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<br />Floodplain. any land area, such as the lowland and relatively flat areas <br />adjoining inland and coastal waters, susceptible to being inundated by water from <br />any source. <br /> <br />Floodway: the channel of a river or other watercourse and the adjacent land areas <br />that must be reserved in order to discharge the base flood without cumulatively <br />increasing the water-surface elevation more than a designated height. The base <br />flood is defined as the one-percent chance flood and the designated height is <br />usually one foot above the base flood elevation; however, this height may vary <br />(but is not more than one foot) depending on what the state has adopted. <br /> <br />Floodway Fringe: the area between the floodway boundary and the 100-year <br />floodplain boundary. <br /> <br />Flow: equivalent to discharge. <br /> <br />Flow Area: the cross section (see discharge) area of the floodplain below a given <br />water-surface elevation. <br /> <br />Hazardous Flow: conditions that exist when the product of the depth of flow and <br />its corresponding velocity are greater than ten (10). For example a flow depth <br />of 3 feet and a flow velocity of 4 feet per second (3 x 4 = 12) would be <br />considered hazardous flow. <br /> <br />Hydraulic Depth: an average depth computed as the Flow Area divided by the top <br />width of the floodplain for a given water-surface elevation. <br /> <br />Lacustrine Flooding. Flooding produced by a lake or pond. <br /> <br />Peak Discharge: the maximum instantaneous discharge of a flood at a given <br />location. <br /> <br />Recurrence Interval: the average interval of time required for a flood of a <br />specific discharge to occur or be exceeded; equal to the inverse of the <br />exceedence frequency. <br /> <br />Riverine Flooding: Flooding produced by a river or stream. <br /> <br />Shallow Flooding: a designated AO, AH, or va zone on a community's Flood <br />Insurance Rate Map with a one percent or greater annual chance of flooding to an <br />average depth of one to three feet where a clearly defined channel does not <br />exist, the path of flooding is unpredictable, and velocity flow may be evident. <br />Such flooding is characterized by ponding or sheet flow. <br /> <br />Slope (Energy): the rate of energy loss of a watercourse. <br /> <br />Slope (Ground). the change in vertical ground elevation over a horizontal <br />distance, usually based on the change in the vertical elevation of the stream <br />bottom. <br /> <br />Steady Flow: state of flow where the depth of flow does not change with time. <br /> <br />Subcritical Flow: state of flow where the gravitational forces are more <br />pronounced than the inertial forces. The flow tends to have a low velocity. In <br />general, in this flow regime, the hydraulic depth is more than twice the velocity <br />head. <br /> <br />Supercritical Flow. state of flow where the inertial forces become dominant. The <br />flow tends to have a high velocity. In general, in this flow regime, the <br />velocity head is equal to or more than half the hydraulic depth. <br /> <br />Unsteady Flow: state of flow where the depth of flow changes with time. <br /> <br />Al-2 <br />