Potential Areas and Assets at Risk
The Rice Fire burned rapidly at a low to moderate burn severity, with large areas left unburned within the fire perimeter. Overall for the fire event 6.9% of the 9,472 acres was rated as high burn severity, 26.0% as moderate severity, 19.8% as low severity, and 47.3% as unburned. In general, the risk from landslides, debris flows and rock falls are possible where roads, residences or other development are located on alluvial fans, colluvial footslopes and debris cones. Soil hydrophobicity was tested in several locations. For those areas of moderate and high severity burn, soil conditions were highly variable, but generally found to have high hydrophobicity at the mineral soil surface, with less hydrophobicity at a mineral soil depth of 1-2 inches. This post-fire condition greatly increases the risk for runoff and flooding.
The principal concern with the Rice Fire was the potential for in-channel floods, hyperconcentrated floods, debris torrents, debris flows and headward expansion of gullies. Houses located in drainage swales at the bottoms of canyons were considered at risk due to debris flows and flash floods. Several houses occuppied steep ridgetops directly above major swales and gullies where headward erosion could undermine their foundations. Another fire consequence was he increased potential for be flooding due to failure of on-site drainage facilities due to increased runoff and sediments. The flooding also could affect water quality at specific sites and downstream creating significant secondary concerns.
The BAER team engineering specialist determined that the areas with highest potential risk to values were the Red Mountain Reservoir and the offices of Kendall Farms in the Stewart Canyon region.
Potential Values-at-Risk (identified prior to and during on-the-ground survey)
1. Red Mountain Reservoir
The Red Mountain Reservoir is owned and operated by the Fallbrook Public Utilities District. This 1300 acre-feet reservoir serves approximately 10,000 domestic and agricultural connections in the Fallbrook area. The reservoir sits in an area surrounded by high ground, including Red Mountain, which suffered considerable burning. The specific concern was water quality degradation to the reservoir if winter storms were intense. Such events have the potential of overwhelming drainage systems. Water quality impacts to the reservoir would likely include sediment, nutrients and turbidity.
2. Rainbow Municipal Water District Reservoirs
3. Houses located on erodable slopes
a. Vista Del Rio
b. Red Mountain Heights
4. Houses located in drainages below steep, burned slopes
a. Daisy Lane (berm constructed across drainage adjacent to home
b. 2 Homes neighboring North Stagecoach Lane (propane tank, 1
5. Buildings adjacent to creek channels
a. Kendall Farms warehouse facility in Stewart Canyon
b. Stewart Canyon Road - The Stewart Canyon region suffered approximately 45% burn. This region was mainly east of Interstate 15 and is drained by Stewart Canyon creek. This creek drains south until it meets with the San Luis Rey River. The area inspected was predominately agricultural with little housing. The main concern was flooding of the region along the Stewart Canyon Creek near the Kendall Farms office. This site had approximately 50% of the watershed above it burned to some extent.
c. Skyline Circle
6. State Highway 15
7. County Roadways
8. Water quality impacts—particularly to Rainbow Creek watershed (a TMDL
watershed listed as impaired by U.S. EPA under Section 303(d) of the
Clean Water Act)
9. Soil resources