PRELIMINARY FINDINGS OF THE SEPTEMBER 16, 2004 DEBRIS FLOW AT PEEKS CREEK, MACON COUNTY, NORTH CAROLINA

Heavy rains from the remnants of Hurricane Ivan triggered the Peeks Creek debris flow in Macon County, North Carolina around 10:10 p.m. on September 16, 2004. The debris flow began just below the top of Fishhawk Mountain and traveled approximately 3.5 km dropping 670 m in elevation to the Cullasaja River. Five people were killed and fifteen homes were destroyed by the slope movement.

Since 1901, there have been 14 recorded, landslide-producing storm or hurricane occurrences (including Hurricanes Frances and Ivan in 2004) in North Carolina. Several of these storms caused landslides in Macon County including the Fishhawk Mountain area. In 1876, debris flows damaged both the northern and southern sides of Fishhawk Mountain. In 1995, Hurricane Opal triggered a debris flow in the Poplar Cove area of Macon County. Colluvial deposits exposed along Peeks Creek indicate prehistoric slope movements may have occurred in the Peeks Creek drainage.

Remnants of Hurricane Frances produced rainfall totals up to 381 mm in portions of western North Carolina. Eight days later, remnants of Hurricane Ivan dropped approximately 229 mm of rainfall across the region. These heavy rainfalls in combination with the thin (<2 m), colluvial soil in sharp contact with the steeply dipping bedrock surface (35–55^o) created the right scenario for a slope failure. Subparallel striations on the bedrock surface in the initiation zone indicated that the initial movement may have been a debris slide that quickly mobilized into a debris flow.

Cross sections measured across the debris flow track provided information to calculate estimates of velocity and discharge. Velocity estimates ranged from 32.7 km/hr to 53.4 km/hr. Discharge approximations ranged from 590 m³/s up to 1,275 m³/s. Velocity and discharge values fluctuated over the length of the debris flow track from changes in stream gradient and streamflow contribution from side channels.

Work to analyze the Peeks Creek debris flow will continue. Preliminary GIS-based slope stability assessments indicate other areas in the watershed may be susceptible to debris flows. Soil testing will improve the data used in the slope stability models to further refine the delineation of areas of potential slope movement.