An effective methodology is needed for an operation of multiple reservoirs water system. The system must contain drought countermeasures to avoid critical reservoir water levels such as an empty storage.
In this study, a method of operation to be capable of showing water conservation policy for water users, was developed based upon the “Method of Required Storage for Drought Curve” theory. Besides, the new method was developed to balance the release from each reservoir to command areas against the actual reservoir water levels, the probability of storage recovery, and the target level of recovery.
This methodology was verified by computer simulation using historical data on an actual river basin where four major reservoirs need to meet agricultural water demands.
The simulation results showed that the new method had advantages over a method to operate each reservoir individually. For instance, water conservation done by the new method was lower than that done by a method to operate each reservoir individually, on command areas which water conservation were higher comparing to others. However, the new method made water conservation on a few command areas be higher, so that several points to improve the new method were also discussed.

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In this paper, three substantial parameters are built in the soil moisture budget model to estimate the water consumption within the root zone, accurately.
They are 1) the reduction factor of evapotranspiration in the rainy day, 2) the capillary contribution factor to the effective root zone, and 3) the crop coefficient change factor induced by the soil moisture depression and the crop growth stage.
Using this new soil moisture budget model, we clarified,
(1) Reduction factor of evapotranspiration in the rainy day decreases amount of water requirement slightly during soybean growing periods.
(2) Reduction factor of evapotranspiration in the rainy day, the capillary contribution factor to the effective root zone, and crop coefficient change factor induced by the soil moisture depression and the crop growth stage were built in the moisture budget model. They decrease the amount of water requirement more because soil moisture in the root zone were not be lost so much.
(3) When rainfall were thought to reach the root zone in the soil moisture budget model additionally, the amount of water requirement is smaller than the previous results ((2)).

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The definition of water supply duration curve (S curve), and the relation betweenwater storage capacity and minimum water discharge has been cited in “Evaluation Method of Water Supply andWater Demand Potential” by Mitsuno (1994). Based on this idea, the evaluation method of the natural waterstorage capacity is developed in this study. The relation between necessary water storage capacity, developeddischarge and the natural water storage capacity has been conducted for two river basins as namely Honden basin andOnozumi basin by applying the evaluation method of necessary storage capacity and adjusting the water balancein the river basin. It is concluded that the natural water storage capacity is dependent on year, degree ofwater utilization and soil type.

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This paper describes a horizontal finite element technique which can analyze a confined groundwater flow around a partially penetrating cut-off wall. A partially penetrating cut-off wall is widely used in the construction of dewatering systems. Since the flow becomes almost vertical on the wall, a vertical two-dimensional or axisymmetric analysis is used to analyze the flow in its vicinity. A horizontal two-dimensional analysis is a suitable method for designing the arrangement of pumping wells and their operations, but it can only be applied to cases with a completely penetrating cut-off wall or without any kind of cutting-off structure. In the method presented here, the effect of the wall is modeled by low permeable elements whose permeability is determined by a theoretical formula. To obtain reliable results from the horizontal seepage analysis, all the nodes must be placed at points where the flow is almost horizontal. Therefore, the elements of the cut-off wall should not be too small. The results of vertical analyses show that the distance between the wall and the nearest node must be equal to the penetrating depth of the wall or larger. Additional calculations are necessary to estimate the groundwater level on the wall because no nodes exist there. Another theoretical formula is used to obtain it from the groundwater level around the cut-off wall elements and the flow rate through them. The results obtained with this method are shown and then compared with a solution from a three-dimensional analysis. It is concluded that the proposed technique is applicable to both steady and unsteady analyses.

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In order to investigate the performance of Kohgo's elastoplastic model for unsaturated soils, we carried out triaxial compression and isotropic consolidation tests for two unsaturated soils, namely DL clay and an artificial soil mixed with Japanese (Toyoura) standard sand and a commercial kaolinite. The triaxial compression tests were conducted under the different initial densities and different drained conditions and they are divided into 4 series of tests (DU, D, S and M) by the used conditions. The results of triaxial compression tests showed that the application of suction had no influences to elastic deformations but had the effect of inhibition to plastic deformations. Moreover, the unsaturated soils might also possess the critical state condition where the influence of difference of initial densities disappeared, the loose and dense specimens could have an unique soil water retention curve and they could occupy the same shear strength if they had the same values of suction and confining pressures. The consolidation tests with two constant values of suction were also conducted. The consolidation test results supported the results of the triaxial tests that the application of suction influenced only plastic deformations.

