amazon.

Our research on fine sediment budgets and fluxes provides process-based, quantitative understanding of sediment dynamics at catchment, regional and global scales. This work has necessitated the development of specialised field instrumentation and measurement techniques. Exeter staff pioneered the application of radionuclides, tracers, and biogeochemical constituents for researching river-floodplain systems, both in the UK and globally. We have one of the best equipped gamma spectrometry laboratories for environmental measurements in the world (16 HPGe detectors) and are at the forefront of developing the application of environmental radionuclides to quantifying erosion and deposition rates in catchments, to establishing overbank deposition rates on river floodplains and to fingerprinting suspended sediment sources. Active research continues in the UK and across a number of large fluvial dispersal systems, with a special focus on tropical floodplain systems and remnant floodplains in temperate rivers. Such information is central to the establishment of catchment sediment budgets.

Research also focuses on the processes that control the evolution of landscape features such as rivers, floodplains, alluvial fans, hillslopes and mountain ranges. We employ a range of field and laboratory-based methodologies including analysis of landscape topography and sediment characteristics (physical properties and geochemistry) and surface dating (using cosmogenic and environmental radionuclides, and OSL). These approaches are combined with numerical modelling and experimental approaches conducted under controlled laboratory conditions. This work seeks to disentangle the relative roles of allogenic and autogenic controls on landform evolution, and to identify the diagnostic characteristics of transient landscapes under steady and time-dependent climatic and tectonic forcings.

We have considerable expertise in the numerical modelling of floodplain processes, including the use of 2D and 3D Computational Fluid Dynamics models of overbank flow and sediment transport, reduced-complexity floodplain inundation modelling, and development of novel model upscaling strategies to quantify floodplain sediment storage rates at the catchment scale. Physical models include floodplain flumes and a large annular “flocculation” flume.

In summary, our analytical and modelling capacity are extensive and unique, as is our broad collection of cores, samples and supporting data from six continents and many of the world’s great rivers.

News stories:

After the gold rush
'Frankenstorm' Sandy bears down on Exeter Critical Zone Observatory

Recent funding:

NERC project NE/I023120/1, Award: £350k (£50k to Exeter). ‘The sedimentology of fluvial megascours’, Exeter Investigators: Andrew Nicholas.

NERC project NE/H009108/1. Award: £529k (£479k to Exeter). ‘Do floods matter? Bridging the gap between fluvial morphodynamics and alluvial architecture’, Exeter Investigators: Andrew Nicholas, Rolf Aalto and Luiz Aragao.

NERC project NE/H006524/1. Award: £607k (£180k to Exeter). ‘Morphodynamics and sedimentology of the tidally influenced fluvial zone’. Exeter Investigators: Andrew Nicholas.

NERC project NE/J021571/, Award: £794k (£210k to Exeter). ‘Climatic and Autogenic Controls on the Morphodynamics of Mega-Rivers: Modelling Sediment Flux in the Alluvial Transfer Zone’. Exeter Investigators: Rolf Aalto and Andrew Nicholas.

Key publications:

  1. Singer, M. B., Aalto, R. et al. (2013). Enduring legacy of a toxic fan via episodic redistribution of California gold mining debris. Proceedings of the National Academy of Sciences of the United States of America 110, 18436-18441.
  2. Perreault, L. M., Yager, E. M., Aalto, R. et al. (2013). Application of 210Pbex inventories to measure net hillslope erosion at burned sites. Earth Surface Processes and Landforms 38, 133-145.
  3. Nicholas, A. P. (2013). Modelling the continuum of river channel patterns. Earth Surface Processes and Landforms 38, 1187-1196.
  4. Nicholas, A.P. (2013). Morphodynamic diversity of the world's largest rivers. Geology 41, 475-478.
  5. Brown, A. G., Tooth, S. et al. inc. Aalto, R. (2013). The Anthropocene: is there a geomorphological case? Earth Surface Processes and Landforms 38, 431-434.
  6. Aalto, R. and C. A. Nittrouer (2012). Pb-210 geochronology of flood events in large tropical river systems. Philosophical Transactions of the Royal Society a-Mathematical Physical and Engineering Sciences 370, 2040-2074.
  7. Grenfell, M., Aalto, R. Nicholas, A. P. (2012). Chute channel dynamics in large, sand-bed meandering rivers. Earth Surface Processes and Landforms 37, 315-331.
  8. Hutton, C. J., Brazier, R. E., Nicholas, A. P. et al. (2012). On the effects of improved cross-section representation in one-dimensional flow routing models applied to ephemeral rivers. Water Resources Research 48, W04509.
  9. Aufdenkampe, A. K., Mayorga, E. et al. inc Aalto, R. (2011). Riverine coupling of biogeochemical cycles between land, oceans, and atmosphere. Frontiers in Ecology and the Environment 9, 53-60.
  10. Ghoshal, S., James, L. A., Singer, M. B., Aalto, R. (2010). Channel and Floodplain Change Analysis over a 100-Year Period: Lower Yuba River, California. Remote Sensing 2, 1797-1825.
  11. Nicholas, A. P. Quine T. A. (2010). Quantitative assessment of landform equifinality and palaeoenvironmental reconstruction using geomorphic models. Geomorphology 121, 167-183.
  12. Nicholas, A. P. (2009). Reduced-complexity flow routing models for sinuous single-thread channels: intercomparison with a physically-based shallow-water equation model. Earth Surface Processes and Landforms 34, 641-653.
  13. Nicholas, A. P., Clarke, L. et al. (2009). A numerical modelling and experimental study of flow width dynamics on alluvial fans. Earth Surface Processes and Landforms 34, 1985-1993.
  14. Singer, M. B. Aalto R. (2009). Floodplain development in an engineered setting. Earth Surface Processes and Landforms 34, 291-304.
  15. Aalto, R., Lauer, J. W. et al. (2008). Spatial and temporal dynamics of sediment accumulation and exchange along Strickland River floodplains (Papua New Guinea) over decadal-to-centennial timescales. Journal of Geophysical Research-Earth Surface 113, F01S04.
  16. Alin, S. R., Aalto, R. et al. (2008). Biogeochemical characterization of carbon sources in the strickland and fly rivers, Papua New Guinea. Journal of Geophysical Research-Earth Surface 113, F01S04.
  17. Goni, M. A., Monacci, N.  et al. inc Aalto, R. (2008). Terrigenous organic matter in sediments from the Fly River delta-clinoform system (Papua New Guinea). Journal of Geophysical Research-Earth Surface 113: F01S10.
  18. Swanson, K. M., Watson, E., Aalto, R.  et al. (2008). Sediment load and floodplain deposition rates: Comparison of the fly and Strickland rivers, Papua New Guinea. Journal of Geophysical Research-Earth Surface 113, F01S03.