Yes, but was the fellow considered a harbor maintainer? I don't know what this constitutes, but there's nothing in the story to indicate he had any such designation.

Seemingly, a dam was built, the diverted water created the channel.

A cubic yard is 7-8 small wheelbarrows worth of material.

It’s nearly impossible to accomplish anything significant by moving a cubic yard of anything. Except gold bullion or Plutonium.

Even diverting a small stream for awhile would require very thoughtful application of something pretty durable (concrete?).

Not impossible, but very improbable.

Which is probably why they set such a small limit. That’s literally ‘dude with a shovel and an hour’ territory.