Section 3(3)(a) in The Bihar Irrigation, Flood Management and Drainage Rules, 2003
(a)Under Section 50 (i) of Bihar Irrigation Act, 1997 (Bihar Act 11,1998) the Divisional Canal Officer or any other Officer, authorised by the State Government shall declare for assured irrigable command area and probable irrigable command areas separately to be irrigated by canal water. Generally those areas shall be included in assured irrigable command area, which have been getting irrigation water continuously since last five years. "Probable irrigable command area" means, the area, the irrigation of which is not assured but whose irrigation is subject to the availability of water in that period.