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The Kashio River (柏尾川)
is a Class II river in central
Japan, about 50 kilometers southwest of Tokyo. It begins near the city
of Totsuka (戸塚)
at the confluence of the Akuwa River (阿久和川)
and the Hiradonagaya River (平戸永谷川)
and flows for 11 kilometers to the city of
Fujisawa, where it merges with the Sakai River (境川).
The conjoined river, which is then known as the
Katase River (片瀬川),
then flows into
Sagami Bay at
Enoshima Island.
The catchment basin of the Kashio River is approximately
84 sq. kilometers. Because the Kashio River is a short, meandering stream,
with a minimal descent, it has long been notorious for flooding. The
predecessor of the Kashio River was the shallow Ofuna Estuary (大船入江),
which existed from the end of the last
Ice Age to about 300 BC. Subsequently, earthquakes caused crustal
uplift, which cut off the estuary from the bay, making it into a floodplain
with the Kashio River at its center. As the river often flooded, it formed a
lake that left behind a swamp as it drained. The early lake formed in the
floodplain of the Kashio River is probably the lake mentioned in the
Enoshima Engi, a history of the area.
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