UBC Theses and Dissertations
Examination of the design procedures for drainage/subirrigation systems in the lower Fraser Valley, British Columbia Prasher, Shiv Om
Techniques for designing drainage/subirrigation systems in the Lower Fraser Valley of British Columbia are examined in the present study. An attempt was made to formally define the overall goal in the design of such systems. Various difficulties were encountered in proceeding formally in the design. Therefore, a "branch and bound" approach was used in which a series of studies are conducted to focus our attention on the key issues of the problem and to regroup or eliminate other issues of secondary importance. A simple study showed that drainage designs seemed to be the limiting factors in drainage/subirrigation system designs for the Lower Fraser Valley. Therefore, subirrigation design was not considered in further analyses. The drainage requirements for different seasons were discussed. It was suggested that a drainage system designed to meet workability requirements in early spring should be more than sufficient to meet other seasonal requirements of interest from a drainage point of view. It was suggested that these requirements will be met by designing a drainage system that ensures at least one workable period of twelve days in March. A Markov chain model was proposed that can simulate the transitions in the water table elevations in response to weather. Design curves were presented for some local soils that can aid designers to perform drainage designs that satisfy requirements of the individual farmers. A study was undertaken to investigate the importance of uncertainty in soil parameters on the drainage system design. First and second order methods of analyzing uncertainty were applied to Hooghoudt's equation of designing drainage systems. The applicability of the uncertainty approach was extended to the numerical model of designing drainage systems based on the Boussinesq equation. An example problem was solved to illustrate how a drainage design criterion can be formulated when uncertainties due to both the climate and the soil parameters are present at the same time. Conclusions were drawn from the present study and recommendations were made for future work. The environmental impacts of agricultural drainage were discussed. They are included in the appendix because the main thrust of the thesis was on the design of drainage/subirrigation systems. Also, a design methodology was proposed in the appendix that can be used in designing drainage systems on a steady state basis in the absence of any knowledge about the saturated hydraulic conductivity of the soil or the location of the impermeable layer.
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