Sustainable development of irrigation system with Sayama-ike reservoir

Abstract

‘Sayama-ike’ is the oldest reservoir in Japan which has been providing an irrigation network to the Osaka plain from the early 7th century. This reservoir greeted the 1400th anniversary in 2016. Up to the present, this reservoir’s dike has been reinforced and heightened repeatedly to increase the reservoir capacity as the irrigation area has expanded. There are many small reservoirs at downstream area where the irrigation network is well developed. The Sayama-ike plays an important role of storing and suppling water to those reservoirs. This network has a unique distribution system with the Sayama-ike as the first-stage reservoir supplying water to the second and then the third ones in cascade, which is known to have been already formed in the late 12th century. In the course of the 16th to the 17th century, the irrigation area of the Sayama-ike became largest, which amounted approximately to 4000 ha. Although the total number of reservoirs at the downstream area is not clear, the main reservoirs counted more than 130 in the early 20th century even though the total irrigation area was decreased. In recent years, the Sayama-ike has been largely upgraded to a multi-purpose one by adding a flood control function, and its name was changed to ‘‘the Sayama-ike Dam’’ after the completion of the upgrading work in 2002. This paper briefly shows its history and current challenges for sustainable management of the irrigation system.