The purpose of this study is to clarify temporal changes in fish assemblage and environmental factors before and after the improvement of the drainage channels by using an eco-friendly construction method. This investigation was carried out from 1997 to 2007 in the Shirotorigawa and Harakawa drainage channels, Isawa, Oushu, Iwate. The findings were as follows. 1) In the section that was improved in a straight manner, natural bars did not form and riparian plants did not grow. Only the density of Misgurnus anguillicaudatus was high, and the similarity index had declined, this index did not recover for approximately 5 years. 2) In the section that was improved in a meandering manner, natural bars were formed and riparian plants grew there. The number of fish species and biodiversity index were similar before and after the improvement of this section. The densities of Misgurnus anguillicaudatus, Rhynchocypris lagowskii and Pseudobagrus tokiensis were high after the improvement of this section, and the similarity index was almost unchanged before and after the improvement. 3) In the section that was improved in a meandering and steep manner, the pools that were constructed on the sinuosity were maintained, but it was possible that the area of calm water in the pools was insufficient.
Habitat Suitability Index (HSI) has widely been applied to the evaluation of habitat suitability of target species. Despite the differences in modelling approaches, no study has clarified the effects of data types and categorization methods of habitat variables on the habitat evaluation. In this paper, we assessed the effects on the habitat preference curves and model accuracy in the HSI-based habitat evaluation for Japanese medaka (Oryzias latipes). As a result, all the preference curves from the different types of data showed the same trend of preference to a deeper water depth, a lower current velocity, a larger lateral cover ratio and a smaller percent vegetation coverage, in which differences were found among the categorization methods. It is also found that the data types and categorization methods have different effects on the habitat modelling, which appeared differently by performance measures used. This case study of Japanese medaka illustrates the importance and effectiveness of a modelling approach with consideration to the ecological characteristics of target species.
The stability analysis for seepage failure of foundations under a weir has been conducted by means of the creep length derived from the creep theory. As this is a simple method developed empirically, it does not show the deformation process of the foundations along with the increase of the water head between upstream and downstream of the weir. In the present study, series of model tests of seepage failure were carried out and the test results were applied to elasto-plastic finite element analysis to reconsider the seepage failure problems. The obtained model test results showed that the critical water head for seepage failure could not be correctly evaluated by the creep length in the previous theory. The newly proposed finite element analysis in which the seepage force is treated as external force to elasto-plastic finite element analysis appropriately reproduced the model test results regardless of its mesh size. The analysis results suggested the applicability of Terzaghi's method to evaluate the critical water head for seepage failure of foundations under a weir.
The objective of our research was to investigate geomorphologic characteristics, statistical laws of stream areas for rill networks in sloping fields, and the capability of two models for predicting drainage densities of the rill networks. Using field data on study rill networks developed in agricultural fields, we examined the average exterior and the average interior link areas, drainage densities, etc. for the rill networks. We also investigated the validity of the laws of stream areas and the capability of the drainage density models for the rill networks by the field data and a theory of channel networks. The results validated the statistical law of stream areas and Horton's law of stream areas for most of the rill networks. Moreover the results indicated that one of the drainage density models was effective for most of the rill networks and another model was capable of predicting drainage densities with reasonable accuracy for the rill networks with more than 46 sources.
This paper aimed to consider about material-recycling, preventing global warming, and economic efficiency on preset and planed 195 Biomass Towns applying DEA (Data Envelopment Analysis), which can evaluate operational efficiency entities such as private companies or projects. In the results, although the Biomass Town can recycle material efficiently, it was clarified that preventing global warming and business profitability was brushed off like it in Biomass Town Design. Moreover, from the point of view of operational efficiency, we suggested an improvement of the Biomass Town scale for more efficiency-enhancing applying DEA. We found that applying DEA was able to catch more improvements or indicator as compared with cost-benefit analysis and cost-effectiveness analysis.
A distributed model was developed in order to simulate the process of nitrogen and phosphorus load runoff in the semi-urban watershed of the Chikugo River, Japan. A grid of cells 1km in size was laid over the study area, and several input variables for each cell area including DEM, land use and statistical data were extracted by GIS. In the process of water runoff, hydrograph calculated at Chikugo Barrage was in close agreement with the observed one, which achieved Nash-Sutcliffe coefficient of 0.90. In addition, the model simulated reasonably well the movement of TN and TP at each station. The model was also used to analyze three scenarios based on the watershed management: (1) reduction of nutrient loads from livestock farm, (2) improvement of septic tanks' wastewater treatment system and (3) application of purification function of paddy fields. As a result, effectiveness of management strategy in each scenario depended on land use patterns. The reduction rates of nutrient load effluent in scenarios (1) and (3) were higher than that in scenario (2). The present result suggests that an appropriate management of livestock farm together with the effective use of paddy environment would have significant effects on the reduction of nutrient loads. A suitable management strategy should be planned based on the land use pattern in the watershed.
