Granted, but what is it doing in the Army? The Army's job is to kill people, break things and otherwise defend the US from threats from abroad.Gotta be able to move men and material to do that. Years ago, that meant building roads, railroads, forts, etc. etc. in addition to making our inland waterways navigable. The rivers are still a major part of our transportation infrastructure, and as such, are considered vital to our national security. The Army retains their historical jurisdiction.
The Corps is also in charge of one of the biggest scams in history, wetlands mitigation, in which builders are allowed to destroy designated wetlands in return for creating wetlands in the same drainage basin (resulting, for example, a small pond and bog in my area, home to local wildlife, being paved over by a Meijer Store which paid a farmer in the Jeffersonville area -over 100 miles away- to create a wetland in the flood-prone area of his farm).
There is much that the Corps does that is valuable, but the wetlands program is out of control. They could probably make up the cuts in the budget by getting rid of wetlands bureaucracy.
So don't act like the Corps is sacrosanct. It isn't.