More than two irrigation districts may merge under RCW 87.03.530(2) and 87.03.845 through 87.03.853 in one merger process. However, only one of the districts may be a "major" irrigation district and the assessed acreage in all of the other districts merging in the process, when taken collectively, shall not constitute more than thirty percent of the combined assessed acreage of all of the merging districts. In such a case, each of these other, nonmajor districts is considered to be a "minor" irrigation district under RCW 87.03.530(2) and 87.03.845 through 87.03.853.