The petition shall set forth a description of the ditch or ditches, drain or drains, stating the boundaries of the ditch or drain, giving the number of sections or fractional parts thereof, and stating that the proposed drain or ditch shall empty into a watercourse or depression or draw whereby the water flowing therein will be carried into a natural watercourse; and that such drain or ditch is necessary for agricultural or sanitary purposes, and that it will be conducive to the public welfare.