SFPUC 2001 Alameda Watershed Management Plan

III. ENVIRONMENTAL SETTING AND IMPACTSC. GEOLOGY AND SOILSIncreases in Soil ErosionImplementation of several types of actions could cause substantial erosion or siltation, resulting inpotentially significant impacts. These are discussed below.The Alameda Watershed Management Plan includes facilities that could result in increased publicvisitation of the Watershed by providing new trails (Policies WA15.2 and WA15.4), golf courseexpansion (Policy WA18.1), and increased information regarding public activities available onthe Watershed, such as public use area maps and brochures or additional information on publicactivity destinations. These facilities include information kiosks (Action pub3), a WatershedVisitor Education Center (Action pub4), public recreation area around the Sunol Water Temple(Action sun14), commercial site (Action sun19), overnight nature study area (Action sun20), andtrail connections (Action sun21). In addition, implementation of actions des8 and sun17 wouldresult in universal access improvements at existing Watershed facilities and trails and provide foruniversal access at proposed facilities.Erosion of surficial soil within the Watershed could occur from direct exposure to wind, water,and physical disturbance. Soil erosion can result in ground instability and water qualitydegradation. Development of new hiking trails, bicycle trails, equestrian trails, and service roadsincrease direct exposure of dirt to erosional forces, particularly if increased use occurs on highuse roads that are sources of erosion and sedimentation. Increased use of existing hiking, bicycle,and horse trails can lead to deepening of existing trails and the development of “shortcut” trailsthat, over time and with sufficient surface water runoff, can become erosional channels. Theexperience of other open space managers has shown that more serious degradation occurs onproperty where bicycles are allowed (MMWD, 1991).Overgrazing by livestock (removal of the protective plant cover) can reduce vegetative cover andlead to soil erosion, especially on hillside slopes. Estimated erosion rates on soils recently usedfor pasture and range were previously higher than those cultivated for dry-farmed grain and grainhay (Environmental Science Associates, 1996).Potentially significant soil erosion may also originate from the relocation of fire and maintenanceroads and new trails or roads at the Watershed facilities described above. In addition, soil erosionmay also originate during construction of new Watershed facilities. Many facilities would beinstalled to ensure and/or improve water quality or resource protection on the Watershed, such asbarriers or fences along identified high-risk spill potential areas (Actions haz6), installation ofinfiltration drainfields and detention basins (Action sto1), installation of long-term sedimentretention basins or other permanent measures (Action aqu12), rehabilitation of shoreline areasand stream segments (Actions aqu5 and aqu7), and the relocation or reconfiguration of existingroads (Action fir7) to improve emergency access.Implementation of policies to reduce the threat of fire hazards or to enhance wildlife habitatthrough fuel reduction (Policy F11 and Action wil7) could ultimately result in increased soilerosion. Typically, vegetative cover reduces the erosive energy of rainfall and promotesinfiltration of rainwater. In addition, plant root systems help stabilize soil horizons below theNOP 96.223E: Alameda Watershed Management Plan III.C-7 ESA / 930385January 2001