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008 240699s1994 th uzm rtt 00| a1eng d
035 _a.b10448809
099 9 _aAIT Diss. no. IR-94-01
100 0 _aOdhiambo Lameck Odeck
245 1 0 _aModeling water balance components in relation to field layout in lowland paddy fields
260 _aBangkok :
_bAsian Institute of Technology,
_c1994
300 _a222 leaves
490 1 _aDissertation ;
_vno. IR-94-01
500 _aA dissertation submitted in partial fulfillment of the requirement of the degree of Doctor of Technical science, School of Environment, Resources and Development
502 _aThesis (Ph.D.) - Asian Institute of Technology
520 _aThe various types of field layout in lowland paddy fields influence the field water balance in different ways leading to different design requirements for different land, hydrological conditions, and water management practices. The aim in this study is threefold; first, to develop a water balance simulation model applicatiable to lowland paddy fields; second to analyze the influence of different types of paddy field layout design on the field water balance condition under different land,hydrological conditions, and water management practices; and thirdly to develop producers for selecting the optimal types of field layout and water management practices when improvment of the field water balance condition is the prime objective. In the first case a water balance simulation model was developed and validated using data collected from controlled plot experiments conducted at the Asian Institute of Technology experimental farm. The model is organized into a main program and five independent modules for simulating specific hidrologic and/ or hydrologic processes in the water balance system. In the second case, the model was applied to analyze the water balance components in a large irrigated area and to dianose the shortcomings in the existing layout structure and water management practices. In the third case, simulation experiments were conducted using the model developed to investigate the influence of idealized field layouts on the water balance condition under different land and hydrological conditions and water management. The results of model application to a large irrigated area show that water loss from the field was mainly by surface runoff (over 50%) due to a combination of field physical conditions, water management and layout factors. Poorly maintained paddy bunds and lack of adequate on-farm water control structures appeared to have a more significant influence. Seepage and percolation losses, contributed less than 15% of the loss. The overall results of the numerical experiments indicate that significant improvment in the performance of plot-to-plot irrigation systems can be achieve by appropriate sizing of stream size, bund heights, spillway size, block size, and number or plots and order of plot arrangement by size. By using the developed water balance-field layout model, appropriate irrigation stream size, bund heights and spillway dimensions can be selected for any field condition. A method of evaluation consisting of an index and scale was introduced to measure the extent to which different layouts impacts either positively or negatively on the field water balance conditions. These were interpreted in the light of results from the simulation experiments and use to develop a criteria for selecting optimal field layout for various categories of land conditions, rainfall, and available irrigation supply. Use of the evaluation indicators and scale facilitated making dicisions about which layout best meets the various water balance objectives. Hence it provided a procedure by which different types of layout could be evaluated for selection, comparison or improvement
650 0 _aWater balance (Hydrology)
700 1 _aMurty, V.V.N.,
_eChairperson
700 1 _aKono, Y.,
_eExamination committee
700 1 _aMurali, N. S.,
_examination committee
700 1 _aMizutani, M.,
_eExamination committee
710 2 _aJapan International Co-oparetion Agency (JICA),
_eScholarship donor
810 2 _aAsian Institute of Technology.
_tDissertation ;
_vno. IR-94-01
856 _3Full-Text
_uhttp://203.159.5.9/ait-thesis/detail.php?q=B00027
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