April 8, 2004

Intense thunderstorms on the evening of April 6, 2004, caused flooding and debris flows in areas along the east bench of Farmington between Farmington and Shepard Canyons. The sources of the floodwaters were mainly small range-front drainages burned in the July 2003 Farmington fire.

Most damage occurred in subdivisions on small alluvial fans below two unnamed drainages south of Shepard Creek. Floodwaters and sediment deposition were mostly restricted to streets and yards, but damage occurred to several vehicles, garages, and homes. At one locality, erosion by floodwaters threatened a section of an aqueduct running along the mountain front.

The lower slopes of the Wasatch Range above Farmington were burned in the July 2003 Farmington wildfire. Factors probably contributing to the flooding in addition to intense thunderstorm rainfall and burned hillsides include steep slopes, ample supplies of sediment, and increased runoff caused by already wet soil conditions from recent low-elevation snowmelt.

Davis County and Farmington have a long history of flooding and debris flows, and as a result many of the larger drainages such as Farmington and Rudd Canyons are protected by debris basins. However, most small drainages are not. Although emergency watershed protection measures completed last fall following the fire are designed to reduce flooding and debris-flow hazards, they do not eliminate hazards and are not permanent. Therefore, the heightened flooding and debris-flow hazard from the 2003 will exist for several more years while the watershed recovers to preburn conditions.

A field survey on April 7, 2004, by UGS geologists found that drainages in the flood area contain ample sediment for future debris flows.

For further information, including photos and maps, click here, or contact Richard Giraud, Utah Geological Survey, 537-3351, richardgiraud@utah.gov