For understanding water environments in urban rivers under rainy conditions, the intensive field measurements of water quality and hydrodynamic environments were carried out at several urban rivers and the Edo River in which the scale and environments of the watershed are different. The observed results indicate that the differences of the water quality environments between urban rivers under rainy conditions are closely related with those of sedimentary environments. The contribution of the sedimentary environments to water quality environments in the Edo River is much smaller than that in the urban rivers due to the property of erosion rate of sediments. The origin of the particulate matters in urban rivers is quantitatively discussed with the observed data for the erosion rate of sediments.

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For the water quality management in wide area of a river course, quantitative evaluation for the processes of sediment transport and nutrient lord is very important Present study is focused on the contamination load in a flooding river. The investigation performed by the observation of seven times of a flood in Abukumagawa River. And, the processes of nutrient load and transportation were evaluated by the numerical model based on a mass loading rate and the channel network system using kinematic-wave method.

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COD was previously measured from sampled water. Then 1 month measurement does not include flood condition because of safety for sampling. 1 hour measurement is automatically sampled and measured in situ at station and then includes flood condition. To clarify difference between 1 month measurement and 1 hour measurement, using both measuring results of flow rate, COD, TB and EC values of the Yamatogawa river, effect of flow rate on COD, TB and EC values was clarified. COD and TB values increased with flow rate. EC value decreased as flow rate increased. The relationships between COD and flow rate, TB and flow rate were very similar. Therefore, COD was more strongly influenced by floating material than soluble substances because TB was concentration of floating material. Using the relationships between COD and flow rate, COD loads were calculated. As a result, the COD load calculated by the 1 hour measurement was more about 2 times than the COD load calculated by the 1 month measurement.

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Elucidation of the supply of substances from land to the sea is important to understand material (biomass) balances and the ecosystems in estuaries and the world's oceans. Especially in reservoirs and estuaries, masses of nutrients and organic matter change as a result of photosynthesis and flooding. This study recorded data for composition of nutrients and phytoplankton in a freshwater region and an estuary of the Kinokawa River to show their changes. Results show that the value of chlorophyll-a increased greatly in July before the Kinokawa floodgate was opened. At that time, it is presumed that dissolved organic nitrogen (DON) was taken in by organisms to form particle organic nitrogen (PON). Regarding the relation between chlorophyll-a and volatile suspended solids (VSS) during flooding, suspended solids (SS) contain much organic matter that originated from riverbed phytoplankton. Moreover, regarding the number and type of phytoplankton, we obtained results showing that diatoms were dominant in spring and summer. However, blue algae or green algae increased in summer. On 29 July, we found that dissolved silicate decreased concomitant with the increase of diatoms.

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Recently, it has been apprehended that the water environment in the upper Chikugo River in Hita, Oita, where the river channel forks in three tributaries: the Chikugo (the Mikuma), the Kuma and the Shode, becomes worse due to the stagnancy of water. In order to provide fundamental informations of 3-dimensional flow structures and temporal and spatial variations of water quality field surveys were carried out from 2003 to 2004. The following relations between the flow patterns and the water quality were found out:(1) the residence time is affected by the existence of horizontal eddy around the riffles, (2) lower discharge can generate the eddy and (3) turbidity and chlorophyll-a are regulated by the river discharge in the ponded area by the Shimauchi movable weir.

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It is necessary to evaluate the characteristics of river environment for planning river works and for setting an environmental target of preservation and improvement of habitats. Therefore the technique to analyze the relation between the distribution of living things and physical, chemical and biological environments of river habitats is required. In this paper, we presented an integrated water quality index and an integrated river flow type index. The latter was based on results of principal component analysis applied to the factors involved in HIM (Morishita, 1998). The integrated indices were used as criterion variables for a multiple regression analysis of fish data and some indicator species were presented. The multiple regression model was used for the estimation of integrated index values of verification rivers and showed good performance.

