The Kanto district suffered from a record rainfall in 1987. As the storage volume of the dams at upper reaches of the Tone River basin rapidly decreased, water intake from the Tone River and the other rivers were restricted. For these reasons, farmers and the staff of the land improvement districts were forced to use great deal of labor for regulation of water use with a great amount of money being spent for drought countermeasures.
Therefore, the definition of drought must be considered from the viewpoint of not only decreasing rice crops but also increasing labor and costs for drought countermeasures.
This paper deals with drought damage and irrigation water management for drought periods in the A river basin of the Kanto district. The actual state of the drought was clarified by questionnaire reseach and an analysis of it.
The following conclusions, as factors of drought damage valuation, were obtained through this investigation.
1) A delay in scheduled puddling. The scheduled puddling was delayed from 5 to 8 days on the average. Therefore, some farmers replanted rice seeds and controlled the growth of the rice plants.
2) Decrease in the rice crop harvest. Ten percent of the farmers suffered a reduction by a few percent compared with last year's crop.
3) Increase in meetings for regulation of water use. Special meetings for drought countermeasures were held 3 to 6 times.
4) Cost for drought countermeasures. The costs for drought countermeasures consisted of purchasing pumps, digging wells, fuel charges and labor costs. Seventy to eighty percent of the farmers were forced to spend more money.
5) Increase in labor for water management of paddy fields. Due to frequent patrolling of the paddy fields during the puddling period, labor for water management increased and so to 70 percent had to work twice as hard compared with the past year.

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In cold and snowy regions as in Hokkaido, snowmelt amounts are the most important resource for supplying water for irrigation. However, there are little meteorological and hydrological data in mountainous catchment areas. For the Toppu basin sites around the higher mountains, it is difficult to design a rainfall-runoff process from the rainfall of the rain gauge station nearest the basin. Some rainfall-runoff method is required to solve the water-balance problem in situations were data is not sufficient. The autoregressive (AR) method used herein is very powerful to inversely estimate rainfall and snowfall amounts at higher altitudes from the discharge output in the rainfallrunoff process.
The main results of the present study are summarized as follows:
i) In the current catchment area study, the response characteristics in both the winter and summer seasons were well reproduced by the identical AR process.
ii) The seasonal correction factors for precipitation between the catchment and the lowest rain gauge station were estimated. The correction factor was 2.2 in summer and fall, and 2.7 for the other seasons.
iii) The seasonal correction factors estimated by the AR method corresponded well with the factors which was derived from the coaxial method between the discharge and rainfall.
The filter-separation autoregressive method was found to be useful for the runoff analysis in the Toppu basin.

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Snowmelt plays an important role regarding water resources problems in Hokkaido where snowmelt runoff accounts for about 50% of the annual runoff in most of the rivers. The degree-day method is the simplest approach to analyze the snowmelt mechanism in mountainous catchments, especially when there are little meteorological and hydrological data. In a previous report, the authors determined that there was a constant flux ratio between interflow and underground water flow that has a day-delay of flux. The present paper addresses the analysis of snowmelt runoff using the degree-day method and these previous results. Information on the change in the snow covered area derived from LANDSAT data is also employed to estimate the catchment-wide snowmelt.
The main results obtained herein are as follows:
i) In the study catchment, the simple model applied with the snowmelt amount resulting from use of degree-day factor and coupled with the previous runoff characteristics was in good agreement with the obierved discharge volume. Snowmelt runoff was systematically explained using this simple model.
ii) The catchment-wide snowmelt was obtained by superposing snowmelt amounts in the subcatchments divided according to elevations in which the mean daily temperature in each divided zone was corrected by using the lapse rate. The result is good from a practical standpoint, so the catchment snowmelt is essentially explained by the degree-day factor.
iii) The model was able to estimate the snowmelt amount from the change in the snow covered area that was derived through LANDSAT data. It was proven that the estimated discharge amount coincided with the observed discharge amount.

