Modeling Non-equilibrium Overland Flow and Reactive Transport Processes Using HYDRUS-1D

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1 5 th International HYDRUS Conference, Prague, Czech Republic Modeling Non-equilibrium Overland Flow and Reactive Transport Processes Using HYDRUS-1D work with Dr. Jirka Simunek and Dr. Scott Bradford Department of Environmental Sciences University of California, Riverside

2 Introduction Contents HYDRUS-1D overland flow and transport model Implementation Main features Numerical examples Non-equilibrium overland flow and transport models Evidences Numerical examples Summary

3 Contamination of Water Source Runoff is primary transport route in the agricultural settings Phillips, S. W. et al, 1999; Pandey et al., 2014.

4 Overland solute transport models Consider only non-reactive solutes X Transport of pesticides, microbes, nutrients etc. Lumped parameter conceptual models X Ignore the processes acting on chemicals at the soil surface X SWAT, HSPF, INCA, COLI etc. Too complicated for efficient applications X ParFlow, CATHY, HGS etc. Assume the homogeneous land surface characteristics

5 HYDRUS-1D overland model 1D Richards equation: 1D Diffusive wave equation: HYDRUS-1D and 2D codes are modified to simulate the overland flow and solute transport Weill et al., 2009

6 Model verification Conditions: The soil profile is 100 m long, the slope is 0.01, precipitation rate is cm/s (24 cm/hour) and the roughness coefficient n equals to min 2min 30 s 2 min 1min 20 s 60 s 25 s Depths of the water layer at the soil profile at selected times and steady state, calculated numerically and analytically (for steady state) for the example.

7 Main features Allows the consideration of many different kinds of solutes e.g., pesticides, nutrients, and microbes reactions e.g., linear and nonlinear equilibrium sorption, kinetic sorption and desorption on multiple sites HYDRUS GUI for pre and post processing Heterogeneity in parameters Inverse parameter optimization

8 Inflow from upland Transport of reactive solutes Impervious soil Conservative tracer 100 m α Solute Retardation (K d =1 cm 3 /g) Solute kinetic attachment/detachment (k a =0.01 s -1, k d =0.001 s -1 )

9 Evidences of non-equilibrium flow and transport processes A 1-m long ruler is shown for scale (a)without overland flow (b)with overland flow (water is dyed bright green). Fiedler et al., 2002

10 Evidences of non-equilibrium flow and transport processes

11 Evidences of non-equilibrium flow and transport processes

12 Evidences of non-equilibrium flow and transport processes 1 Non-reactive solute transport C/C D uniform model 2D solute Time (s) Manning s roughness coefficient n= 0.1( passive) and n=0.005 (active)

13 Evidences of non-equilibrium flow and transport processes Manning s roughness coefficient Solute transport

14 Physical non-equilibrium models Subsurface Equilibrium Model Non-Equilibrium Models Surface (a) Uniform (b) Horizontal MIM (c) Vertical MIM (d) Active-Passive Regions Model (e) APR with HMIM (f) APR with VMIM Simunke and van Genuchten, 2008

15 Equilibrium model vs Non-equilibrium models for Wash-off examples Simulated outflow rates and concentrations at the bottom boundary using equilibrium (UFT) and non-equilibrium flow and transport models (HMIM, APR, and APR-H).

16 Soil Erosion Under developing based on the Kineros2 (Kinematic Runoff and Erosion Model) soil erosion model

17 Conclusion and future works Physical non-equilibrium models may be better suited for studying hydrological processes at the plot and field scale than equilibrium models when spatial patterns of land surface characteristics are poorly characterized. The newly developed equilibrium/ non-equilibrium models will provide a comprehensive tool to numerically investigate many important research problems Additional modifications to the code are needed to consider other infiltration equations, and the full coupling between runoff water and the subsurface Describe the real world data will be the next step

18 References Fiedler, Fritz R., Frasier, Gary W., Ramirez, Jorge A. and Ahuja, Lajpat R., 2002, Hydrologic Response Of Grasslands: Effects Of Grazing, Interactive Infiltration, and Scale, Journal of Hydrologic Engineering, Vol. 7 (4): Pandey K.P., Kass H. Phillip, Soupir L.M., Biswas S., Singh P.V., Contamination of water resources by pathogenic bacteria. AMB Express 2014, 4:51 Simunek, J., Van Genuchten, M.Th, Modeling nonequilibrium flow and transport processes using HYDRUS. Vadose Zone J. 7 (2), van Genuchten, M. Th., A closed-form equation for predicting the hydraulic conductivity of unsaturated soils, Soil Sci. Soc. Am. J., 44, , Weill, S., E. Mouche and J. Patin A generalized Richards equation for surface/subsurface flow modelling. J. Hydrol., 366, 9 20.

19 Acknowledgment Dr. Jirka Simunek Dr. Scott Bradford Anne Hartmann Sarah Helalia All who ve been in the HYDRUS Group at UCR

20 Weill et al., 2009; Hromadka et al., 1985; Wasantha Lal, 1998 Fully-coupled surface/subsurface models surface water 2D Surface flow (Diffusion wave equation) h ground surface 2D Subsurface Flow (Richards equation) subsurface

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