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The large-scale experimental channels were constructed in the Takaya river course which a branch of the Ashida river, in Fukuyama-city. This study is one of the experiments by plants purification method. In this study, three channels were used for purification tests by plants such as reed, sweet yellow flag and another channel which called a control channel were paved by nothing. The polluted river water is conducted into 3-plants channels by pumping during about 6 months, from May to October, 2003. The purification effects were estimated by several items of water quality and biological. At three points so as upstream, midstream and downstream in the three experimental channels. In this paper, items such as characteristics of BOD, nitrogen and phosphorus were especially considered from both particle component and the dissolved component. The biological investigations were considered from 3-kinds investigation items such as epiphytic algae, phytoplankton and zooplankton were evaluated due to those population density, appearance genera, etc.

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The declines of river corridor vegetation density strongly affect to the river heat environment, and that change makes big impact to the ecological systems. In this study, stream temperature analysis model related with river corridor density was developed and applied to Nam Song River, Laos. Metrological data (air temperature, relative humidity, wind speed) were used, and sink or source terms of heat transfer equation were estimated from those data. Land cover GIS data was used for vegetation density analysis along the main river. As the result of simulation cases with several vegetation densities, river water temperature was more sensitive to river discharge change as decreasing of vegetation densities.

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At Isahaya of Nagasaki, Japan, a big project called construction of sea-dyke and reclamation project is now going on. It is well known that deterioration of water quality has been frightened in a closed water body, if runoff load of pollutants is not sufficiently controlled. In this paper, pollutant runoff loads from the watershed into the regulation pond of Isahaya are first identified, classifying those from point and non-point sources. On the other hand, it becomes very urgent to reduce the pollutant runoff loads, so efficiency of constructed wetland as one of the Best Management Practices (BMPs) is briefly discussed, based on a field observation and an experiment in campus of Nagasaki University. Finally, some discussion has been done, related to a strategy for reducing the pollutant runoff loads into the regulation pond of Isahaya.

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Calculated Pollutant load per unit production and actual pollutant load of Yamato River were estimated. The actual pollutant load was determined from measured flow rates and concentrations. As a result, actual BOD load showed seasonal changes with low values of summer and high values of winter. The change depended on temperature because a rate of decomposition of organic compound depends on temperature. The actual BOD loads between two pints along the Yamato River with no branch river and no drainage were measured and a rate of decomposition between them was calculated. The calculated seasonal BOD load from pollutant load unit production method including rate of decomposition showed the same pattern of the actual BOD load. The total BOD load value by unit production including decomposition calculated method was 4 times of the actual load. As BOD was not measured at flood condition, the actual BOD did not include floating material at the condition of high flow rate and then was smaller than the calculated load per unit production.

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In the regional development, a balance of development and preserving of natural resource should be considered. The precious natural environment has to be maintained. The Lake Ogawara in Aomori Prefecture is one of large brackish lake where the most dominant water organism for fishery is Corbicula japonica. And the water quality and the flow of the lake is very related to the habitation of the clams. The field observation of water quality was carried out for this lake in the period for three years from August 2002. From a viewpoint of water quality environment, egg-l aying and hatching of them are performed on the north side of the lake, and they diffuse throughout the lake by the flow.

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The runoff characteristics of NO₃-N in forested mountain areas located in the northwest of Kanto Plainis investigated by field observation from 2001. The observation consists of two components, one is NO₃-N concentration in mountain stream water and the other is vertical profile of NO₃-N concentration in soil water. It is clarified that the large difference of NO₃-N concentration in mountain stream water exists between the west side and the east side of Tone River. Though NO₃-N concentration in soil water shows the almost similar tendency, vertical profile shows three types that do not exactly correspond to the areal distribution of concentration. By the correlation analysis, there is positive correlation between rainfall events and increase of NO₃-N concentration in mountain stream water in the east side of Tone River, where the concentration is low. On the contrary, no correlation is found out in the west side of Tone River, where the concentration is high. These phenomena correspond to the nitrogen saturation.

