PURPOSE:To make it possible to form nesting places for river fishes and to manage nests for small animals and protect the river fishes from foreign enemies by forming sufficiently spaced cavity portions inside the wall structure of a bulkhead wall or a defense wall and setting respective parts thereof open on the surface portion side. CONSTITUTION:Sufficiently spaced cavity portions 2 are formed inside the wall structure 1 of a bulkhead wall B-1 to set at least one of parts thereof respectively open on the surface portion side 1a so that river fishes can freely go in and out, and are utilized as nesting places for rest and refuge portions of river fishes etc. These cavity portions 2 are provided at every stage from a lower stage side near the bottom portion of a river of normal water level 1 or less to the highest level IV as predicted in a swollen river. The structure may be available, for which the surface portion 1a is set open with any given paths, or a cavity member with a cavity portion formed inside is implanted into the wall structure 1. It is still applicable to a defense wall at a hilly district or others for protecting small birds and animals.
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