出し平ダム排砂における濁水の1年後の特徴

The dam sediments of both Dashidaira and Unazuki Dams equipped with a flushing gate had been flushed out almost every year since 1991. The sediments are black and gray in color with smell sludge. Benthic fish counts have decreased year by year due to repeated flushing of clay-rich dam sediments associated with high organic contents. In June 29-30 2005, the fl ushed river water and sediments were collected from Yamabiko Bridge on Kurobe River, Toyama, Japan. The suspended river water showed low dissolved oxygen (DO), high electrical conductivity (EC), and large amounts of suspended substance (SS). After one year the flushed river water and sediments occurred reddish brown microbial films inside the bottle. The sediments contain high C, N, and S elements, suggesting large amounts of organics under reduction condition after one year. Optical microscope, SEM-EDX, TEM, STEM-EDX, and EF-TEM observations revealed coexistence of abundance microorganisms, clays and altered minerals. Coccus and bacilli type bacteria existed on the surface of minerals attaching with hydroxyl iron filaments and spherules in nm size. The XRD analyses of the sediments after one year identified clay minerals as chlorite, smectite, mica clay minerals and kaolin minerals after EG, HCI, and heating treatments. The XRD results clearly indicated that smectite is rich in the flushing dam sediments in June 29, 2005, correlating with Al/Si ratio (over 024). Characteristics of flushing dam sediments from Dashidaira after one year reflect the condition of bottom of the dam where deoxidized bacteria lead to anoxia circumstance