1. 1 THE EVALUATION / APPLICATION OF HYDRUS-2D MODEL FOR SIMULATING MACRO-PORES FLOW IN LOESS SOIL XU Xuexuan, HUA Rui, GAO Zhaoxia 24 Aug. 2016

2. 2 CONTENTS 1.Research Background 2.Materials and Methods 3.Hydrus2D Simulating 4.Discussion and Conclusions

3. 3 Step 1 Step 2 Step 3 Perferential flow discovery Schmachaer(1986) Lawes(1982) Beven(1982) Methods to describe macropores Dye tracing CT scanning permeability testing Solution penetration curve mathematical model Perferential flow Mechanism MIM, DP, CDE model Influencing factor Boundary condition 1 Research Background ISWC, CAS/MWR, YANGLING,CHINA

4. 4 Tableland and gully Region in the South part of loess plateau

5. 5 Soil properties Particle size 2~0.25mm0.25~0.05mm0.05~0.01mm0.001~0.01mm0~0.001mm %0.107.1757.7820.8914.18 Table 1 soil particle size distribution The experimental soil was Heilu soil. The initial bulk density was 1.3 g∙cm -3 。 2 Materials and Methods According the particle size distribution, it is the clay soil

6. 6 Soil Types n KsKs l Heilu soil0.0360.485*0.0081.57080.0270.5 Quartz sand0.05490.4470.03524.03391.072060.5 θr : soil residual moisture, cm 3 ∙cm -3 ; θs : soil saturated water content, cm 3 ∙cm -3 α : parameters related to soil physical properties, cm -1 ; Ks : saturated hydraulic conductivity, cm∙min -1 ; n : fitting parameters; l : the pore continuity parameter, generally take 0.5; h: soil water pressure soil parameters used in Van Genuchten-Mualem model 2 Materials and Methods

7. 7 experimental device stainless steel wire mesh (60 mesh) f ɸ = 0.5 cm steel wire strips 2 Materials and Methods

8. 8 Fig. 1, macropores and its tortuosity in Heilou soil  macro-pores tortuosity types ( Ti) : T0(CK), T1, T1.2, T1.5, T2 and T3.  i represented tortuosity values. Macro-pores’ tortuosity-- Tortuosity is ratio of macro-pores actual length to vertical depth. 2 Materials and Methods

9. 9 Figure 2: Six types of macro-pores Continuity O—Open, means connected with soil surface or the bottom of the outflow port; C---Closed, means disconnected with the soil surface or not connected with the bottom of the outflow port; N(n) was the length and number of macro-pores. L or S was macro-pores shape. The macro-pores’ Continuity 2 Materials and Methods

10. 10 2 Materials and Method— HYDRUS-2D

11. 11 Definite conditions of soil macro-pores flow movement soil box contained three layers : quartz sand(EH) = 1 cm, soil (HI)=60cm, and quartz sand(ID)= 3cm AE=6cm, AB=30cm. h0 is the initial suction. It could be considered that water instantly filled pores after experiment started in open macro-pores soil column. the pressure head linearly increased with macro-pores depth increased 3 Hydrus2D Simulating

12. 12  Close macro-pores boundary: When the water did not reach, the water flux was zero. When the water reached and the soil was saturated, the water pressure was zero.  Neither of upper nor lower connected macro-pores : due to the larger longitudinal computational domain, it could be considered soil water couldn’t reach the bottom boundary in the calculation time, and no water exchanged in boundary.  Both up and down connected macro-pores in the soil column, the water would quickly flow through the soil and produce runoff. Where: t0 is the critical value of the flux change time, min; q1, q2 represent flux values: determined by the measured values. 3 Hydrus2D Simulating

13. 13 Tortuosity-- note ： 1 ） white line ---measured 2 ） Legend is for soil moisture ， cm 3 cm -3 Simulated processes of wetting front migration with different tortuosity T1T2T1.5 CKT3 T1.2 10 min60 min120 min240 min 300 min 420 min180 min 3 Hydrus2D Simulating The numerical simulation of wetting front movement

14. 14 Continuity- The numerical simulation of wetting front O-C-30(3) C-C-30(3)C-O-30(3)O-O-30(2)-60(1)O-C-L-S O-O-L-S 10 min 60 min20 min 30 min 120 min 240 min300 min 420 min 10 min20 min 30 min note ： 1 ） white line ---measured 2 ） Legend is for soil moisture ， cm 3 cm -3 Simulated processes of wetting front migration with different continuity 3 Hydrus2D Simulating

15. 15 The CONPARING of simulated and measured values of wetting area dynamic under different continuity and tortuosity of artificial macro-pores Left: Tortuosityof artificial macro-pores Right : Continuity of artificial macro-pores 3 Hydrus2D Simulating. The measured values ___The simulated values

16. 16 T1T1.2T1.5T2T3CK MRE1.09%-2.44%-0.98%1.77%2.05%-0.57% R2R2 0.9900.9970.999 O-C-30(3)C-O-30(3)C-C-30(3)O-O-30(3)-60(1)O-C-L-SO-O-L-S MRE4.59%-0.80%5.79%1.12%2.18%4.49% R2R2 0.9880.999 --0.9950.989 Table 2. The evaluation on the simulation results of macro-pore’s tortuosity Table 3. The evaluation on the simulation results of macro-pore’s continuity 3 Hydrus2D Simulating

17. 17 4 Discussion and Conclusions  Convection–dispersion equation (CDE model) in porous media is not fitted for structured soil.  Two-domain flow models is much good at simulating water flow when preferential flow occurs. DP (dual- permeability) model is better than MIM model (mobile and immobile regions moddel)  Hydrus model (MIM and DP models) was based on the theory of soil water movement in heterogeneous medium. Therefore, the Hydrus model was much more perfect theoretically than CDE models.

18. 18  Hydrus-2D can be used to simulate soil wetting front process containing different tortuosity and continuity macro-pores in loess soil. MRE less than 5%, R2 greater than 0.9.  It was illustrated that the established Hydrus-2D model and the definite conditions of model were feasible and reasonable. Namely, Hydrus-2D model could simulate the infiltration behavior in loess soil, and the basic hydraulic parameters of Heilu soil are also reasonable.  Our research therefore agree with many previous researches, and also support that structure soil obviously contained more macopores, and its water flow could be chartered largely by the hydrus 2D model. 4 Discussion and Conclusions

19. 19 Contact Us Phone: 13709229201 Email: xuxuexuan@nwsuaf.edu.cn Thank you Thank you Prof. XUXue-xuan Institute of soil and water conservation, CAS & MWR No. 26, Xinong Road, Yangling, Shaanxi,CHINA Postcode: 712100