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<br />Another method of insuring conservative results was the direct <br />summation of the peak flood flow out of Atkinson Creek to the <br />peak of the San Miguel River. Due to the difference in drainage <br />areas between the two streams, the time of concentration for each <br />basin would be different. The time of concentration is that time <br />required for the most hydraulically distant portion of the water- <br />shed to contribute runoff to the point of study. The shorter time <br />of concentration of Atkinson Creek would indicate that the peak <br />runoff from a basin-wide storm event would pass through the study <br />area prior to the peak in the main river channel. Directly adding <br />the peak flow out of Atkinson Creek to the peak of the San Miguel <br />without lagging is a conservative technique that results in a <br />higher flow downstream of the confluence. <br /> <br />3.3 Water Surface Profile Calculations <br /> <br />3,3.1 General <br /> <br />As previously stated, the u.S. Army Corps of Hydrologic Engineering <br />Center computer mode 1 HEC-2: "l.Ja ter Surfa ce Prof'il es", \'Ia s emp 1 oyed <br />to calculate the maximum water elevations resulting from the various <br />flood events, This computer program is used by the Federal Insurance <br />Administration in all of its flood studies across the u.S. <br /> <br />The program calculates water surface profiles <br />varied flow in natural or man-made channels. <br /> <br />for steady, gradually <br />The effects of various <br /> <br />obstructions such as bridges, culverts, weirs, and structures in the <br />flood plain may be considered. The computational procedure is based <br />on the solution of the one-dimensional energy equation with energy <br />loss due to friction evaluated with Manning's equation. The program <br />is also designed for application in flood plain management and flood <br /> <br />9 <br />