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Chapter 5 MITIGATION CONCEPTS AND APPROACHES The main goals of landslide hazard mitigation are to preserve lives, property, and revenue and to prevent the disruption of critical services and the economy. These goals are accomplished by reducing the frequency of oc- currence and the extent and severity of landslides, and by redistributing social and economic impacts when Iandsliding does occur. Three general methods used to accomplish these goals are 1) modification of community vulnerability, 2) modification of the physical system, and 3) modification of the consequences. MODIFYING COMMUNITY VULNERABILITY Vulnerability to landslide hazards is a function of a site's location, type of activity, and frequency of landslide events. Thus, the vulnerability of human life, activity, and property to Iandsliding can be lowered by restric- ting, prohibiting, or imposing conditions on hazard-zone activity. Local governments can accomplish this by adop- ting grading and building codes, land-use regulations and policies, redevelopment restrictions, hazard-monitoring and warning systems, and emergency preparedness programs. Land-use regulations and policies are most economical and effective if enacted prior to development. However, when potentially hazardous land is privately owned with the expectation of relatively intense development and use. or in communities where land optimally suited for development is in short supply, there is strong motiva- tion to use the land intensively. Land-use regulations must be balanced against economic considerations, political pressures, and historical rights. However, if con- struction is allowed to occur in a hazardous area, there is a moral and legal obligation to disclose the hazard to future owners and occupants. Avoidance Reducing Losses from Lands/wing in the United States by the National Research Council's Committee on Ground Failure Hazards, (1985, p. 15) discusses avoid- ance and building codes: Avoidance involves eliminating or restricting development in landslide-prone terrain. While total avoidance, i.e., a total prohibition on the use of landslide-prone lands, is not possi. ble it is feasible to use these lands in a way that minimizes landslide losses. Thus, it is possible to use such land for recreational open spaces, watersheds, agriculture, and other activities for which the loss in the event of a landslide wiD be small. It is even possible to aDow low-intensity pbysical deYelopment in such areas if appropriate precau- tions are taIren. The principal issue [leading to COlllr<Morsy] in __ of aYOidance is the loweriDg of land values associated with ~ as a landslide-prone area. Building and Grading Codes Design, buiJdiDg, and gradiDg cocIes are regulatory tools awiIabIe to local government agencies for achieving desired design and buiIdiDg pnctices. They can be applied to both new construction and preexisting buildings. In me cases, such as those involving large offshore structures. the effect of 1=1<IUl.. can be considered explicitly as part of the design, and the facility can be built to resist landslide damage. In some cases, existing structures in landslide- prone areas can be modified to be more accommnn"">g to 1andsIide movement. The extent to which this is successful depends on the type of landsIiding to wbicb the structure is exposed. Facilities other than buildings (e.g., gas pipelines and warer mains) can also be designed to tolerate ground IJlOYement. Codes and regulations governing grading and elCCaValion can reduce the IikeIibood that construction of bui1dings and higbways wiD increase the degree to wbicb a location is prone to 1"".I~. -. codes that have been developed for !edeIlIl, state, and local implementation can be used as modeJs for ~ mitigation. A fundamenla1 concern with design and buildiDg codes is their enforcement in a uniform and equitable way. Land-Use Regulations . \mous types of land-use regulations and development policies can be used to reduce landslide hazards. These methods are often the most economical and the most effective regulatory means for local governments. Types of regulations include hillside-development regulations, zoning, subdivision ordinances, rebuilding moratoriums, and abatement districts. These and other landslide management techniques are listed in Table 6 and discussed in detail in Appendix 2. Responsibility for their implementation resides primarily with local govern- ments, with some involvement of state and federal governments and the private sector. Table 6. landslide-management techniques modi- fying vulnerability to landslides. REGULATIONS State . Designation of areas of state interest · Siting and construction standards for water and 29