This study aims at improving the accuracy for estimating probable extreme values with long return periods, such as 200 or 500 years, and this analysis utilizes annual daily maximum rainfall data observed in more than 100 years at 83 observatories of the Japan Meteorological Agency. At 71 observatories, the parameter k, known as the GEV shape parameter, had a value from -0.2 to 0.0, and it had a tendency to converge in a narrower range or on a particular value as the sample number increases. In this study, the shape parameter k was fixed to a certain value, which is equivalent to reducing GEV parameters from 3 to 2, and this procedure had an effect to reduce the unstableness of estimating probable extremes. It suggests this procedure will increase the reliability of probable extreme value estimation, for such observatories as having shorter observation periods, by applying the k value at -0.1 as the nation-wide average value or at the average value obtained within a certain smaller region.
Predicting soil moisture of arable lands under climate change is important and useful for yield prediction and adaptation under the climate change. For predicting soil moisture condition of agricultural lands, spatial and temporal scale of input climate data is favorable to have similar scales of water and heat transport phenomena at agricultural lands. We investigated methods of downscaling the General Circulation Model (GCM) projections, which generally have monthly resolution, to hourly scale for predicting soil water condition of agricultural lands. In this study, stochastic weather generators were used to reproduce climatic variables. Predicted soil moisture well responded to rainfall events when downscaled hourly rainfall records produced by using weather generators and the monthly GCM projections were used as input data. Direct use of rainfall records of monthly GCM projections could not produce acceptable response of soil moisture content. These results suggested proper methods for temporal downscaling of rainfall records are important to give precise prediction of soil moisture of agricultural land under future climate change. Also, weather generator is one of the useful tools for acceptable temporal downscaling.
In Taiwan, decontamination of heavy-metal polluted land has been conducted since 2000 under the Soil Contamination Countermeasures Act. The large part of polluted-farmland has been decontaminated successfully. However, the recent study shed the light on the issue of fallow and abandoned farmland which experienced decontamination treatment. The objective of this study is to clarify the present land use of decontaminated farmland and to identify the geography factors affecting re-cultivation of farmland after the decontamination treatment. We took Chang-hua as a case study area, which is known to have the largest number and area of contaminated farmland. We conducted GIS and statistical analysis based on the field survey to identify the present use of farmland after the decontamination treatment and factors affecting the distribution of contaminated farmland and re-cultivation after the decontamination treatment. Our analyses clarified that 1) less number of decontaminated farmland sites have been re-cultivated, 2) farmland located in urbanized areas with heavily-polluted farmland in its vicinity tend to be fallowed or abandoned after the decontamination treatment, and in contrast, 3) farmland surrounded with paddy farmland tend to be re-cultivated after the decontamination.
Recently, the irrigation pipelines gradually lose its performance due to the deterioration and other factors, and the replacement or the improvement are required. It is necessary to develop a diagnosis technique which is advantage in the cost in order to maintain the performance of the pipeline. In the present study, in order to discuss the application of a shear wave resonating method to the diagnosis technique for ductile iron pipes, several experiments were carried out using an examination object in which the corrosion was simulated. As a result, it is found that the corrosion can be detected by comparing the measurement wave form of normal part and damage part. In addition, in order to evaluate the deterioration degree, the classification method has been proposed on the basis of the power spectrum by the plurality of frequency bands.
Earth-dam breaches arise from earthquakes and severe rainstorms and sometimes cause downstream floods. Floods have the greatest influential effect on hydraulic structures for irrigation and drainage, and estimating the costs of damage to these structures is important for risk assessment and management in agricultural land improvement projects. Although some methods for estimating damage costs have been proposed, most of these methods require many types of asset data and usually a long time because of complications. This paper proposes a simplified method for estimating damage costs in flood zones due to breach of earth-dams. The proposed method is based on asset data that are freely available, economical and easier to apply to practices in land improvement projects. Flood analyses of three actual earth-fill dams were performed, and the costs of damage in their flood zones estimated based on the results of the flood analyses using the proposed method. The proposed method estimated damage costs with ease, and accuracy was almost the same as other existing methods. Therefore, the proposed method can be a useful tool in agricultural land improvement projects.
