Section 10(6)(a) in The Orissa Grama Panchayats Act, 1964
(a)the Grama Panchayats in relation to Gramas in which the density of population of the Scheduled Castes and the Scheduled Tribes is higher in the Block shall be reserved by the Collector for the Scheduled Castes and the Scheduled Tribes respectively and shall rotate in the descending order at every general election; and