A Levee Policy for the National Flood Insurance Program (1982)

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APPENDIX A: GLOSSARY This appendix defines many terms used in the text of this report. The definitions are generally simplified and applicability may be limited to understanding of usage in the context of this report. ACTUARIAL INSURANCE RATES—insurance rates that fulfill the financial need in risk transfer, are responsive to competitive market conditions, improve the availability and reliability of insurance, and result in insurance premium charges that are not excessive, inadequate, unfairly discriminatory, or otherwise unreasonable. AVERAGE ANNUAL FLOOD DAMAGE—the average flood damage one could expect over a period of many years should neither flood hazard nor floodplain occupancy change nor inflation occur. BERM—a horizontal strip or shelf of material built contiguous to the base of either side of a levee embankment for the purposes of providing protection against underseepage, erosion, increasing stability of the embankment, or reducing seepage. Can be located on either side of a levee, depending upon the berm's purpose. CLOSURE DEVICE—any movable and essentially watertight barrier, used in flood periods to close an opening in a levee, securing but not increasing the levee's design level of protection. COMMUNITY—any state or area or political subdivision thereof, or any Indian tribe or authorized tribal organization, or Alaska native village or authorized native organization that has authority to adopt and enforce floodplain management regulations for the areas within its jurisdictions. COMPACTION—the placement in layers and densifying of fill materials in an earthen levee or dam structure, ordinarily by rolling or vibration. CRITICAL FACILITY—a structure housing a community service of such a nature that the loss associated with discontinuity of service from even extremely remote (less than 0.2 percent chance per year) -75-

incidences is not ordinarily acceptable. Examples of such facilities are electrical substations, natural gas terminals, and hospitals and schools where evacuations and other proper safeguards might not be able to be taken. DISCHARGE—a rate of water volume flowing at a particular location in a given period of time, normally expressed in cubic feet per second. EXECUTIVE ORDER 11988—a presidentially established policy (May 24, 1977) directed to all federal executive agencies discouraging actions that would do any thing to increase flood losses in the 1 percent chance (annual) or 100-year floodplains. FEMA—Federal Emergency Management Agency, an agency of the federal government, established by Reorganization Plan No. 3 of 1978, to create a central point of management for emergency planning and response activities of the federal government. FIA—"Federal Insurance Administration," a unit within the Federal Emergency Management Agency responsible for the administration of the insurance operations aspects of the National Flood Insurance Program as defined under the National Flood Insurance Act of 1968. FLOOD—an overflow from a normal water course onto adjacent land not normally covered by water or a hydrologic event contained within levees but having discharges or stages higher than normally occur. FLOOD, BASE—in the NFIP, the flood having a 1 percent chance of being equalled or exceeded in any given year. FLOOD, DESIGN—the flood magnitude adopted to determine the dimensions of a hydraulic structure, normally expressed in terms of stage, frequency, discharge, or as a generic standard. FLOOD FREQUENCY—based on statistical analyses; in terms of probability, the percent chance of an event being equalled or exceeded per year; the reciprocal of recurrence interval that is the average interval of time in years between floods equal to or greater than a specified discharge or stage. FLOOD FRINGE—all that land lying within the 100-year floodplain that is not within the floodway. FLOOD HAZARD DESIGNATION—NFIP classifications delineating flood zones encompassing defined ranges of annual probability of flooding. The classifications relevant to riverine levees are: Zone A—areas subject to flooding by 100-year or smaller events. Zone B—primarily, areas subject to flooding by events rarer than the 100-year and up to 500-year events. -76-

Zone C—areas not subject to flooding by 500-year or smaller floods. FLOODPLAIN—an area, adjoining a body of water, that has been or may be covered by floodwater. FLOODPLAIN MANAGEMENT—nonstructural measures employed to reduce the exposure of people and property to floods, e.g., land-use planning, warning schemes, insurance, flood-proofing, evacuation, relocation. FLOOD PROFILE—a graph showing the relationship of a flood water surface elevation to location, the latter generally expressed as lineal distance along a stream. FLOODWALL—a concrete wall constructed adjacent to a stream for the purpose of preventing flooding of property on the landside of the wall; normally constructed in lieu of or to supplement a levee where the land required for levee construction is more expensive or not available. FLOODWAY—the regular channel of a river or stream plus any adjacent floodplain areas that must be kept free of encroachment in order that the 100-year flood can be carried without substantial increase in height or the introduction of hazardous velocities. The basic NFIP standard for allowable increase in height is 1 foot, but some states are more stringent. FREEBOARD—the vertical distance between a design flood elevation and the top of a hydraulic structure. In the context of this report, a levee or floodwall. Freeboard is provided to assure passage of the design flood without overtopping and is necessary to account for hydrologic and hydraulic uncertainties. HUMAN INTERVENTION—engagement by people in defensive activity immediately prior to or during a flood period, e.g., installation of stop-logs, sand bags, operation of pumps, streetgates, etc. HYDROGRAPH—a graphical representation of discharge, stage, or other hydraulic property with respect to time for a particular point on a stream. INTERIOR DRAINAGE—the runoff or ponding of water, either overland, or channelized, or pooled, that originates from the landward side of a levee and drains to the levee-protected area. Seepage must also be considered in interior drainage planning. LEVEE—an earthen embankment generally built parallel to a shoreline to prevent flooding of the landside of the embankment and engineered to accepted standards. -77-

