Studying the rill link characteristics and statistical laws of geomorphology of rill networks in fields is essential to clarify the effect of rill networks upon sediment yield from fields with rill networks and to construct a model for predicting the sediment yield. We investigated the rill link characteristics of study rill networks developed in sloping fields using the concept of link for drainage network. Furthermore, we investigated the relationships between the total rill link length, the rill link slope and link magnitude on the basis of link magnitude theories. We obtained several fi ndings:(1) The exterior and interior rill link lengths had gamma distributions, and the slope lengths of the source basins were nearly uniform for half the study rill networks.(2) The link magnitude theories were useful in predicting the number of rill links of any link magnitude within each of the study rill networks.(3) The average of the total link lengths within sub-basins whose outlets are at the upper ends of rill links with magnitude was accurately predicted by linear functions of magnitude for each study rill network.(4) The average gradient of rill links with magnitude was approximated by an elementary function of magnitude for some of the study rill networks.

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We developed a new method for predicting sediment yield from a rill network on a sloping field during a rainstorm. This method was developed by combining characteristic geometric models, which are functions of the link magnitude and have rill link characteristic parameters, with a sediment yield prediction model proposed previously. By applying the functions to the study rill networks, we showed that the characteristic geometric models are valid. The results of this study indicated that the method to predict the sediment yield is effective when a given rill network is well developed and rill erosion is detachment limited within the rill network. This method can be used to predict sediment yield from a rill network on steep slope without the need to compute the erosion along all links within the rill network. The method does not require knowledge of the complete geometry of the rill network, nor tedious calculations when suitable values of the rill link characteristics are given. Moreover, it can analyze the effects of the rill link characteristics on the sediment yield.

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The settling velocity of a single floc of Na-and Ca-montmorillonite was measured as a function of floc diameter to investigate effects of ion species and its concentration on the structure of montmorillonite floc. The structure of montmorillonite flocs were analyzed in the light of scaling relation between the settling velocity and the diameter of settling floc. In the scaling relation, the fractal dimension and the proportional constant were compared for each experimental conditions. In the case of Ca-montmorillonite, the proportional constant of lower ionic concentration turned out to be bigger than other cases. This result was interpreted as that structure unit of montmorillonite change into compact one or that size of the structure unit change into big one. This is consistent with the picture of the formation of tactoid array.

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According to the calculated salt balance of the entire Hetao Irrigation District, the district is gaining 1.7 M ton of total dissolved salt annually. In spite of the fact, irrigation engineers and farmers assert that salinization of the district has improved in recent years. Furthermore, the LANDSAT image analyses show a recent decrease in the saline area. The first objective of this paper is to clarify the riddle in salt dynamics, by a systematic sampling and analysis of canal water, groundwater and soils. All of the water soluble and insoluble cations including exchangeable cations were analyzed. The results showed that most of calcium precipitated in the soil, consequently, sodium predominantly accumulated in the top layer and drained to the drainage canal water. The second objective is to propose a new leaching requirement based on sodium balance, LR_Na and to apply it to the whole district. The estimated LR_Na in 2005 was 0.12, which agreed with the present observed drainage fraction 0.11. It means that sodium balance of the whole district is almost attained at present time and that the new leaching requirement, LR_Na indicates the actual salinization status of the district better than the conventional leaching requirement. Furthermore, risk of salinization was evaluated on each branch drainage canal block. The risk was found to be high in the central blocks.

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Investigation of situation of riprup is very important to examine the function of the dam used for long period. Among several investigations, the picture of the riprup is very useful to know the particle distribution and existing ratio of classification of rock. However, this is very time consuming and troublesome work when the investigation is carried out by manual procedure. In this paper, it is examined that the procedure is carried out automatically by using the image analysis. The most likelihood method and the maximum posterior probability method are used to judge the difference among rock classifications. The data used for judge is RGB data of each pixel. Moreover, the discrimination method of each rock from the binarized image is newly developed. The proposed method is applied to regular and irregular riprups. The results are compared with the ones from manual procedure. The particle distribution form image analysis is very similar to the ones from manual method. While the existing ratio of classification of rock is a little different, the practical application would be effective.

