It is important to estimate the right amount of irrigation water necessary to maintain soil surface moisture to prevent wind erosion. However, there has been no standard approach developed to estimate the appropriate amount of irrigation water required for this purposes. To develop an irrigation plan to prevent wind erosion, we utilized the Tank model in this research as a method to reconstruct surface soil moisture dynamics due to changes in weather and submergence, In this model, for a soil stratum up to 40cm depth, in addition to rainfall and evaporation, gravitational water and capillary forces are taken into account. This model has two soil layers consisting of surface soil layer and lower soil layer. Surface soil layer has a single grained structure and lower soil layer has an aggregated structure with large pores. Lower soil layer is intermingled into two structures, first which soil water moves into, and second which soil water penetrates from the first structure. This model was identified using weather and soil moisture data collected from the farmland during the period of April to July 2005, and so soil moisture on April to May in 2007 was estimated using this model. As a result, the estimated soil moisture coincide with the observed figures both surface and lower layer. It can be concluded that changes in soil moisture were well reconstructed.
This study examines whether the adequate population of loaches, one of the main food resources of Japanese Crested Ibis (Toki), can be maintained by the implementation of limited-scale improvement works of the habitat. As a result of the monitoring survey with the mark-recapture method, it was confirmed that the number of loaches was estimated to be 1.5 per m2 in the study paddy field, and 5.2 per m2 in the study canal, which in turn, exceeded the necessary amount for feeding Japanese Crested Ibis reported by Japan Wildlife Research Center. The major factors leading to this favorable outcome are considered to be the existence of the intercepting drain in the paddy field, the canal fishway, the paddy field fishway, and environment-conscious canal. It is also supposed that the loaches' range of activity is quite limited in comparison with the spatial extent of improvement works. These outcomes leads to a conclusion that the limited-scale improvement works are effective for the maintenance of loach population.
In form land consolidation area drainage canals, fish habitat environments are worsening because the banks of rectilinear canals are protected by concrete. In order to improve fish habitat environments, void structural objects such as a log mattress have recently been constructed for river bank protection. This study aims to grasp the characteristics of fish habitats in the context of log mattresses used for river bank protection. The author constructed an artificial log mattress for research, which was positioned in an agricultural drainage environment (St.I (a monotonous environment)) and a small-sized river (St.II (a natural waterside environment)), in order to conduct investigations. This study revealed the following. (1) The artificial log mattress functioned as a habitat for a lot of fish, 10 species of six families in St.I and 11 species of seven families in St.II. (2) Dominant fish were Carassius sp., Misgurnus anguillicaudatus and Pseudobagrus tokiensis in St. I, and Phoxinus logowskii steindachneri, Misgurnus Anguillicaudatus and Pseudobagrus tokiensis in St.II. (3) In the concrete structure environment (St.I), the internal fish habitat density was high. (4) The difference in habitat density between the surrounding area and inside showed that Pseudobagrus tokiensis have a specific inside preference for both St.I and St.II
Mill treatment was applied to digested liquid taken from a methane fermentation plant in order to miniaturize particle size of suspended solids. The particle size of the digested liquid decreased from 2-590μm to 0.45-105 μm with a 3 hour mill treatment using 1 mm diameter glass beads (RUN-1). An additional 3 hour mill treatment with 0.3 mm diameter zirconium beads (RUN-2) reduced the particle size to 0.19-11μm. Coliform bacteria were not detected in the 1 h treated liquid of RUN-1, although the raw digested liquid contained 3,600 CFU·ml-1 of coliform bacteria (CFU: colony forming unit). Viscosity of the digested liquid was approximately 11 mPa·s at 15°C and negatively correlated with temperature. RUN-1 and RUN-2 decreased the raw liquid viscosity by approximately 20%. RUN-1 improved the permeability of the liquid into the soil. A significant difference in the measured relative densities existed between the digested and treated liquids after RUN-1 and 2. However, the difference was less than 2% of the digested liquid density.
A case study on the Hoji Pond and its source river (the Todoroki) located at Konoyama area, Kishiwada, south part of Osaka prefecture, Japan indicated demonstratively that irrigation pond, even though it is a "off-stream type" without continuous inflow from the source river, could reduce nutrient load in the source river through the regular operation for irrigation. It was resulted that the annual average of the reduction ratios for each form of nutrient (Nitrogen and Phosphorus) loads in the river were 36% for T-N, 42% for D-N, 52% for T-P, 46% for D-P, and 62% for P-P. For P-N load, there were several months when the output from the pond exceeded the input to the pond, so that the pond had contributed negatively though it was very slight. The result of additional survey carried out from June to December 2007 indicated that the negative contribution for P-N load by the pond was due to transformation of D-N into P-N by the growth of phytoplankton in the pond.
The aim of this study was to establish the method for estimating leaf area index (LAI) using satellite data. LAI is one of the most important land area ecosystem parameters which characterize the quantity distribution of the vegetation and even water balance of the watershed. In this study, we estimated LAI based on absorption and dispersion processes of electromagnetic waves in the vegetation canopy. The validation of LAI estimation using Terra-ASTER data was tested by comparing that of result to measured LAI using plant canopy analyzer. As a result, validity of LAI estimation method was confirmed as exhibited by a high correlation(r=0.91) with 1:1 ratio of regression line between calculated and measurement of LAIs. In addition we compared spatial average of LAI estimated from ASTER data with a MOD15A2 LAI product and proved the precision of mutual LAI.
