Hikawa Dam redevelopment business
Purpose of redevelopment
After Hikawa Dam of construction rising from the popular name fives-so of Yatsushiro-shi, Kumamoto including Hakusan (1,073m above sea level) of Kyushu Mountains west offset at first, and being located, and starting construction of upper basin, Izumimachishimodake, Yatsushiro-shi of second grade river Hikawa (basin area 148.6km2, main line duct extension 30.7km) where the west style does Middle Kumamoto by amount of bank 56.5m for the purpose of supply of flood control, indefinite water, irrigation water, water supply water, gravity type concrete dam of total storing water 6,300,000m3 in capacity (valid storing water 5,100,000m3 in capacity) in March, 1971, and having been completed in July, 1973, it is multipurpose dam which finishes examination flooding in March, 1975, and started operation.
Flood control method of conventional Hikawa Dam adopted spare discharge method that lowered water level beforehand when flood was expected, and found capacity that was necessary for flood control. However, response to guerrilla type rain whom late years had much was very difficult and, also, recovery of 550,000m3 (irrigation capacity and overlap) for spare discharge became difficult and might affect irrigation supply depending on rainy way of going down. Furthermore, in the Hikawa downstream part, maintenance flow rate of river was short, and influence on river environment and ecosystem was worried about.
Therefore, for the purpose of planning maintenance of normal function of running water of the lower valley of dam, we worked on Hikawa Dam redevelopment business (bank body padding) from 1990 by padding dam bank body, and dissolving preliminary discharge, and carrying out certain flood control, and finding stable irrigation capacity, and the body construction was completed in June, 2010 and we powered up to amount of bank 58.5m, total storing water 7,100,000m3 in capacity (valid storing water 5,900,000m3 in capacity) and started operation.
Summary of redevelopment business
We reinforce storing water capacity of 800,000m3 as 2m raises bank body of Hikawa Dam for the purpose of maintenance (250,000m3) of cancellation (550,000m3) of preliminary discharge and normal function of running water by Hikawa Dam redevelopment business.
1. Cancellation of preliminary discharge
By dissolving preliminary discharge, plan more certain flood defense and securing of stable irrigation capacity.
2. Maintenance of normal function of running water
We reevaluate natural environments of ice riverside river and social environment, characteristic of basin and plan maintenance and the reinforcement of normal function of running water.
Construction summary of redevelopment business
1. Padding construction of dam bank body : Concrete casting about 13,000m3 (in the original construction dam about 100,500m3)
2. Reconstruction work of emergency discharge facilities accompanied with padding of dam ： The crest gate 2 gate
Reconstruction work of spare gate : The roller gate 1 gate
Reinforcement work of common use discharge facilities : The conduit gate 1 gate
3. Padding construction of section affected by rise in water level of reservoir
4. Update of control processing equipment (damukon) for reconstruction work and dam management of management ridge
6. The quality of the water improvement measures
7. Road meeting and parting point setting construction for construction
Figure of dam bank body
Summary of *sa dam