Farm irrigation near seashore has become a problem due to the influence of saltwater from sea and the high salt content contained in the irrigation water. As a solution of this problem, irrigation is planned for the Kashima-Nanbu area and the purpose of this paper is to analyze the diffusion of low salinity irrigation water. We carried out experiments with equipment as a trial and performed a simulation during these experiments. As a result of our work, it was found that although long-term and heavy irrigation is not really being carried out, irrigation water did not seem to reach the lower aquifer.
As the irrigation position is setted landwards, irrigation water reaches to low aquifer. Movenent and diffusion of irrigation water are influenced by the irrigation rate, irrigation period and permeability.

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The distribution of soil moisture tension under the conditions applied to the sub-irrigation method by use of the finite element method in case of the bare soil condition and crop cultivation. In the above case, the movement of soil moisture was dealt with in the non-steady state, and investigations were attempted to reappear and predict the distribution of soil moisture tension occuring around the ceramic watering pipe.
The results are as follows.
First, the distribution of soil moisture tension with regard to the difference in the negative pressure head, the difference in soil texture, and the existence of root zone were understood to be able to reappear due to the use of the finite element method in the non-steady state.
Second, to predict the distribution of soil moisture tension under the bare condition, the qualitative tendencies of the results obtained from the calculations were understood to be same as the actual measurements.
Third, to predict the distribution of soil moisture tension under the crop cultivation condition, the qualitative tendencies of the results obtained from the calculations were different from the actual measurements to a slight extent. These differences were guessed to be influenced by the strength of water absorption of the roots and the initial conditions setted.

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This study was carried out to decide the range of the negative pressure given to porous ceramic pipe under different soil textures and to make an exclusion system trial of the entrapped air bubbles in porous ceramic pipes and water pipes.
The experiments in this study were carried out to investigate the difference in water quantity and the infiltration situations by the use of Masa soil, Kuroboku soil and Fudai field surface soil, the influences under the conditions of entrapped air bubbles in porous ceramic pipes and water pipes, and to test the performance of the air bubbles exclusion system tried.
These results are as follows.
1) Water quantity and infiltration situations were to be influenced by the difference in soil texture under the same conditions of negative pressure given
2) Water quantity and infiltration situations are influenced by the amount of entrapped air bubbles in the porous ceramic pipes.
3) The air bubble occurred in the porous ceramic pipes and the water pipes could be excluded about scores of second under the condition of 50 cm plus pressure head given by the use of the performance of the air bubbles exclusion system tried.

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In this paper, on the basis of hydrological properties of the pipe drainage from a clayey agricultural field with shrinkage cracks, water movement toward a drain pipe in the soil of a field is investigated quantitatively.
The test field was a lysimeter 30×70 m in area with a depth of O.7m. Drain pipe was installed at the bottom and through the center of the field. In addition, mole drains was installed orthogonally to the drain pipe at intervals of 1.2 m and at a depth of 0.35 m. The field consisted of heavy clay type soil. Many cracks in the subsoil existed, and the densities of the cracks were about 20m/m² at a depth of 0.1 m andabout 10m/m² at a depth of 0.6 m. So, structure of the subsoil was largely prismatic. The hydraulic conductivities of the subsoil without the cracks (soil matrix) were ranged from 10^-6 to 10^-7 cm/s.
Changes in flow rate of the pipe drainage from the field with time was measured according to the rainfall and after the field was ponded, when the water level was just near the soil surface (pipe drainage test). It was found that the recession property of the pipe drainage could be divided into two parts due to water level in the field.
In case that the water level was high, water flowed mainly through the mole drains toward the drain pipe, and flow rate of the pipe drainage decreased linearly with time. Thiswas similar to flow property from an orifice of a water tank, and could be interpreted by rapid flow through the mole drains and limit of the flow rate of the drain pipe.
In case that the water level was low, water flowed through the cracks in the subsoil toward the drain pipe and flow rate of the pipe drainage decreased exponentially with time. This could be approximated very well using Glover's equation, which are solutions of the differential equation of unsteady Darcy flow. Then, hydraulic conductivity was estimated to be (4-8) ×10^-2 cm/s.
As a result, it was concluded that the property of the pipe drainage from the field could be reflected by flow path of water toward the drain pipe according to the water level in the field, and that when water flowed through the cracks in the subsoil, the flow could be expressed by Darcy's law for a field as a whole and the actual hydraulic conductivity for the entire field was estimated in the order of 10^-2 cm/s.

