Sixteen reservoirs which will not be used for irrigation are preserved for the purpose of environmental conservation in the benefit area of the public works of farm land consolidation constructed in the Isawa area in southern Iwate. In order to manage the reservoir with such background, it is important to understand in advance the actual condition of the budget of heat and water which have an indivisible relation. Observation of hydrological and meteorological elements was carried out at Hoonoki reservoir from May to Oct. in 2006, of the previous year when the farmland consolidation around the reservoir was constructed. The observation results clarified the budget of heat and water of the reservoir, and suggested that formation of the water temperature environment of the reservoir was characterized with a large volume of inflow water.
Some of irrigation tunnels, that service not only irrigation water but also tap water, industrial water, and irrigation water for farming crops in winter, have high social importance as lifeline. But it is very difficult to diagnose these agricultural facilities because they can never stop water supply through a year. To diagnose these facilities under water servicing, the authors developed a survey system for irrigation tunnels. This system can record various defective events such as cracks, water inflow, calcium efflorescence, and so on. The advantage of this system is a high sensitive CCD camera, which is automatically controlled in order to follow the concrete lining of irrigation tunnel to take continuous digital front view. As a result of onsite experiment, this system can detect cracks that have more than 1.5mm width, free lime, and leakage of water. So it is effective as the mean for a primary survey.
A fish ladder was created to optimize fish habitat in a paddy field area. The ladder was constructed from a series of small weirs built in a drainage canal beside paddy plots to provide staircase-like steps allowing fish to pass between the drainage canal and the paddy ponds. Successive weir steps were progressively higher towards the upstream part of the ladder. Fish could run up these steps to spawn in the paddy ponds, and juvenile fish could return to the drainage canal to disperse. We examined the fish habitat and water balance in a paddy plot with this type of fish ladders and their implications for irrigation and drainage management, and fish conservation. The ponding depth of the paddy water was maintained at the top of the flashboard at the outlet of the paddy plot and water drained efficiently following periods of high rainfall. Fish could swim in the deep paddy pond. The volumes of irrigation and, in particular, drainage water were increased compared with conventional paddies without fish ladders. The amount of ineffective rainfall for cultivation and the lot-management water requirement both contributed to the increase in drainage water. It is necessary to consider both “the water requirements of the fish ladders” and “the effective rainfall required for fish conservation” to optimize paddy water management for fish conservation in paddies with ladders.
It is a big subject to secure the sand capping material when executing the overlaying sand method for the countermeasure of eutrophication at stagnated and enclosed water. Functional Overlaying Sand (FOS) granulated with cement and Fine Demolished Concrete (FDC) was clarified not only to be safety but also to restrict the dissolution of phosphate ion, higher restriction effect than natural sand. In this study, another additional material, waste roof-tile, is studied for the replacement material of FDC, comparing the physical and chemical characteristic between them. Moreover, granulating the FOS replacing with waste roof-tile (FOSWR), and evaluate the various performance as the sand capping material. Density, pH, dissolution and removal ability of toxic matters, and restriction ability of phosphate and sulfate ions dissolved from sedimentation mud are evaluated for each material. As a result, waste roof-tile has ability to remove some toxic matters such as Pb, Cd,, Cr. It was clarified that utilization of waste roof-tile for FOS components led the decrement of ability on phosphate ion removal comparing with FOS. However, the use of waste roof-tile can decrease the density, restrict the raise of pH and dissolution of toxic matters from FOSWR itself.
This study aims to investigate changes in runoff characteristics due to the increase of abandoned terrace paddies in hilly areas. To do so, 3 experimental watersheds were selected based on land use and cultivation status of paddies: namely Cultivated Paddy-dominant Watershed, Abandoned Paddy-dominant Watershed and Forest Watershed, whose areas are approximately 1km2. The retention capacity, runoff ratio and peak runoff coefficients for large discharges from each watershed were analyzed using rainfall and discharge data observed at 10-minute intervals. First, it was determined that the peak runoff coefficients of the Cultivated and Abandoned Paddy-dominant Watersheds were 0.24 and 0.30, respectively. In addition, the runoff ratios of the Abandoned Paddy-dominant Watershed were, under wet conditions, found to be 31.4% higher than those of the Cultivated Paddy-dominant Watershed at the maximum. These results indicate that abandonment of paddies lead to larger peak discharges and direct runoff, suggesting a higher flood risk in the area. Meanwhile, the maximum retention capacity of the Abandoned Paddy-dominant Watershed decreased by approximately 10mm compared with those of the Cultivated Paddy-dominant and Forest Watersheds, suggesting lower water availability in dry periods.
In this study, for the purpose of efficient use of paper sludge which was industrial waste generated from paper manufacturing company, we verified the characteristic and utility of air mortar that used paper sludge as admixture. After the filling material had been set as a usage, basic physical properties, durability, and the segregation resistance were confirmed by the indoor examination and the practicality was examined on the construction site. As a result of the indoor examination, it was confirmed that a basic performance as the filling material was satisfied enough, and deterioration due to the repetitions of dry-wet and freeze-thaw was not seen. In addition, the great improvement of the segregation resistance was confirmed compared with usual air mortar. Similar characteristic was demonstrated in the construction site, and the improvement of construction was confirmed. Therefore, the paper sludge could be considered to be useful as the mixture material for the air mortar.
