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<br />GLOSSARY RH The ratio of a specified recurrence-interval flood to <br /> the 2-year recurrence-interval flood. (Harley, <br />A The contnbuting drainage area, in square miles. In 1978). <br /> urban areas, drainage systems sometimes cross RIlOO Rainfall intensity, in inches, for the 2-hour lOO-year <br /> topographic divides. Such drainage changes occurrence. Determined from Weather Bureau <br /> should be accounted for when computing A. (1961) or Miller and others (1973). <br />BDF The basin development factor, an index of the prev- R12 Rainfall intensity, in inches, for the 2-hour 2.year <br /> aIence of the drainage aspects of (a) stonn sew- occurrence. Determined from Weather Bureau <br /> ers, (b) channel improvements, (c) impervious (1961) or Miller and others (1973). <br /> channel linings, and (d) curb-and-gutter <br /> streets. The range ofBDF is 0-12. A value of RQx The peak discharge, in cubic feet per second (ft'/s), <br /> zero for BDF indicates the above drainage as- for an equivalent rural drainage basin in the <br /> peets are Dot prevalent, but does not necessar- same hydrologic area as the urban basin, and <br /> ily mean the basin is nonurban. A value of 12 for recurrence intetval x. For this study equiva- <br /> indicates full development of the drainage as- lent rural discharges were computed from ap- <br /> peets throughout the basin. See text for details plicable Geological Survey regional flood- <br /> of computing BDF. frequency reports, as indicated in table I. <br />CN A soil-cover-<:omplex curve number as described by S The logarithmic standard deviation of annual peak <br /> the Soil Conservation Service (]97S). discharges for a gaging station. <br />E An index of local runoff volume, in inches, for the SCSS An index of potential infiltration, in inches, com- <br /> 2-hour 2S-year rainfall, computed by proce- puted by the equation SCSS = (],OOO/CN) - ]0 <br /> dures described by the Soil Conservation Ser- (Soil Conservation Service, 1975). <br /> vice (]97S). SL The main channel slope, in feet per mile (ft/mi), <br />Gs The logjuithmic skew coeffICient of t!te annual peak measured berween points which are 10 percent <br /> discharges for a gaging station. and 8S percent of the main channel length up- <br />IA The percentage of the drainage basin occupied by stream from the study site. For sites where SL <br /> impervious surfaces, such as houses, buildings, is greater than 70 ft/mi, 70 ft/mi is used in the <br /> streets, and parking lots. equations. <br />K An index of impervious area, computed by the <br /> equation K=I +O.OlS'IA (Carter, 1961). ST Basin storage, the percentage of the drainage basin <br />L The basin length. in miles, measured on topographic occupied by lakes, reservoirs, swamps, and <br /> maps along the main channel from the gaging wetlands. In.channel storage of a temporary <br /> station to the basin divide. nature, resulting from detention ponds or <br />LT Lagtime, in hours, for the urban watershed, com. roadway embankments, is not included in the <br /> puted as the time from center-of-mass of rain- computation of ST. <br /> fall excess to the center-of-mass of the corre- UQx The peak discharge, in cubic feet per second (fl'/s), <br /> sponding runoff. Computed only for stations for the urban watershed for recurrence interval <br /> having continuous rainfall and runoff data. x. That is, UQ2 = 2-year urban peak discharge, <br />R' Coefficient of determination, a measure of the pro- UQS = S-year urban peak discharge, and so <br /> portion of the total variance of the dependent forth. <br /> variable that is accounted for by the indepen- X The logarithmic mean of annual peak discharges for <br /> dent variables in a regression analysis. a gaging station. <br /> <br />VI Glos....,. <br />