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<br />Topographic Mapping -- Mapping which graphically represents the exact <br />physical configuration of a place or region, includfng elevations, water <br />bodies. and man made features. <br />Torrential-' Resulting in a raging flood or deluge. <br />Undermining -. The weakening of a structure or of ground by wearing away of <br />the base material from below by water, <br />Ungauged.. (see Gaugecf) <br />Un-Numbered A Zones -- A zone on a Flood Insurance Rate Map that <br />delineates in an approximate fashion the 1 DO-year floodplain without precise <br />engineering information showing detailed water surface elevation and flood- <br />plain boundary information. <br />lJ.S,G.S. Flood-Prone Area Maps -- Maps prepared by the U.S. Geological Sur- <br />vey on topographic quadrangle map bases showing areas of potential flood <br />hazard as determined through approximate methods. <br />Vertical Datum.. An assumed elevation used as a reference in surveying or <br />mapping and expressed in feet above Mean Sea Level. <br />Water Surlace Elevation -- The heights, usually in relation to Mean Sea Level, <br />reached by flows of various frequencies and magnitudes at pertinent pOints <br />in the floodplain. <br /> <br />58 <br />