OAR 690-507-0800
Stage Gulch CGWA: Method for Determining the Sustainable Annual Yield
(1)
The Department shall determine the sustainable annual yield for each subarea by comparing the volume of groundwater pumped annually from each subarea for a given year to the average of the annual changes in groundwater levels for the area for the same year:(a)
The Department shall calculate pumpage from each well based on data collected by the Department and as submitted under OAR 690-507-0780 (Stage Gulch CGWA: Duties of Water Users). The pumpage for each subarea shall be calculated by totaling the pumpage from each well in the subarea required to have a flow meter;(b)
The Department shall calculate annual change in groundwater levels for a subarea by subtracting the current year’s February or March water level from the previous year’s February or March water level. The average shall be calculated by adding the change at each well in the subarea and dividing by the number of wells with available water level data. Data from all permitted or certificated wells in each subarea that are measurable shall be used to calculate the average annual change. If water level data cannot be collected at a particular well, data from a nearby well may be substituted.(2)
The total volume of groundwater pumped from each subarea for a given year shall be plotted against the average change in groundwater levels from that subarea for that year.(3)
A line of regression is drawn through the data using the least squares fit method and extended through the zero decline axis.(4)
The initial determination of sustainable annual yield for subareas B, C, and F of the Stage Gulch Critical Groundwater Area shall be based on the average annual pumpage in each subarea during the period 1985 through 1989, rounded upward to the nearest 50 acre-feet.
Source:
Rule 690-507-0800 — Stage Gulch CGWA: Method for Determining the Sustainable Annual Yield, https://secure.sos.state.or.us/oard/view.action?ruleNumber=690-507-0800.