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Figure 2. Loss of pro- tective vegetation due to fire; Laguna Beach, CA., November 1993 . . . mary mechanism for soil erosion. Vegetation also increases the infiltr.uion of water into the soil. reduces runoff velocities. filters out sedi- ment, and provides plant roots to hold the soil together (Figure 3). Without vegetation and its benefiu, sediment production and runoff in fire-affected areas and more important, its de- livery down slope: increases. Burned watcrsheds erode in differem ways. depending on soil type, climate, vegetation. bur- rowing and grazing animals. mpography and human activicy. Dry creep. or dry ravel, is the downhill movement of soil and debris during dry periods, and is caused by gravitational forces. Where fire burns the vegetative cover, the: me- chanical resistance [0 gravitadonal forces decreas- es, and the soils become more susceptible to this eype of erosion. Dry ravc:1 is a major erosional force in post-fire condidons. Soil and debris ac. cumulates at the base of slopes and remains stored until mobilized by intense runoff. This is known as channc:lloading. Intense runoff often occurs after a fire and can be the result of the de- velopment of soil hydrophobicity. Hydrophobic. or water-repellent soils can de~ vc:lop from substances in the soil which are va- poril.ed during the burning of surface litter. particularly on sandy soils. Hydrophobic soils are created as the fire breaks down organic mat- ter and chemicals in the soils, releasing a gas fire haurd assessment and mitigation planning conducted by Woodward-Clyde Consultants (WCe) for the California Office of Emergency Services (OES) and its implementation in the communities of Malibu, Thousand Oaks, la- guna Beach, and Orange County. The post-fire hazard Considerable information is available on post-fire sediment production rates and debris flows in California, particularly in Southern California, including studies by Wells (1981.1985.1987), the Handbook of Appli.d Hydrology by Yen Te Chow, and the [0, Ang"-' County Hydrology Manual These studies show that fire accc:lerates erosion rates in California chaparral to such an extent that it must be con- sidered the major factor which drives sediment production on these lands. The surface process- es of dry ravc:l and rill network formation are major contributors to this accc:lerated erosion, and debris flows are a common occurrence. These flows move most of the sediment pro- duced after a fire, and can occur following very little rainfall. The incidence of fire temporarily reduces the beneficial effects mat plants provide in reducing soil erosion (Figure 2). Planes provide cover that intercepts and reduces rainfall impact, the pri- Table 1. Summary of fire damage Oakland-East Bay Southern California Flrestorm Fires :. .:. IJ ~r"". ,.. 11:""'. I~' . . '";. .....~ 11'J":.: ~ .'. ,......,~ '..,.,..\ . , ~ri':i!i1l1':"l-111;i"li .I&t;: ' ;!liJI'l:';::. "'~ [!',J. ~'.. '1..!:., I ,.1l.."'J!!" '~]I .:1 .1 rj '..~\.!'l~. . 536 JOURNAL OF SOIL AND WATE.R. CONSERVATION o ~b