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To clarify environments of road deposits, one of non-point sources in urban area, we present a simplified monitoring method for road-deposit environments in which one can easily obtain road deposits under simulated rainy conditions. The present method collects road deposits suspended in water by a simple operation in a short time and then analyze water qualifies for samples obtained here. With the present method, we conduct a field observation in urban area before and after a hydrologic event, and then examine the variations of suspended solids and particulate matter on road through the hydrologic event We also conduct field measurements to clarify horizontal distributions of deposits on road. The observed results indicate that the spatial fluctuations of deposits on road are dominant, showing the importance of the simplified monitoring method for road-deposit environments presented here.

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In urban areas where there is a high density of property, infrastructure and population, it is an urgent task to develop an engineering tool for predicting the quantity and quality of stormwater from the viewpoints of disaster prevention and preservation of the water environment. In the present study, a field measurement and a runoff analysis of stormwater in a small urban area were performed, and the effects of rainfall hyetograph on the pollutant runoff process were examined. Excellent agreement between the SWMM simulation and the field data were found not only with the runoff discharge, but also with the concentration and transporting rate of nutrients. A response analysis of pollutant runoff was carried out for design storms of single-peaked triangular hyetographs with various durations and peak intensities. The results provide information useful in the management of sewage and river systems, such as the design and operation of sewage treatment plants, planning of river restoration for increasing river self-purification capability, scheduling of road cleaning operations, land use planning, and so on.

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A basin-scale pollutant load and its transportation processes are discussed in this study. The unit loading method combined with census and GIS data is used to estimate spatial distribution of pollutant load within the basin. the method allows grid-base representation of pollutant load, and makes it possible to link the pollutant production with distributed hydrological model. The spatial distribution of pollutant load and channel purification process model are then integrated into the distributed hydrological model to simulate dynamic behavior of water quality and quantity along the stream. These methods have potential to be used for understanding the water quality over the large area with less data requirement, and could be applied for integrated river basin management.

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Owing to overflows form combined sewer pipe systems, water quality of receiving waters, including urban rivers, in Japan, has been become worse year by year. Therefore, appropriate counter-measures that can mitigate the overflows must be developed promptly. In order to achieve this, a distributed simulation model of water quality and stormwater runoff is investigated, which can simulate precisely both open-channel and surcharged flows and a temporal and spatial variation of runoff-water quality in the pipe systems.
The model proposed here consists of two well-known models: one is PWRI (the Public Works Research Institute, the Ministry of Construction, Japan) Model for water quality simulations; the other is MOUSE Model for stormwater runoff simulations.

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To conduct the water quality improvement properly, it is necessary to estimate the dynamics of pollutant loads at watershed scales. We have attempted to quantify the watershed information by GIS to estimate the relation between water quality and watershed imformation, and carried out the field observation and sample collection, and then we have analyzed the run-off of NO₃-N in Chikuma Basin. As a result, it became clear that the land use of watershed had significant influence on NO₃-N dynamics in the river. Since, the amount of NO₃-N from the vegetable field changes, NO₃-N in the river water changed seasonally. Also, nitrogen stable isotope ratio increased in downstream of the river, where N discharge from city area increase.

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Basin-wide hydraulic and material behaviors of a river are important factors reflected in basic indicators that are used to form consensus among residents for a river project in both environmental aspects and flood control and water utilization aspects. These indices are used for preserving ecosystem and maintaining river channels, banks and structures. We studied how runoff characteristics and water components of a river relate to the geology, climate and land use in some river basins in Hokkaido using multiple regression analysis. We found that hydraulic parameters tend to vary according to geology, which confirms past studies. We also found that water quality components were greatly affected by geology, such as the distribution of plutonic rock, metamorphic rock and unconsolidated sediment, although the data covers normal time only. This could prove to be an important consideration in river management.

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