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Engineers propose adaptable gate structure at causeway to manage salt flux; preliminary estimate ~$40M
Summary
Jacobs and state engineers presented a gated flow-control concept at the causeway to allow seasonal control of north↔south flux and reduce long-term salt export; the concept prioritizes flexibility and replaceable panels to limit corrosion and encrustation but carries high geotechnical and pile-driven cost uncertainty.
Engineers presented a concept design for a flow-control structure at the railroad causeway intended to give the state a flexible means of managing net salt flux between the Great Salt Lake's North and South arms.
Concept and design drivers: Jacobs and state staff said the existing berm works well to limit north→south flow in low lake conditions but cannot import North Arm water to the South Arm if future conditions require added salt mass in the South Arm. The proposed solution is a single concrete (or sheet-pile) wall with five gated bays (each ~16 feet wide) that combine a lower orifice-type opening to encourage salt-laden bottom flow and an adjustable upper weir to limit south→north overflow. Engineers emphasized two main physical controls: hydraulic head differential (elevation differences between arms) and density differential (salinity-driven density contrasts).
"The berm has been great. It's great at low and falling lake levels," Jeff Dembleyker said, explaining why the team looked beyond simple berm fixes. He and modelers described a design that prioritizes replaceable steel panels, diffuser channels to flush gates with South Arm water, and removable frames to allow seasonal replacement if salt encrustation locks panels in place.
Modeling and validation: The team ran computational fluid-dynamics slices and calibrated velocity profiles to available field cross sections and USGS measurements. The modeling suggests it is hydraulically feasible to create controlled north→south flows under some head/density conditions, though achieving sustained high-volume north→south transfers would require favorable head differentials and possibly dredging the channel to increase capacity.
Costs, risks and alternatives: Engineers said pilings and geotechnical uncertainty drive the largest share of cost. A conservative preliminary estimate for the concept—including deep piles to resist settlement and wave forces—approached roughly $40 million; the structural concrete portion alone was estimated nearer $15 million. The team recommended geotechnical borings, a targeted validation of gate-flushing/diffuser hydraulics, and coordination with lake-modelers to specify required net flux before final design. Participants recommended evaluating lower-cost options—stacked concrete blocks, culverts, or a modest pump station (an example $500,000 pump option was discussed)—as stop-gap or complementary measures.
Operational considerations: Salt encrustation, corrosion and wave forces are major operational challenges. The design therefore favors removable, gravity-set gate panels and seasonal manual operations (crane work and occasional panel swaps) rather than permanent automated motors that would quickly corrode. Staff suggested creating a 'library' of panel shapes to match seasonal targets.
Next steps: Engineers requested lake-model-derived net-flux targets so they can optimize structure capacity and costs; they asked committee members to submit comments on the draft memo within the week and agreed to pursue geotechnical investigation and diffuser validation in the next design phase.
"We need to know how much water we need to move in different lake conditions," Jeff Dembleyker said, summarizing the team's top priority for refining design and cost estimates.