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The purposes of this study are to clarify the process of paddy plots' alteration and evaluate its influence on rice production in Don Daeng Village, one of the traditional villages in Northeast Thailand. In this study, shapes of paddy plots for 1981, 1992 and 2005 were determined by using aerial photos, satellite images and field surveys. Due to the integration of each paddy plots, the numbers of paddy plots for each corresponding years have decreased by 8, 401, 7, 312 and 2, 885, respectively. Within the period of 23 years (1982 to 2005) the average plots' size have extended three times. In addition, impacts of paddy plots' alteration on rice productivity was also analyzed by performing leveling surveys on “Nong(concavity landforms) ” and rice crop performances. The results indicated that the rice productivity has increased at high-land of “Nong” due to the reclamation of water condition, where paddy plots were previously smaller and rice production was lower. Contrary to that rice productivity has decreased at low-lands due to the flooding, where rice productivity was previously higher.

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It is well known that water repellency of sand affects the hydrological process and soil erosion. However, detailed effect of sand wettability on the downward infiltration has not been clarified. We conducted rainfall infiltration experiments using sand samples with different contact angle to assess the relationship between the contact angle and the fingertip velocity and finger width. It was found that fingertip gained almost constant velocity in the sand layer with apparent contact angle from 50° to 75°, and that finger width showed the minimum value when the apparent contact angle was about 72°. Fingertip velocity became faster as the rainfall intensity became higher, but finger width showed only slight increase. We applied an existing model to estimate finger width, which did not explain the feature of finger width mentioned above though the model apparently well fitted to the measure values.

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The purpose of this paper is to examine the point of problems and subjects related to the control of land use by means of investigating the trend of cancelling the designation of agricultural land zone, conversion of agricultural land and development permit in suburbs which is the outside of urbanization promotion areas, picking out factors related to development permit and grasping spatial characteristic of development permit in Nagano City which is the site of the Winter Olympic Games. As a result, the following matters became clear. The change of land use was greatly influenced by the construction of facilities and the preparation of a network of roads related to the Winter Olympic Games. Especially, cancelling the designation of agricultural land zone by the administrative agency and the public conversion of agricultural land have quickened the urban sprawl in Nagano City. Cancelling the designation of agricultural land zone and conversion of agricultural land were performed without consideration of land use planning for the while city, and the control of land use thereafter was not done properly. A comprehensive system of land use all over the city is necessary.

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In the diagnosis of irrigation and drainage channels and tunnels, the difference between the present performance and the required performance that agricultural facilities should originally demonstrate must be understood. According to the result of diagnosis, the provision is decided whether extending the service period by the repair and reinforcement, or improving the function by renewal. For that reason, it is important to monitor the progress of defective events and to evaluate the performance of agricultural facilities. Authors developed continuous digital scanning system which can record defective events as a digital format, and also developed penetro meter which could measure the strength of ground at the back of concrete lining in tunnels. Through a result of field tests, which had many kind of scales and types, it was demonstrated that the new system could take not only visual information about agricultural irrigation channels and tunnels quickly, efficiently, and accurately, but also efficient information about the back of concrete lining in tunnels.

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Rice terraces are not considered well-conserved if sustainable paddy rice planting cannot be carried out on them. In contrast to farmlands where upland crops or grasses are grown, in Japan, most rice terraces need irrigation systems, that is, irrigation facilities and their operation and maintenance for their conservation to obtain water for paddy rice planting. This paper focuses on the irrigation systems. necessary for conserving the rice terraces and investigates 3 rice terrace areas to clarify the irrigation facilities and their operation and maintenance. The main findings of this study are as follows:(1) A full-set of upstream to downstream irrigation facilities for rice terraces, like for a paddy-field area in the plains, comprises a reservoir, small river, intake works, diversion canals, distribution canals, delivery canals, plot-to-plot irrigation systems, and drain canals.(2) Maintaining the diversion canals and distribution canals requires a lot of work by farmers since the length of these canals per irrigated rice terrace area is rather long.(3) High skill and much working hours are required for supplying plot-to-plot irrigation systems in the rice terrace areas with few intake works from delivery canals.(4) Longer working hours are also required for water management in each plot by mowing levee, preventing water leaks, etc.

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