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Engineers outline long-term Coal Creek recharge plan, propose interim measures to reduce flooding
Summary
County engineers described a multi-decadal plan to manage Coal Creek flooding by routing high flows into nearby gravel pits for sediment settling and recharge, and said they will pursue an MOU with Cedar City and seek NRCS participation; some measures could begin within a few years but full implementation may take decades.
County engineering staff presented a multi-phase plan to reduce flooding on lower Coal Creek that pairs sediment settling with managed recharge in nearby gravel pits, and told the commission the long-range effort could take decades to complete.
Rich, the county engineer, explained that consultants recommended routing some high flows into a nearby pond to capture silt ahead of the airport recharge pits and that the Natural Resources Conservation Service (NRCS) wants the county to coordinate use of a Cedar City-owned pit during short-duration high-flow events. The approach would divert part of an extreme flood to the pit for 24–48 hours to keep Stevensville Ditch flows near the ditch’s roughly 1,000 cubic-feet-per-second capacity; the diverted water would be intentionally dirty and would require settling and maintenance.
Engineers said the concept is already being used in a smaller form: Coal Creek’s dirtier water is moving into the Schmidt Pit so sediments settle there and cleaner water overflows into county recharge pits through an HDPE 24-inch pipe. That arrangement reduces sediment load to the county pits and limits the number of pits that need dredging.
Long-term options discussed include acquiring adjacent private pits (Western Rock, Mel Clark, Blake Demille) and installing pipes and gates between pits so managers could direct dirty water to settling ponds while moving cleaner water into recharge basins. County staff called the plan a multi-decade undertaking — as long as 50–70 years — because it depends on partners’ mining schedules and pit availability; however, staff said certain interim steps, design work and an MOU with Cedar City could begin within a few years.
Engineering staff also reported other near-term flood-preparation work: channel inspections ahead of monsoon season, localized riprap repairs (including near Ladybug Nursery), and maintenance of crossings and debris catchers. The county is exploring gated splits and control structures at the Woodbury split to better direct flows once additional recharge capacity is available.
Commissioners and staff discussed logistics and environmental considerations, including the need to keep the “top” or cleaner water separate from silt, options for partitioning pits for easier excavation, and opportunities to partner with NRCS to fund or permit works. Staff said detailed designs and agreements with Cedar City and gravel-pit owners would be next steps.
