A large conurbation spreading from Kyoto and Osaka is located in the Biwako - Yodo River catchment area. These cities, their suburbs, and satellite towns are densely populated and account more than 9% of the people in Japan. After Keihin (Tokyo - Yokohama), it is the second most populous area in Japan.
After the start of the Showa Period, the population began to gradually increase from just under 5 million in 1925. After the war, however, in the wake of the Japan′s economic recovery, the population increased rapidly, adding 1.7 million people in just the ten years from 1965 to 1975. Thereafter the rate of increase slowed, rising by only 300,000 between 1985 and 1995. Since then, the number of residents has remained fairly stable.
In recent years, the number of people living in Osaka City, Kyoto City, and other inner city areas has remained the same or tended to decrease, while surrounding cities have grown by absorbing the influx of residents leaving the inner cities. Over the catchment area overall, however, the trend has shifted from growth to stasis. As of 2007 the population of the catchment area was 11,980,000.
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In the upper catchment areas, including around Biwako and the Kizu River, land is mainly used for agriculture. In the lower reaches the major use is industrial, commercial, and residential.
Cities have long existed in the Biwako - Yodo River catchment. In particular, after the period of high economic growth, industry and population were concentrated particularly in the Keihanshin District (Kyoto - Osaka - Kobe), leading to general urbanization. Consequently, around the fringes of large cities, farmland has been turned over to residential development.
In 2006, rounding the figures, 45% of the land surface of the Biwako - Yodo River catchment was covered wooded slopes, 26% was cultivated and 22% was given over to residential use, which leaves 7% for miscellaneous uses. Compared with 1971, woodland had declined by 6% and cultivated land by 7%. Meanwhile, residential land was up 9%.
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In the premodern era, water from the Yodo River was mainly used for irrigation and transportation. In 1890, however, the first Biwako Canal was completed. It was a multipurpose waterway that fed the first hydroelectric power station in Japan, provided transportation and irrigation water, enable domestic water supply and sewerage systems. Later, in 1912 a second canal was constructed, mainly as an aqueduct to increase the public water supply and to provide more hydroelectric power. Later, when the Uji Hydroelectric Plant and other facilities were built, the power of the Uji River was harnessed.
After this, to meet the demand for water, which increased along with the development of an industrial economy, The First Yodo River Water Control Project was implemented, and a controllable water supply was obtained by managing the level of water in Biwako.
This was followed, in April 1962, by formal designation of the Yodo River System based on the 1961 Water Resource Development Promotion Act. In August the same year, the Yodo River Basin Water Resource Development Basic Plan (commonly called Yodo River Full Plan) was agreed and work began on projects in the plan. Since then, work has proceeded in response to social and economic needs by carrying out supplemental works and modifying the plan.
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