N.C. Gen. Stat. § 156-93.7
If there shall be more than one drainage district in a drainage basin, or watershed, the board of drainage commissioners of any of the districts may initiate or join separately or collectively with the commissioners of one or more of other drainage districts, in the drainage basin or watershed, and/or with the owners of land within the drainage basin, whose lands are not included within an existing drainage district in a petition to the court, asking for the creation of a larger drainage district, or the extension of boundaries of one of the existing districts.
The joinder in the petition by the commissioners of an existing drainage district, acting in the name of the district, shall have the effect of including all of the land assessed within the drainage district, in the petition asking for the creation of the larger drainage district or the extension of boundaries of an existing district. The total area of assessed land, within the existing drainage district shall be included, as land in the petition, in determining whether or not the requirement of G.S. 156-93.3(3) b have been fulfilled.
The provisions of this section shall apply in proceedings provided for in G.S. 156-93.2 and 156-93.3.
N.C. Gen. Stat. § 156-93.7