The purpose of this study is to seek the methodology of leaf area index (LAI) and evapotranspiration (ET) control by silvicultural practice for Japanese cypress (Chamaecyparis obtusa) and cedar (Cryptomeria japonica) on the basis of stand age focusing on LAI, the stand structure concerning LAI, and ET, LAI was measured using Plant Canopy Analyzer, LAI-2000 for 15 stands (age 10-about 300), and the corresponding ET was calculated applying ET model based on Penman-Monteith equation which includes LAI as a major parameter. Both measured LAI and calculated ET showed large values at around age 10-20 followed gradual decline. The literature data of measured ET scattered around the same range of the calculated ET. The relationship between total basal area at breast height and LAI based on literature has suggested that the pipe model theory would be applicable in the young forests, because LAI increases with total basal area at breast height for young stands (basal area at breast height < about 30 m2ha-1) which have almost the same total basal area at live branch. The future plan on the quantification and modeling of stand structure and its dynamics due to silvicultural practice has been proposed.

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To clarify the characteristics of stream chemistry in Tatsunokuchi Hydrological Station (THS) in Okayama City. Okayama Prefecture (lat E133°58', long N 34°42'), we observed the chemistry of streamwater in the Kitadani and the Minamidani catchments at THS. The concentrations of constituents evaluated were extremely high compared with those in the other streams in Japan. The concentrations of Ca2+, Mg2+, Na+, HCO-3 and Cl- abruptly decreased with increased discharge whereas the concentration NO-3, total nitrogen (T-N) and dissolved organic carbon (DOC) showed rising peaks after rain events. The high concentrations of constituents in the streams were explained by the concentration by evapo-transpiration and the dissolution from geology such as basic rocks. We estimated that water stored was small in the catchments after rain event in THS so that the concentration by evapo-transpiration was strong and the streamwater of high constituent concentrations was produced at no rainy days. In rain events, the constituent concentrations in the streams decreased by direct flow with low concentrations, but NO-3, T-N and DOC increased due to the leaching from surface soils. The concentrations of Ca2+, Mg2+, HCO-3, Cl- and So2-4 were higher in Kitadani catchment than Minamidani catchment in THS and pH and the concentrations of Na+, NO-3 and SiO2 were higher in Minamidani catchment. The difference of the inclination of the slope and the geology between two catchments might have effected the constituent concentrations in the stream waters.

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To investigate the dependence of surface soil moisture and evaporation on topography, a 19-site network of observations was carried out in a small watershed near Tiksi, Eastern Siberia, during July 1999. A topographic index of relative elevation, the difference between the elevations of the observation sites and the stream (DZ), was the dominant factor affecting the spatial distribution of surface soil moisture and evaporation. Both surface soil volumetric water content and evaporation decreased as DZ increased, the former exponentially and the latter logarithmically. A significant difference was evident between adjacent regions to the east and west of the stream, even though DZ was the same.

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Precipitation accuracy greatly affects hydrological forecast and calculation, particularly to mountainous drainage basins where rainfall is extremely non-uniform. This paper develops a spatial model of precipitation based on relationship between the gauged rainfall at 9 sites and the DEM implemented by the GIS. The Thiessen method and the spatial model are applied and compared to estimate daily, monthly and annual basin-mean rainfall. The results show a significant difference, implying the need for a spatial model of precipitation to be used for a distributed hydrological model. The basin daily, monthly and yearly rainfalls by the Thiessen method are underestimated respectively, 40∼190%, 14∼40% and 17∼28% less than those by the spatial model. The basin storage, therefore, in the hydrological model used for flood prediction has to be overestimated largely to fit to the gauged stream flows. The basin-wide water balance in monthly interval is examined to verify the spatial rainfall based on the discharges from 2 sub-basins in high altitude, and the results illustrate that the runoff depth in a few months are larger than or equal to the rainfall estimated by the Thiessen method leading to the stored water ΔS by soil, generating the negative values in the rainy months. The surplus rainfall stored in saturated soil in the summer is drained as the surface flow which is larger than precipitation during the autumn. This is reflected on the hydrographs due to the soil frost so that the ΔS shows the maximum negative value in the autumn.

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In the irrigation systems of Japan, the water demand is usually supplied by the river flow caused by tributary inflow and any shortage is offset by dam release. In this case, excess water is generated easily due to the decrease of water demand in the command area and the increase of river flow by unexpected rainfall. Generally, such excess water is invalidly discharged by the water intake facility such as head work. In this study. we propose the construction of a mid-storage reservoir between the dam and the water intake facility, so that excess water is temporarily stored by such a reservoir. Also, we propose an effective operation method of the dam and the mid-storage reservoir for using the excess water effectively. In this operation, it is necessary to predict the river flow at the water intake facility when dam release arrives there. Therefore, we use the simple prediction model of river flow in order to determine the dam discharge. Furthermore, the operation method is applied to the actual irrigation system whose water use is limited due to water shortage, and the effect is examined by using a simulation method. From this result, the effect of the mid-storage reservoir was clarified quantitatively in drought years by applying the method we suggested.

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Rainfall characteristics is said to be changed in recent decades due to global climate change. In order to find the changes, a statistical analysis was performed for 100-year (1898-1997) daily rainfall record at Okayama Meteorological Observatory. For this purpose, a storm is defined as a succession of rainy days, and we examined frequency and distirbution of total rainfall and duration of a storm, storm inter-arrival time and interval between storms. The result of frequency analysis shows that frequency of 100-year storm rainfall during 1899-1931 becomes almost thirteen times larger during 1965-1997. Besides frequency of 100-year interval between storms during 1899-1931 becomes five times larger during 1965-1997. The change in frequency of these hydrological characteristics shows us necessity to reconsider magnitude of design floods and/or droughts for constructing hydraulic structures.

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The pricing policy of irrigation water in Japan is evaluated by trend analysis, assuming the following two trends: expansion of the market mechanism which is linked with globalization, and expansion of the increasing value of the environment, especially the ecosystem, which is linked with localization. Two aspects of irrigation water are considered: water rights and onfarm use. Using these two trends, past irrigation projects were classified into those of the age of expansion of the market mechanism and those of the age of both trends. Water management and DSM (demand side management) of on-farm irrigation water by village communities were gradually replaced by the market mechanism of paying money. But the pricing system of on-farm irrigation water could not be widely introduced because of the physical limitation of distribution capacity. In spite of the principle that water is a public good and so should be excluded from trading, water is actually traded at the cost of substitute water projects for saving water. The trend towards environmentalism raises the value of the ecosystem. With the expansion of environmental water, the water rights system will be reformed. Similar to in the EU, it will be important to build the PPP (pollutant pay principle) in the watershed management system.

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