(1) If actual stream gaging records are available, or the source has been otherwise measured, or quantified by a public entity, the records shall be used to estimate the median of the mean monthly flow rates and volumes for the stream gaging station period of record during the proposed months of diversion at the source of supply in the amount the applicant seeks to appropriate.

(2) If actual stream gaging records are not available, or the source has not been otherwise measured or quantified by a public entity, an accepted method for estimating surface water flow rates and volumes shall be used in conjunction with discharge measurements to validate the estimation technique used.

(3) Except as provided in (4), stream flow measurements in cfs or gpm must be collected at least once every month during the proposed period of diversion at the most suitable location on the source of supply, which is typically at or directly upstream of the proposed point of diversion.

(4) If it is not possible to take measurements every month due to high spring flow conditions or other limiting conditions, the department may grant a variance to the measurement requirements in (3).

(a) A request for a variance from measurement requirements must be submitted in writing to the appropriate regional office.

(b) A variance may not completely relieve the applicant of the requirement of taking measurements.

(5) Measurements must be submitted on Form 649 in electronic format with all information and data provided.

(6) In addition to validating estimation techniques, measurements may, in some cases and upon approval of the department, be used as evidence of physical availability.

(7) The methods described in the following reports may be acceptable for estimating surface water flow rates and volumes:

(a) "A Method for Estimating Mean and Low Flows of Streams in National Forests of Montana," USGS Water Resources Investigation Report 85-4071;

(b) "Estimated Monthly Percentile Discharges at Ungaged Sites in the Upper Yellowstone River Basin in Montana," USGS Water Resources Investigation Report 86-4009;

(c) "A Method for Estimating Mean Annual Runoff of Ungaged Streams Based on Characteristics in Central and Eastern Montana," USGS Water Resources Investigation Report 84-4143;

(d) "Estimates of Monthly Flow Characteristics at Selected Sites in the Upper Missouri River Basin, Montana, Base Period Water Years 1937 - 86," USGS Water Resources Investigations Report 89-4082;

(e) "Mean Annual Runoff and Peak Flow Estimates Based on Channel Geometry of Streams in Southeastern MT," USGS Water Resources Investigation Report 82-4092;

(f) "Mean Annual Runoff and Peak Flow Estimates Based on Channel Geometry of Streams in Northeast and Western Montana," USGS Water Resources Investigation Report 83-4046;

(g) "Estimates of Mean Monthly Stream Flow for Selected Sites in the Musselshell River Basin, Montana," USGS Water Resources Investigation Report 89-4165;

(h) "Synthesis of Monthly and Annual Streamflow Records (Water Years 1950-2003) for Big Sandy, Clear, Peoples, and Beaver Creeks in the Milk River Basin, Montana", USGS SIR 2005-5216;

(i) "Synthesis of Monthly Natural Flows for Selected Sites in the Musselshell River Basin, Montana, Base Period 1929-89", USGS WRIR 96-4094;

(j) "Synthesis of Natural Flows at Selected Sites in and near the Milk River Basin, Montana, 1928-89", USGS WRIR 95-4022;

(k) "Estimates of Monthly Streamflow Characteristics and Dominant Discharge Hydrographs for Selected Sites in the Lower Missouri and Little Missouri Basins in Montana", USGS WRIR 94-4098;

(l) "Streamflow Characteristics of Small Tributaries of Rock Creek, Milk River Basin, Montana, Base Period Water Years 1983-87", USGS WRIR 89-4206;

(m) "Methods for Estimating Monthly Streamflow Characteristics at Ungaged Sites in Western Montana", USGS WSP 2365; and

(n) "Streamflow Characteristics of Mountain Streams in Western Montana", USGS WSP 2260.

(o) Other professionally documented hydrologic methods for estimating stream flow or annual runoff which may be applicable and acceptable to the department, including the Orsborn method, Mannings equation, U.S. Natural Resources Conservation Service-developed mean annual runoff data, and drainage area information paired to gaged streams in similar type basins may be acceptable. The department will determine the acceptability of other methods on a case-by-case basis.