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This paper presents a fast converging iterative algorithm for implicit flood routing in channel networks of general configuration. Flood routing in a looped network can be simplified to the problem of dendritic networks by either dividing the original network into dendritic blocks or/and simply opening the loops. The dendritic subnetworks are then solved separately by the effective double sweep method assuming flow conditions (water levels) for the dividing nodes which are called interior boundaries. Water levels at these interior boundaries will be adjusted using a bisection-like iteration procedure until achieving the desired accuracy, i.e., flow discharges obtained for any pair of the interior boundaries which come from the same channel node become approximately equal. Test using data of a real river system proves the model's validity and its superiority in reducing computation time. The required number of iterations is independent from the network'scomplexity, and estimated at only 2 to 3 times more than that for a dendritic network of a similar size. Since each dendritic subnetwork is solved by the double sweep algorithm, the proposed model eliminates any difficultyconcerning the network size and computer capacity.

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Knowledge of retention characteristics of watershed is essential for conducting proper watershed management. However, the methods for quantification of retention characteristics of watershed in long-term period have not been developed yet. This paper proposes a method using reservoir model for quantifying retention capacity of watershed as a retention capacity index. The method was applied to four catchment areas located in Tochigi and Ibaraki Prefecture. Simulations were carried out to analyze the effects of different rainfall pattern on retention capacity of watershed. If the same rainfall pattern was used as input to the model, the order of retention capacity indices among study areas were the same. That order were reasonably explained by general recognition on relation between physical and geomorphologic characteristics of watershed and retention capacity. For comparison of retention capacity among watersheds based on their retention capacity index values, standard rainfall to beused as input to the model has been decided through simulation with hypothetical rainfall.

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Complicated surges in a large-diameter subteranean diversion channel with six surge tanks and a pumping station are studied with a nonlinear state equation based on a rigid water column theory.
The state equation consists of flow continuity equations for the tanks and momentum equations for large-diameter pipes with nonlinear resistance.
Under rectangular pulse inputs conditions where the pumped rate of outflow is equated to the total rate of inflow, the state equation and its linearized equation both yield almost identical oscillations of water levels. This shows that effects of pipe resistance on the surges are small, and justifies a free oscillation analysis.
Free oscillation equation has six eigen modes of different periods, including a rigid mode which is excited when the pumped rate of outflow differs from the total rate of inflow. The six modes constitute a variety of surges dependent on different inflow and outflow conditions.
Presence of the rigid mode needs sophisticated pump operations adjusted to real flood inflows.

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An analytical and experimental investigation is made on the compression index equation for remolded clays.
Choosing plasticity index I_p and liquidity index I_L as indices for sort and condition of clays and using I_p×I_L (= w₀-w_p) as a parameter, compression index for remolded clays C_c' is expressed by the following function, C_c' = F (w₀-w_p), where w₀ and w_p are initial water content and plastic limit, respectively.
Since the relationship between water content w and void ratio e for perfectly saturated clays is expressed as w = 100eρw/ρs, and G_s=ρs/ρw, where ρ_w, ρ_s and G_s are density of water, density of soil particle and specific gravity of soil particle, respectively, C_c'-(w₀-w_p) relationship can be transformed as C_c'= F [(e₀-e_p)/G_s], where e₀ and e_p are initial void ratio and void ratio at plastic limit, respectively. The above equation can be expressed simply as C_c' = F (e₀-e_p).
Experimental equation C, ' applicable to sorts of remolded clays is given for each parameter as follow:
1. For (w₀-w_p): C_c'=0.007 (w₀-w_p) +0.099 (coefficient of correlation γ= 0.981), or
Cc'=0.700 [(e₀-e_p)/ Gs] + 0.099
2. For (e₀-e_p): Cc' = 0.302 (e₀-e_p) + 0.064 (γ=0.976)

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The soil plant atmosphere continuum (SPAC) model was adopted for computing irrigation water demand on various topographic conditions (it stands for fields with south facing, north facing and flat topography) through analyzing radiation energy balance on each topographic conditions, which is inevitable for precise analysis of evapotranspiration and it was still lacking to be investigated. The precise analysis of evapotranspiration is required for reliable computation of water consumption. The proposed SPAC model was consisted of three sub-models to perform the soil water consumption analysis on various topographic conditions. Those three sub-models were:(1) Radiation energy evaluation sub-model, (2) Soil moisture and heat flow analysis sub-model and (3) Soil water uptake evaluation sub-model. Experiments were conducted in October on suitably prepared south and north facing fields, with 20° inclination, as well as on flat field to verify accuracy of the simulation model. Analysis was performed with considering LAI 0, 2.0 and 4.0 for comparision of results. Results have shown that at each level of LAI evapotranspiration of south facing field was about 1.5 times higher than that of north facing field. Similarly, soil temperature of south facing cropped field at various depths in day time were also remarkably higher than in north facing cropped field. The results of simulation model were well matched with their respective observed values. Therefore, this model could be used for analysis of crop water consumption on various topographic conditions and thereby contribute for irrigation planning on those areas.

