All grades established by this chapter or that may be hereafter established shall be calculated from the datum plane described in IGCC 1.15.010. All ordinances with reference to the fixing of a datum plane or a permit bench mark within the incorporated limits of the city of Ida Grove, Iowa, adopted prior to July 6, 1965, are hereby repealed because of the loss of evidence governing a permanent bench mark or datum plane. [Code 1975 § 8-1.0606.]