The soil rectangular blanket, whose design method has been already built up, is widely used as measures against the seepage from a reservoir of embankment dam or an irrigation tank on pervious foundation. This paper demonstrates an analytical solution of a seepage model for a triangular blanket and reveals that the analytical solution for the triangular blanket and the resultant solution for the seepage discharge can be successfully expressed by introducing the modified Bessel function of the first kind of orders 0 and 1. Compared with the seepage discharge of the model and the numerical solution by Boundary Element Method (BEM), the seepage discharge is shown to be accurate when the blanket length is practicable, though it is overestimated when the blanket length is relatively small. Moreover applying both the analytical solution of the model and the BEM solution to a large number of model cases, in each of which the length and the area (volume) of the triangular blanket are the same as those of the rectangular one, it is concluded that the triangular blanket is more effective against the seepage.
Host fish of each mussel was examined in a biotope pond, a drainage canal and fishway between them in Gifu Prefecture from May to October 2008. The main host fish was Zacco platypus in Unio douglasiae and Lanceolaria grayana, Nipponocypris sieboldii in Anodonta sp. and Pronodularia japonensis. In the fish caught at fishway, intensity and total number of glochidium were more the descending fish from the biotope pond than the ascending one from the drainage canal, which suggests that the biotope pond is now the base of supply of juveniles to the neighboring areas.
This paper presents the estimation procedure of a flood envelope curve originally developed by Kadoya and Nagai (1979) on the basis of depth-area-duration (DAD) analysis of radar precipitation data in order to examine the availability of spatial distribution data of precipitation for statistical flood peak analysis. The estimated flood envelope curves by applying the presented procedure to the Yoshii River Basin located in Okayama Prefecture of the western Japan well enveloped the flood peaks observed in the Hiroshima and Okayama Prefectures; the curves tended, however, to overestimate flood peaks for small catchments. It was explained by the fact that very limited areas are with regionally maximum areal rainfall arising maximum flood peak discharge and the other areas are with smaller areal rainfall than maximum in the objective region. Flood envelope curve equation considering spatial probability of regionally maximum areal rainfall was presented and applied to the Yoshii River Basin to show the effect of adjusting the spatial probability for mitigating overestimation of maximum flood peaks for small basin. This result shows probabilistic aspects of flood envelope curves deterministically estimated from hydrological records, which should be considered when determining design flood discharge for dam planning.
Image data from an AVNIR-2 sensor of the ALOS satellite was used to distinguish whether a paddy parcel in a flat region with many pasture planted paddy fields and fallow paddy fields had rice planted. First, the pixels of the AVNIR-2 image were classified into 40 classes using the unsupervised classification method. Next, the 40 classes were integrated by subjective judgment into 2 classes according to whether rice was planted in the paddy fields. Last, the parcels planted with rice were extracted by overlaying the image data of the integrated classification with paddy parcel boundary data, and consolidating the integrated classification results for each parcel. The accuracy for distinguishing parcels with an area of 1,000 m2 or more was 99.0%, 97.9%, 95.4%, and 95.5% in the AVNIR-2 image data observations on June 15 (early period of the tillering stage of rice), July 2 (late period of the tillering stage of rice), September 17 (maturation period of rice) and October 16 (period for harvesting of rice), respectively. Factors of misjudgment in the spatial resolution and positional precision of the AVNIR-2 image data and similarities in spectrum reflection characteristics between fields with rice planted and other paddy fields were also considered.
The drainage efficiency of a subsurface drainage system for avoidance of standing water on the plow pan of clayey field was evaluated. A subsurface drainage system with a main drain and orthogonally adjoined rice husk trench drains joined by vertical rice husk drains was constructed on a test plot and compared to an identical control plot of paddy field converted to upland use under soybean cultivation. The ratio of total underdrain discharge to rainfall in the improved plot greatly increased over two years compared to that in a control plot. In the improved plot, the peak underdrain discharge per hour associated with some heavy rainfalls was around 3 mm/h in the first year but decreased to about 2 mm/h in the second year. By improving drainage in the paddy field, standing water on the plow pan was quickly eliminated after rain events and the period of flooding on the plow pan during the soybean growing season was greatly reduced. However, underdrain discharge in the improved plot decreased greatly in the third year to be at the same level as in the control plot, and rain water flooded the plow pan for extended periods of time.