Any large-scale projects for mitigating drought in the U.S. would fall under the direction of the Bureau of Reclamation, which is the federal agency tasked with water management.
While technically feasible, transporting surface water from flood areas (or the ocean) to drought areas faces many challenges including water rights, property rights, environmental impacts, and more. Then there's the considerable expense of building pipelines and pumping the water. Pumping large amounts of water from one place to another--especially if it must be pumped uphill--can require enormous amounts of energy. Pumping seawater (which is corrosive) adds a new set of complications.
Cost estimates for projects like this vary, but the cost of re-routing new sources of water is often too expensive, which is why cities in the Western U.S. are emphasizing water conservation.
Desalination of seawater and desalination of brackish groundwater are other expensive options. Some cities, like San Diego, have already built desalination plants, but desalination comes with its own set of issues, including the large amount of power required and some serious environmental consequences.