Section 6(3)(a) in The Orissa Zilla Parishad Act, 1991
(a)Seats shall be reserved for the Scheduled Castes and the Scheduled Tribes in every Parishad and the number of seats so reserved shall bear, as nearly as may be, the same proportion to the total number of seats to be filled up by direct election in that Parishad as the population of the Scheduled Castes in that Parishad area or of the Scheduled Tribes in that Parishad area bears to the total population of that area and such seats shall be allotted on rotation to different constituencies in a Parishad :