Benefits from assistance projects to achieve participatory irrigation management in developing countries do not always continue. One reason for this is the difficulty faced in providing appropriate incentives to the members of water users' organizations to continue their activities. In order that the organizations continue their activity after the assistance projects finished, it is necessary to make approaches to appropriate influencing factors that efficiently raise farmers' willingness for their activity. In this paper, we examined the farmers' willingness for performing maintenance activity, investigated factors related to this willingness, and analyzed the current situation of the relationship between the willingness and influencing factors in a case-study area with a questionnaire given to farmers. We found that the willingness was influenced by factors such as the awareness of benefits of the facilities and irrigation water. We also found that the farmers who were more concerned about the unreliable water distribution due to broken ditches showed increased willingness. Thus, we conclude that “preventing the loss of benefits that are already obtained” should be introduced as an important incentive.
The main purpose of this research is to develop a calculation method to assess the probability of liquefaction and a reliability-based design method to mitigate the liquefaction in sandy grounds. The probability of liquefaction is evaluated with the proposed model by considering the spatial variability of soil parameters. The liquefaction resistance is calculated from the SPT N-value, and the fines content, Fc, through the empirical relationship. The statistical models for these two soil parameters are determined with the maximum likelihood method. In this study, the probability of liquefaction is evaluated multi-dimensionally using the conditional simulation method. Finally, the reliability-based design method is discussed in order to determine the optimum design for ground improvement using sand compaction piles (SCP) based on the calculated probability of liquefaction.
The coastal lakes, which are designated for inclusion of Rishiri-Rebun-Sarobetsu National Park, are located in the northern part of Hokkaido Pref, Japan and nurse rich ecosystems. This study is associated with environmental isotope-based investigation of hydrological aspects of the coastal lakes. The zero concentration of radioisotope 222Rn observed in the lake water means that groundwater discharge might not occur in the lakes. It is thus deduced that the coastal lakes with no direct surface water inflow and outflow are isolated closed lakes and the lake water is of rain water origin. The enrichment of stable isotopic composition of oxygen and deuterium in the lake water clearly implies the evaporation from lake water bodies. The ratio of evaporation loss from the lakes to rainwater input estimated by a static isotopic mass balance model including a kinetic isotopic fractionation effect ranges from 14.4 to 71.9% with an average of 45.1%, and the difference of the evaporation loss in each lake can be explained by lake's morphology. The lakes have a significant influence on groundwater flow system as “recharge lake”, and thus precipitation and groundwater level in the lower region have a dominant impact on hydrological environment of the coastal lakes.
We verified reliability as well as safety of water supplies and water usability at a regulating reservoir. The regulating reservoir is included an irrigation canal system, was expanded regulating capacity by rehabilitation of agricultural irrigation facilities. As a result, we have reached two important conclusions. First, expansion of the regulating reservoir capacity raised the safety of air entrainment for the pipeline located downstream of the regulating reservoir. Then, reduction of excess water attended with expansion of the regulating reservoir capacity and modification of water supply management raised the efficiency of water conveyance and distribution. In addition, we considered the trends of the performance indicator values (efficiency of water conveyance and distribution etc.) before and after rehabilitation. It was shown that expansion of the regulating reservoir capacity was especially effective when the change of water supply operation caused a trade-off between the performances and made all the performances difficult to exceed the target performance.
The energy input for irrigation and drainage in three lowland paddy areas was investigated. The energy input in the lowland paddies range between 4.5 and 15 GJ/(ha·year) for the irrigation, and between 0.2 and 3.3 GJ/(ha·year) for the drainage, respectively. The long-distance transmission of the irrigation water requires much energy input for the remote paddies from the source river, which amounted more than 5GJ/(ha·year) for supplying about 600 mm of the irrigation water. These amounts of energy are comparable to the directly consumed energy in the cultivation of rice, such as the fuels for the agricultural machinery and post-harvest processing of the grains. These results show that reduction of the energy input for irrigation and drainage is an important issue for the stably productive paddy farming. It is important to build energy-efficient irrigation and drainage system by considering the balance between the construction costs and long-term running costs.
In our country, the view of the Green Dam that a forest has a function of the dam of storage and disaster prevention has circulated, and recognition that the broadleaf tree, especially beech forest have an outstanding dam function has permeated widely. In this research, verification of this recognition was tried through the river runoff model for the river which makes a basin World Natural Heritage Site Shirakami mountain range which consists of the beech primeval forest. The distributed type runoff model was applied to the beech primeval forest basin and the parameters of the model were identified, and as a result, it was clear that the subsurface flow was dominant and contribution of the surface flow was slight. As new extension of a paired watershed approach, as a result of applying the same runoff model to the contrastive basin where development of farmland had been performed highly, the great difference was observed in the identified parameters, and it was shown that by contrast contribution of the surface flow to the runoff form was large.
The purpose of this study is to evaluate the effect of subsurface water flow on herbicide residues in stream water. Pesticide concentrations and loads were monitored three times in Yasu River and twice in Hino River from May to June 2005. Surface water always flowed and reached to river mouth in Hino River, although infiltration of all of the surface water was observed in some part of the Yasu River channel. Pesticide concentrations returned to the surface streams were < 1/100 lower than that of surface water before infiltration. Possible reason may be the dilution and diffusion with shallow ground water and/or lake water. Runoff coefficient at the end of receiving stream was calculated to 1.0 for Hino River and 0.01 - 0.1 for Yasu River.