EGU24-18718, updated on 11 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

When one becomes many: Including complex channel systems in large scale flood models

Laurence Hawker1, Jeffrey Neal1, Michel Wortmann2, Louise Slater3, Yinxue Liu3, Solomon H. Gebrechorkos3,4, Julian Leyland4, Philip J. Ashworth5, Ellie Vahidi6, Andrew Nicholas6, Georgina Bennett6, Richard Boothroyd7, Hannah Cloke8, Helen Griffith8, Pauline Delorme9, Stuart McLelland9, Andrew J. Tatem4, Daniel Parsons10, and Stephen E. Darby4
Laurence Hawker et al.
  • 1University of Bristol, Geographical Sciences, Geographical Sciences, Bristol, United Kingdom of Great Britain – England, Scotland, Wales (
  • 2European Centre for Medium-Range Weather Forecasts, Shinfield Park, RG2 9AX, UK
  • 3School of Geography and the Environment, University of Oxford, South Parks Road, Oxford, OX1 3QY, UK
  • 4School of Geography and Environmental Science, University of Southampton, Southampton, SO17 1BJ, United Kingdom
  • 5School of Applied Sciences, University of Brighton, Sussex, BN2 4AT
  • 6Department of Geography, Faculty of Environment, Science and Economy, University of Exeter, Exeter, EX4 4RJ, United Kingdom
  • 7Department of Geography & Planning, University of Liverpool, UK
  • 8Geography and Environmental Science, University of Reading, UK
  • 9Energy and Environment Institute, University of Hull, Hull, United Kingdom
  • 10Geography and Environment, Loughborough University, Epinal Way, Loughborough, Leicestershire, UK

Over 70% of flood events recorded in the past two decades in the Global Flood Database and WorldFloods dataset have occurred in locations where complex channel systems occur. Here we define complex channel systems as parts of the river network that diverge, such as bifurcations, multi-threaded channels, canals and deltas. Yet, large scale flood models have, until now, used only single-threaded networks due to the lack of a river network that reflects complex channel systems . Therefore, these large-scale models fundamentally misrepresent the physical processes in these often highly populated areas, leading to sub-optimal estimates of flood risk.

Using the new Global River Topology (GRIT) dataset, a global bifurcation and multi-directional river network (Wortmann et al. 2023), we extend the river channel bathymetry estimation routine of Neal et al. (2021) to model multi-channels with LISFLOOD-FP. We compare the multi-thread model results to observations and to previous versions of LISFLOOD-FP using a single-threaded river network in the Indus, Mekong and Niger rivers at 1 arc second (~30m). By using GRIT, we find marked improvements in model results, observing better connectivity to areas of the floodplain that are far from the main channel and more channel floodplain interactions in wetlands. This work paves the way to further our understanding of global flood risk and to finally consider the diverse, evolving nature of geomorphologically active river networks. As this work progresses, we will continue to model a typology of bifurcations and multi-directional rivers to help further our understanding of the significance of complex river systems.

Neal, J., Hawker, L., Savage, J., Durand, M., Bates, P., & Sampson, C. (2021). Estimating river channel bathymetry in large scale flood inundation models. Water Resources Research57(5), e2020WR028301.

Wortmann, M., Slater, L., Hawker, L., Liu, Y., & Neal, J. (2023). Global River Topology (GRIT) (0.4) [Data set]. Zenodo.

How to cite: Hawker, L., Neal, J., Wortmann, M., Slater, L., Liu, Y., Gebrechorkos, S. H., Leyland, J., Ashworth, P. J., Vahidi, E., Nicholas, A., Bennett, G., Boothroyd, R., Cloke, H., Griffith, H., Delorme, P., McLelland, S., Tatem, A. J., Parsons, D., and Darby, S. E.: When one becomes many: Including complex channel systems in large scale flood models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18718,, 2024.