The purpose of this study is to develop a new enhanced IDP (Incremental Dynamic Programming) model which is suitable for analysis of operation policies of multipurpose and multi-unit water resources system. The proposed new IDP approach deals with the optimization of trajectories is applied to a four reservoir system in the Nakdong River. The results of optimization in system operation show significant benefits. From this optimization two kinds of benefits are obtained; increasing benefit of domestic, industrial, irrigation, power generation water supply and reduction the computing time.

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A soil model is presented to estimate daily and annual variations of the evaporation, the ground surface temperature and the soil water content. In the model, diffusion of water vapor in the soil pores and the pipe flow which functions effectively in rainy time are taken into consideration. This model for practical use is a modification of a multilayer soil model (Kondo and Saigusa, 1994), and is based on a five-layer soil model (Kondo, 1994). The model calculations are found to agree with observed results by Fukumoto and Hirota (1994), obtained at a field of Ando-soil (clay loam) for a period of 92 days from May to August. The total amount of observed evaporation is 189 mm and that of calculated one is 197 mm. The difference between the observed and calculated daily means of the ground surface temperature is within ±1°C. When the pipe flow does not exist, the simulated result shows that calculated soil water content of the top soil layer becomes considerably large during few days after a rainfall. In this case, however, the total amount of evaporation increases to a slight degree, namely, by 11mm.

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A calculation model is presented for prediction of the river water temperature. In the model the heat exchange at the air-water interface and the ground heat conduction at the river bed are taken into consideration. The input meteorological parameters to the model are incoming radiation flux, daily maximum and minimum air temperature, daily mean specific humidity, and daily mean wind speed. The river parameters are the depth of water, current speed, and the distance from the riverhead. Daily mean water temperature is expressed as a function of the distance from the riverhead lx with a response time τ0, and it tends to the equilibrium temperature at the downstream. The value of τ0 is in proportion to the depth of water. The amplitude of diurnal temperature variation increases with the distance lx.

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In the previous paper, Kondo (1995) has shown a calculation model of the river water temperature. Using the model, the daily variation of the water temperature at a fixed point and the temperature profile along the river can be estimated from routine meteorological parameters. These estimations well simulate the observations. The first observation of the daily maximum and minimum water temperature was made for four summers at Akiyamazawa Brook, Miyagi prefecture. The second observations of the water temperature profile was carried out at Akiyamazawa Brook and Hirose River. The third one of the daily temperature variation was made at Hirose River. An estimation of a rise in water temperature followed by river conservancy shows that the maximum water temperature is sensitive to the water depth and current speed. An incident of mass death of fish, occurred in extraordinary hot summmer of 1994 at a pond of fish farm which draws water from Akiyamazawa Brook, may be caused by unusual hot water as a result of brook conservancy which widens the width and shallows the water depth.

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In this paper, the characteristics of distribution of surface soil moisture in bare fields are discussed by using the field data obtained by the direct soil sampling. The volumetric water content is used to express the condition of soil-water constituents. At first, statistical characteristics of the volumetric water contents and thier coefficients of variability in cases of two playgrounds and an area of paddy field are summarized. In the next, the relation between the water content and the dry bulk density of soil is examined. At last, the spatial scale of distribution of soil moisture content in the playgrounds and the paddy fields is discussed by using the both the Size Method newly defined here and the spatial auto-correlation coefficients of the soil water content.

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