Stream type fishways are more desirable for various species than classic pool type fish ladder. However, there exist many old type fishways that have been already built into Sabo facilities. They need certain improvement in the structure and discharge control to maintain fish passage conditions. In our former study, the desirable minimum pool length of fishway and critical nap velocity were studied. Hence, in this study, fish behavior about masu salmon with various discharges and step heights comparing with two inner structure, that is, “slope separation wall type” or “step separation wall type” concerning with pool separations were studied by experiments to extract the versatile information for the improvement of fishways already built. Eventually, the critical relationship for the swimming behavior between pool depth and drop height was obtained, and it was also found the difference of fish behavior among inner structure types that is meaningful in the assessment of appropriate structures.
This paper presents the experimental approaches on the shock absorbing effect of rubber-cushion by impact tests. First, the static compression test was performed to compare the filled rubber with the hollow rubber. Second, the preliminary impact test was carried out in order to examine the effect of rubber-cushion depth. It is found that the rubber-cushion depth has no influence on the maximum impact load within the preliminary impact test. Finally, the model impact test was executed in order to investigate the effect of impact speed for the rubber-cushion. It is confirmed that the rubber-cushion can reduce about 40-50% of impact load for the velocity of more than 5m/sec.
Debris flows recurred on August 8 th 2003 in Fujiwara town, Mie prefecture where debris flows have occurred in 2002 since occurring in 1999. The debris flows occurring at Nishinogaito stream and Kotaki-stream, were trigged by the 10 th typhoon which caused total rainfall 333mm, maximum hourly rainfall 43mm and maximum 10-minute rainfall 19mm. The debris flows may occur when the maximum 10-minute rainfall was recorded because of response of debris flow sensors. By the field survey, it is revealed that sediment deposition at uppermost gravel sediment zone was eroded, and accumulated as results of the behavior of flow at midstream. At Nishinogaito stream, especially, an unstable sediment deposition still remains.
Sediment monitoring has been started at a branch of the Sumiyoshi River in Rokko Mountains. Rainfall, water level, bedload discharge and turbidity are measured. Bedload discharge rate are measured continuously with a hydrophone and a pit (slit) bedload sampler. Pressure pillows are used to measure the weight of trapped bedload in a pit on a torrent bed. The pit bedload sampler was adopted for the calibration of the hydrophone. They have worked properly and water and sediment monitoring were successful. The hydrophone's data were converted into instantaneous bedload discharge with the pit bedload sampler's data.