A new grid-free, hysteretic, and scale-dependent approach to modelling hillslope hydrology

Lead Research Organisation: Lancaster University
Department Name: Lancaster Environment Centre

Abstract

Classic 'physically-based' models of hillslope hydrology based on continuum mechanics have strong limitations when applied to the discrete water flow pathways that are often dominant in structured soils in the field. This project proposes a new modelling paradigm based on multiple interacting pathways, in which the water is represented as a very large number of discrete particles and exchanges between pathways are controlled by probabilistic rules. This allows flexibility in allowing for features of hillslope hydrology that are not easily handled within the continuum framework, such as the effect of vegetation on inputs rates at the soil surface, the effects of macropores and preferential flow pathways, and probabilistic representations of variable soil depths both across and down a slope. The particles representing the water can also be labelled by time of entry to the slope so that transport, mixing and residence time characteristics can be assessed within a single integrated framework (rather than requiring an additional dispersion equation in the continuum approach). The model has already been programmed for the simple case of a constant slope of unit width, but will be developed to allow for an arbitrary slope geometry and soil transmissivity characteristics. Mass balance is automatically achieved by accounting for all particles (including partial losses to evapotranspiration). There is also an intrinsic scaling of velocities and length scales so that the scaling characteristics of slopes can be investigated. This type of model is ideally suited to implementation on low-cost Graphics Processing Cards with high parallelism and this will be investigated to speed up the calculations. The model will be applied to data sets for flow and transport, for both steady state and transient flows, from the UK, Sweden, USA, Switzerland and Czech Republic, and there will be an opportunity to participate in planned tracer experiments in Czech Republic, China and the USA. Since much of the detail of flow pathways in field applications is inevitably unknowable, calibration of the model will be carried out within a multiple working hypothesis framework such that the multiple retained models will reflect the uncertainty arising from the characterisation of an application site.

Publications

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Rinaldo A (2011) Catchment travel time distributions and water flow in soils in Water Resources Research

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Davies J (2015) Hysteresis and scale in catchment storage, flow and transport in Hydrological Processes

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Semenova O (2015) Barriers to progress in distributed hydrological modelling in Hydrological Processes

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Beven K (2012) Causal models as multiple working hypotheses about environmental processes in Comptes Rendus. GĂ©oscience

 
Description That a fully integrated flow and transport model can be developed, and can reproduce field observed flow and tracer observations at catchment scales (The MIPs model).
Exploitation Route New applications of the MIPs model are currently being carried out in collaboration with Uppsala University, G P Lippmann Institute, Luxembourg and University of Zurich to test the model on new data sets. Initial work has also been carried out on the issue of scale-dependent parameterisations that are needed in hydrological models. Further work needs doing on efficiency of computation.
Sectors Environment

 
Title Multiple Interacting Pathways (MIPs) model 
Description Uses particle tracking technique to model both water flow and solute transport at hillslope and catchment scales 
Type Of Material Computer model/algorithm 
Year Produced 2013 
Provided To Others? Yes  
Impact Research articles only 
 
Description Application of MIPs model to the S Transect, Kryklan, Sweden 
Organisation Uppsala University
Country Sweden 
Sector Academic/University 
PI Contribution Provision of model code and supervision of PhD student
Collaborator Contribution Provision of field data and supervision of PhD student
Impact None as yet
Start Year 2012
 
Description Application of the MIPs model to the Weierbach catchment, Luxembourg 
Organisation Luxembourg Institute of Science and Technology
Department GP Lippmann Public Research Institute (CRP)
Country Luxembourg 
Sector Academic/University 
PI Contribution Provision of model code and supervision of PhD student
Collaborator Contribution Support for field experiments and supervision of PhD student
Impact None as yet
Start Year 2013