The City of Los Angeles shall continue in the ownership and enjoyment of all the rights to the water of the Los Angeles River, vested in it and its predecessors, including the Pueblo of Los Angeles, and is hereby declared to have the full, free and exclusive right to all the water flowing in the river and also the exclusive ownership of, and the exclusive right to develop, economize, control, use and utilize all the water flowing beneath the surface in the bed of the river at any point from its sources to the intersection of the river with the southern boundary of the City.