https://en.wikipedia.org/wiki/United_States_Army_Corps_of_En... has a good overview. Note that 97% of the employees are civilians.

In addition to sibling comments for intent, the book Cadillac Desert documents how this government agency can be used to further moneyed interests, ie subsidize developments that would otherwise not be economically viable from local funding but become viable when federal taxpayer foots the bill. (The big examples in the book is building cities and farmland in deserts.)

Not sure about the exact thrust of your question but a few points:

- flood management is not easy to monetize so there is not much incentive for private industry. The timelines for design decisions (100 year, 500 year) often don’t mate well with private incentives

- it crosses many property boundaries which makes it hard to manage unless you have the rights of a government

- much of the work is still done by private companies but managed by the government, just like other infrastructure works like roads, bridges etc.

The US did not have a civilian engineering school for a few decades after the founding. West Point was the only institution creating engineers. Given they had responsibility for port defenses the civil engineering of waterways was an easy addition.

They're decentralized enough as well that some of their local offices have hilarious online presences. For example, Portland...

https://www.instagram.com/corpsofengineers_portland/