The influence of pH and ionic strength on transport properties of imogolite particles through porous media were investigated by column experiments. Imogolite suspensions varying in pH and NaCl concentration were flowed into the column packed with Toyoura standard sands. Breakthrough behavior of imogolite was affected by their colloidal stability. That is, at low pH or low NaCl concentration, where imogolite particles were dispersed, the effluent concentration of imogolite rapidly reached to that of influent, indicating that the particles were not significantly captured in the column. On the other hand, at higher pH value or higher NaCl concentration, where imogolite particles were aggregated, the effluent concentration of imogolite was lower. We consider that the imogolite deposited on the sands are able to capture suspended imogolite in pore fluid and thus reduce the effluent concentration. In pH 6.4, at which imogolite are in the transition condition between dispersion and aggregation, the onset of breakthrough was delayed 2 pore volume at NaCl concentration I=1.0×10-2 M. The delay period was longer under the higher ionic strength condition.
The soil contamination countermeasures law, implemented from February 2003, was revised in April 2010 to include contaminants of natural origins, and the development of immobilization technology for arsenic in natural soils is an urgent necessity. The authors reported that waste gypsum powder is effective for the immobilization of this kind of arsenic and suggested the precipitation of calcium arsenate by the reaction between calcium ions from gypsum and arsenate ions from soil. This study aimed to investigate the effect of gypsum on immobilization for soil samples with different arsenic dissolution properties and to check numerically the possibility of the precipitation of calcium arsenate by the calculation of its solubility. The concentration of arsenic dissolved from soils decreased to below the value of 0.01mg dm-3 (the environmental quality standards. e.q.s.) by the addition of gypsum powder from 0.5 to 5 %. The solubility of calcium arsenate was calculated to be 0.2 mg dm-3 as the lowest value in the pH range examined, which is much larger than the e.q.s., and the precipitation of calcium arsenate cannot be the cause of the immobilization. It was shown that gypsum promotes the adsorption of arsenate ions on soil particles due to adsorbed calcium ions. The adsorbed calcium ions are likely to neutralize the negative charge on soil, to provide positively charged adsorption sites for arsenate, and to promote the adsorption and fixation of negatively charged arsenate ions on soil particles.
To estimate CO2 and CH4 fluxes from an agricultural land accurately using the energy balance flux ratio method, first, the temperature difference and the mixing ratio difference between two heights, which are variables in the method, were corrected with the law of propagation of error. Next, the relationship between friction velocity and turbulent diffusion coefficient was obtained using data with relatively larger corrected temperature and mixing ratio differences, and fluxes were estimated using the turbulent diffusion coefficient calculated from the relationship. To verify the applicability of the method, the quantities of net photosynthesis calculated with estimated CO2 fluxes were compared with those calculated using the photon conversion efficiency (the increment of carbon content in plant per 1mol of photon). Both quantities coincided satisfactorily with 0.95 of proportional coefficient and 0.97 of correlation coefficient. In conclusion, gas fluxes from an agricultural land could be estimated satisfactorily using the energy balance flux ratio method if the gas concentration could be measured accurately.
Main habitat of Grey-headed Lapwing (Vanellus cinereus) is rice fields. Recently, it is reported that habitat area of this species has been expanding in rice paddy districts in Japan. On the contrary to this, rice field area has decreased and fallow field has increased during the last few decades because of rice acreage decrease policy of the Japanese government. Thus, we examined how increase of fallows field influences the habitat area of this species by observing its predatory behavior and foraging sites. Our observation revealed that this species used the run-stop-peck method as visual feeding and the analysis of its predatory behavior demonstrated that open field was required to have good visibility as foraging environment. In addition, as a foraging site, this species preferred the place where the plant height was low, and the ground surface was partially or not flooded. Therefore, this species moved from the rice paddy fields to weeded or plowed fallow fields after the stage of midterm drainage when rice plants became higher than this species and feeding became difficult in the rice fields.
Return levels of daily rainfall at 21 observatories all over Japan were estimated by applying Peak-Over-Threshold (POT) theory, which is statistics theory of extreme value dealing with data exceeding some specified value, and characteristics of POT estimates were examined by comparing with estimates from Annual Maximum Series (AMS) by applying conventional extreme value theory. Threshold value required to apply POT theory was standardized by using average and standard deviation of annual maximum daily rainfall for summarizing relationship between threshold values and return level estimates at all observatories. Results show that POT and AMS estimates of return level were close for short return period for all observatories; however, significantly different for long return period for some observatories where the largest daily rainfall is far from the second largest.
