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Agency hydrologist reports modest October recharge, Key Well near annual low
Summary
Agency staff reported modest October rainfall and a Key Well depth-to-water around 139.6 feet, modest surface outflow and continued “bouncing along” near the annual low; presenters said recent storms produced limited recharge and emphasized DWR reporting requirements and ongoing monitoring.
Jordan, a staff presenter, told the Hawaii Basin Groundwater Management Agency that recent storms produced modest recharge in October, measuring about 3.94 inches on the ridge and roughly 1.91 inches on the valley floor to date. “This particular time frame, were at a 139.56 feet to water in the Keywell,” Jordan said, noting a recent localized nadir of 140.78 feet on Oct. 10 before the water table rose by roughly two feet after rain.
Jordan said the basins estimated capacity was about 74.5 percent, or roughly 59,600 acre-feet, and that surface outflow measured at the basin boundary totaled about 1.14 cubic feet per second, with about a tenth of a CFS at the Montgomery/Stuart Canyon drain and a little over 1 CFS on San Antonio Creek proper. ‘‘What that does to the basin...is recharge it and allow for the discharge over the recession periods,’’ Jordan said.
In comparing conditions to 2012 and 2024, Jordan noted 2012 had higher winter rainfall and a shallower depth-to-water; 2025 so far is drier than 2012 but benefits from antecedent wet years in 202324. Jordan described hydrograph behavior as "bouncing along" near the basins annual low and cautioned that warm afternoons can depress measured flows, producing short-term fluctuations.
Directors asked whether debris removal and improved catchment efficiency on upstream drains (Ventura Watershed/Stewart area) could increase percolation to the perched system. Jordan said improved catchment efficiency can route more water into the perched system and, in turn, affect San Antonio Creek flows, though much of that water is unlikely to infiltrate into deeper main production zones.
The presentation closed with a forecast discussion: seasonal outlooks showed equal or higher chances of warmer temperatures for NovemberJanuary and below-average precipitation probability for JanuaryMarch, with a return to average chances for AprilJune 2026. Jordan invited questions and said monitoring well work is planned into the spring.
The agency did not take formal action on the presentation. Staff said data and slides would be posted to the agency website for review.
