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I I I I I I I I I I I I I I I I I I I GLOSSARY Backwater Effect. The rise in surfal!e elevation of flowing water upstream from and as a result of an obstruction to flow. Channel. A natural or artifil!ial waterl!ourse of perceptible extent with definite bed and banks to I!onfine and I!ondul!t <!Ontinuously or periodically flowing water. Cloudburst. A sudden and extremely heavy downpour of rain that is small in areal extent; of short duration; and may be accompanied by lightning, thunder and strong gusts of wind. Conveyance Capacity. a. Channell!onveyance I!apal!ity is the rate of discharge, in cubic feet per second, whil!h oon flow in a water <!Ourse with the water surface not greater than the height of the channel banks. b. Floodway conveyance oopacity is the rate of discharge in the overflow portion of the floodway which oon pass through a spel!ified area at depths and velocities governed by the hydraulic dimensions of the floodway. Designated Floodplain. The area designated as a floodplain by offil!ial al!tion of the board of I!ounty commissioners or city <!Ouncil with the prior <!Oncurrency of the Colorado Water Conservation Board. Flood. An overflow on lands not normally <!Overed by water and that are used or usable by man. Floods have two essentiall!haracteristics; the inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river or stream or an ocean, lake or other body of standing water. Normally a flood is <!Onsidered as any temporary rise in streamflow or stage, but not the ponding of surface water, that results in signifil!ant adverse effects in the vicinity. Adverse effects may inl!lude damages from overflow of land areas, temporary backwater effects in sewers and local drainage I!hannels, I!reation of unsanitary <!Onditions or other W1favorable situations by deposition of materials in stream channels during flood recessions, use of ground water I!oincident with inl!reased streamflow, and other problems. -17- Flood, IOO-Year. A type of flood, inl!luding the water surface elevation and territorial occupation thereof, which oon be expected to ool!ur at any time in a given area based upon recorded historical prel!ipitation and other representative data, with an average statistical chance of one perl!ent being equalled or elmeeded during anyone year. The term is used interl!hangeably with a one percent flood or Intermediate Regional Flood. (See definition for Intermediate Regional Flood.) Flood Crest, The maximum stage or elevation reached by the waters of a flood at a given looation. Flood Frequency. (See Probability) The average recurrence interval of specifil! discharges or water stages whil!h oouse flooding. Flood Peak: The maximum instantaneous discharge of a flood at a given location. It usually oCl!urs at or near the time of the flood crest. Floodplain. An area in and adjacent to a stream, which area is subjel!t to flooding as the result of the oocurrenl!e of a lOO-year flood and which area thus is so adverse to past, current, or foreseeable <!Onstruction or land use as to <!Onstitute a signifil!ant hazard to publil! health and safety or to property. Flood Profile. A graph showing the relationship of water surface elevation to location, the latter generally expressed as distance above mouth for a stream of water flowing in an open channel. lt is generally drawn to show surface elevation for the I!l"est of a specifil! flood, but may be prepared for <!Onditions at a given time or stage. Flood Stage. The stage or elevation at which overflow of the natural banks of a stream or body of water begins in the real!h or area in which the elevation is measured. Floodway Zone. The channel of a stream and those portions of the adjoining floodplain whil!h are reasonably required to oorry and discharge the floodwaters of a lOO-year flood. It is the designated floodplain less than the low hazard zone, if any such low hazard zone has been identified. If no low hazard zone has been identified, then the terms "designated floodplain" and "floodway zone" shall be <!Onsidered as being synonymous.