Water resources projects usually fall into one of four categories depending on their purpose and cost. Congress must approve the study and construction of large-scale, costly projects, such as river diversion and major hurricane protection. Smaller projects, like clearing a bayou for navigation, can sometimes be performed by the Corps under existing laws. Additionally, there are specific programs in place to allow the Corps to perform work on a project for a non-Defense federal agency, state, local government, or Native American tribe or to provide planning assistance to those entities. Regardless of the program that provides for Corps involvement, the work on that project is managed by PPMD.