This study aims to examine the effect of embankments for expanding double rice cropping area in the Cambodian Mekong Delta, where many traditional embankments called Tum Nub. For realizing double rice cropping in the flood plain, securing the cropping period and irrigation water during non-submerged days is essential, for which utilization of Tum Nub is considered to be effective. The field investigation revealed that some villages are practicing double rice cropping by introducing early rainy season rice. Hence, for introducing early rainy season rice, the effect of combination of two types of embankments was simulated for a target area selected: Type 1 embankment is making a reservoir for storing water, but single rice cropping is allowed in the inside of the reservoir after consuming stored water; and Type 2 is that for delaying the start of inundation. The result of the simulation showed that the combination of the embankments can increase rice production of the target area by 24-30% from the current level.
To investigate the mechanism of seismic damage to irrigation tanks, the irrigation tanks damaged during the Mid Niigata Prefecture earthquake in 2004 were analyzed. The damaged irrigation tanks were classified into damage conditions. It was found that a large embankment located near the seismic center had a high risk for seismic disaster. The circular slice method was applied to damaged and undamaged irrigation tanks. The slide at the upstream slope of the embankment was considered as a possible failure pattern. Sensitivity analyses of the parameters used in the calculation of safety factors were also conducted to examine damage prevention. Since the slope angle was as influential as the internal friction angle, widening of the embankment would be effective for earthquake resistance. The conditional damage probability of a given irrigation tank was calculated using a Monte Carlo simulation, which is useful for risk management.
This study examined salinization and desalinization in an agricultural area of Nagapatttinam district, Tamil Nadu state, India due to the December 2004 tsunami. To examine the damage and recovery of agricultural environment from the tsunami, we observed and collected soil, groundwater and vegetation data. Soil electrical conductivity steeply increased after the tsunami and soil pH slightly increased, but returned to pre-tsunami levels in the following year. Groundwater salinity might return to pre-tsunami levels by 2006. MODIS EVI values measured before and after the tsunami showed that vegetation damaged by the tsunami recovered to its pre-tsunami state by the next rice cropping season, called samba, which continues from August to February. These rapid rates of recovery were due to leaching salt from the highly permeable soils in the area by the monsoon rainfall. From these results, we conclude that agricultural environment of the district has mostly recovered one year after the tsunami.
In concrete structures used for irrigation and drainage, there occurs a kind of deterioration that mortar in concrete matrix is abraded selectively. To estimate the progress of such abrasion and evaluate the resistivity to abrasion of repair material, a prototype of abrasion tester was developed. It sprays water including sand to specimens. In this research, the comparative tests between this prototype, Taber type abrasion tester and Water jet abrasion tester ware executed using the specimens of concrete, Polymer Cement Mortar and High Performance Fiber Reinforced Cement Composite. As a result, it was clarified that the prototype can simulate the selective abrasion more quickly than existing method. Therefore, this prototype can be used to evaluate the resistivity to abrasion of repair material.
Carex dispalata, a native plant species applied in cold districts for water purification in constructed wetlands, has useful characteristics for landscape creation and maintenance. In this study, seasonal differences in purification ability were verified, along with comparison of frozen and non-frozen periods' performance. A wetland area was constructed using a “hydroponics method” and a “coir fiber based method”. Results show that the removal rates of BOD, SS, and Chl-a were high. On this constructed wetland reduces organic pollution, mainly phytoplankton, but the removal of nitrogen and phosphorus was insufficient. The respective mean values of influent and treated water during three years were 26.6 mg/L and 12.2 mg/L for BOD, and 27.9 mg/L and 7.5 mg/L for SS. The mean value of the BOD removal rate for the non-frozen period was 2.99 g/m2/d; that for the frozen period was 1.86 g/m2/d. The removal rate followed the rise of the BOD load rate. The removal rate limits were about 4 g/m2/d during the frozen period and 15 g/m2/d during the non-frozen period. For operations, energy was unnecessary. The required working hours were about 20 h annually for all maintenance and management during operations.
The acceleration ratio of the abrasion tester using water jet with sand was investigated to enable the progress estimation of abrasion which is needed to the asset management. The abrasion test was executed by using specimens taken from the sound part of concrete canals, and the results are compared with the abraded specimens from submerged part of the identical canals. Then, the acceleration ratio was calculated from the service period and the test duration needed to achieve the similar abrasion on the sound specimen. As a result, the acceleration ratio was 1.05-1.72y/h in the case assessing with the abrasion depth, and 0.50-8.85y/h in the case with the unevenness. The progress of abrasion could be estimated by using the calculated acceleration ratio. Moreover, it was confirmed that the unevenness converged at constant value while the abrasion depth kept increasing with service period.
We propose the trenchless box culvert construction method to construct box culverts in small covering soil layers while keeping roads or tracks open. When we use this construction method, it is necessary to clarify deformation and shear failure by excavation of grounds. In order to investigate the soil behavior, model experiments and elasto-plactic finite element analysis were performed. In the model experiments, it was shown that the shear failure was developed from the end of the roof to the toe of the boundary surface. In the finite element analysis, a shear band effect was introduced. Comparing the observed shear bands in model experiments with computed maximum shear strain contours, it was found that the observed direction of the shear band could be simulated reasonably by the finite element analysis. We may say that the finite element method used in this study is useful tool for this construction method.
The authors developed the diagnosis tool on regional biomass use. The tool is consisted of the material cycle model for rural area as computer software and some information such as biomass components, capacity and cost of biomass conversion technology, and productivity of energy crops. The model diagnoses the areas of one to ten municipalities mainly from material cycle. The analysis items are nitrogen, phosphorus, potassium, carbon and weight of biomass. The tool tells present condition in the target area. Some new biomass use plans can be diagnosed and compared from points of demand and supply balance, environmental impact, and sustainability. The tool is useful to make a persuasive draft of the biomass town plan.
Long-term changes in 10-year daily, hourly, and 10-minute rainfall in Japan were examined by applying Gumbel distribution to regional annual maximum rainfalls, where regional maximum rainfall is defined as the largest value in all rainfall records at rain gauging stations in a region. Here Japan was regionalized into 11 hydro-climatic regions. The objective record length varies by objective rainfall durations, as 105 years for daily rainfall, 58 years for hourly and 47 years for 10-minute. The daily rainfall record was divided into four periods, and the hourly and 10-minute rainfall records into three periods, respectively, and then change in 10-year rainfall for each recording interval was examined by comparing that estimated in the first period and that in the last period. Beside, change in estimated parameters of the applied Gumbel distributions was also examined. The result shows that the numbers of regions where 10-year regional rainfall has increased by more than 10 % were eight out of eleven for daily rainfall, three for hourly and two for 10-minute. The result also clarified that change in parameters of Gumbel distribution mainly arises from increase in standard deviation of annual maximum rainfall, not from increase in its average. It suggests that increase in 10-year rainfall is mainly due to larger fluctuation in annual maximum rainfall.
Biomass use system is consisted of 1) production or generation, collection, transportation and storage of feedstock biomass, 2) conversion of the feedstock biomass to demand-oriented material and energy (renewal resources), 3) storage, transportation and use of the renewal resources, and 4) adequate disposal at above respective stage. This paper arranged the discussion points on evaluation methods of new biomass use scenarios in terms of lifecycle cost and lifecycle fossil energy consumption. An evaluation format was proposed. The evaluation clarifies the structure of cost and energy for a planned biomass use scenario. The results will provide an suitable project cycle management by cost saving and mitigation of global warming. The analysis from lifecycle view is important to ensure the sustainability of biomass use system.