The dam and Irrigation system benifit the people around for 2000 years.

History from Wikipedia:

Around 250 BC during the Warring States Period (475-221BC), Li Bing, a governor of Shu in the Qin state (present Sichuan Province) with his son directed the construction of Dujiangyan. The governor gave up the old way of dam building, which was simply trying to catch the floodwaters. Instead he employed a new method by channeling and dividing the water to harness the Min River. He accomplished this by separating the project into two main parts: the headwork and the irrigation system. The project effectively put flood waters under control. For over two thousand years the whole system has functioned perfectly, serving not only for flood prevention but also as an immense source for irrigation and a means to facilitate shipping and wood drifting. It has contributed greatly to the richness of Chengdu Plain with its reputation as "The Land of Abundance".