There is hereby established minimizing, measuring and fixing elevations and grades in the city, which base or datum plane shall be known under the stale and name of “Kewanee City Datum.” The plane referred to is a horizontal plane which is 99.37 feet vertically below the south side of the top of the manhole frame at the center of the intersection of Second and Tremont Streets in the city, the elevation of the said point being hereby established of 99.37 feet.
('71 Code, § 9-2-1)