LEVEED AREA, LEVEE-PROTECTED AREA—the landside area and properties protected from inundation by the presence of a levee (or floodwall). LEVEE, COASTAL—an earthen embankment or seawall, constructed adjacent to the sea or an estuary for the purpose of preventing flooding on its landside. LEVEE FAILURE—any structural insufficiency, overtopping, or inability to close openings that results in flooding of a levee-protected area. LEVEE PENETRATION—any placement of a pipe, utility conduit, or other facility through a levee embankment perpendicular or skewed to the direction of flow. LEVEE, RIVERINE—an earthen embankment, constructed adjacent to a river or other watercourse, for the purpose of preventing flooding of the landside of the embankment. Levees may also be used to tie embankments paralleling a river to high ground to reduce inundated area during levee failure. MAP, FLOOD HAZARD BOUNDARY (FHBM)—a community map of a preliminary nature, prepared by FEMA, and identifying, by approximate methods, areas of special flood, mudslide, or related erosion hazard. MAP, FLOOD INSURANCE RATE (FIRM)—an official community map, prepared by FEMA and showing risk zones and base flood elevations within special hazard areas. MAP, FLOOD BOUNDARY AND FLOODWAY—a map prepared for the purpose of floodplain management showing flood and floodway boundaries curvilinearly. NATIONAL FLOOD INSURANCE PROGRAM—The program, created by the National Flood Insurance Act of 1968 as amended, and further defined by the Flood Disaster Protection Act of 1973, as amended, under which communities may be eligible for federally subsidized flood insurance on the condition that the communities enact satisfactory floodplain management regulations. The program is administered by the Federal Emergency Management Agency. 100-YEAR FLOOD—a flood estimated to be equalled or exceeded on an average of once in 100 years (1 percent chance of exceedance in any given year). PONDING AREA—a relatively low, designated space within a levee-protected area where water is temporarily stored during floods and then drained by gravity or pumping, depending on the relative elevation to adjacent receiving waters. -78-

RIVER STAGE—the height of water surface of a stream above some discretionary datum. RISK—the probability or chance of loss or damage occurring. RISK PREMIUM ZONE—a zone delineated on a Flood Insurance Rate Map, which identifies the Risk Premium Rate structure applicable to that area. RISK PREMIUM RATE (see Actuarial Insurance Rates)—those rates established by the Federal Insurance Administrator pursuant to individual community flood risk studies undertaken to provide flood insurance in accordance with Section 1307 of the National Flood Insurance Act of 1968 and accepted actuarial principles. Risk Premium Rates include provisions for operating costs and allowances. SEEPAGE—the movement of water through or under the materials of a levee earth embankment. SIDE SLOPES—the inclined side faces of a levee, numerically expressed as a ratio of horizontal to vertical dimensions. STABILITY ANALYSIS—a series of engineering calculations to determine the ability of an earthen structure, e.g., levee, to resist movement when loads are applied to it. STANDARD PROJECT FLOOD (SPF)—a flood that might be expected to result from the most severe combination of meteorological and hydrological conditions considered reasonably characteristic of the geographical area in which the drainage basin is located, excluding extremely rare combinations. The SPF is often used as a Corps of Engineers' design goal for hydraulic structures in urban areas. STOP LOG—a log, plank, cut timber, steel, or concrete beam fitting into end guides between walls or piers to close an opening in a levee, floodwall, dam or other hydraulic structure; the logs usually being handled or placed one at a time. STREET GATE—a closure gate used during flood periods to close a roadway opening through a levee or floodwall. WATERSHED—the area contributing runoff to river flow at a particular location; also river basin, catchment. -79-