Simulation of water flow in the soil under subsurface porous clay pipe | |
| Author | Ashrafi, Shahram |
| Call Number | AIT Diss. no.WM-00-03 |
| Subject(s) | Hydraulics Subirrigation |
| Note | A dissertation submitted in partial fulfilment 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-00-03 |
| Abstract | Subsurface irrigation can be used to improve irrigation uniformity and water use efficiency in a number of different cropping systems by supplying a low volume of water to crop root zones. Application of the porous clay pip in subsurface irrigation is an improvement to the traditional subsurface irrigation method in which both conveyance and seepage of the water can be carried out instantaneously by the same pipe. Knowing the effect of soil texture on the emission characteristics of the pipe and the relationship between the hydraulic head-emission rate in different soil textures is important both for the design and management of subsurface irrigation system. Determination of the relationship among the lateral spacing of the pipelines, installation depth of the pipe, i1rigation run time, hydraulic conductivity of the pipe, and the required hydraulic head in the system was the major objective in this study. Advances in the subsurface porous clay pipe irrigation rely on knowledge of the distribution of water in the soil. Part of this information can be obtained from numerical models developed for water flow in unsaturated soils. The computer model adopted here is an extension to the VS2D computer program developed by the U. S. Geological Survey, which simulates the movement of water through variably saturated porous media. The body of the pipe is considered as a part of the flow domain with a special class of soil. A special soil bin was designed and laboratory experiments were conducted on two different soil textures, fine sand and sandy loam, to validate application of the proposed model for simulating the infiltration from porous clay pipe in subsurface irrigation method. The obtained result suggests that the model is applicable to many field conditions in the subsurface porous pipe irrigation method. To determine the effect of the soil texture and capillary conditions of the soil in the flow domain on the emission characteristics of the pipe, the soil bin and experimental soils were used and laboratory experiments were carried out at different hydraulic heads on each soil. It was found that, when the pipe is not buried in the soil, the emission rate of the pipe is a linear function of applied hydraulic head and it can be calculated using Darcy's Law. Under unsaturated condition, interaction between the capillary forces in the flow domain and body of the pipe causes significant changes to the emission rate. Experimental fine sand had more effect on the emission characteristics of the pipe compared to sandy loam soil. The main contribution of this study to the science is that, we developed a method for designing the subsurface porous clay pipe irrigation system. The lateral movement of the moisture and wetted soil profile beneath the pipe during the infiltration and redistribution processes are calculated using the developed equations in this study. To determine the effect of different hydraulic and physical factors on the wetting zone geometry, computer simulations were carried out using the developed model in the first part of this study. It was found that the soil type, the volume of water applied to the soil, and the installation depth of the pipe, are the major factors affecting the wetting zone geometry. Dimensional analysis was employed to develop the relationships among the hydraulic and physical variables in the system. Three different soil textures were used in the computer simulation and a dimensionless graph was obtained for each. To design the system, the relationships among the hydraulic and physical variables in the system are presented in the developed dimensionless graph for each textural class of the soil. It was found that, the unsaturated 11 hydraulic conductivity of the soil is an important factor for creating the wetted zone in the soil. For a given volume of water soils with higher values of unsaturated hydraulic conductivity provide a wider wetted zone. It was found that in a uniform soil profile, the depth of wetted soil profile beneath the pipe during the infiltration and redistribution processes is independent of the installation depth of the pipe. |
| Year | 2001 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-00-03 |
| 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;Loof, Rainer; |
| Examination Committee(s) | Izumi, Norihiro ;Clemente, Roberto ;Babel, Mukand Singh ;Noppadol Phien-wej ;Bouwer, Herman ; |
| Scholarship Donor(s) | Iranian Agricultural Research, Education and Extension Organization (AREEO) ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology,2001 |