Overland Flow Module
Note that this module is not a standard part of HYDRUS (2D/3D) or version 5 of HYDRUS. It is a nonstandard extension that we share with HYDRUS users without guaranteeing its numerical stability and robustness.
Warning: This boundary condition, i.e., the atmospheric boundary condition with overland flow, is less numerically stable than the regular atmospheric boundary condition!
Water flow and transport on a hillslope is a complex nonlinear problem. Precipitation water infiltrates into the soil profile at a rate that is equal to the rainfall rate until the soil infiltration capacity is reached. Surface runoff is generated once the soil infiltration capacity is exceeded. Surface runoff redistributes water at the land surface and moves it to lower parts of the hillside where it can infiltrate providing there is larger soil infiltration capacity. HYDRUS software package (its two-dimensional computational module) (Šimůnek et al., 2006) has been modified so that it can now simulate overland flow. For that purpose the existing numerical solver for subsurface flow was coupled with the newly developed overland flow routine. The updated HYDRUS program was tested using multiple examples given below.
The overland flow module does not consider solute transfer from the soil into the surface water layer present during overland flow. Infiltrating water from the surface layer is assumed to have concentration equal to the specified boundary condition concentration.
Download a brief description of implementation of overland flow into HYDRUS, as well as selected test examples below (pdf).
Download the executable module h2d_calc.exe, which considers overland flow (HYDRUS Version 1, (Version 2, (Version 3), and (Version 5). To use this module, copy h2d_calc.exe into the folder where HYDRUS (2D/3D) is installed (After first making a backup of the standard h2d_calc.exe for future use!).
- Project Group: Overland Flow
- Description: Examples demonstrating the use of the special module of HYDRUS-2D that considers overland flow
- Availability: Download HYDRUS projects now (Version 1, Version 2, Version 3, and Version 5) (24.3 MB)
Flow Examples
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Project
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Description
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Test1
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Transect dimensions: 100*0.5 m, q=0.00666 cm/s, N=201, T=600 s, slope=0.01, n=0.01.+ Regular Hydrus-2d is run without the overland flow. Excess water is removed instantaneously.
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Test2
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The same conditions as for Test1, but with the enabled overland flow. Loam with very low Ks=2.8889e-09 cm/s. Comparison with the analytical solution.
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Test2a
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The same conditions as for Test2, but with Ks=2.8889e-06 cm/s, T=300 s, and simulation time = 3600 s. This run considers larger infiltration and also simulates the overland flow recession.
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Test2b
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The same conditions as for Test2a, but with Ks=2.8889e-05 cm/s.
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Test2c
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The same conditions as for Test2b, but with roughness of 0.05 for nodes with x < 50 m and 0.01 for nodes with x > 50m.
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Test2d
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The same conditions as for Test2a, but with evaporation.
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Test3
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The same conditions as for Test2, but with Ks=2.8889e-04 cm/s, i.e., regular loam, T=300 s, and simulation time of 3600 s.
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Test4
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Surface runoff with multiple rainstorms (otherwise the same conditions as for Test3). Transect dimensions: 100*0.5 m, q=0.00666 cm/s, N=201, T=600 s, slope=0.01, n=0.01, ET=0.4 cm/d.
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Test5
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The same conditions as for Test3, but with variable slope, i.e., Ks=2.8889e-04 cm/s, regular loam, T=300 s, and simulation time of 3600 s.
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Test6
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The same conditions as for Test3, but with inflow at the upper end of the slope, i.e., Ks=2.8889e-04 cm/s, regular loam, T=300 s, and simulation time of 3600 s.
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Test6s
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The same conditions as for Test6, but with solute transport, i.e., Ks=2.8889e-04 cm/s, regular loam, T=300 s, and simulation time of 3600 s.
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MultiLay
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The same conditions as for Test3, but with Ks=2.8889e-02 cm/s for the material in the middle of the transect. This run generates overland flow in one section of the transport domain and allows infiltration in another.
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MultiLaZ
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The same conditions as for MultiLay, but with the slope in the opposite direction.
