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<br />Rationa/lvlethod (Q = CIA) .. A method for determining the maximum rate of <br />runoff in cubic feet per second accordin!l to the Rationai Formula (0 = CIA) <br />where 0 i8 the maximum rate of runoff, C is a runoff coef1icient expressing <br />the ratio between the maximum rate of runoff and the average rate of rainfail <br />intensity in inches per hour, I is the average rate of rainfall intensity, and A is <br />the area from which the runoff originate8. <br />Reach~. A hydraulic engineering term to describe longitudinal sHgments of a <br />stream or river. <br />Rectified Photographic Map .. A composite of aerial photograph8 of an area <br />that have been corrected for the tilt of the airplane but that have not been <br />adjusted t,) assure true scale throughout the composite. <br />Regime of Flow.. A categorization of flow based on its specific energy allow. <br />ing for throe categories of flow: subcritical, critical, and supercritical. <br />Regional Skew Coefficient ... A numerical measure of the lack of symmetry in <br />a frequency distribution of peak flows, specific to a particular geographic <br />region. <br />Aegressio'1 Curve n An algebraic curve which correlates a dependent vari- <br />able with one or more independent variables allowing the prediction of <br />values of the dependent variable based on the observed correlation between <br />past values of the dependent amJ independent variables. <br />Retention.. The prevention of runoff from entering a stream, storm sewer <br />system, or combined sewer system by storing it in some lype of "torage <br />basin. <br />Riprap" An assemblage of broken stones erected in water or adjacent to <br />water, as on a stream bank, to protect the ground in or near the flooclplain <br />from erosion. <br />Rise.. An 'ncrease in water surface elevations due to increased flow, <br />obstructions to flow, or some combination of those factors. <br />Riverine u Located on or near thE! banks of a river. <br />Roughness Coefficent.. A measure of the degree of resistance to water flow <br />offered by a stream channel and the adjacent floodplain, which 1$ a function <br />of vegetation, rocks, channel rnatHrial, and other such stream characteristics. <br />Runoff.. That portion of rainfall or snowmelt that is not absorbed by the soil. <br />Seepage." The act or process of water passing through small openings or <br />pores. <br />Side View.. (see Profile View). <br />Staff Gallpe .. A vertical board or I'Od graduated in hundr'9dths of a foot to <br />measure stream depths; a rating curve i8 used to convert the deptlls to flows <br />in cubic feet per second. <br />State Plane Coordinates.. A network of coordinates which define any point <br />using horiwntal projection of latitudes and longitudes, a" administered by <br />the State Surveyor. <br />Static.. (s'le Hydrostatic) <br />Stationing.. An arbitrary system lor locating a position along a baseline, <br />(reference line) usually a stream centerline. by starting from one end of the <br />baseline and numbering at re!lular intervals. <br />Structural Measures.. Designed to address floodplain problems by con. <br />structing,f.acilities which reeluce or eliminate flooding of a given area thHreby <br />protecting facilities that would otherwise be subject to greater flooding and <br />more frequent flooding. (also Corrective) <br />Subcritica' Flow" That tYPE> of flow. for a given discharge of water, where the <br />depth is greater than critical depth and velocities are low. <br />SlIpercritical Flow.. That type of flow, for a given dischar!le of water, where <br />the depth is less than critical depth and velocities are hi~lh. <br />Synthetic aainfall . Runoff Metho(t.. A mathematical method to calculate <br />runoff on a particular stream reach based on rainfall amounts, dura.tions, and <br />distributions and on average water losses, ground slopes, and othm hy. <br />draulic parameters. <br /> <br />57 <br />