The effect of alluvial thickness on hyporheic flow quality from the point of view of chum salmon spawning environment — ASN Events
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  3. The effect of alluvial thickness on hyporheic flow quality from the point of view of chum salmon spawning environment

The effect of alluvial thickness on hyporheic flow quality from the point of view of chum salmon spawning environment (#250)

Masaaki Yano 1 , Yasuharu Watanabe 2 , Kouki Sugihara 1 , Yasuyuki Hirai 1
  1. Civil Engineering Research Institute for Cold Region, Sapporo, HOKKAIDO, Japan
  2. Kitami Institute of Technology, Kitami, Hokkaido, Japan

Alluvial thickness decreasing caused by bed degradation has been progressing on middle and upstream area, where Salmonidae species utilizes for spawning in Japan. To understand influence of alluvium thickness decreasing on hyporheic flow quality from the point of view of chum salmon spawning environment, filed survey was conducted in 2 sections which have different characteristics, such as thin alluvial thickness (thin alluvial section) and thick alluvial thickness (thick alluvial section), on upstream of Ishikari River, Hokkaido, Japan. Cross sectional profile, hyporheic flow velocity, dissolved oxygen, chronological temperature and spawning redds distribution were surveyed along around bar front, longitudinally every 50m in the sections. And numerical calculation of hyporheic flow was also conducted.
The results show that mean value of hyporheic flow velocity and temperature were low, and dissolved oxygen was high in thin alluvial section. And little spawning redds was confirmed there. On the other hands, mean value of hyporheic flow velocity and temperature were high, and dissolved oxygen was relatively low in thick alluvial section. And many spawning redds were confirmed there. Numerical calculation results show that hyporheic flow velocity was low and that flow path was short in thin alluvium section. On the other hands, many variations of hyporheic flow velocity and flow path length, including higher temperature and longer flow path one, was confirmed in thick alluvial section. These results indicate that thick alluvial thickness contributes to spawning environment by supplying various hyporheic flows which include enough dissolved oxygen and warm temperature hyporhric flow.

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