Glendale (PDF) - Hazard Mitigation Web Portal - State of California

Natural Hazards Mitigation PlanCity of Glendale, CaliforniaSection 8 – Floodsrealize that FIRMs only identify potential flood areas based on the conditions at the time of thestudy, and do not consider the impacts of future development. To prepare FIRMs that illustratethe extent of flood hazards in a flood-prone community, FEMA conducts engineering studiesreferred to as Flood Insurance Studies (FISs). Using information gathered in these studies,FEMA engineers and cartographers delineate Special Flood Hazard Areas (SFHAs) on FIRMs.SFHAs are those areas subject to inundation by a “base flood” which FEMA sets as a 100-yearflood (see definitions below).The NFIP also reduces flood losses through regulations that focus on building codes and soundfloodplain management. In the city of Glendale, the NFIP and related building code regulationswent into effect on August 31, 1984 (City ID No. – 065030). NFIP regulations (44 Code ofFederal Regulations (CFR) Chapter 1, Section 60, 3) require that all new construction infloodplains must be elevated at or above base flood level.Flood TerminologyFloodplain:A floodplain is a land area adjacent to a river, stream, lake, estuary, or other water body that issubject to flooding. This area, if left undisturbed, acts to store excess floodwater. Thefloodplain is made up of two sections: the floodway and the flood fringe.100-Year Flood:The 100-year flooding event is the flood having a one percent chance of being equaled orexceeded in magnitude in any given year. Contrary to popular belief, it is not a flood occurringonce every 100 years. The 100-year floodplain is the area adjoining a river, stream, orwatercourse covered by water in the event of a 100-year flood. A 100-year flood is defined bylooking at the long-term average period between floods of a certain size, and identifying the sizeof flood that has a 1 percent chance of occurring during any given year. This base flood has a 26percent chance of occurring during a 30-year period, the length of most home mortgages.However, a recurrence interval such as “100 years” represents only the long-term averageperiod between floods of a specific magnitude; rare floods can in fact occur at much shorterintervals or even within the same year.Floodway:The floodway is one of two main sections that make up the floodplain. Floodways are definedfor regulatory purposes. Unlike floodplains, floodways do not reflect a recognizable geologicfeature. For National Flood Insurance Program (NFIP) purposes, floodways are defined as thechannel of a river or stream, and the overbank areas adjacent to the channel. The floodwaycarries the bulk of the floodwaters downstream and is usually the area where water velocitiesand forces are the greatest. NFIP regulations require that the floodway be kept open and freefrom development or other structures that would obstruct or divert flood flows onto otherproperties.Glendale regulations prohibit all development in the floodway. The NFIP floodway definitionis "the channel of a river or other watercourse and adjacent land areas that must be reserved inorder to discharge the base flood without cumulatively increasing the water surface elevationmore than one foot.” Floodways are not mapped for all rivers and streams but are generallymapped in developed areas.Flood Fringe:The flood fringe refers to the outer portions of the floodplain, beginning at the edge of thefloodway and continuing outward. Generally, the flood fringe is defined as "the land area whichis outside of the stream flood way but is subject to periodic inundation by regular flooding.”2006 PAGE 8- 11