30 Tex. Admin. Code § 303.61
An excess flow permit authorizes the use of the Texas share of the Rio Grande below the International Boundary and Water Commission gaging station near Brownsville, Texas, (United States geological survey (U.S.G.S.) Identification (ID) Number 08475000) for irrigation purposes when there is unanticipated flow which would pass unused to the Gulf. The permit holder does not have a call on storage from Amistad or Falcon Reservoirs nor shall priority be attached to such flows on any water availability analysis for any possible future reservoirs on the Rio Grande. Permittee must contact the watermaster prior to diversion to obtain a certification and to determine whether water is available at the authorized point of diversion, excluding releases made by the watermaster for water rights holders below permittee's diversion point. Application requirements are the same as those required for the Texas Water Code, § 11.121, permits. As between holders of this type of water right, the priority will be first in time, first in right. Permits previously authorized as surplus water permits will be considered henceforth as excess flow permits.
30 Tex. Admin. Code § 303.61