Hydraulic study on scouring downstream of Funagira Dam spillway apron (Japan)

Kitamura, Y. and Takagi, S. (2016) Hydraulic study on scouring downstream of Funagira Dam spillway apron (Japan). In: ICSE 2016 (8th International Conference on Scour and Erosion), 12-15 September 2016, Oxford, UK.

PDF PA_7_2-Kitamura-Y.pdf Download (4MB)

Abstract

Funagira Dam is a concrete gravity dam having a height of 24.50 m and a dam crest length of 220.00 m, and is located approximately 30 km upstream from the mouth of the Tenryu River. The Funagira Dam is owned by the Ministry of Agriculture, Forestry and Fisheries, Shizuoka Prefecture, and Electric Power Development Co., Ltd. (J-POWER), and its objectives include power generation and supply of agricultural water, public water, and industrial water. For energy dissipation, the downstream area of the dam was designed as a hydraulic jump-type dissipater using bed protection blocks. The dam has experienced several large storm events in the 40 years after its completion. The protection blocks were damaged and the scouring downstream of the dam began soon after completion. About 6,300 tetrapods were added stage by stage to the bottom. In recent times (2011), however, flood events have been more intense and of longer duration, with maximum spillway releases of up to approximately 6,396 m3/s. This resulted in increased scouring at the foot of the dam. Emergency measures were taken just downstream of the dam apron from 2011 to 2013. The scouring process is a function of several variables, such as water discharge, water level downstream, bed protection, bed materials, transport, morphological riverbed conditions, and gate operations. Experimental studies with field observations, mathematical model tests, and vertical 2-dimensional and fully 3-dimensional hydraulic scale model tests have been carried out to examine the scouring processes and to determine long-term measures. These studies indicate that scouring was caused by a horizontal secondary flow with non-uniform discharge releases, and by changing the types of hydraulic jump because of long-term morphological riverbed changes. The study especially indicates that severe scouring would occur not only for extreme planned discharge but also for small discharges, because of the downstream water level of the dam.

Actions (for site administrators only - login required)

View Item