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Shiraishis' multiple regression runoff model is effective for analyzing bad data. This model was calculated on the linear part of runoff separated by the condition of rainfall or discharge. The former is called the FMD method and the latter the FMR method. These two methods seemed to be equivalent. This model treats Y intercept b₀ as the base flow. The author clarified that these two points are wrong for paddy field areas. For separation of the base flow in paddy filed areas, a new method, a dummy variable method was proposed and used in the Naka River basin. This method can separate the base flow caused by rainfall from that caused by intake. In this basin, it was clarified that FMR method can separate the effect of intake from the effect of rainfall and intake. Additionally, a multiple regression intake model by rainfall was first developed in this basin in Japan.

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On the assumption that the heat properties of sandy soil are known, the validity of estimation for the apparent thermal conductivity of gravel was examined by means of an unstationary comparison method. The feature of this method can be stated to be rather simple outdoor practice for the experiment, but in the analytical case, the method must have the Newton's cooling law for the surface boundary condition. Then, the heat transfer coefficient must be known to evaluate the thermal conductivity of the sample exactly. However, the heat transfer coefficient has some troublesome properties depending on the surface characteristics of the object used in the experiment and atmospheric stabilization. But this heat transfer coefficient has a special characteristic, in case of introducing the fluctuation of its value, having an influence on only thin surface layer's soil temperature, meanwhile the thermal conductivity has that, in case of introducing the fluctuation of its value, having an influence on the soil temperature to greater depth. The feature of this method, in other words, arrives at a conclusion of singularity between the heat transfer coefficient and thermal conductivity. In a soil temperature analysis, both values can be obtained by trial and error. Lastly, the availability of the unstationary comparison method was verified by means of the claim of the heat transfer theory.
In this unstationary comparison method, Cary's β that is the phenomenological enhancement factor of the water vapor transfer in the pores, is adopted as an average value of 2.0 for wet sandy soil.
The above two samples were put in the two cylindrical columns A (dia. 50 cm, length, 60 cm) and B (dia. 30 cm, length, 60 cm) bound with insulating material. Columns A was then covered by uplayer gravel (grain size: mm) and down-layer wet sand, and column B was completed by three layers such as top layer dry sand, middle layer gravel and bottom layer wet sand. At the center portion of the cylindrical columns, 7-8 thermocouples (Cu-Co) were inserted for soil temperature measurements.
All the columns were placed on a concrete surface of a building top. The sun was used as the heat source for the columns. Then, the global radiation, albedo of the soil, air temperature, humidity and wind velocity were measured.
In addition, another two experiments were carried out. One was carried out to check on the insulating effect of the columns A and B. The second one was preformed in the glasshouse for the availability of the unstationary comparison method may be said to be good for directly evaluating the thermal conductivity of gravel.
The ratio of the convection value to the total heat transfer in the gravel layer may be evaluated to be about 40% by means of obtaining the difference of the effective thermal conductivity, called the stagnant conductivity estimated by S. Yagi & D. Kunii's theory from the above apparent thermal conduct ivity.

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In accordance with the expansions of length and discharge of pipes in agricultural water use projects, the number of diversion apparatuses set along the pipe restricts the control characteristics of the entire accuracy of the pipe system in water use.
So far, we have developed an automatic constant diversion apparatus for open canal by means of the effects of buoyancy. However, due to the lack of a precise formula for the discharge coefficient and dynamic pressure coefficient on a stop plate, some improvements were unsatisfactorily obtained.
In our preceding paper, we have analyzed such unknown coefficients using hydraulic experiment. Namely, discharge coefficient and dynamic pressure distribution coefficient on a stop plate were clearly defined. Due to this, we were able to go to the next stage to improve the accuracy of the automatic constant diversion apparatus with a float and submerged orifice.
Generally, the fundamental functions of a diversion apparatus are those of constant diversion discharge with no mixing of air into the water. To realize these objectives, in this report, we studied the automatic constant diversion apparatus with a float and submerged orifice. The errors of such a diversion apparatus were analyzed for constant diversion characteristics under the condition of varying pressures and various upstream main pipe pressures.
Also, a field test was successfully performed at the Kisogawa water use project.

