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Chapter 6: Natural and Cultural Systems Element <br /> based on severity of slope. Protected stream buffers are measured <br /> from the edge of the stream bank of defined special flood hazard <br /> areas. <br /> Floodplains are mapped areas of the County adjoining streams in which <br /> a frequency of flooding may be expected to occur in a given timeframe. <br /> The most frequently used floodplain measure is the special flood <br /> hazard area. This denotes the floodplain area subject to a chance flood <br /> occurrence of one percent (1%) in any given year. Map D-11 of the <br /> County Profile Element, located in Appendix A, illustrates the location <br /> of special flood hazard areas in the County, along with other <br /> development constraints. <br /> One of the impacts of land development over time is an increase in <br /> surface water runoff during storm events. <br /> Another type of land that is of significance in terms of both natural <br /> areas and water quality is wetlands. Wetlands in Orange County and <br /> other upland areas are primarily associated with streams and water <br /> bodies. Wetlands are important to overall health and environmental <br /> diversity, providing habitat for aquatic and riparian species, and also <br /> serving as in important natural water filtering device. More information <br /> about the wildlife habitat associated with wetlands may be found in <br /> section 6.4.4 <br /> SURFACE WATER QUANTITY <br /> Surface water quantity and availability is, as previously noted, <br /> considerably limited due to the "headwaters" nature of the County. A <br /> standard measurement of the amount of water in reservoirs and water <br /> systems is the calculation of "safe yield." While definitions of this term <br /> vary, and the term for safe yield is changeable, safe yield is generally <br /> defined as the demand for water that can be met under drought <br /> conditions. For example, a 30-year safe yield is the demand that a <br /> water system can support under drought conditions that would occur <br /> on an average of once every 30 years (or have a one in 30 chance of <br /> occurring in any one given year). <br /> The following table, Table 6-6 illustrates existing and planned <br /> expansions of water supply sources in Orange County, their owner, and <br /> safe yield of supply. <br /> Ora*iq-e,Couvity Co-Ynpreh 4uive'Pla+w Page 6-81 <br />