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<br />• NOTATION <br />The hydrologic or hydraulic equations used in the calculations are <br />shown: <br />EQUATION NOTATION REFERENCE N0. <br />Tc = X11.9 L 3) .385 Channel flow-nomograph method for 1 <br />H determining Tc (Time of concentration) <br />where: <br />L = Length channel in miles <br />H = Elevation difference from beginning <br />of defined fl ow to outflow point in <br />feet. <br />Q = (P - 0.25)2 SCS equation for determining peak flow 2, 3 <br />P+.85 <br />Qp = qAQ Equation for determining peak flow (Qp) 3 <br />where: <br />• q = Flow in CSM/irt. <br />A = Drainage area in sq. miles <br />Q = Runoff in inches <br />CSM/in. = cubic feet sec/mil/in. runoff. <br />The size of culverts was determined by the nomograph contained in <br />Reference 4 where: <br />HW = Head water at culvert inlet <br />D ~ Diameter of culvert. <br />Type 3 Entrance =Culvert edge projecting from roadway fill <br />Type 1 Entrance =Steel end section conforming to fill slope <br />DEFINITIONS <br />Time of Concentration (Tc) The time it takes for runoff to travel from <br />tie hy~rau ica y most istant part of watershed to the point of reference. <br />Usually refers to channel flow. <br />Travel Time (Tt) The time it takes for runoff to travel from the uppermost <br />part of the water shed to a defined inlet or channel. Overland flow only. <br />C1 <br />-2- <br />