Advisory council: Great Salt Lake levels up, spring salinity forecast projects modest dilution

The Utah Great Salt Lake Advisory Council discussed recent lake measurements and a new spring salinity forecast, with staff noting higher-than-seasonal water levels and a mixed but cautiously optimistic outlook for dilution.

At a presentation of monitoring data, a staff presenter said the Saltaire Boat Harbor gauge’s most recent daily elevation was 4,194.1 feet and the north‑arm gauge was 4,190.8 feet, roughly 2 feet above seasonal lows. "We have a 3.3‑foot difference between the north and the south arms of the lake," Speaker 4 said, underscoring continued inter‑arm imbalance.

Streamflow records from USGS gauges on the Bear River, Weber River (Plain City), Goggin Drain, and the Farmington Bay outflow were shown tracking at or above median for the water year, evidence participants said supports ongoing elevation gains upstream.

Water‑quality staff from the Juice Lab reported the most recent surface salinity sampling (Feb. 12) and described spatial and vertical patterns: surface values ranged roughly 100–128 grams per liter across sampled sites, with lowest surface salinities recorded near the Bear River inflow and higher salinities at 3‑meter depth at many locations. A new breach sample measured 114 g/L on March 6; Saltaire recorded about 106 g/L on March 11.

Using a volume‑weighted starting concentration of about 130 g/L for the south arm (Feb. 12) and an estimated south‑arm volume near 6,400,000 acre‑feet, the Juice Lab presenter described a simple mass‑balance forecast. The model incorporated estimated breach flows (February mean ~2,250 cfs), assumed breach salinity dilution, and two climate scenarios (median and 90th percentile inflows). Under the average scenario, the presenter’s June 30 projection for the south arm was roughly 119 g/L. "That's my best guess," Speaker 5 said, adding that the calculation is an iterative exercise with many assumptions.

Speakers emphasized uncertainty: field discharge measurements at the new breach had notable measurement error (core measurements with reported uncertainty of at least 8%), and model assumptions (instantaneous mixing, breach salinity evolution, and monthly flow estimates) could materially alter projections. Council members urged continued monthly water‑quality profiles during runoff and more refined hydrodynamic work to improve the forecasts.

The group noted the NRCS forecast (Jordan Clayton) that was discussed in the meeting projects an additional 1.0–1.2 feet of lake rise from March 1 under a median scenario, though several participants said that projection is uncertain and that the actual rise could differ. Council members agreed that forecasts are useful for risk assessment but cautioned against hinging major management decisions solely on them until forecasting confidence improves.

The council scheduled a follow‑up meeting post‑runoff in late June and asked staff to continue monthly sampling and to refine model inputs, with particular attention to breach flows and salinity sampling frequency.