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In order to understand the macroscopic behaviors, i. e., the compaction and strength charcteristics of non-ash-derived Kuroboku soil, the response of coarse (2-4mm) and fine (<1mm) aggregate to drying and compaction have been investigated. Aggregate samples were separated by sieving from both topsoil (organic) and subsoil (organic-free).
(1) Both coarse and fine aggregates from topsoil showed numerous cracks but never broke into smaller units after drying. In contrast, those form the subsoil disintegrated rather easily, indicating a weak inter-particle bond deterioration.
(2) The changes in number and configuration of the cracks formed in the coarse and fine aggregates after compaction were much greater for the subsoil than for topsoil in the earlier stage of drying, and the reverse was true in the later stages of drying. Almost the same tendency was observed for the shape of the fine aggregates.
(3) The overall macroscopic behavior of soil, in terms of compaction characteristics or compaction curves, could be understood as a consequence of the combination of several factors such as the linking aggregates, formation and growth of cracks, increase in mechanical strength of the aggregates themselves, induction of pore pressure, etc., after drying and compaction.
(4) Both topsoil and subsoil samples, attained the values of q_u, max, where fine aggregates arranged in a complex way with uneven and angular shapes and certain mechanical strength conferred by drying and compaction.

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(i) Earthworm In order to understand the response of Kuroboku soil to external mechanical forces, the changes in soil aggregate shapes caused by drying and compaction have been analyzed by the Mandelbrot fractal dimension procedure.
Samples of aggregates, 2-1mm in size, were separated by wet sieving from topsoil and subsoil samples of allophanic and non-allophanic Kuroboku soil.
(1) Mandelbrot fractal dimension procedure proved to be useful in the quantitaive formulation of the change in the shape of soil aggregates ocurring on drying and compaction. Themagnitude of fractal dimension (D) obtained for the samples used were 1.9-1.3.
(2) The fractal dimension (D) changed, as a function of drying, in the form of a curve with an exsreme value (maximum or minimum) at the maximum dry density (ρ_{d max}) for topsoil, but in a linearly decreasing way for the subsoil samples. Such a difference was presumed to be due to the difference in the microstructure of aggregates between topsoil and subsoil.
(3) Relationship between fractal dimension (D) and water content (ω) of the samples after compaction was expressed by a concave curve with a minimum at the maximum dry densityn (ρ_{d max}) for all samples used. The sample from allophanic topsoil showed, however, a small convex at the maximum unconfined strength (q_{u max}). The fractal dimension attained a maximum when the non-allophanic samples were compacted at an air-dry state.

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In the design of drip irrigation systems, special attention must be paid to investigation that the variations in the discharge along the lateral is in specified allowance. Accordingly, in the design of a drip irrigation system, from the designers viewpoint, how to control the variation of pressure along the lateral is to regulate the discharge difference from the emitter.
In estimating the pressure distribution along the lateral line, it is. necessary to obtain information about the friction factor in the drip tubing.
So, the friction factor was experimentally measured. The results are as follows:
Re<2, 000 f=64/Re
Re>2, 000 f=0.316Re^-0.25
Where, Re: Reynolds number
f: Friction factor
On the assumption that the arrange method of pipe size is summarized as follows:
(1) In the case of utilizing the single pipe size along the field, the relationship between uniform application water and pipe size must be investigated. From the standpoint of hydraulics and economy, the suitable pipe size must be chosen.
(2) The discharge through the lateral line in drip irrigation is gradually reduced from the upstream end to the downstream end. Usually, in the upstream reaches, the high friction head occurs, on account of the high discharge, the uniform application of water breaks down. If pipe of varying sizes is adopt the cost is lower than the larger size pipe that would be used in the fields.

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The purpose of this paper is to investigate farmland conversion to urban uses in the rural-urban fringe and to find out the orderly tendencies concealing in the conversion. The results are summarized as follows:
· Number of farmers, who have converted their farmland to urban use, become larger in proportion due to the weaknesses in the farming structure,
·No correlation between the number of farmers converted and the size of their holdings,
·Number of farmers converting become larger in proportion to the degree of farmland fragmentation
·Conversion takes place more often in proportion to the distance from farmhouse to actual farming plots,
·No correlation between the size of land parcels and the number of land parcels converted.
The phenomena of farmland conversion are analyzed from the social structural aspect of farmland because most land being developed for urban use is small in scale and scattered, and mainly because it is presumed that they are closely connected with the structure of farmland ownership which is characterized by small holdings having a fragmentary pattern.

