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1
Modeling reactive solute transport
coupled with flow in Cathy :
preparatory work.
Laura Gatel (Irstea Lyon, France)
23 s...
2
Context
Flow and solute pathways in agricultural hillsopes are complex to
precisly caracterize, particularly for what co...
3
Objectives
3-years PhD objectives :
● To develop a coupled surface / surbsurface flow and solute reactive transport mode...
4
Existing tools
Cathy flow
Coupled subsurface flow (FLOW3D)
and surface routing
(SURF_ROUTE) model
Variably saturated flo...
5
Context
Flow and solute pathways in agricultural hillsopes are complex to
precisly caracterize, particularly for what co...
6
Method
- Two study cases from the
literature (Gureghian 1983
and Huyakorn et al. 1985)
Merging of the two models
Validat...
7
Merging of the two model
Merged model
- Initialisation of surface and flow calculation
- Initialisation of reactive tran...
8
Validation
Test case 1 (Huyakorn et al. 1985) : case description
Transport of non-conservative solute in a unsaturated s...
9
Validation
Tran3d
Mergedmodel
0,053 d (1 h 15 min)0,165 d (4 h) 0,508 d (12 h)
Test case 1 (Huyakorn et al. 1985) : resu...
10
Validation
Vertical concentration
profiles at x = 3 cm and
three different times
Horizontal concentration
profiles at z...
11
Validation
Test case 2 (Gureghian 1983) : case description
Flow and transport in a ditch-drained aquifer with incident ...
12
Validation
Test case 2 (Gureghian 1983) : results
Concentration contours
Tran3dCombined model
15 days
45 days
13
Validation
Test case 2 (Gureghian 1983) : results
Concentration contours
Tran3dMerged model
→ Little differences observ...
14
Validation
Test case 2 (Gureghian 1983) : results
Mass balance
Inside mass
Entering mass
Exiting mass
d = 15
Solute inf...
15
Discussion
Even if there is little unexplained differences in the results of case 1, and inconsistent mass
balance for ...
16
Perspectives
Short-term objective :
From the last version of Cathy with non-reactive transport (probably Carlotta's
ver...
17
Perspectives
Mid-term objective :
● Validation :
1- Apply the new model to a hillslope (Morcille's
catchment, Beaujolai...
18
Thank you for your attention !
References :
Camporese M., Paniconi C., Putti M., and Orlandini S. (2010). Surface and s...
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Laura Gatel

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Reactive solute transport coupled with flow in Cathy: preparatory work

