The board of commissioners of any drainage district organized under the provisions of this chapter shall, on or before the third Monday of September of each year, make an estimate of the cost of maintenance of the drainage system constructed in such district, which estimate shall include the cost of making any necessary repairs that it might become necessary to make in the maintenance of such system. Such estimate shall be made for the succeeding year, and the amount so estimated shall be certified by the board of commissioners to the auditor of the county in which such district is located, on or before said date, and the amount thereof shall be apportioned to the landowners in such district benefited by said improvement in proportion to the benefit apportioned or reapportioned, and such amount shall be added to the general taxes of such landowners and collected therewith; provided however, that at the option of the commissioners the amount apportioned to every landowner on any parcel or piece of land shall be not less than one dollar ($1.00), which amount shall be a minimum assessment to be collected as a tax for the year on every such parcel or piece of land.