This study aims to simulate pollutant runoff using the Macro Model and examine the characteristics of pollutant runoff into Lake Biwa. As a result of the simulations in all rivers flowing into Lake Biwa, annual runoff load from every river basin was shown. The characteristics of pollutant runoff into Lake Biwa were examined with consideration to characteristics of river basin and rainfalls. In the results, it was shown how we should control pollutant runoff effectively in order to protect the water quality of Lake Biwa, and some knowledge concerned with the environmental management of the Lake Biwa basin was obtained.

The objectives of this study are to establish a runoff model and show profiles of pollutant runoff by simulating the change in runoff load with variance in the characteristics of river basins (i.e. population, urban area, rate of sewerage, etc.). The model, hereinafter referred to as “MACRO MODEL”, consists of three main sections. The first one shows pollutant runoff from point sources taking into consideration the sedimentation of pollutants in sewers. The second and third ones show pollutant runoff from nonpoint sources in an urban and rural area taking land use into consideration. Since it was proved that MACRO MODEL could simulate runoff load accurately enough to predict profiles of pollutant runoff, it has become possible to estimate the effect of characteristics of a river basin on pollutant runoff. As a result, some available knowledge concerned with the environmental management of water was obtained by using MACRO MODEL.

This study aims to simulate pollutant runoff into Lake Biwa using the Macro Model and examine the runoff characteristics of pollutants from urban nonpoint sources. As a result of the simulations of all rivers flowing into Lake Biwa, the characteristics of urban nonpoint source pollution and the basic units of urban nonpoint pollutants in the Lake Biwa basin became clear. It was shown that the control of pollutant runoff from nonpoint sources during storm events was significant in order to protect the water quality of Lake Biwa. From these results, valuable data concerning the environmental management of the Lake Biwa basin was obtained.

Many strategies for water quality conservation in Lake Biwa are being carried out mainly by reducing runoff pollutant loads into the lake. But influence of the runoff load reduction on the water quality in Lake Biwa has not been clarified enough so far. This study is aimed at discussing methodology to estimate water quality distribution in Lake Biwa using runoff pollutant loads from its basin. The runoff loads from the basin are calculated by Macro Model with GIS database of the Lake Biwa basin, and the water quality distribution in the lake is estimated by the spline technique with the calculated runoff loads. As a result, it has been proved that the methodology has enough reproducibility to estimate the water quality distribution in Lake Biwa and is available to examine the water quality in the lake.

The objective of this study is to clarify the statistical characteristics of pollutants deposited in urban areas, taking account of stages (road surfaces, street inlets and streams) and land uses where they accumulated, from surveys over a period of 16 years in Kyoto City. The result of correlation analysis showed that there are intimate relationship between grain size and such pollutants as organic matter and nutrients. It showed the dependence of pollutants on grain size. After principal component analysis, the distribution of principal factor loading showed that the first and the second components meant the type of pollution and the physical property of pollutants. The distribution of the principal factor score showed that each land use had different pollutant characteristics. On the other hand, the characteristics of the pollutants that accumulated on a road surface were shown to be affected by storms, and nutrients were more likely to run off in a storm than organic matter. The content rate of pollutants accumulated in a stream was shown to decrease in proportion to the progress of sewer construction, but it was also shown that the rate of some pollutants has not changed in the area of a separate sewer system. As a result, some valuable information for the control of nonpoint pollutants in urban area was obtained.