This study aims at developing a procedure to calculate two-dimensional ponding water movement winding through rice plants which are regularly and numerously planted in a paddy field plot. This procedure consists of two kinds of calculations; a microscopic calculation in a small limited area, and a macroscopic calculation in a whole plot. The first one uses the finite volume method employing fine unstructured grids (about 1cm) to represent flow around the rice plants, and derives a collective drag coefficient depending on flow direction, velocity and depth. The collective drag coefficient averages microscopic complex flow to be applied to macroscopic simple flow calculation keeping flow resistance totally unchanged. The second one uses coarse structured grids (1m) to calculate flow in a paddy plot. In this step, the drag coefficients are assigned to each part of the paddy field according to flow regime instead of considering flow resistance caused by paddy plants. Finally, flow movements are compared in relatively large area (10m square) using two methods; the fine and coarse grid ones, to examine and confirm the effectiveness of this procedure.
Under budget cuts in public investments, aging of capital stocks for agricultural and rural development appears severe. This paper aims to present a quantification method for such capital stocks including farmland consolidation facilities and analysis of chronological changes and necessary amounts of future investments. Results demonstrated that (i) retirement profiles according to the Weibull distribution, which is more suitable for real deterioration processes of public facilities, show slower decreases in capital stocks when capital stocks enter the decline phase, (ii) capital stocks accumulated by paddy field consolidation account for the largest part of agricultural public capital stocks, and decline more rapidly than others, (iii) future necessary investments fluctuate annually and cannot be decreased by stock management measures, and (iv) the peaks of necessary investments differ by year and amounts among prefectures. Policy implications are discussed based on these findings.
In order to measure the first resonance frequency based on Japanese Industrial Standard, it is necessary to prepare specimens with the specific shape and size. This means that core specimens sampled from structures are required to be evaluated in their dynamic modulus of elasticity. In this study, we propose a new method for measuring the first resonance frequency in non-destructive field test. The measurement accuracy of the method and its applicability to real structures are evaluated under the conditions where a vibration generator and a wave-form recorder are separately set on the same surface. As a result, it was clarified that our method could measure the first resonance frequency with the same precision as previous testing method. Also, it was found that this method was applicable to wall-shaped members having wide surface, which are characteristic to structures for irrigation and drainage. In addition, the proposed method could evaluate the internal deformation of the above members like other existing methods.
Generally, the damage of pipeline becomes heavy when liquefaction occurs. However, the seismic behavior of pipeline in the liquefied ground is unknown enough. Therefore, the seismic design are not established systematically. In particular, the thrust force due to internal pressure constantly acts on pipe bend of the pressure line, such as irrigation pipelines. The resistance for the thrust force is passive earth pressure behind the pipe bend, but it is not considered that the passive earth pressure decreases when the liquefaction occurs. In the present study, model experiments were carried out in order to discuss the mechanical behavior of the pipe bend laterally loaded in the liquefied ground. As a result, it was revealed that the horizontal displacement of the pipe is increase and the horizontal resistance force is decrease significantly during liquefaction. In addition, it was found that the coefficient of subgrade reaction in the liquefied ground was reduced to 1/7 to 1/8 compared to that in non-liquefied ground.
Two conventional methods are available for the inspection of microcracking in concrete structures: microscopic examination and fluorescent epoxy infiltration. Here, we discuss a third method that utilizes low-pressure injections of silane oligomer into hardened cement paste to make any microcracking within it easily visible. To date, assessment of related materials and techniques has been largely confined to the laboratory. In this study, we conducted a field verification of the proposed method by applying it to the inspection of sidewall cracking within an existing RC open channel.