Clear water separation and sediment bypass of the oldest masonry dam in Japan

Abstract

Kobe City's Nunobiki dam is the oldest masonry dam in Japan. It was completed in 1900. And it had been supplying the world-famous "Kobe Water", which was supplied to vessels stopping at Kobe harbor and to be said to maintain its freshness even if crossing the equator. Off course, it has been supplied to Kobe citizens without dam cleaning more than hundred years. The secret of "Kobe Water" comes from the unique "Clear Water Separation" system. This system is closely linked with By-pass system. As a result, Nunobiki dam could prolong its lifespan. The structure of this bypass was designed to mitigate reservoir sedimentation according to some knowledge from the book of Mr. W. K. Burton, a British water engineer. And the sediment bypass itself was equipped to Karasuhara Dam from the beginning, completed in 1905. The Nunobiki system is the second installation, based on the experience of Karasuhara Sediment Bypass. The author will explore these sediment bypass systems of the classic dam in Kobe and reveal the detail structure and function.