トンネル貯水工法による自己水源開発に関する技術指針

Abstract

A technique for developing self-reliant water supply system with tunneled water tanks, proposed by the author, was first and foremost employed for controlling the ravages of drought in the Island of Tuwaji-shima, Nakajima-cho, Ehime Prefecture. For dissemination of its appliance, it is a basic need to bring out and strengthen its engineering framework. This paper thus aims to provide guideline for planning and designing this small-scale water supply system. The technical aspects of tunneled water tank, inclusive of its installation technique is indeed meritorious in many respects : (a) no need of dam and reservoir sites, (b) freedom from meteorological disasters such as typhoon, (c) less impacts on the natural environment, and (d) averting water quality degradation. Additionally the paper addresses a few useful techniques for water harvesting in the a micro catchment that can successfully be combined with tunneled water tanks to form an entire water supply system. These are : (a) harvesting and collecting rainwater running over farm roads laid on a steep, (b) selectively withdrawing excess surface water from an irrigation tank by installation of glory-hole or bellmouth spillway, and (c) extracting excess water from a small stream resorting to the well-designed hydraulic structure that gives precedence to instream water uses and downstream water right. Finally emphasis is made that beneficial reuse or disposal of the cut-off rocks and soil produced by earthworks should be taken into account in the stage of planning to render the project much more valuable.