1. 1. The unsaturated zone MetaSWAP-package Recent developments Paul van Walsum Wageningen Environmental Research
2. 2. Overview 1. Introduction 2. MetaSWAP concept for the unsaturated zone 3. Coupling to salinity model TRANSOL 4. Coupling to crop growth model 5. Conclusions 2
3. 3. Introduction Why MetaSWAP? Simple MODFLOW packages for unsaturated zone: EVT, ETS extinction function for capillary rise; soil water dynamics ? UZF1 kinematic wave for infiltration; capillary rise ? Advanced MODFLOW packages: VSF/REF1 Richards Equation Flow ; computation time ? 3
4. 4. MetaSWAP Water balance of 1D-Richards equation: : moisture content (m3 m-3) q : vertical flux (m d-1) : source term (m3 m3 d-1) 4 + =
5. 5. MetaSWAP Water balance of Richards equation: : moisture content (m3 m-3) q : vertical flux (m d-1) : source term (m3 m3 d-1) Solution procedure in two steps: Generate steady state profiles, store in database Combining steady state profiles with water balance during simulation coupled to groundwater model 5 + =
6. 6. MetaSWAP Steady state profiles: detailed vertical resolution 6 q (mm d-1 ) 1 0 -1 -2 -5 m 3 m -3 0.00 0.30 0.32 0.34 0.36 0.38 0.40 0.42 z (m) -2.0 -1.5 -1.0 -0.5 0.0 root zone h T > 0 I > 0
7. 7. Metafunction for the vertical flux q 7 q(pr,h): pr : mean pressure head root zone h : groundwater level
8. 8. Aggregation boxes for water balances Subgrid computational method 8 Aggregation box 1 (root zone) Aggregation box 2 Swap compartments Aggregation box 3 Aggregation box 4
9. 9. p (m) -0.8 -0.6 -0.4 -0.2 0.0 z (m) -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 4 d3 dt = 2 d box 1 (root zone) box 2 box 3 9 q (mm d-1) qtot (mm) Simulation of percolation: comparison with SWAP Infiltration = 16 mm/d
10. 10. Coupling to MODFLOW Two possible options for balances: System Control volumes volume 10 Groundwater Unsaturated zone Unsaturated zone Groundwater
11. 11. Coupling to MODFLOW Balance equation for communal control volume Implementation with Control volume dynamic storage coefficient (sc1) (hn ho) = (qmsw + qmod) t 11 Unsaturated zone Groundwater
12. 12. Verification of coupling MODFLOW-MetaSWAP Comparison MODFLOW-MetaSWAP with SWAP MODFLOW-dummy : only drainage flux 12 -2,5 -2 -1,5 -1 -0,5 0 3655 4020 4385 4750 SWAP MF-MSW h (m) Model N (mm/j ETact (mm/j) R (mm/j) SWAP 809 484 325 MF-MSW_1d 809 485 324
13. 13. Coupling to salinity model TRANSOL Dynamic mixing cell model of solute transport Analytic integration of time steps Vertical resolution same as Richards model Aggregation box 1 (root zone) Aggregation box 2 Swap compartments p(m) -0.8 -0.6 -0.4 -0.2 0.0 z (m) -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 4 d3 dt = 2 d box 1 (root zone) box 2 box 3
14. 14. TRANSOL dispersion, verfication with SWAP-CD Numerical dispersion Ldis,num=0.5*z For z = 5 cm Ldis,num=2.5 cm Equivalent to SWAP Ldis,num = 0.5*z = 0.5*1 cm Ldis,CD = 2 cm Ldis,tot = 0.5 + 2 = 2.5 cm
15. 15. Coupling to crop growth model WOFOST Simulation of production based on assimilation Feedback to hydrologic model with dynamic crop parameters canopy resistance
16. 16. Computational performance
17. 17. Conclusions MetaSWAP, the pros: fast (10-50X SWAP) emulator of Richards model water balance and groundwater dynamics stable and efficient coupling to MODFLOW Limitations: hill slope situations (1D instead of 2D) deep groundwater when timing of infiltration front is critical (cf. UZF1) 17
18. 18. Questions ? 18