The authors conducted a swimming experiment in the field using cultured masu salmon (Oncorhynchus masou masou) fingerlings in order to study the relationship between tail beats and swimming speed. The experimental equipment used was a stamina tunnel with a rectangular cross-section channel, which was installed at a local fishway. The experiment was conducted using an average cross-sectional water flow velocity of 48 to 137 cm·s-1, and using masu salmon fingerlings with a total length of between 4.4 and 8.8 cm (from 3.7 to 7.5 cm in the body length). Movement of tail beats were recorded during the swimming experiment using a high-speed camera. The results showed that the ratio of the amplitude of tail beats to the total length of the masu salmon fingerling was constant, even with an increase in frequency or swimming speed, and its value was 0.12. Masu salmon fingerlings swam with a tail beat frequency of 20.8 to 39.1 times per second, and a positive correlation was found between the swimming speed and the frequency even in the high frequency region. This allowed us to obtain an experimental formula defining the relationship between swimming speed and the frequency of tail beats.
Damages caused by the recent large-scale earthquakes such as the Mid Niigata Prefecture Earthquake in 2004 and the 2011 off the Pacific coast of Tohoku Earthquake vary a great deal both in form and in scale from those of the past natural disasters. Those damages revealed the limitation of existing institutions such as laws and programs for post-disaster restoration. As for the restoration of farmland and agricultural facilities, “the restoration to original-form” is a basic principle, which does not allow their improvements. In restoration process of disaster-affected areas, however, there is a compelling need for a new principle of restoration that allows the improvement of farmland and facilities for disaster prevention and agricultural rationalization. In addition, well-coordinated implementations of different restoration works, using an administrative plan, such as reconstruction plan, are of crucial importance in restoration process. The current mode of restoration under the idea of “the restoration to original-form” does not provide such an opportunity, which sometimes causes wasteful investments. In this paper, we examined limitations of existing institutions for the post-disaster restoration of farmland and agricultural facilities and suggested their improvements and the way of coordinating different restoration works based on disaster level.
The abundance of the freshwater mussel Inversiunio jokohamensis was investigated in a reservoir where management has been abandoned. The investigation was carried out on September 12, 2009, and composition of microalgae investigated on November 8, 2009. The results obtained were summarized as follows: 1) individuals in shore side habitat were more abundant than in offshore side; 2) there was a noticeable absence of individuals with < 50 mm body length; 3) the ratio of old individuals was high while diversity of generation was minimal; 4) no fish were caught using a trap method in the reservoir. This research indicated that recruitment had not occurred for several years.
Since the Serviceability of the sediment pavement on farm road is not clarified, a performance-based specification of the sediment pavement is not progressing. Pavement for an examination was carried out on the road of Tottori University, and the serviceability of the sediment pavement was evaluated. The measuring instruments that soil pressure meter and water meter were installed in pavement, and the state of stress and water content in the pavement was observed regularly. Moreover, the longitudinal surface profile and the vibrating acceleration were measured. This paper showed clearly that the longitudinal surface profile and the vibrating acceleration were normal distributions. And the Surface roughness was considered from the result.
The countermeasures that enable frogs to cross agricultural canals have been developing because frogs often drown in agricultural canals with vertical concrete walls in Japan. The objective of this study was to develop a method for evaluating the population viability of the Japanese Brown Frog Rana japonica after countermeasures are installed. Two types of simulation models were examined; a ‘basic model’ based on the age-structured model and a ‘crossing model’ to consider the proportion of frogs crossing canals. Parameter values such as survival rate and fecundity were estimated from observation data of age-dependent population fluctuations. Comparison of a basic model simulation with the observation data suggests model validation. The crossing model simulation with an initial population of 1,000 showed that a crossing proportion of 100% would achieve a 95% population viability after 40 years, suggesting frog migration should be ensured in this case.
In order to grasp the actual condition and the characteristics of stone walls in farm land, firstly ambiguous terms regarding stone walls were clearly redefined and secondly field investigations and interviews were conducted at the twelve selected regions in western Japan where there are terrace fields with stone walls. In the study regions, the farm land stone walls were made with locally produced stones with the intention of ensuring larger farmland in steeply sloping areas. The farmland stone walls were mainly constructed by dry rough masonry with boulder stones or broken stones. Though typical characteristics of masonry in each study region could be grasped, the features of the masonry were quite diverse within a study region because of difference of time from the construction or restoration work. Comparing the typical profile of farm land stone walls with that of road side stone walls, differences in the slope gradient, the materials and the amount of back filling, and the foundation structure were observed.
When improvement works for overage irrigation tanks are performed, existing embankment is first excavated, then a new outlet conduit is established and is buried with backfill material. In this case, the stress generated in the backfill between outlet conduit covered with reinforced concrete and the existing embankment may decrease. This phenomenon is called arching action and causes a large reduction of stress. Consequently, the backfill under the arch becomes a weak point in the structure and poses a risk of hydraulic fracturing. In this study, the arching action is evaluated quantitatively. Parametric studies on inclination angle of excavation, excavation width, stiffness of foundation and existing embankment and compaction stress are performed to reveal the influences on the stress condition. Moreover, the effect on the arching action of the stiffness of flexible conduit, which has recently become popularly used in the improvement of irrigation tank, are discussed.