Eutrophication in reservoirs is one of worldwide environmental issues. Eutrophication causes deterioration of landscape due to blooming of blue green algae and red tide, foul smell of drinking water and deterioration of water quality due to water-bloom. In particular, the problem of musty odor of tap water is serious. Severe problems of musty odor occurred since 1984 to 1990 in four dam reservoirs, which are managed by Water Resources Development Public Corporation. The cause of musty odor was 2-MIB derived from Phormidium. The water quality in four reservoirs was observed around 2 times a week for the period when Phormidium grew in those reservoirs. As a result, we obtained valuable information on the relation between 2-MIB and musty odor, and found that most of the produced 2-MIB are dissolved in the water.

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This paper examines the applicability of the Mann-Kendall test, which is one of the statistical tests for trend analysis, to hydrological time series. The test is applied to peaks-over-threshold series (POT), annual maximum series (AMS) and annual rainfall series (ARS) obtained from daily rainfall series generated under the assumption that daily rainfall, inter event time and duration of rainfall are independent. The Monte Carlo experiment shows that it is better to use ARS or POT than AMS, especially the POT has possibility to detect year-by-year trend using shorter period than ARS. A length of 110 years is necessary to detect a trend of r >25% and 160-180 years record to detect a trend of r >10%, for example.

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Deeply under the ground, drainage pipe system with huge-diameter has been laid in recent years. The water flow containing air-mass or bubbles in a drainage pipe shows the different hydraulic characteristics than usual open channel flow, and the compressed air in horizontal pipes occasionally blows manhole covers off when heavy and concentrated rainfall occurs and massive water rushes into the drainage pipe system. The present authors had proposed a numerical simulation model containing the effects of compressed air to the water flow. In the present paper we introduced some modifications to our model. Applying the modified model to the general and practically-used drainage system, it was verified that the type and form of the inlets to vertical pipe connected to long horizontal pipe plays the important roles in compressing air in horizontal pipe, and that the vertical pipe laid in the middle of two vertical pipes as an inverted siphon works well to release the air and reduce its pressure.

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Research in the field of river hydrology has been mainly concerned with the investigation of the rainfall-runoff phenomenon through the analysis of hydrological factors such as meteorology and geography, with the focus being on each river basin. Recently, various forms of digital information such as GIS and RS data have been made available in worldwide digital map format. Therefore, there has been a shift in focus from lumped-parameter models to distributed runoff models, as the latter can consider temporal and spatial variations in water quantity. Distributed runoff models have made possible the comparison of runoff field and rainfall-runoff characteristics considering spatial distribution.
In this paper, a comparative methodology using a GIS-based distributed runoff model and AHP (Analytic Hierarchy Process) for the analysis of river basins based on their regional hydrological characteristics and considering their temporally and spatially-distributed physical properties is developed. Based on the method, the Comparative Hydrology is proposed to make clear the characteristic and similarity for each river basin. An application of the Comparative Hydrology approach is presented for the comparison of three river basins located in the Asian-Pacific region.

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In order to solve the acute water shortage problem in Huabei Plain, China, water saving in the irrigation sector is seriously needed because it is the largest water user. Based on a field survey in the Shi-jin Irrigation District, this study analyzes the water management system from the viewpoint of water saving, with special focus on the rules and practice of irrigation management over the whole system from water source to terminal plots. This paper clarifies, (1) The Administrative Bureau, which depends on water fees collected from the farmers, has little incentive to make farmers save water, while farmers are not sensitive to saving water because of area-based charging systems in their villages, (2) Actual water application to the field is much more than necessary, despite high water charges, which suggests the ineffectiveness of high water fees for water saving, and (3) Considering the costs of land and labor, a reasonable method for water conservation would involve shortening the present interval of lateral canals by adding new ones, thus shortening the lengths of the plots.

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The intensive observation, including many turbulence observations distributed in the area, was performed over paddy field in northern Shiga prefecture, Japan in a few weeks in November 2002. Sixteen points of turbulence observation, a radio sonde observation, two SODARs observation, four scintilometers observation and thermal images taken from airplane were done in this campaign. The outline is presented here.

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Structural complexity of contemporary numerical models causes problems for use: a problem of examining numerous conditions, and a problem of checking a program code. These problems are reduced by non-dimensionalization of numerical models. This paper explained how the problems are, and how the problems are reduced by non-dimensionalization of numerical models, by taking an example of non-dimensionalization of a multilayer canopy model. This paper will enable more effective use of contemporary numerical models.

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