When melt water remains on the soil surface for a long time in rotational paddies in Hokkaido, a snowy cold region of Japan, machine work in the early spring is delayed, resulting in growth delay of crops and decrease in income. Ice plates can be made in paddies in Hokkaido by filling the paddies with water before the continuous snow cover, and melt water flows from the edges of the ice plate. It is expected that the surface soil water after disappearance of the snow cover can be reduced if melt water can flow to an underdrain through open channels along the levees in the paddy. In this study, the effects of an ice plate formed by inundation before the continuous snow cover on surface soil water after disappearance of the snow cover at a rotational paddy in the period from autumn of 2007 to spring of 2008 were examined. It was found that the volumetric water content in the ice plate area was lower than that in the conventional area after disappearance of the snow cover.
Regarding the issue of the long-term stability of slopes in farmlands composed of clayey materials, experimental results of tests on mechanical properties and localization of displacements were presented, with special reference to first-time failures. Shear band width at the medium strain range (up to about 15 percent of axial strain) observed in a consolidated and drained triaxial compression test of an undisturbed sample seemed to be appropriate as the width of the displaced zone composed of soil masses between discontinuities such as fissures, and this was different from granular materials for which particle size had great importance. Based on this result, parameters of Tanaka's finite element model were evaluated and a simulation of a triaxial compression test was performed. The result of finite element analysis of an elastic and strain-softening plastic model showed that the finite element solution matched the experimental results in the sense that it matched the average value of specimens which showed various behaviors owing to their stress history in landslides.
Terzaghi's method is a standard stability analysis for seepage failure around sheet pile. Terzaghi developed this method based on seepage failure experiments with fixed sheet pile. However, seepage failure often occurs at the construction field. We regarded the one of factors as what the sheet pile was not spatially fixed perfectly. Although it is difficult that the condition of fixed sheet piles is remained perfectly, there are few studies to evaluate seepage failure under the condition of unfixed sheet pile. The purpose of this paper determines the impact of condition of fixed and unfixed sheet pile on seepage failure with model experiments. These experiments made clear that the critical water head of fixed sheet pile condition was about four times larger than unfixed. The fact needed the analysis method to be able to analyze seepage failure with interaction between soil and the construction. We made an attempt on this problem with our elasto-plastic FEM. It was clear that this FEM had possibilities to solve this problem.
To establish a method for monitoring the fluctuations of river or lake sedimentary volume by means of time domain reflectometry (TDR), the surface levels of sediments composed of sand or gravel were measured using a 48cm-length TDR probe in laboratory and compared with two dielectric estimation approaches. In the experiments, the probe was vertically set under water surface to be across two layers of water and sediment. Giving microwave step-pulse to the probe, we could obtain the TDR waveform which contained the pulse reflections at the water-sediment interface and the end of probe. The sediment surface level hsed estimated by partial-range propagation method PPM, where a linear function of the travel time (tw) determined from the former reflection is employed, was in good agreement with the actual level. In whole-range propagation method WPM based on the travel time (tt) given from the latter reflection and the sediment relative permittivity εsed, the estimation error of εsed augmented with increase in grain size of the sand or gravel resulted in low accuracy of hsed. The inaccuracy, however, was improved by modifying εsed with the correction coefficient (Cg) expressed as a linear function of the middle grain size (Dmid). PPM and WPM could be reasonably used for the hsed-estimation with TDR.
When melt water remains on the soil surface and in surface soil layer for a long time in rotational paddies in Hokkaido, machine work in the early spring is delayed, resulting in growth delay of crops and decrease in income. With the expectation that surface drainage would be effective in such fields, the effects of the combination of sloped farm field, crawler compaction and open channels on volumetric water content, soil hardness and soil temperature of the surface soil layer after disappearance of the snow cover were examined. It was found that volumetric water content of surface soil layer after disappearance of the snow cover in a sloped area in which the combination of sloped farm field, crawler compaction and open channels were used was lower than that in the conventional area in which only open channels were used. Soil hardness and soil temperature in the daytime in the sloped area were higher than those in the conventional area. The combination of sloped farm field, crawler compaction and open channels seems to accelerate the surface drainage of melt water and to facilitate machine work after disappearance of the snow cover.
To restore the small-scale damages of the agricultural infrastructure in the Mid-Niigata Prefecture Earthquake in 2004, the government of Niigata Pref. created the Small-scale Disaster Restoration Project (SDRP: In Japanese “Tezukuri-tanaoshi-tou-shien” Project) funded by the Emergency Restoration Fund. The principal mission of this project is to complement the Disaster Restoration Project (DRP) that targets damages with a certain scale or more. In this research, by comparing the number and the details of the damages restored by the SDRP with those restored by the DRP etc., the following characteristics that a large-scale infrastructure disaster brings about were clarified: 1) There were small-scale damages as many as large-scale ones. 2) The small-scale damages occurred at a higher rate in the hilly and mountainous area, and gave rise to a greater impact on the disadvantaged areas. 3) The patterns of the large-scale and small-scale damages differ. In addition, the contributions of the SDRP were evaluated with respect to the facts that the following cases could be accommodated by the SDRP: 1) Restoration of roads and waterways managed by the limited members. 2) Restoration of the damages discovered some period after the occurrence of the earthquake. 3) Restoration of the damages which could not be accommodated with the existing project.
