Hydraulic analyses using two-dimensional shallow water equations for functional evaluation of the Yamadazeki barrage in the Chikugo river, Japan.

Hizume, Daisuke; Tabata, Toshinori; Hiramatsu, Kazuaki; Harada, Masayoshi; Ozaki, Akinori

The Yamadazeki Barrage, located in Fukuoka Prefecture, Japan, is an oblique weir that was constructed at the middle reach of the Chikugo River in 1790 and is still operational. The weir was recognized as a World Heritage Irrigation Structures by the International Commission on Irrigation and Drainage. This study used hydraulic analyses of the Yamadazeki Barrage to understand its function. Two-dimensional shallow water equations were utilized for the hydraulic analyses, and the calculated velocity distribution under ordinary flow conditions (approximately 40 m3/s) showed good agreement with the measured data. In addition, the bedload transport rate was calculated from the water velocity and depth distributions using the Ashida-Michiue formula to simulate riverbed variations. The results suggested that there was slight erosion and deposition in the vicinity of the weir under ordinary flow conditions. In contrast, under flood flows of approximately 3500 m3/s, riverbed variations occurred in most of the calculation area, with extensive erosion and deposition of more than 2.0 m over 24 h. To reevaluate the structural functions of the Yamadazeki Barrage, elimination scenarios of both the Southern Ship Way and the Sand Sluiceway, which are considered important sand removers, were determined and analyzed. These scenarios revealed that the flow became unstable, and riverbed variations were significant. Therefore, these structural elements stabilized the water flow and maintained a safe and reliable water withdrawal. Additionally, the relevance of the weir structures, which was carefully calculated and designed to match the river flow rate and water level, was evaluated numerically.

FUKUOKA-ken (Japan); JAPAN; SHALLOW-water equations; FUNCTIONAL equations; BARRAGES; WATER withdrawals; WATER levels; RIVER channels

Paddy & Water Environment, 2024, Vol 22, Issue 1, p109

1611-2490

Academic Journal

10.1007/s10333-023-00956-4