PURPOSE: To apply cut-resisting property and expanding and shrinking property to a covering unit made of flexible diaphragm, by putting knitted goods organized with the yarns of metallic fiber, together with the flexible diaphragm coated with rubber or plastics, outside the covering unit made of the flexible diaphragm.

CONSTITUTION: The bed section 7 of a river or the like is provided with the covering unit 9 made of flexible diaphragm of a cloth sheet coated with rubber or plastics, and on a part at least outside the covering unit 9 made of the flexible diaphragm, a flexible diaphragm 10 excellent in cut-resisting property is set in one layer, or is set in two layers or more to be put together. The flexible diaphragm unit 10 is organized with yarns with metallic fiber 12 used as knitted organizers 12 coated with the rubber or plastics 11 of flexible material. The covering unit 9 made of the flexible diaphragm is formed as a fabric 2 with the used yarns of organic fiber coated with rubber or plastics 1. By this organization, the metallic fiber 12 is used for the flexible diaphragm unit 10, and so the covering unit 9 is excellent in cut-resisting property and also in expanding and shrinking properties.