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0(f, 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 -1 1 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 />Oravc ,Cony t Co-nVre li�e,PLa+v Page 6 -81 <br />237 <br />