Case Study: Little Cottonwood Creek Flood — Alta/Snowbird Record Snowpack, Sandy, UT

Event date: May 2023 | Property: 1979-era ranch within the Little Cottonwood Creek historical floodplain, approximately 2 blocks south of the creek corridor, Sandy, UT | Event type: Category 3 outdoor floodwater intrusion from Little Cottonwood Creek overbank flow during 2023 Wasatch Range record snowpack melt | NFIP flood insurance: Partial coverage provided | HO-3: Denied under flood exclusion | Total out-of-pocket after both policies: Approximately $9,100

What Happened

In May 2023, Little Cottonwood Creek carried near-record flow through Sandy from Alta and Snowbird at the head of Little Cottonwood Canyon. The Natural Resources Conservation Service’s SNOTEL station data for the Little Cottonwood watershed recorded 178% of average snowpack on April 1, 2023 — the deepest snowpack in the recorded dataset for this station. Peak flow on Little Cottonwood Creek reached approximately 660 cubic feet per second in the Sandy reach during the late-May melt acceleration, approaching the creek’s historically documented minor flood stage threshold and entering the historical floodplain sheet flow zone approximately 2 to 4 blocks south and north of the active channel.

This homeowner’s 1979-era ranch sat approximately 2 blocks south of the Little Cottonwood Creek active channel — within the historical floodplain boundary shown on Sandy’s FEMA Flood Insurance Rate Map. Sheet flow reached the exterior foundation wall and entered the finished basement through a window well that had been overwhelmed by the overland flow depth. Approximately 2.5 inches of outdoor floodwater covered 210 square feet of the finished basement game room when the homeowner discovered the event on a Friday evening after returning from work.

The Little Cottonwood Canyon Trace Metal Context

Little Cottonwood Creek is not the same Category 3 floodwater as Mill Creek in Sugar House or Jordan River corridor overland flow. Little Cottonwood Canyon has a documented history of 19th-century silver and lead mining operations at Alta — including the Emma Mine, the Flagstaff Mine, and associated smelter operations that produced tailings and processing waste that remain in the Little Cottonwood Canyon drainage basin. The Utah Division of Environmental Quality’s watershed assessments have identified elevated lead and arsenic concentrations in Little Cottonwood Creek sediment in sections of the canyon watershed above Sandy, attributable in part to historical mining and smelting activity. During high-flow events when suspended sediment load is elevated, these trace metal-bearing materials can be mobilized from the historical deposit sites in the canyon and transported downstream in the floodwater.

The Category 3 classification for this event was based on the outdoor floodwater source — which is always Category 3. The trace metal context added an additional documentation element: we noted in the project file and in the homeowner’s written assessment that Little Cottonwood Creek floodwater during high-flow events should be considered as potentially carrying elevated trace metal concentrations based on the historical canyon mining legacy and the UDEQ watershed assessment findings. We are not licensed environmental testing contractors and do not perform trace metal testing — but we recommend licensed environmental testing before any reconstruction closes surfaces over materials that contacted this specific floodwater source during significant flow events.

What We Did

Full Category 3 biohazard protocol: hydrogen sulfide assessment at the window well entry point (H₂S below detectable threshold — not characteristic of this floodwater source, noted as distinct from sewage-source Category 3 events). HEPA air scrubbers in negative air pressure containment at the staircase boundary. Full PPE throughout. All carpet, pad, and lower 12 inches of gypsum drywall removed and transported as regulated waste. Three passes of EPA-registered broad-spectrum disinfectant at required concentration and 15-minute minimum dwell time. We noted in the project file that this specific floodwater source warranted licensed environmental sampling before reconstruction based on the trace metal context — and provided the homeowner with the UDEQ watershed contact information and the FEMA Flood Map for this address.

Structural drying ran for five days. All 10 monitoring points confirmed dry standard on day five. The homeowner elected to have licensed environmental sampling performed before reconstruction closed any surfaces — results from the sampling, completed by a separate licensed environmental contractor, returned lead concentrations at the concrete slab perimeter within USEPA residential soil action levels. No additional remediation was required. Reconstruction proceeded on schedule.

The Insurance Reality: Two Policies, One Flood

The homeowner had a standard HO-3 policy and a separate NFIP flood insurance policy purchased two years earlier after a neighbor had warned him about the Little Cottonwood Creek floodplain risk when he bought the house. The HO-3 denied the flood claim under the flood exclusion — expected and correct. The NFIP policy provided partial coverage under the standard flood policy form’s basement limitations: cleanup, certain permanent appliances, and electrical system components were covered; basement carpet, gypsum drywall, and finished basement materials were not. Total NFIP coverage applied to this scope: approximately $5,400. Total homeowner out-of-pocket: approximately $9,100.

The two-year-ago neighbor conversation that prompted him to buy the NFIP policy was worth more than the premium he had paid on it. Without the NFIP policy, the entire $14,500 restoration scope would have been out-of-pocket.

Frequently Asked Questions

What makes Little Cottonwood Creek floodwater different from other Salt Lake Valley flood events?

Little Cottonwood Canyon has a documented history of 19th-century silver and lead mining at Alta. The UDEQ watershed assessments identify elevated lead and arsenic concentrations in canyon-section creek sediment attributable in part to historical mining. During high-flow events, trace metal-bearing materials may be mobilized from historical deposit sites. Licensed environmental sampling before reconstruction closing surfaces over flood-contacted materials is a reasonable precautionary step for significant inundation events from this specific creek.

How do I know if my Sandy home is in the Little Cottonwood Creek floodplain?

FEMA publishes Flood Insurance Rate Maps (FIRMs) designating Special Flood Hazard Areas based on the 100-year flood boundary. Sandy’s FIRMs are publicly available at msc.fema.gov. Properties within 2 to 4 blocks of the Little Cottonwood Creek active channel in the Sandy reach should consult their FIRM. Properties just outside the SFHA boundary are not immune — the FIRM is the 1% annual chance threshold, and smaller events still produce sheet flow to adjacent properties.

Should I buy NFIP flood insurance near Little Cottonwood Creek?

If your home is within the historical floodplain, the NFIP premium cost is straightforward to compare against the out-of-pocket restoration expense for a flood event that your HO-3 will not cover. The NFIP basement limitation means finished basement materials are not covered — but cleanup, certain appliances, and electrical systems are. The year you choose not to renew is the year of the next record Wasatch Range snowpack.

← All Case Studies | Get Help Now →

True Day Water Damage Restoration | 11268 S 2865 W, South Jordan, UT 84095 | (385) 247-9359 | Utah Contractor License: #960332-3505 | IICRC Firm ID: #927354-5258