| 摘要 |
PURPOSE:To prevent the reduction of effective area of farming land by using a waterway structure consisting of an irrigation canal having an opening on its bottom, a drainage ditch being arranged under the irrigation canal and having an opening on its upper part, and a cover to close the opening. CONSTITUTION:A waterway structure consists of an irrigation canal constituent part 1, a drainage ditch constituent part 2, and a cover 6. The part 1 has an opening 4a on its bottom, and the part 2 has an opening 4b on its upper part, which is formed in the lower part of the part 1 and is led to the opening 4a. One or both of the openings 4a and 4b are closed by the cover 6 which enables the irrigation canal and the drainage ditch to be separately used as needed. The irrigation canal and the drainage ditch are vertically provided in two stages. The construction work for water channel and drainage ditch can thus be concurrently performed, while the reduction of effective area of farming land suitable for vegetation can be prevented.
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