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Laura Gatel

  1. 1. 1 Modeling reactive solute transport coupled with flow in Cathy : preparatory work. Laura Gatel (Irstea Lyon, France) 23 septembre 2015
  2. 2. 2 Context Flow and solute pathways in agricultural hillsopes are complex to precisly caracterize, particularly for what concerns surface/subsurface exchanges and lateral transfers. Modelisation can help, and in order to obtain accurate results on those kind of domains, the use of a physically-based model is required. Study site at the Morcille catchment (Beaujolais) First work centered on vagatative buffer strip zones : Those areas are a way to limit solute transfers from the field to aquatic environments and particularly activ for what concerns water infiltration. → About the influence of soil heterogeneity on surface and subsurface flow Example of 3 saturated conductivity statistical fields Generation of statistical fields with variable characteristics (correlation, enforcement with measured conductivity values, ... ) Comparison of the runoff and subsurface patways with field data on three events → Results are very sensitive to the conductivity dictributions → Generated hydrodynamic parameters with enforcement are quite close to data → Need to take into account microtopography
  3. 3. 3 Objectives 3-years PhD objectives : ● To develop a coupled surface / surbsurface flow and solute reactive transport model in 3D based on the Cathy model. ● Validate the model at the hillslope scale with a global sensitivity analysis and the comparison with field data (large database from Irstea Lyon on two hillslopes of the Morcille catchment, Beaujolais, France) ● Upscaling from hillslope to catchment INRS summer 2015 session obectives : ● Merge a calculation flow model and a reactive transport model ● Compare the results of this new model with two litterature examples and control the mass balance.
  4. 4. 4 Existing tools Cathy flow Coupled subsurface flow (FLOW3D) and surface routing (SURF_ROUTE) model Variably saturated flow 3D subsurface calculation : finite elements (FLOW3D) Tran3d Solute transport model with decay and linear sorption Variably saturated flow 3D Advection, sorption and decay resolved with finite elements BUT no flow calculation → steady state cases only
  5. 5. 5 Context Flow and solute pathways in agricultural hillsopes are complex to precisly caracterize, particularly for what concerns surface/subsurface exchanges and lateral transfers. Modelisation can help, and in order to obtain accurate results on those kind of domains, the use of a physically-based model is required. Study site at the Morcille catchment (Beaujolais) First work centered on vagatative buffer strip zones : Those areas are a way to limit solute transfers from the field to aquatic environments and particularly activ for what concerns water infiltration. → About the influence of soil heterogeneity on surface and subsurface flow Example of 3 saturated conductivity statistical fields Generation of statistical fields with variable characteristics (correlation, enforcement with measured conductivity values, ... ) Comparison of the runoff and subsurface patways with field data on three events → Results are very sensitive to the conductivity dictributions → Generated hydrodynamic parameters with enforcement are quite close to data → Need to take into account microtopography
  6. 6. 6 Method - Two study cases from the literature (Gureghian 1983 and Huyakorn et al. 1985) Merging of the two models Validation Application to a real hillslope (Beaujolais, France) Massbalance calculation
  7. 7. 7 Merging of the two model Merged model - Initialisation of surface and flow calculation - Initialisation of reactive transport calculation Beginning of the time loop - Surface flow calculation - Subsurface flow calculation Backstepping if necessary - Reactive transport calculation (only one resolution for advection, sorption and decay) End of the time loop Tran3d : - Initialisation of reactive transport calculation - Integration of steady-state results Beginning of the time loop - Reactive transport calculation (only one resolution for advection, sorption and decay) End of the time loop Cathy flow : - Initialisation of surface and flow calculation Beginning of the time loop - Surface flow calculation - Subsurface flow calculation End of the time loop At each time step, reactive transport calculation is based on the flow calculation results : the merging allows the study of no-steady state cases ● At each step, flow and transport are calcultated with the same Δt (if necessary, backsteping occurs after subsurface flow and before transport) ● Surface transport isn't take into account.
  8. 8. 8 Validation Test case 1 (Huyakorn et al. 1985) : case description Transport of non-conservative solute in a unsaturated soil. 3D mesh as modelised in the merged model (surface of 10 cm * 15 cm and 10 cm deep) with steady-state pressure in the domain. Boundary conditions used for the test case. 2D mesh (15 cm wide and 10 cm deep). Reactive transport : Dispersion αL = 1 cm αT = 0 Diffusion 0,01 cm²/d Sorption Rd = 2 Decay 0,001 d-1
  9. 9. 9 Validation Tran3d Mergedmodel 0,053 d (1 h 15 min)0,165 d (4 h) 0,508 d (12 h) Test case 1 (Huyakorn et al. 1985) : results Concentration contours Mass balance : For each time step of this run, mass balance error stayed between 0,01 % and 1 %
  10. 10. 10 Validation Vertical concentration profiles at x = 3 cm and three different times Horizontal concentration profiles at z = 10 cm and three different times t = 0,053 d t = 0,165 d T = 0,508 d Tran3dMerged model Test case 1 (Huyakorn et al. 1985) : results Relative concentration
  11. 11. 11 Validation Test case 2 (Gureghian 1983) : case description Flow and transport in a ditch-drained aquifer with incident steady rainfall and infiltration of solute 3D mesh as modelised in the merged model (surface of 10 cm * 15 cm and 10 cm deep) with steady-state pressure in the domain. → 176 nodes for the plan (XZ) Boundary conditions used for the test case. 2D mesh ( 100 cm wide and 50 cm deep). → 176 nodes The mesh is not exactly reproduced, because Cathy flow does not allow unregular mesh. Reactive transport : Dispersion αL = 0,5 cm αT = 0,1 cm Diffusion 1e-5 cm²/d Sorption - Decay -
  12. 12. 12 Validation Test case 2 (Gureghian 1983) : results Concentration contours Tran3dCombined model 15 days 45 days
  13. 13. 13 Validation Test case 2 (Gureghian 1983) : results Concentration contours Tran3dMerged model → Little differences observed between tran3d and merged model results in the shape of the non-zero concentration zone. In this case, the slightly different used mesh could explain this variations. 90 days 120 days
  14. 14. 14 Validation Test case 2 (Gureghian 1983) : results Mass balance Inside mass Entering mass Exiting mass d = 15 Solute infiltartion stops d ~ 70 Solute shape reaches seepage faces If we continue the run until 600 d ...
  15. 15. 15 Discussion Even if there is little unexplained differences in the results of case 1, and inconsistent mass balance for seepage faces, the coupled model gives good results on those two simple examples. But in other situations, when concentration evolutions are less « smooth » (less or no dispersion or diffusion for example), the model becomes unstable and the user have to carrefully choose the time stepping to avoid concentration explosions. → It will not be enough stable to modelise complex hillslopes caracterized by important heterogeneity (with no string conditions on mesh or time steps) Solution : separate advection and reaction parts and calculate advection as finite volumes (see S. Weill et al. 2011).
  16. 16. 16 Perspectives Short-term objective : From the last version of Cathy with non-reactive transport (probably Carlotta's version with velocity fields reconstruction), integrate sorption and decay equations. Construction scheme of the last version of transport on Cathy : Initialisation Beginning of the time loop Surface flow Surface transport Subsurface flow Subsurface transport - advective part → finite volume - reactive part (for now, only dffusion and dispersion) → finite elements End of the time loop Addition of linear sorption and first order decay
  17. 17. 17 Perspectives Mid-term objective : ● Validation : 1- Apply the new model to a hillslope (Morcille's catchment, Beaujolais). The site is instrumented since more than a decade → a large database to compare with the model. 2- Global sensitivity analysis • Upscaling : Apply the model to the entire Morcille catchment and compare results with actual data (all in all 3 sites instrumented sites on the catchment). Rabiet et al. (2015) Boivin(2007) St-Joseph site on the Morcille Catchment
  18. 18. 18 Thank you for your attention ! References : Camporese M., Paniconi C., Putti M., and Orlandini S. (2010). Surface and subsurface flow modeling with path-based runoff routing, boundary condition-based coupling, and assimilation of multisource observation data. Water Resources Research, 46(2). Gambolati G., Pini G., Putti M. and Paniconi C. (1994). Finite element modeling of the transport of reactive contaminants in variably saturated soils with LAE and non LEA sorption. Environmental Modeling vol. 2, ch. 7, pp. 173-212. Paniconi C., Wood E. (1983). A detailed model for simulation of catchment scale subsurface hydrologic processes. Water resources Research, 29(6):1601-1620. Weill S., Mazzia A., Putti., Paniconi C. (2011). Coupling water flow and solute transport into a physically-based surface-subsurface hydrological model. Advances in Water Resources vol 34, pp 128-136.

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