This paper focuses on clarifying the present water management practice at the on-farm level in the upper Chao Phraya Delta based on detailed field surveys, and discusses the problems of water management including the development of farmers' water management organizations. The Thai government has implemented a target area policy to give farmers equal opportunities to access water during the dry season and created systematic water management plans including farmers' participation in water management. The target area policy is not fully successful because of the difficulty in controlling farmers' intakes. According to the field surveys, upstream farmers have an advantage of taking water from both lateral irrigation canals and irrigation ditches. In the upstream area of the lateral canal, rice planting was finished in about 40 days, the shortest duration of the survey areas. Downstream of the irrigation ditch, due to insufficient water, farmers reuse drainage water by either pumping up from a lateral drainage canal or by checking a field drain. This reveals that the thorough reuse of drainage water contributes to increasing the area of the dry-season rice cropping. Variations in both the timing and the water sources for rice planting make the farmers difficult to cooperate within the beneficiary area of an irrigation ditch, thus the farmers' water management organizations are not functioning effectively.

View full abstract

A contingent valuation method (CVM) was applied to data from an original survey of 2, 584 in Kohoku region in Shiga prefecture to quantify residents' appreciation of multiple function of regional water. The survey was used a double-bounded dichotomous choice to elicit residents' willingness to pay (WTP) and WTP were derived from a probit model. The results indicate that residents in Kohoku area are willing to pay as much as those in Nagahama city. The median annual values per household are 2, 350 yen and 2, 073 yen respectively, and the mean annual values per household are 4, 571 yen and 4, 302 yen. These estimates are seem to be correlated closely with responses about maintenance of irrigation canals. Sex, age, and whether he or she is a member of a farm household or not are shown to have no influence on the WTP estimates. Comparisons with similar studies suggest that residents of each region appreciate the regional water equally.

View full abstract

A contingent valuation method (CVM) was applied to data from an original survey of 2, 584 in Kohoku region in Shiga prefecture to compare residents' appreciation of multiple function of regional water between groups divided by personal attributes/characteristics and characteristics of settlements. The survey was used a double-bounded dichotomous choice to elicit residents' willingness to pay (WTP) and WTP were derived from the Turnbull Scheme. The results indicate that the difference in the WTP estimates is negligible between the groups divided by sex, age, and whether he or she is a member of a farm household or not. One of the problems in Kohoku region is a share of the expense and work for maintenance of irrigation canals between farm households and non-farm households. Non-farm households appreciate the multiple function of regional water in Kohoku Canals as much as farm households. The WTP estimates have statistically significant differences between upstream settlements and downstream ones. This result would stem from consciousness derived from the geographical condition.

View full abstract

An operation model is developed to control flow size of irrigation water by combining two sub-models. These are: Sub-model 1 to determine the necessity of changing the flow size using the Hayashi's “Quant 2” theory; and Sub-model 2 to determine the magnitude of the necessary change in flow size using the fuzzy set theory. A parameterization technique is applied for deriving the production rule tables in Sub-model 2. This operation model is named as integrated operation model to be applied to the decision-making process for controlling intake flow size of irrigation water. An application example demonstrates the validity of this integrated model. The model performance is improved when threshold values for decision indicators are introduced.

View full abstract

A lot of methods for in-situ measurement of saturated hydraulic conductivity have so far been proposed, however, most of them rarely focused on the measurement in and land or discussed on the suitable measurement method considering soil structure. In the present study, saturated hydraulic conductivity in the research area of Leonora in Western Australia, classified to semi-dry area, was measuretl by using falling head method, Guelph permeameter method and cylinder intake rate method. We also made their characteristics and mutual correlation clear and analyzed the soil structure of each measuring point. The results on saturated hydraulic conductivity for bare soil measured by falling head method indicated that the coefficient of variation was small, 30.6' 58.9% compared to the results for wet land. The geometric mean of the values measured by falling head method for vertically different points was close to the overall value estimated from the results on permeation rate by Guelph permeameter method. It was concluded that application of multiple measurement methods for saturated hydraulic conductivity with different principles and their mutual comparison are essential to analyze the soil structure.

