The division heretofore made by the legislature of the alluvial land of the State into two levee districts, viz: The Yazoo-Mississippi Delta Levee District, and the Mississippi Levee District, as shown by the laws creating the same, and the amendments thereto, is hereby recognized, and said districts shall so remain until changed by law; but the legislature may hereafter add to either of said districts any other alluvial land in the State.