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Commissioner outlines $20 million NRCS plan to redirect monsoonal flows into mining pits for recharge and flood control
Summary
A long-range Coal Creek watershed project presented to the commission would tie sediment-control, recharge and flood-protection structures to nearby gravel pits; the presenter said the NRCS plan costs about $20 million with an estimated county match of $1.8 million and requires a Cedar City MOU to proceed.
A county commissioner presented a multi-year Coal Creek watershed proposal to the Iron County Commission on Monday that would use nearby rock pits to capture monsoonal and runoff flows, limit sedimentation downstream and recharge groundwater.
The presenter described the project as an NRCS-identified suite of storage, spillway and diversion works that would redirect high-volume flows into the Cedar City and Western Rock pits rather than allowing heavy sediment loads to travel down Stevensville Ditch toward the wastewater treatment plant and Rush Lake.
"This is about protecting us against a hundred-year event," the commissioner said while explaining the hydrology and the role of the Woodbury Split in directing flows. The presenter and staff showed mapping of the Schmidt Pit, the county gravel pit and the Cedar City and Western Rock pits and said piping and gated spillways would be used to direct and settle sediment in stages.
Key figures from the presentation:
- The presenter characterized the full NRCS project as approximately a $20,000,000 undertaking with a county match of about $1,800,000.
- The report calculated an average annual sediment load in the system of roughly 88,000 cubic yards and modeled storage and plug-flow alternatives to trap sediment upstream of critical conveyance structures.
- Work items discussed included concrete walls and extensions at the Woodbury Split to maintain flow velocity, additional piping between pits for recharge, automated diversions with gate control, gabion baskets and engineered spillways to reduce velocity and drop sediment, and maintenance plans to manage harvested fill.
The presenter said the proposal depends on Cedar City agreeing to a memorandum of understanding for use of city-owned pits and on Western Rock's lease status for mining pits to be resolved. The presenter also noted potential long-term benefits: increased gravel harvesting for the city and a recharge system that could capture monsoonal events.
Commissioners discussed the cost, maintenance and logistics of storage and sediment disposal. No action was taken; presenters asked staff to continue coordination with NRCS, Cedar City and private pit owners and to return with more detail and cost-sharing options.
The commission was shown video and aerial maps during the presentation; the discussion included technical specifics (flow rates, storage scenarios and haul volumes) and possible staging to accommodate sediment settling before recharge.