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In plowed fields on slopes, soil erosion occurring due to rainfall is one of the most important and dangerous natural disasters. It is, therefore, valuable to investigate the rainfall intensities on mountain slopes.
The authors estimate the slope precipitation with 2 equations, which are derived from the relations between the slope precipitations and plane precipitations. One of the equations is based on wind data and another one is with data of a vector rain gauge being made on an experimental basis by the authors.
To examine these equations, the authors compare the estimated values with the observations on the slopes of Mt. Aso.
The following results are obtained:
1) With an increasing slope gradient and/or wind speed, the slope precipitation becomes larger than the plane precipitation on the windward side of the hill.
2) When the wind data are obtained, the slope precipitation is approximately calculated by the next equation,
R_d=R_c {tan α_a· tan α_b· cos (β_a-β_b) +1}
where, R_d: slope precipitation, R_c: plane precipitation, α_a: angle of the falling raindrops, α_b: slope gradient, β_a: azimuth angle of the falling raindrops, β_b: azimuth angle of the slope.
3) Without the wind data, the slope precipitation is estimated easily and approximately from the data obtained with the vector rain gauge.
On analyzing relations of the rainfall to soil erosion, the plane precipitation was used in the past. After this, it is desirable to use the slope precipitation and the vector rain gauge is suitable for a simple estimation of the slope precipitation.

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In the previous paper, we proposed a model named the long and short terms runoff model, LST-II, for analyzing both flood and long term runoff successively, on the basis of the data observed at a small experimental basin of O.24 km². This paper examines the applicability of the model in the Eigenji Dam Basin of 132 km².
There are six telemetering gauge stations for precipitation. Hourly data at three stations are available since 1975, but the data at the residual stations are only for the seasons without snow since 1981. First, therefore, the method for estimating areal precipitation is examined including the supplementing technique for non-gauged data. The estimation method for evapotranspiration is also discussed.
The model parameters are idntified using the SP method for the two years of data. The results of simulation agree well with observed flood and long term runoff hydrographs not only for the identification period but also for the residual period for verification.

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River mouth closing is one of several troubles which are caused by an interaction between the incident waves and the opposing river flow. This is closely associated with the formation of sand bar near the river mouth. In order to solve these problems, it is necessary to have a deep understanding of sand movements occurring in the wave-current field.
This paper describes the results of the experiments on bottom transformation in a two dimensional wave-current coexistent system, and examines the distributions of the sand transport rates which induce the bottom profile change.
First, we proposed a method of calculation to predict the position and the scale of river-mouth sand bar on the basis of the experimental results.
Second, we classified the distribution patterns of the sand transport rate into three categories.
Third, we proposed a new criterion to judge the predominant direction of the sand transport on the wave-current coexistent system.
Fourth, the calculations of the distributions of the sand transport rate using the above relations have a good agreement with the experimental results.

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The diameter exponent used for evaluating bifurcations of arteries, trees, rivers and so on was introduced to discuss the bifurcation in a pipeline water conveyance system. The relation between the discharge and diameter was discussed using numerical experiments.
1) It was clarified that optimum diameter exponent Δ to reduce construction costs given as a function of the diameter and length was about 2. Therefore, at the bifurcation, the location of each pipeline or water head at the bifurcation point is desired to be given as each velocity is equal. By applying this parameter Δ to a pipeline water conveyance system, the optimum location of each pipeline at bifurcation can be obtainded directly and easily from optimum duty of water.
2) In numerical experiments, it was recognized that the construction costs at each bifurcation was reduced 1.7-14.4% by researching the position of bifurcation point of pipelines. This perecntage was largest in the case that the length of each line was almost the same, and that one of them being at the end of the flow. The locations of each pipeline as a result of this precise calculation and locations easily obtainded by applying optimum diameter exponent Δ showed close agreement.
3) It was recognized that diameter exponent δ given by investigating the general relations between velocities and diameters used for construction was about 2, the same as optimum diameter exponent Δ. Therefore, it was clarified that parameter δ can be used as a condition to obtain the optimum location of pipelines if it is defined as a constant.

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