How does the corps help prepare people who live in the basin for floods?

I am not sure which corps you are asking about, nor which basin. Perhaps you are asking about the Army Corps of Engineers, who have designed a number of projects to improve the flow of water and make sure optimum levels are maintained. There is a well-known tidal basin in Washington DC that they helped to construct, along the Potomac River. The Army Corps of Engineers is also known for their work maintaining and improving dams and canals, and they are involved with flood protection as well. (It should be noted that during Hurricane Katrina, the quality of their work was called into question, but historically, they have had a good reputation.)

As for floods, there have been a number of occasions when flooding occurred around the Tidal Basin in Washington DC. In most of these cases, it was the result of a hurricane. But it is usually not the Army Corps that helps to prepare people for an impending weather crisis. Generally, each major city has its own disaster preparedness plans, often administered by the state's governor and appropriate civil defense agencies; there are also other organizations like the National Guard who might be called in. But in a serious flooding emergency, the Army Corps might be called upon to help shore up a damaged levee or canal.