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12 route upstream flows and sediment around the entire urbanized fan. Structures must be designed to withstand scour, erosion, sediment deposition, hydrostatic and hydrodynamic forces, and high- flow velocities. Regular inspection and maintenance are necessary for optimal operation of these structures. For smaller-scale protection, debris fences, local dikes and channels, site plans to convey flow, drop structures, street design/alignment to convey flow, and elevation on armored fill can be adopted as structural measures. These measures can be used to trap debris, and to route water and sediment around or through individual residential developments. The design must prevent formation of new flow paths and/or the relocation of existing paths, and the structures must resist high velocities, erosion, deposition, and hydrostatic and hydrodynamic forces. For single structure protection, piles, columns, or posts can be used to elevate the structure to minimize the structure's exposure to flood hazards, eliminate obstructions to natural flow paths, and reduce the hydraulic effect of flood flow. The design must provide structural support to the building, resist uplift and lateral forces, and withstand scour and erosion. Floodwalls or berms can also be used to protect single structures. However, they must only be used in areas with very low velocities/depth where large sedimentation and debris loads are not likely. These floodwalls or berms must be able to resist erosion and avoid diversion of flood flows to adjacent or downstream property. Adopting and Enforcing Regulations Local government officials throughout California should adopt and enforce regulatory controls for areas at risk. Local authorities should establish zoning ordinances, subdivision regulations, and other regulatory guidelines applicable to Federal, State, and local standards to limit or prohibit growth in high hazard areas. Strict building codes can help ensure safe residential construction and reduce the potential loss of property and life during major flood events, Higher flood insurance premium requirements may discourage future development for high hazard areas as a mean to enforce regulations and limit growth. TEST APPLICATION Sample Assessment Studies Alluvial fan areas in San Diego, Kern, and Butte Counties were selected to evaluate the validity of the definition and base classification system. These three examples represent alluvial fans throughout California, from the northern to the southern parts of the State. Each study area was analyzed by using the established procedure for identifying, analyzing, and classifying alluvial fans as outlined in this report and Appendix C. Each example also demonstrates the basic procedures for compilation of geologic, topographic, and soil maps and aerial photographs, and the recommendation of fieldwork procedures. Details of the three example studies are included in Appendix D.