The amount of open space required to be reserved under a planned unit development shall either be held in corporate ownership by the owners of the project area building sites for the use of each owner who buys property within the development or be dedicated to the City and retained as open space for parks, recreation and related uses. All land dedicated to the City must meet the City Planning Commission's requirements as to shape, size and location. Public utility and similar easements and rights of way for watercourses and other similar channels are not acceptable for open space dedication to the City unless such land or right of way is unable as a trail or similar way and approved by the Commission. The developer may be required to contribute a reasonable sum to the City for maintenance of open space held by the public.