Complex sentence: RiverCenter retains authority over the management and redevelopment of a defined central business district, which includes Broad Street from the post office to Marine Park and from Maple Avenue to one block east of Broad Street.
Split into simpler sentences: RiverCenter retains authority over the management and redevelopment of a defined central business district. The downtown district includes Broad Street from the post office to Marine Park and from Maple Avenue to one block east of Broad Street.