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An improved method for determining the specific surface area of clays using ethylene glycol monoethyl ether (EGME) is proposed that uses reduced amounts of EGME and CaCl2 at the optimum ratio of these agents to keep EGME vapor pressure constant in a desiccator. The optimum ratio was 2.0 cm³ EGME to 14.4 g CaCl₂ for clay samples of about 0.5 g. About 20 times the expected adsorption volume of EGME was dropped on to the sample, the rest being added to the CaCl₂ in a separate vessel. The desiccator was evacuated to seal it for about one minute so as not to change the ratio of the agents and not to contaminate the air in the laboratory with EGME vapor. Desorption equilibrium was reached in 2-4 days. The final EGME retention in the desorption process agreed well with that in the adsorption process. Accordingly, the relative vapor pressure of EGME was found to be very close to the pressure which completes monomolecular layer adsorption. A fairly good linear relationship was found between EGME retention and the specific surface area for three different kinds of clays that retained 0.264 mg EGME on each square meter of surface. Effects of the specific surface area and CEC on EGME retention were estimated separately. The effect of CEC was not significant in this method.

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Authors have already indicated that it is important to ensure impermeability at the joint and the contact part with concrete, when GCL is applied to the surface lining system of reservoirs. However, the test method and the quantitative estimation method of the impermeability at the contact face of GCL still remains to be studied. Permeability test method has been improved and a new test apparatus was developed for GCL. Permeability tests were conducted under several actual conditions to estimate permeability at the contact face of GCL. This paper shows the results of permeability tests by a new method and proposes a simple estimation method for permeability at the contact face of GCL. After calculation of the leakage through lining system in situ with proposed estimation method, it is found that leakage along the contact face of GCL amounts to nearly 30 percent of all leakage.

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Thermodynamic equilibrium condition between the liquid and vapor phases of water at soil surfaces has often been assumed for modeling evaporation from soil surfaces. In this paper we assess the validity of the assumption by experiment and simulation. An evaporation experiment under a steady condition for a sandy loam was carried out. Using its hydraulic and heat transfer properties measured independently, numerical simulations of evaporation, liquid water flow, water vapor movement and heat transfer were performed for various space increments. Simulated evaporation rates and soil temperatures given by the equilibrium model were in agreement with observed values if the topmost space increment was so small as to be 0.05cm. This confirms that the equilibrium assumption is valid so long as the topmost space increment is small enough to describe the steep pressure head profile near the soil surface.

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Undrained Shear Strength Properties were investigated by the consolidating, swelling, and reconsolidating undrained shear test using K₀ consolidated triaxial test apparatus. Test mutt indicated that the e-log σ_v' curves of swelling and.reccesolidating process have not straight line.
Therefore, authors assumed swelling index or reconsolidating index as function of OCR, and proposed the relational expression between the rate of tmdrained shear strength and them. The estimated values of our proposed method agreed well with the experimental values at the range of 1<OCR 10 in the case of remolded Kahokugata-clay.

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Waterside space is commonly considered to have various environmental values. Local government bodies in Japan have been carrying out environmental development projects to enhance such values. This study tried to estimate environmental benefits derived from recreational activities at waterside spaces by using the environmental economics techniques. For two study areas, the environmental benefits and the cost including construction cost and maintenance cost were calculated. Based on comparison between the cost and the environmental benefits, validity of the environmental development project was examined. As a result, the following points were concluded. 1) Value of consumer's surplus was found between 500 and 600 yen. 2) The investment cost of the waterside environmental development of the two study area were found at appropriate level in comparison with the environmental benefits. 3) It was confirmed that the waterside environmental development projects were effective to materialize potentially existing environmental values of waterside.

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Authors had proposed a method for estimating the probability of time concentration based on the annual maximum 24-hours rainfall in Japan. One significant application of such method is, when the probability range of the annual maximum 1-hour rainfall at a station is known, it will become possible to estimate the annual maximum 1-hour rainfall corresponding to the annual maximum 24-hours rainfall. Using the available annual maximum 1-hour rainfall from the Japan Meteorological Stations (120 stations), this paper presents the calculated probability range and the necessary regional parameters required for the Gumbel distribution to generate the variable x for estimating the annual maximum 1-hour rainfall. In addition, some regional distribution characteristics of the parameters are described. The estimated annual maximum depths for each station were in good agreement with the observed ones with the same return period. Thus, the general suitability and wide applicability of the method were verified.

