Witch Fire

Potential Areas and Assets at Risk

Geologic Overview

The 197,990 acres Witch Fire burn area consisted of mild to moderately steep granitic bedrock slopes that are served by small drainages, large steep canyons, and broad alluvial valleys. Elevation of the area ranges from 400 feet in canyon bottoms to 3100 feet above mean sea level at the highlands (e.g., Mt. Woodson and Mt. Gower in the San Pasqual and Ramona areas). The topography reflects historical uplift and erosion of the granitic terrain, and consists of relatively flat alluvial valley areas, and surrounding elevated mountainous bedrock areas with widespread areas covered with large boulders.

The values at risk considered in this assessment included the possible loss of life and property due to landsliding, debris flow, rock fall, debris torrents and flooding from increased surface water runoff. It should also be noted these specific hazards are part of natural processes in this environment; some of these risks may have been present prior to the Witch Fire. The potential for these hydrological processes to be exacerbated by fire is primarily dependent upon burn severity and slope steepness, both of which are variable in the Witch Fire area. “The magnitude of post-fire damage will be determined by the intensity and duration of storms that impact the area.”

The following locations were identified as high priority status for further evaluation and mitigation:

Rattlesnake Creek (Numerous homes near/below culvert crossing)

• High risk to human life(debris flow; mud slide, flooding)

• High risk to property, culverts and roadways (debris flow, mud slide,

   flooding)

Eagle Crest Subdivision

• High risk to human life and property (debris flow, mud slide, rock fall,

   flooding)

Sycamore Creek Road

• High risk to human life and property (debris flow, mud slide)

Fenton Ranch (numerous structures at 16351 Bandy Canyon Road)

• High risk to human life and property (debris flow, flooding)

Bandy Canyon Road (homes and other structures at 16251, 16486, 16777)

• High risk to human life and property (debris flow)

 

Highland Valley Road (one house at 16129)

• High risk to human life and property (debris flow, rock fall)

Old Survey Road (several residences; addresses 16850 thru 16888. High risk to

life from debris flow)

Sutherland Reservoir

• High risk to property and utility infrastructure; moderate risk to water

   quality and supply(debris flow, mud slide, flooding)

Note: Ramona Dam, Poway Dam and Hodges Dam not inspected by this

  team; same conditions possible.

Rockwood Canyon Bridge at Highway 78

• High risk to bridge structure (debris flow; flooding)

Green Valley Truck Road

• High risk to culverts and paved roadway (debris flow, flooding)

Various buildings throughout area, including homes

• Moderate to low risk to occupants and properties (debris flow, mud slide,

   flooding)

Culverts and roads throughout area

• Moderate to low risk to transportation routes (debris flow, mud slide,

   flooding)

Utilities throughout area

• Moderate to low risk to utility infrastructure, including power and telephone

   lines (debris flow, mud slide, flooding)