Soil hydraulic characterization and hydrologic modeling of sloping agricultural lands in Uma Oya Watershed, Sri Lanka | |
| Author | Rivas, Aldrin Alameda |
| Call Number | AIT Thesis no.WM-04-05 |
| Subject(s) | Hydrologic models Soils--Quality Slopes (Soil mechanics) |
| Note | A thesis submitted in pa1tial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | The highlands of Sri Lanka are generally considered as agriculturally productive and yield potentials are high. However, in recent years, most agricultural lands in the hilly areas are being over-exploited, ignoring long-term negative impacts on the soils and the environment. Different forms of cropping can also modify soil conditions which can have positive or negative consequences on the soil quality. Thus the objective of this study was to evaluate the effects of different cropping patterns under different terrains in the Welimada division of the Uma Oya watershed on soil quality using selected soil hydraulic characteristic indicators, to identify which among the considered land use or cropping patterns provides favorable effects on soil hydraulic quality for crop growth and production, and to characterize behavior of hydrologic processes on sloping lands in relation to soil hydraulic properties. The soil hydraulic characterization involved measurements of infiltration, hydraulic conductivity, moisture retention characteristics, texture and organic matter in selected zones of the watershed. Typical transects or hillslopes were selected based on varying land use and slope. These transects were divided into 3 or 2 field sites which are categorized as upland (rainfed) or lowland (irrigated). The slope ranges considered per rainfed or irrigated fields are: <30%, 30-60%, and >60%, and several cropping patterns are selected at different slope ranges along the hillslope. A more integrated approach was also adopted to compare the hydraulic quality of soils under different land use or cropping patterns. Analysis of the data gathered indicated that the effects of different cropping patterns on soil hydraulic properties are more pronounced in the rooted subsoil layer. Some soil properties had significant differences with respect to different slope ranges but there was no clear trend among them. Also, among the measured soil properties, principal component analysis (PCA) identified the dominant factors that affect soil hydraulic quality between cropping patterns as follows: field saturated hydraulic conductivity, soil organic matter, permanent wilting point, pore size and distribution, percent sand, root density, aggregate size, and packing density. Further, applying PCA to rank the soil hydraulic quality of different cropping patterns, the potato-fallow-vegetable-fallow two-year cropping rotation was identified as providing the more favorable effects on the soil hydraulic quality in the context of enhancing crop growth and production. Hydrologic modeling was also applied to describe the behavior of hydrologic processes of two different watersheds in relation to the hydraulic properties of soils. The two small sub-watersheds selected for comparison consisted of a cultivated watershed of 1.69 ha in size with mixed characteristics, covering terraced and non-terraced fields of varying slopes (25-60%), and a noncultivated watershed (secondary forest) of 0.35 ha in size and has 23% average slope. With the use of HEC-HMS model to relate soil hydraulic properties and hydrologic processes, it was found that infiltration capacity has a very high influence on rainfall-runoff relationship. This was obtained through a sensitivity analysis of selected input parameters measured in the field. |
| Year | 2005 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Clemente, Roberto S. |
| Examination Committee(s) | Gupta, Ashim Das;Ranamukhaarachchi, S. L.;Babel, Mukand S. |
| Scholarship Donor(s) | Government of Denmark (DANIDA) / Asian Institute of Technology Fellowship |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2005 |