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A simple formula is derived to estimate the longshore sediment transport rate. The derivation is based on modification of procedures developed by Coastal Engineering Research Center (CERC). Several aspects of the CERC's original formula are elaborated and modified. The proposed formula is based on the assumption that the appropriate beach slope in the surf zone is the ratio of the breaker depth to the surf zone width. Consequently, the formula is expressed as a function of sediment grain size and deep water wave climate to account for the dependence of the beach slope on deep water wave climate. An attractive aspect of the proposed formula is that it does not require bathymetric data and can therefore be easily applied at places where detailed bathymetric data are lacking. The proposed formula agrees reasonably well with CERC's approximate formula which uses deep water wave data as input. However, the proposed formula has an advantage over the CERC's approximate formula in the sense that it considers the effects of the beach slope and the width of the surf zone on the longshore sediment transport rate. These are important transport parameters which are not considered in the CERC's approximate formula.
To investigate the applicability of the formula, net monthly transport rates along the Hyuga Nada Coast, Miyazaki, Japan, are estimated. Estimated results show that northward rates are predominant and these can be interpreted from aerial photograph and satellite imageries.

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Recent earthquake damaged a large area of farmland and many agricultural facilities. Although the factors that caused damage to earth dams and pipe lines were widely studied, there has been no thorough study on damage to reclamation land. This paper investigates the damage and its causes by the 1993 Hokkaido Nansei-oki Earthquake to reclamation land embankment that have been made by field reclamation at improvement slope.
Reclamation land that is made by field reclamation at improvement slope not sufficiently tamped nor designed for slippage resistance. This paper studied damage to reclamation embankment in detail, and the following conclusions were obtained:(1) The property of the foundation ground, on which soil has been filled, determines the damage distribution and severity, (2) Damage was generally more serious in sections where the amount of fill was higher, (3) Damage was serious in reclamation lands that have been made by filling valleys, (4) There was a significant difference in N-value between damaged embankment and embankment not damaged. Since soil is usually not compacted in making embankment, this difference should be attributable to the difference in fill materials. Selection of fill materials affects the earthquake resistance of the embankment.
Reclamation land embankment that are created by present reclamation land methods are not sufficiently earthquake resistant. However, under the present reclamation system, it is difficult to adopt antiseismic design in all reclamation lands. Soil should be filled after thorough investigation of the topographical and geological conditions of the site: and sections that are deemed to have very poor earthquake resistance should be sufficiently compacted, improved so as to lower the groundwater level, and be designed for stability against slippage. etc.

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Snowmelt amounts are important water resources in cold and snowy region. However, snowmelt amounts in discharge aren't clarified quantitatively.
Therefore, in this paper, we have tried to separate the snowmelt runoff depth from the total runoff one, and to estimate the dependence of the total runoff on the snowmelt runoff in the snowmelting season (March to May), that is, a ratio of the snowmelt runoff to the total runoff. For the estimation of these values, we used the improved degree-day method of computing snowpack and snowmelt. And snowmelt runoff analysis was carried out by the serries tank model. The Okura dam basin in Miyagi prefecture and the Touri dam basin in Toyama prefecture are chosen for this estimation.
The results obtained from this study are summarized as follows:
(1) The mean snowmelt runoff depth is 433 mm at the Okura dam, and 1, 166 mm at the Touri dam, in the snowmelting season from 1980 to 1989.
(2) The mean ratio of the snowmelt runoff to the total runoff is 61% at the Okura dam, and 73 % at the Touri dam.
(3) The maximum value of the snowmelt runoff depth and the ratio appeares in April at both dam basins. The mean value for a period of 10 years is 263 mm, 71 % at the Okura dam, and 628 mm, 83 % at the Touri dam respectively. And there have been not many changes in the values for these years.

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The present study was performed to investigate the actual conditions of thewater utilization at zone level in upland irrigation zone from the observations of variations of planted area of each crop, potential ET and daily amount of water utilization. The observations were carried out for many years in 4 zones of the Kantou area. The study-spot were in SH and HO zones of Mikatahara irrigation district in Shizuoka, MH zone of Hokusoutoubu irrigation district in Chiba, and MO zone of Fuefukigawa irrigation district in Yamanashi. In each irrigation district, more than ten years have been passed since the main upland irrigation facilities were constructed by the govenment supported project.
The findings are as follows; 1) There is a positive correlation between the potential ET by using the Penman method and the daily amount of water utilization per planted area. 2) The maximum daily amount of water utilization is caused by supplemental water demand in summer. 3) Much daily amounts of water utilization except in summer are caused by water demand for cultivation management. 4) Frequent water utilizations throughout the year occur in the upland irrigation zone including greenhouse cultivation.5) The maximum design amount of daily consumption of water is reasonable. 6) It is desirable to consider no-planted area to design upland water requirement.

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