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Some apprehension exists regarding wind damage to arable land around large-size agricultural structures. Wind tunnel testing was carried out to investigate the airflow characteristics at arable land around the large-size structures, by examining pumping facilities and a surrounding lotus field. The experimental results demonstrated that the distribution of mean velocity and turbulent kinetic energy on a lotus field was strongly influenced by the pumping facilities. When the reference wind velocity at a height of 20m in actual size was 8.0m/s, the wind velocity of the lotus field was about 4m/s at an actual height of 1m before constructing the pumping facilities. After the construction, the wind velcity decreased to 2 m/s and the kinetic energy increased to 2-3 times more than before the construction, on the leeward side of the pumping facilities of the lotus field. Meanwhile, the wind velocity on the east and west side of the main pumping building increased to 5-6m/s.
Especially, the strong kinetic energy area on the leeward side of the pumping facilities corresponded to the wind damage area of lotus.
Also, a numerical simulation means of k-ε 2 equation model was carried out under nearly the same wind tunnel testing condition. The experiment results showed that compared to the wind tunnel testing results, the simulation results reproduced the distribution of the mean velocities well. The distribution pattern of kinetic energy of the arable land was similar to the wind tunnel results, although the values of kinetic energy were different from the wind tunnel results.
Wind tunnel testing needs a wind tunnel facility and a vast sum of money, time, and labor. A numerical simulation is expected to be useful to save wind tunnel testing cases for the design of airflow for arable land around large-size agricultural structures.

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In Japan, lots of lakes are greatly eutrophicated, so every summer blue-green algae, socalled water bloom, occurs to a massive extent in these lakes. It causes a very serious problem for irrigation systems. It is considered that gas vacuoles of microcystis would be destroyed by the excess pressure of the pumps in an irrigation system, and then water bloom will loose its floating ability.
We studied the characteristic of sedimentation of some kinds of water blooms under applied pressure. The pressure were applied using a compressor from 0 to O.6 MPa during one minute. The kinds of water blooms were investigated using a microscope (Photos. 1-10) and the state of gasvacoules were examined by an electron microscope.
Blue-green algae belonging to Microcystis (aeruginoza and viridis) did not sink under small applied pressure of less than 0.2 MPa, and it began to sink under the pressure of 0.3 MPa as shown in Fig. 1. Under the pressure of 0.4 MPa all of them sank. Gasvacoules were destroyed as shown in Photo. 8. However, algae belonging to Anabena started to sink under the pressure of 0.2 MPa.
Only one second is need to apply the pressure to sink the algae as shown in, Fig. 5. Thus, blue-green algae can be sank by applying a pressure of more than 0.4 MPa. Based on this result, it would be useful to plan some systems to remove blue-green algae from the irrigation systems.

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Puddling is the most important practice under the transplanted rice culture. The object of this study is to clarify the mechanism of percolation control by puddling in the laboratory experiment using three types of soil. In this paper, consideration was given to this based on the results of the changes in the soil surface and in the hydraulic head differences. The results are summarized below:
1. In clayey soil, the soil consolidation developed slowly, and over a long time from the lower part of the mixed layer to the upper part, and consequently, the flow rate was slowly reduced.
2. In medium-textured soil, it was considered that the sudden reduction in the flow rate just after the mixing was caused by the consolidation in the lower part of mixed layer and the filling of the consolidation layer and just below the mixed layer with fine particles.
3. In coarse-textured soil, the flow rate after the mixing was quickly reduced with the hindered. settling and the sedimentation rate of which was approximately constant. The flow rate after the sedimentation was influenced by the movement of fine soil particles and the filling with them.
4. The lower the permeability at the subsoil and the larger the dispersion of mixed soil, the longer the time which the hindered settling and the consolidation continued was. As a result, the flow rate kept decreasing over a long period of time.

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