At the August 1, 2018 North Fork Kings GSA Special Board Meeting, Kevin Johansen of Provost&Pritchard briefly reviewed the alternative methodologies considered for allocating the estimated 206,000 AF of annual groundwater overdraft within the Kings Subbasin. The North Fork Kings GSA Board moved to select its preferred methodology for recommendation to the Kings Subbasin coordination group. The coordination group must still reach an agreement on the methodology that will be used by the entire subbasin.

Below are the five alternative methodologies to determine groundwater overdraft allocation:

Methodology 1: equal subbasin overdraft distribution by GSA acreage

Methodology 2: storage change only within boundaries of individual GSA

Methodology 3: storage change plus groundwater boundary flows between GSA’s

Methodology 4: storage change plus groundwater boundary flows between GSA’s, including historical flow patterns

NEWIteration 4A: same as methodology 4, except an adjustment is made for aquifer thickness caused by declining water levels, and uses bookend years of 1999 and 2011 to determine current groundwater flow conditions

NEWIteration 4B: same as iteration 4A, except rather than bookend years, averages data from multiple years between 1999 to 2011 to determine current groundwater flow conditions (thus, more data is used in the calculation than in iteration 4A)

Methodology 5: water budget concept: utilizes calculated water demand, and assumes demand not met by surface water delivery/precipitation is met by groundwater pumping

Click here to read our previous post for more detail on the methodologies, including their benefits and shortcomings. 

Acknowledging that overdraft numbers will change as quality and quantity of monitoring data is made available, the Board moved to select iteration 4B as its primary preference citing its parameters and data quantity as key indicators of accuracy.

In the absence of coordinated group consensus on iteration 4B, the Board moved to select methodology 4 and 4A as alternative preferences. The difference between current estimated overdraft amounts assigned to the North Fork Kings GSA between methologies 4, 4A, and 4B is minimal, with all falling between 72,000-75,000 AF (numbers are preliminary and subject to change).

The Board’s goal is to set realistic mitigation targets and implement projects to successfully reach sustainability goals. An accurate representation of groundwater conditions will equip the GSA for that goal.

Please note that all numbers are preliminary and subject to change pending data improvements.

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