Abstract
Cross sectional profile, hyporheic flow velocity and spawning redds distribution were surveyed, and hyporheic flow was also calculated, to understand influence of bed morphology, alluvium thickness and groundwater level along river on hyporheic flow distribution and chum salmon spawning environment. Water surface elevation distribution on the field bed surface, alluvium thickness and groundwater level beside the river were considered in the hyporheic flow calculation condition. The results revealed that welling up hyporheic flow velocity was low and little spawning redds was found in thin alluvium section. On the other hand, in the section which has characteristics with thick alluvium and higher groundwater level than river water level, groundwater flowing into river bed and welling up with hyporheic flow which was caused by a bar morphology, was confirmed. In the case that groundwater level were lower than river water level, hyporheic flow flowing out from river bed and reduction of hyporheic flow welling up were confirmed. These results suggest that thick alluvium thickness, hyporheic flow caused by bed morphology and ground water intrusion into river bed are satisfactory for spawning environment because of various length of hyporheic flow path exist.
