Gilbert Bay, the expansive Artemia-producing arm of Great Salt Lake, is currently at a low stand due to drought and water use in the basin. However, a recent breach in the solid fill causeway bisecting the lake provides an unprecedented tool for managing the salinity of Gilbert Bay in the face of reduced lake volume. The causeway separates Gilbert Bay, which receives all three inflowing rivers, from Gunnison Bay, which stores a substantial portion of GSL salt away from the Artemia-producing waters of Gilbert. A 55-meter breach in the causeway constructed in 2017 included an adaptive management berm which can be modified to increase or reduce the flow of water and salt between the bays. Through salinity data collected from 2010-2021, we demonstrate the previously unobserved mass movement of salt through this causeway opening, observe an important changing relationship between salinity and surface elevation in Gilbert Bay, and present berm management strategies for keeping salinities within an acceptable range for Artemia at a variety of lake elevations.
In the 5 years preceding the breach, the relationship between Gilbert Bay salinity and elevation was linear and consistent with the annual concentration and dilution of a stable salt load. This changed in 2017, when high runoff coupled with the opening of the breach to force nearly 17% of the Gilbert Bay salt load into Gunnison Bay. The salinity-elevation relationship was lowered, resulting in more dilute salinities. The salt load of Gilbert Bay began increasing measurably again in 2020, demonstrating a return flow of Gunnison Bay heavy brine through the opening. In response, and under advisement of a scientific panel, management agencies modified the berm to restrict the return flow with the goal of preserving salinities conducive to the Artemia population. As of September 2022, return flow of heavy brine has reportedly been almost entirely halted.
This multiyear bidirectional transfer of salt mass across the causeway illustrates remarkable potential for managing salinity for Artemia during periods of limited river inflows in the near and long term. Spring runoff can export salt from Gilbert Bay to reduce salinities in individual years, with the berm utilized to prevent return flow of heavy brine. In the long term, existing hydrologic models can be refined to provide berm geometries that optimize salinity across multiple lake elevation scenarios.