Modeling of water flow and solute transport through unsaturated zone using dual-porosity approach | |
| Author | Nguyen Duy Binh |
| Call Number | AIT DISS. no. WM-02-05 |
| Subject(s) | Streamflow Hydrologic models |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WM-02-05 |
| Abstract | It is recognized that macropores in soil contribute to rapid movement of water and solute through soils. The present study is an attempt to analyze the transport of water and solute in integrated unsaturated-saturated porous media considering macropore effect from agricultural fields. Chlorine-tracer experiments were conducted in relatively large soil columns ( 40-cm inside diameter and 120-cm length) in a field set-up to investigate effect of decayed plant root channels to solute transport process as well as to provide data for model calibration and verification. The columns were packed previously with air-dried soil samples collected in Kangpangsen and Kanchanabury, Thailand. Root channels were generated in the soil columns by growing maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] crops, and leaving the columns intact for one year before conducting chloride-tracer experiments. The solute concentration was monitored at two points along the column. The effluent quantity and quality were monitored in each partition at the bottom of the column during the experiments. The macroporosity in each of the soil columns was determined by using dye tracer technique. The macropores distribution showed a tendency of decreasing with depth. Majority of macropores were found in the 50-cm upper soil layer. The cross-area ratio of macropores with total column area varied from 0.03 m3 m-3 to 0.02 m3 m-3 in columns with plant root channels and less than 0.005 m3 m-3 in control columns. Experiment results showed that significant preferential movement of chlorine occurred in the decayed root channels. This preferential tendency was more pronounced in finer soil than in coarser soils. The two additional measured breakthrough curves at positions along each soil columns showed the effect of plant root channels was more significant at location near the soil surface. This effect is noticeable in term of both solute arrival times as well as of solute concentration peaks. A water flow and transport model based on dual-porosity approach (Gerke and van Genuchten, 1993) has been developed. The governing dual-porosity water flow and solute transport equations were solved numerically using the Galerkin finite element method assuming linear basis functions. An important aspect in the conceptual formulation of the model is that the macropore volume fraction is allowed to vary with space as well as time. The developed model was extensively tested for its validity by comparing its results with the known numerical solutions and published experimental data for a variety of initial and boundary conditions. The model was also tested and validated by, the above-mentioned field leaching experiment involving soil columns with quasi-created macropores. The good agreement in all the cases indicated that the developed model is useful and provides acceptable results. Numerical results obtained demonstrated the flexibility of the dual-porosity approach for simulating preferential movement of water and reactive chemicals in unsaturated-saturated macroporous soils. Discrepancy in measured and simulated breakthrough curves is attributed to inaccuracy of the estimated transport parameters of the dual-porosity medium. This estimation of realistic hydraulic and transport parameters is still considered as the biggest challenge remaining for applying models to macroporous fields. NOTE 502 Thesis (Ph.D.) - Asian Institute of Technology, 2003 |
| Year | 2003 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-02-05 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Gupta, Ashim Das; |
| Examination Committee(s) | Huynh Ngoc Phien;Clemente, Roberto S.; |
| Scholarship Donor(s) | Asian Institute of Technology; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2003 |