SFPUC 2001 Alameda Watershed Management Plan

III. ENVIRONMENTAL SETTING AND IMPACTSG. FIRE MANAGEMENTcigarettes). In the Alameda Watershed, lightning is a fairly uncommon occurrence, leavinghuman actions as the most prominent source of fire ignition.Fire HazardFire hazard refers to the fuels on a site, typically represented by plant biomass (plant material)and its configuration and condition, which may lead to difficult-to-control fires. The vegetativefire hazard represented by plant material fuel complexes within the Watershed consists of shrubs(chaparral and scrub), grasslands, and woodlands and forests. (Refer to Section III.E, NaturalResources, for a complete description of vegetative resources within the Watershed.) Thesubsurface gasoline pipeline that runs along the north side of San Antonio Reservoir represents anonvegetative fire hazard.Watershed fire hazards were assessed using three methods:! Fire hazards (or severity) were mapped in accordance with the California Wildfire SeverityLaw;! Static fire behavior predictions (how different types of fuel burn) were estimated using amodel from the U.S. Forest Service; and! Fire spread and growth potential were estimated using a model from the National ParkService.Figure III.G-1 shows the fire severity categories within the Watershed in terms of low, medium,and high severity. Results of the static fire behavior and growth models are shown for variousscenarios on maps contained within Appendix A-1 of the Alameda Watershed Management Plan.In general, the distribution of areas designated as high fire severity correlate with the distributionof heavily vegetated areas (scrub and woodlands). Areas of high fire severity are roughly dividedinto the following areas:! steep drainages south of San Antonio Reservoir,! east-facing slopes above Calavaras Road,! north aspects of Alameda Creek,! north-facing slope of Niles Canyon, and! north aspects of Arroyo Hondo Creek and its tributaries.Fuel Type DistributionAs indicated above and in Figure III.G-1, the Watershed contains areas of significant firehazards. The distribution of fuel in the natural communities in the Watershed is primarily ofthree fuel types: grassland, woodland, and shrubs. Grassland fuel types dominate theWatershed, with pure open grassland covering over 20,000 acres, or slightly over 50 percent ofthe landscape. Spatially, these fuels pervade the landscape throughout the Watershed,intermixing with heavier fuel types in the canyons. The high probability of ignition and fast rateof spread associated with grassland fuel types indicate a significant risk of grass fire occurrenceNOP 96.223E: Alameda Watershed Management Plan III.G-2 ESA / 930385January 2001