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MultiMat
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The same conditions as for MultiLay, but with the each material repeated four times within the transect.
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Transport Examples
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Project
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Description
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Test2Sr
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The same conditions as for Test2, but with T=300 s, and simulation time T_end=3600 s. Solute of unit concentration in rainfall in the top half of the domain.
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Test2bSr
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The same conditions as for TestSr, but with Ks=2.8889e-05 cm/s. T=300 s, T_end=3600 s. Solute of unit concentration in rainfall in the top half of the domain.
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Test2Si
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Uphill inflow (h_Top=1 cm) with a concentration of 0.5 (c=0.5) for T=300 s, and simulation time T_end=3600 s.
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Test2Sri
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Both uphill inflow (h_Top=1 cm) with a concentration of 0.5 (c=0.5) and rainfall with a unit concentration for T=300 s. Simulation time T_end=3600 s.
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Additional Examples with Irregular Geometries
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Project
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Description
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Irreg
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Transect dimensions: 100*2.0 m, q=0.00666 cm/s, N=544, T=600 s, simulation time = 3600 s, average slope=0.02, n=0.01, regular loam. Irregular surface of the transport domain.
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Irreg1
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Transect dimensions: 50*1.0 m, q=0.00666 cm/s, N=425, T=600 s, simulation time = 3600 s, average slope=0.08, n=0.01, regular loam. Irregular surface of the transport domain.
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Irreg2
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The same conditions as Irreg1, but with fixed vertical discretization at the soil surface using internal lines.
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Irreg3
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The same conditions as Irreg2, but with finer discretization.
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Irreg4
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The same conditions as Irreg3, but with time units of days.
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Irreg5
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The same conditions as Irreg4, but with multiple rainstorms.
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+ q - rainfall, N - number of surface nodes, T - duration of the rainfall, T_end - simulation time, n – surface roughness, h_Top - inflow depth.
References
The mathematical description of the module:
- Šimůnek, J., HYDRUS-2D Code Modification: Modeling Overland Flow and Dynamic Interactions Between Plants and Water Flow in a Hillslope Transect, Idaho National and Environmental Laboratory, Final report for project under contract number 00021013, 55 pp., 2003.
- van Genuchten, M. Th., and J. Šimůnek, Integrated modeling of vadose zone flow and transport processes, Proc. Unsaturated Zone Modelling: Progress, Challenges and Applications, Eds. R. A. Feddes, G. H. de Rooij, and J. C. van Dam, Wageningen UR Frontis Series, Vol. 6, Chapter 2, pp. 37- 69, x-xi, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2004.
- Šimůnek, J., M. Th. van Genuchten, and M. Šejna, Modeling Subsurface Water Flow and Solute Transport with HYDRUS and Related Numerical Software Packages, In: Garcia-Navarro & Playán (eds.), Numerical Modelling of Hydrodynamics for Water Resources, An International Workshop, Centro Politecnico Superior, University of Zaragoza Spain, June 18-21 2007. Taylor & Francis Group, London, ISBN 978-0-415-44056-1, 95-114, 2007.
The Overland module has been extensively used in multiple studies, including:
- Köhne, J. M., T. Wöhling, V. Pot, P. Benoit, S. Leguédois, Y. Le Bissonnais, and J. Šimůnek, Coupled simulation of surface runoff and soil water flow using multi-objective parameter estimation, J. of Hydrology, 403, 141-156, 2011.
- Chen, L., J. Šimůnek, S. A. Bradford, H. Ajami, and M. B. Meles, A computationally efficient hydrologic modeling framework to simulate surface-subsurface hydrological processes at the hillslope scale, Journal of Hydrology, 614, 128539, 15 p., doi: 10.1016/j.jhydrol.2022.128539, 2022.
- Chen, L., J. Šimůnek, S. A. Bradford, H. Ajami, and M. B. Meles, Coupling water, solute, and sediment transport into a new computationally efficient hydrologic model, Journal of Hydrology, 628, 130495, 14 p., doi: 10.1016/j.jhydrol.2023.130495, 2023.