Impact of the flush discharge from a dam on the biotic and abiotic river environment

R. Tsubaki, Y. Kawahara, Y. Nakadoi, Y. Iwakoke and H. Yoshitake

Hiroshima University, Kagamiyama, Higashi-Hiroshima, Japan

Riverflow 2010, Braunschweig, Germany.

ABSTRACT: Due to regulation of river flow, there have been gradual but drastic changes on the biotic

and abiotic environment of rivers. These changes may have led to lowering of the quality of ecosystem

services provided by affected rivers. In this study, a flush discharge release was observed to estimate the

impact of a flush discharge on the river environments of an upstream reach of the Jyouge River, which

flows through the northern part of Hiroshima, Japan. The river reach that was assessed in this study is 8

km in length and is located just downstream of the Haiduka dam, which released a maximum flush discharge

of 100 m3/s. Water stage hydrographs at 21 stations were recorded using the water gauges installed

in the river. At two stations, water sampling had been conducted to quantify suspended sediment

(SS) and chlorophyll a (chl.a.) Two-dimensional flow simulation was performed to represent timedependent

flow and material transport processes. Using the observed and simulated results, transport of

chl.a during the flush discharge was investigated．Then transport distance of chl.a and its relation to the

flood duration are discussed.

Keywords: Flushing flow, Dam, Attached algae, Numerical model, Environmental impact