To inexpensively provide a water distribution pond having an external reinforcing structure for minimizing structural clearance being the cause of crevice corrosion of the water distribution pond by solving the problem of increasing in cost for requiring a large number of field welding works for restraining the crevice corrosion, and causing the demerits of restricting a reinforcementless width in the internal reinforcing rectangular steel water distribution pond.

This structure is adopted for reinforcing a wave part of a member having a C-shaped cross section called a vertical reinforcing material by side plates arranged on both sides. The reinforcementless width can be largely increased so that the water distribution pond having the external reinforcing structure can be inexpensively manufactured.