View full abstract

Cracks play important roles in drainage efficiency in clayey agricultural fields. Controlling location, depth width of cracks has a substantial meaning in utilizing clayey paddies for cultivating various crops. Many researchers pointed out that cracking pattern in the agricultural fields is determined by many factors. Among them, effect of transpiration from cultivated crops is one of the most important determinants of cracking patterns when we aim to control them as farming operations. The present study clarified the effect of transpiration from row-planted crops on the location of linear inter-row cracks using numerical simulations based on two-dimensional elastic consolidation model. The model describes bidirectional movement of water induced by transpiration, and predicts the locations where tensile effective stress is generated. The validity of the model was tested by laboratory experiment. The experiments revealed occurrence of cracks induced by bidirectional water movement, and correspondence between the locations of cracks and predicted distribution of tensile stress as well. Further numerical simulations demonstrated that the distribution of tensile effective stress has single or double peaks depending on the row spacings, which possibly account for the number of linear cracks at inter-row spacing.

View full abstract

An activated sludge reactor was integrated into an anoxic-aerobic submerged biotilter process to improve its performance. The reactor integrated was divided into a small sedimentation and activated sludge compartments. To enhance settling characteristics of the sedimentation basin, an inclination plate was set. From the laboratory experiment, angle of the inclination plate and distance between the divider and inclination plate were approximately 70° and 2 cm, respectively. It was also concluded from the laboratory experiment that performance of activated sludge process was higher than that of submerged biofilter process on COD removal and nitrification. After completing the laboratory experiments, the pilot-scale experiment was carried out using a plant based on the principle of the anoxic-aerobic submerged biofilter process. Primary aerobic compartment of the pilot-scale plant was used as submerged biofilter or activated sludge tanks. As the results obtained in the laboratory experiments, nitrification performance of the plant was increased by using the primary aerobic compartment as the activated sludge tank.

View full abstract

As lake sediments are one of the cause of eutrophication, their effective use has been considered. When they are used as soil in a land, proper permeability is required. However, soil permeability has not completely been understood due to diversity of clays and organic compounds. We clarified permeability characteristics of Lake Kojima sediment, non-swelling clayey soil, by measuring saturated hydraulic conductivity (K). Decrease in K with percolation of dilute electrolyte solution was small when Ca was adsorbed by the soil. Particularly, decrease in K at pH11 was the smallest, because soil structure became stable with chemical reaction between soil particles and Ca. On the other hand, when Na was adsorbed, decrease in K was the smallest at pH5, and it became larger as soil pH increased. The obtained results could be explained qualitatively by the diffuse double layer theory.

View full abstract

Various methods exist to predict settlement of a soft ground by using measured data. The hyperbolic method is the most popular one. While, the logt method is often used for prediction of the secondary consolidation. It is sometimes difficult to determine the starting time of the logt prediction. The method to identify the parameters of the primary and the secondary consolidation simultaneously is proposed to solve this problem in this study. To verify the applicability of the method, following data sets are analyzed: 1) long term consolidation test results, 2) kaolin clay consolidation test result, 3) undisturbed alluvial marine clay test results, and 4) measured settlement data of an actual soft ground.

View full abstract

The mechanisms of in-situ rock shear tests were investigated for the sake of constructing a theoretical method for the estimation of the strength of rock masses. Localized failure in the testing process was especially noticed, and it was treated with Mohr's failure criterion. The investigation consisted of experiments on gypsum models whose conditions were similar to those in in-situ rock shear tests and of stress analyses for these experiments. Theoretical interpretations of the characteristic cracking process and of the mechanisms of the appearance of shear strength, measured by in-situ rock shear tests under relatively low normal stress with the uniaxial compressive strength, were obtained from the results. No macroscopic discontinuity was considered for the sake of the resolution of the fundamental characteristics of the testing method.

View full abstract

Farmland consolidation was carried out in the terrace paddy field areas in Ishikawa prefecture, and the production basis was greatly improved. Water management investigation was carried out in this region, and the situation after the improvement was examined. The results obtained are as follows: 1) Almost three years were needed after the farmland consolidation for all beneficiaries to have a confirmation that the consolidation had improved the conditions of water utilization. In 1999, the total water supply for the paddy field during the irrigation season was 910mm, 46% of which was from irrigation ponds and 54% from rainfall. The ratio of available rainfall was 77%. 2) Irrigation pond managers carried out supply management following the standard measurement of supply discharge indicated by the levels of the storage set for each Irrigation pond. They had to watch the timing of optimal supply discharges for 24 hours, which was as hard a labor as had been required before the consolidation. 3) The storage rate of the irrigation pond kept decreasing from the start of irrigation. A critical phase would be caused if the storage rate went down to 50% or less by the middle of June (the beginning of intermediate drainage from the paddy field). In order for irrigation ponds to be filled and to maintain storage discharge after the intermediate drainage, the simulation result indicated that about 700mm of rainfall, which corresponds to a period of four return years, would be needed from the beginning of irrigation until the end of the rainy season.

View full abstract