Hyporheic Flow Caused By Bar Morphology On Chum Salmon Spawning Area

Masaaki Yano, Yasuharu Watanabe, Kouki Sugihara, Kazuyoshi Watanabe, Yasuyuki Hirai

Tuesday 30 june 2015

12:00 - 12:15h at Amazon (level 1)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 5G. Environment – Ecosystem

Introduction The chum salmon (Oncorhynchus keta) is an important fisheries resource in Hokkaido, Japan, with this prefecture accounting for about 80% of Japan’s catch. To enable chum salmon to reproduce, river works must preserve the spawning environment. Hyporheic flow is an important factor of the spawning environment. And bar morphology contribution for generating hyporheic flow is indicated. To understand hyporheic flow distribution, usually vertical hydraulic gradient and coefficient of permeability are surveyed at many points. But a lot of time and works are needed for these surveys. And hyporheic flow path which is important to describe its quality, is not able to be understood. For a solution of this problems, numerical calculation is considered. Thus, we attempted numerical calculation to understand hyporheic flow distribution around bar morphology in this study. Method We carried out surveys in Toyohira River, in which chum salmon are observed to spawn every year in Hokkaido, Japan. To understand relationship among bar morphology, hyporheic flow and spawning environment, the cross sectional profile, hypoheic flow were surveyed around a bar. And numeric calculation of hyporheic flow was also conducted. The_hyporheic flow calculation grid was made by cross sectional profile survey result. And distribution of water surface elevation which was also calculated was inputted on the hyporheic flow calculation. Results and discussion The results of hyporheic flow survey revealed that welling down hyporheic flow was distributed on bar crest and welling up hyporheic flow was distributed on bar front. Hyporheic flow calculation revealed bar crest to front hyporheic flow path existence. And spawning points were located where hyporheic flow welled up. Thereby, we conclude that bar morphology contribute generate suit hypoheic water for spawning environment.