037-1 Wyo. Code R. § 1-11
Whenever the supply of water in a stream exceeds the total amount required to satisfy all existing appropriations established on or before March 1, 1945, the stream is said to be in a surplus flow condition.
When surplus flows are available during the water year, they are divided proportionally among the irrigation water rights holders with priorities on or before March 1, 1945, up to an additional one c.f.s. for each 70 acres irrigated. Rights with priorities later than March 1, 1945, may be regulated to meet the demands for surplus water made by the owners of water rights with priorities earlier than or equal to March 1, 1945 (see W.S. 41-4-317 through W.S. W.S. W.S. 41-4-324 ) . Surplus water only applies to irrigation water rights that are based on the statutory diversion rate of 1 c.f.s. per 70 acres, and not to volumetric awards made in acre-feet per acre.
037-1 Wyo. Code R. § 1-11