| 摘要 |
PROBLEM TO BE SOLVED: To freely respond any channel gradient with a combination with a conventional U-shaped ditch by forming horizontal surface portions with different depths on the upper surface of the bottom of a U-shaped channel block, and a step surface portion for continuously interconnecting these. SOLUTION: A horizontal surface portion 4A with a shallow bottom, a horizontal surface portion 4B with a deep bottom, and a step surface portion 4C are formed in a U-shaped ditch 1 having a step comprising both-side wall portions 2 and a bottom wall portion 3. A projection 5 for connecting a conventional U-shaped ditch having no step is disposed on the bottom wall portion 3. When a channel with 1% gradient is built, one U-shaped ditch 1 having a 2 m long stem with 10 cm step H and four conventional U-shaped ditches with the same length are arranged and interconnected. Repeating this working pattern builds a channel with a predetermined length, and combination of number of connections forms the channel with a predetermined gradient. Water in the channel gently flows on the horizontal surface portion 4A with the shallow bottom, drops onto the horizontal surface portion 4B with the deep bottom through the step surface portion 4C, and is accelerated adequately. This improves productivity and allows free response to any channel gradient.
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