Also.............to the very north of the tidal basin............on one of the seawalls..........by a bridge..................for cars..............there is an opening.............the water in the tidal basin at the point flows at it............

How Does The Tidal Basin Work?

The Cherry Blossom trees, Jefferson Memorial, FDR Memorial, and MLK Memorial all border the Tidal Basin. Ever wonder what it does and how it works?
The concept for the Tidal Basin originated in the planning for the reclamation of the Potomac flats in the 1880s. This broad marshland of silt deposits along the river shore hampered access to the city’s waterfront, was a dumping ground for sewage and a breeding ground for malaria, and detracted from the capital city’s visual appeal. In 1882, Maj. Peter Hains of the U.S. Army Corps of Engineers submitted a plan that called for the dredging of the flats to create a large parkland with the reclaimed fill. A key feature of the plan was a tidal reservoir to serve both as a visual centerpiece and a means of flushing out the Washington Channel, a harbor separated from the river by the new fill lands. The reservoir would release 250 million gallons of water captured at high tide twice a day, flushing the channel free of sediments and impurities. The Reservoir and the Outlet Bridge, the structure that released the water to the channel, were completed in 1889; an Inlet Bridge to control the stored water was added in 1909.