The Tokyo Metropolitan Government (TMG) has conducted a variety of river projects to protect citizens and their property from damage due to flooding, storm surges, and landslides. Projects have also been undertaken to improve and create riversides that support nature, and to protect and restore the natural environment. The hardening of urban and inner city areas with high population densities and developed areas have relatively poor water retention and flood prevention properties. Consequently, these areas have sustained extensive water damage during times of heavy rainfall and flooding. Indeed, extensive flood damage was observed in downtown areas as recently as September 2005 and August 2008, demonstrating the need to implement additional flood mitigation measures to prevent flood damage in the metropolitan area. The number of rivers currently under the direct management of the TMG is 61 class A rivers and two class B rivers, which together measure 494.82 km. In addition, the city office of the TMG also controls 33 class A rivers and 13 class B rivers, which together equal 215.91 km. The main projects undertaken by the TMG is small river development, reinforce of lowland, improvement of the river environment for ecology, improvement of sediment disaster control facilities, development of software programs, river enlightenment activities and improved shoreline protection measures. In 2010, the total costs of river projects amounted to approximately JPY 65 billion. Small river projects are primarily concerned with the construction of several regulation reservoirs and river diversion channels. Conversely, the development of high tide breakwater structures and the reinforcement of rivers in lowland areas using super levees

The hazardousness of potential flooding and environmental deterioration face river basins throughout the world. Rivers in Japan are relatively short in length and steep in elevation along the banks, which are supposed to funnel rainwater and create floods due to heavy rain from typhoons/hurricanes. In addition, the clearing of forested areas due to widespread residential development in Japan and a lack of forestry workers have led to a broad decline in the riparian forest ecosystems. The study examined the recovery of the Maruyama River basin following the flood disaster in 2004. The Maruyama River disaster-relief and restoration projects addressed the mitigation of environmental damage as well as economic impacts. The Maruyama River basin is a noted habitat of the Oriental white stork, which became extinct in 1971, and was reintroduced as the basin through the breeding program in 2003. The 2004 flood destroyed the stork habitat. As a part of the recovery effort, the Japanese government has worked with the Toyooka City government and the Maruyama River Basin Committee to rebuild and expand the habitat of the stork. Preserving the habitat of another endangered species, the committee has added the Japanese giant salamander into a species name list in the restoration plan. These projects are expected to reinvigorate the local economy and preserve the environment of the river basin.

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The Isewan Typhoon caused considerable damage to the downstream regions of the Kisosansen River Basin on 26 th September 1959. It caused approximately 4,500 deaths in and around Nagoya City, the most industrial city in Japan. This study describes the history surrounding the major flood mitigation projects related to land use in the Kisosansen River Basin since 100 A.D. when paddy fields were first established on the alluvial plain. Land use of the area gradually evolved to cover the entire alluvial plain, developing from subsistence farming to modern sophisticated industry. This study shows that economic development in the both side plains of the river has been altered since the construction of the eastern side dike on the Kiso River. The Kisosansen River Basin, with a catchment area of 9,100 km 2 , is drained by the Kiso River, the Nagara River and the Ibi River. These rivers previously flew in the Nobi Plain as a single river, with successive floods producing a change in the main channel.

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