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<br />e. Draw flood contours as wiggly lines at each dot. perpendicular to <br />the stream. and stopping at the corresponding ground contour line. <br /> <br />f. Starting at the abutments of the dam. connect the endpoints of the <br />flood contours. Flood boundaries should cross ground contours on a tangent <br />and only at the ends of a flood contour. <br /> <br />Steps e and f are illustrated in figure 12. <br /> <br />The example of Log Lake Dam was idealized and avoided the problem of <br />elevated road crossings. narrow canyon restrictions on the stream. and <br />islands. It also assumed that adequate stream channel cross sectional data <br />was obtained from the topographic map. It is possible to refine the mapping <br />technique by field measuring typical cross sections. calculating backwater <br />curves. and using weir equations to determine overtopping depths for roads. <br />However. these refinements may not be justified to the final purpose of the <br />map. <br /> <br />The map produced by plotting data available from table IV will provide a <br />reasonable estimate of flood hazard zones for emergency planning purposes. <br /> <br />19 <br />