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1. The unsaturated zone MetaSWAP-package Recent developments
Paul van Walsum Wageningen Environmental Research
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. 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. 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. 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. 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. Metafunction for the vertical flux q 7 q(pr,h): pr : mean
pressure head root zone h : groundwater level
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. Coupling to MODFLOW Two possible options for balances:
System Control volumes volume 10 Groundwater Unsaturated zone
Unsaturated zone Groundwater
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. 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. 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. 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. Coupling to crop growth model WOFOST Simulation of
production based on assimilation Feedback to hydrologic model with
dynamic crop parameters canopy resistance
16. Computational performance
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