The design and operation factors on the effluent ATU-BOD·N-BOD concentrations in sedimentation tank were investigated by using observed data in the rural sewerage facilities with biofilm processes. It was found that the effluent N-BOD accounted for approximate 50 percent of the effluent BOD concentration in sedimentation tank because of the effluent ATU-BOD decrease(about 70 percent) and the effluent N-BOD increase (about 4 times) by treatment processes of contact aeration tank. It was recognized that the effluent ATU-BOD concentration in sedimentation tank was influenced by the design and operation factors such as influent ATU-BOD concentration, specific surface area of contact filter for fixed bed submerged filter, and average DO in contact aeration tank. The effluent ATU-BOD concentration in sedimentation tank was assumed to be governed by first-order function with complete-mix system of biological treatment processes. The effluent ATU-BOD concentration in sedimentation tank was found to be predicted by the empirical formula of hydraulic retention time, influent ATU-BOD concentration, specific surface area of contact filter for fixed bed submerged filter, and average DO in contact aeration tank. It was recognized that the peak effluent N-BOD concentration in sedimentation tank occurred in the around 10∼15 hour of hydraulic retention time under the influence of biological nitrification reaction and nitrogenous compound. The effluent N-BOD concentration in sedimentation tank was also influenced by the effluent SS concentration in sedimentation tank.
A swimming experiment of cultured fingerling masu salmon (Oncorhynchus masou masou) (measuring 3cm to 6cm in length) was conducted in a round stamina tunnel (cylindrical pipe) installed in a fishway of a local river with a water flow velocity of 64cm·s-1 to 218cm·s-1 in order to study the burst speed of the masu salmon.The results show that: (1) the faster the swimming speed,the swimming time of the fingerling masu salmon shortened, and the ground speed also decreased as the flow velocity increased; (2)the faster the flow velocity,the shorter the swimming distance became; (3) the burst speed was calculated for the fingerling masu salmon with the considerably excellent swimming ability(measuring 4.6cm to 6.2cm in mean length) in conditions of a high velocity(218cm·s-1), and the result was: mean burst speed:229cm·s-1(S.D.8cm·s-1) to 232cm·s-1(S.D.:8cm·s-1).
In bends, unbalanced force, which is called thrust force, is generated. Generally a concrete block is installed at the bend to provide the lateral resistance. However, the heavy concrete block is weak point in earthquake. In our previous study, a lightweight thrust restraint using geogrid was suggested and the effect was proved by laboratory small tests. In the present study, the large-scale tests for the new method were carried out in a large pit (8.4m×5.4m×4m), using a pipe bend having a diameter 300mm. As the results the lateral displacement of the bend was reduced by the proposed method. In addition, it was revealed that the effect was depended on the stiffness, length and installation of geogrid.
Depopulation and aging of agricultural settlements due to the lacking in heir and the aging of residents has been becoming a major concern in planning the system of regional disaster prevention. To reveal the geographic characteristics of the depopulation and the aging in agricultural areas, we investigated the demographic characteristics in Saga prefecture based on web-browsing community database. Although only one precinct currently indicated high population aging rate more than 50%, we found that 50 precincts has high potential of becoming such aging precinct within 10 years. Additionally, local depopulation and aging are detected in urban areas such as shopping streets near station and aging public housings.
In this research, the basic shape of the device for prevention of inflow and accumulation of buoyant refuse at the intake of headworks is investigated by hydraulic model test. As results, it is clarified that an enough result is not obtained if the prismatic bar that floats on the water is set as the device for prevention so that it may cross the intake. On the other hands, it is clarified that the inflow and accumulation of buoyant refuse at the intake is decreased greatly if the bar is set so that it may be diagonally thrust out from the upstream edge of the intake to the downstream on the river side. In this case, it is necessary to decide the length and setting angle of the bar so that it may intersect with the boundary line of the area where the refuse flow into the intake with no device for prevention.
In this study, the variation of decaying level of the “pore system formed by roots”(hereafter P.S.R.) found in the Holocene series and upper, middle and lower Pleistocene series in volcanic ash soil formation at the northern region of Iwate prefecture was investigated. The result was that the vicissitude of the P.S.R. was divided in the three periods. The first is a multiplication period and the second is a durability period and the last is a decaying period. Also, it was estimated that the dividing line between the durability period and the decaying period was not older than 250,000 years ago. After these years, the P.S.R. was shifted from the durability period to the decaying period. In the decaying period, the horizons ranked 2∼4 decaying levels formed about 80% of all the horizons. The horizons ranked 3∼4 decaying levels that showed a heavy decay to disappearance of the P.S.R. formed about 60% of all the horizons.