The Dam’s Structure and Functions
Ikeda Dam is a 24-meter-high gravity concrete dam. Its weight and the force of gravity help resist the pressure of the water it holds back. The dam has several important functions: controlling floods downstream, replenishing existing water supplies, maintaining the river environment, and generating electricity.
It helps reduce the risk of flooding in the lower reaches of the Yoshino River while supporting supplies of domestic, industrial, and agricultural water. The facility also has a maximum hydroelectric generating capacity of 5,000 kilowatts, contributing to the region’s energy supply.
One of the most striking features is its enormous floodgates. Their scale is so impressive that a gate is described as being large enough to accommodate the building of the Yoshino River Dam Integrated Management Office, located on the river’s left bank. These huge structures illustrate the engineering required to regulate the flow of a major river.
History of Ikeda Dam
The first proposal for Ikeda Dam appeared in 1950, when the Economic Stabilization Board put forward a development plan commonly known as the “Yasumoto Plan.” Around the same time, Electric Power Development Co. considered building a dam for hydroelectric generation, but that proposal was abandoned following opposition from local residents.
Planning later advanced under a government construction program based on the original proposal. In 1966, the Yoshino River system was designated a water resources development river system, paving the way for a comprehensive development project intended to secure a stable supply of water across the region.
As part of this wider Yoshino River development program, Ikeda Dam was completed in 1975. It became a key piece of infrastructure for managing water resources in Tokushima and neighboring Kagawa Prefecture.
A Vital Water Source for Two Major Canals
One of Ikeda Dam’s most important roles is supplying water to two major canal systems: Kagawa Irrigation Canal and Yoshino River North Bank Irrigation Canal. These projects have helped address long-standing water shortages in areas where rainfall and local water resources were not always sufficient to meet demand.
Kagawa Irrigation Canal
The Kagawa Irrigation Canal carries water through the 5,032-meter-long Asan Tunnel, which passes beneath the Asan Mountains separating Tokushima and Kagawa prefectures. Construction of the tunnel presented considerable engineering challenges, but water began flowing through the system in May 1974.
The project brought a reliable water supply to Kagawa Prefecture and the Sanuki Plain, an area that had struggled with chronic water shortages for centuries. By transferring water from the Yoshino River system, the canal helped support agriculture, daily life, and regional development.
Yoshino River North Bank Irrigation Canal
Construction of the Yoshino River North Bank Irrigation Canal began in 1971 as part of a national agricultural water-management project led by Japan’s Ministry of Agriculture, Forestry and Fisheries. Extending for 69.2 kilometers, the canal was completed in 1990.
The project fulfilled a water-supply concept that had been proposed as far back as the Meiji period. It significantly improved agricultural water availability for communities north of the Yoshino River, helping areas that had long experienced persistent shortages secure a more dependable supply.
Ikeda Lake and Its Fish Ladder
The reservoir created by the dam is known as Ikeda Lake. An especially interesting feature is its stepped fish ladder, which allows fish to move upstream past the dam. This passage helps maintain movement along the river and supports aquatic life despite the physical barrier created by the structure.
Fish including ayu sweetfish, eels, and carp have been observed moving upstream through the ladder. From May through July, large numbers of ayu may gather and ascend the steps, creating an impressive natural spectacle. For visitors interested in river ecology, this seasonal activity offers a different perspective on the relationship between large-scale engineering and wildlife conservation.
Ikeda Hesokko Bridge: A Landmark Across the Reservoir
The Tokushima Expressway crosses above Ikeda Lake on a bridge over the Yoshino River. Its official name, Ikeda Hesokko Bridge, was selected through a public naming competition. The bridge serves as an important transport link for the region and has become a familiar landmark for local residents.
The view of the bridge above the reservoir highlights the combination of transport infrastructure, water management, and the surrounding river landscape. Together, the dam, lake, and bridge illustrate how the Yoshino River supports both the natural environment and modern life in Shikoku.
Discover the Engineering and Nature of the Yoshino River
Ikeda Dam is an essential part of the Yoshino River system, helping protect downstream communities from floods while providing water for homes, industry, and agriculture. Its hydroelectric facilities and fish ladder demonstrate the many demands placed on a modern river-management project.
For travelers exploring Miyoshi City and the scenic valleys of Tokushima Prefecture, Ikeda Dam offers an opportunity to appreciate the engineering behind the region’s water supply. Visiting the dam and its reservoir also provides a chance to observe the Yoshino River from a different angle, where large-scale infrastructure and the rhythms of nature meet.