Dam 1. A dam is barrier across the flowing water that obstructs, dissects or retards the flow, often creating a reservoir, lake or an impoundment 2. It is a traditional concept. Multipurpose project. 1.A multipurpose project is that which fulfils a variety of purposes at the same time, for example - irrigation, generation of electricity, flood control, fish breeding, soil conservation, etc. 2.It is a modern concept.