| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1997: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1996: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
The studies were divided into two subjects ; 1) researches on ground water in a floodplain and its influences on geomorphology of stream and floodplain, 2) role of underground water on the stream environment.
In the first subject, a small stream located in northern Hokkaido was chosen as study site. The stream was kept in natural condition, many old channels and abandoned channel existed in the floodplain. There were lots of seepage along the stream and strange topographical features were formed by erosion. These features were small hole with semi-globular shape and trench-like grooves (trenches), both were adjacent to the channel and dug in the flood basin. In order to make clear how ground water contributed to the formation of these topographical features, ground water flow was examined by means of the following activities: detailed topographic survey, installation of piezometers, investigation of water levels of the stream and piezometers, tracer test of ground water, analysis of water quality, etc. These researches showed that there were at least two types of ground water, and that water levels in some piezometers fluctuated with remarkable correlation to that of the stream water level. These results showed the existence of active ground water which flowed through highly permeable part, and this ground water was then suggested to have contributed to the formation of the trenches.
As for the second subject, the floodplain studied here corresponds to hyporheic zone which has been taken attention in stream ecology. This study showed that fluvial processes closely related to the formation and development of the hyporheic zone, ground water flow and structure of floodplain made complication of the stream environment. Thus the stream ecosystem is essentially defined by dynamic processes of stream such as erosion, sedimentation and channel course change.
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