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3. Require pilings below scour depth (see Figure 3-5), 4. Require slope protection for fill. 5. Require that fill be provided not only for individual structures but also for roads and public utilities since much of the damage due to alluvial fan flooding is to infrastructure. Non-Regulatory Approaches Regulations should be combined with non-regulatory options depcnding upon the lcvcls of existing dcvelopmcnt (see Figure 3-6), Two of the principal non-regulatory approachcs for rcducing losscs on fans arc to acquire fans or portions of fans and to construct debris basins and other engineering works to stabilize the drainage pattern on the fan and reduce erosion as well as flooding. Acauisition Fans may be kept in an undeveloped condition through public purchase rather than regulation. Fans can be used as parks, recreation areas or open spacc where public access is desirablc. Such an approach is expensive but avoids constitutional problems and allows active public use of the fan. Dcbris Basins Dams may be constructed on the upper portion of fans or along drainage channels to collcct sediment, rocks and floodwaters. Such dams and the resulting debris basin are cffective in temporarily stopping debris flows but are expensive and must be periodically emptied. Disposal of a large amount of debris is a major problem. The cities of Los An- gcles and San Diego ha ve constructed debris basins. Floodwalls. Channels. Other Engineering Works A variety of engineering works such as flood walls and concrete channels can help prevent channel migration and accommodate runoff. If any engineering works are to be constructed on a fan, a master plan for development and drainage should be prepared. The loca tion and design of roads must be part of such a plan since roads often block or con vc y flood wa tcrs. C-?