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(1) Physical availability for perennial or intermittent streams will be determined based on monthly flow rate and volume.

(a) If stream gage records are available, or the source has been otherwise measured, or quantified, those measurement records will be used to quantify physical availability using the median of the mean monthly flow rate and volume during the proposed months of diversion.

(b)  If measurement records pursuant to (1)(a) are not available, mean monthly flow rate and volume of water physically available may be estimated using a department-accepted method in conjunction with applicant collected flow measurements to validate the estimation technique.  The applicant must collect a minimum of three measurements that reflect high, moderate, and low flows during the period of diversion.  The applicant shall explain how the measurements are representative of high, moderate, and low flows.

(2)  Physical availability for ephemeral streams will be determined based on annual runoff volume above the proposed point of diversion using climate and drainage area data.

(3)  Physical availability for a lake will be determined based on stored volume.

(a)  If the volume of a lake has been quantified by a qualified entity based on bathymetric data, that volume will be used to quantify physical availability.

(b)  If the volume of a lake has not been quantified pursuant to (3)(a), volume may be quantified by a qualified professional based on department-approved methodology.

(4)  For all other source types, physical availability of water will be determined based on monthly flow rate and volume.  The applicant is required to collect measurements for these sources once monthly at department-approved intervals during the proposed period of diversion.

(5) Streamflow measurements required in (1)(b) and (4) must include a description of the methodology used to collect measurements and include all data collected.

(6)  The department will determine the acceptability of measurements based on the information submitted.  Measurements collected by an applicant must be measured in CFS or GPM and be collected at a department-approved location on the source of supply. The department may require from the applicant additional information and data necessary to complete its analysis.

(7)  An applicant may make a written request for a variance from the measurement requirements in (1)(b) or (4) as provided for in ARM 36.12.123.


History: 85-2-113, 85-2-302, MCA; IMP, 85-2-302, 85-2-311, MCA; NEW, 2005 MAR p. 264, Eff. 1/1/05; AMD, 2012 MAR p. 2071, Eff. 10/12/12; AMD, 2013 MAR p. 1344, Eff. 7/26/13; AMD, 2018 MAR p. 451, Eff. 2/24/18; AMD, 2023 MAR p. 1872, Eff. 1/1/24.

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