Any county together with any port district therein and first-class city in such county may participate jointly in surveys, investigations and studies for determining the location, type and design, with cost estimates, of a project plan for the improvement of any section or sections, within or without the limits of such city, of any navigable river emptying into tidal waters in such city, in aid of commerce and navigation and in aid of the comprehensive land use and development of such river valley, including present and future industrial and manufacturing uses.