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3.2.1.3 TRASH CAUGHT IN TREES, ON POLES AND ON FENCE POSTS - Swiftly flowing water may etch a line in the soil and deposit foam and other debris along the cut as the flood crests. Cut lines must be used with caution if there have been any other floods near that elevation in recent history. The foam and small debris are often necessary to make a positive identification of the true high water line. 3.2.1.4 DISCOLORATION LINES ON BUILDINGS - High water often leaves a stain on painted wood or brick after a flood. The material should be carefully examined to make sure that capillary action didn't carry the stain higher than the flood elevation.' 3.2.2 LAY OUT THE CROSS SECTIONS - The cross sections should be laid out in enough detail, with enough points, to define major changes in bank or flood plain slope and where major changes in roughness occur. Guidelines on where to locate them are provided as follows: 3.2.2.1 As mentioned previously, the cross sections must be far enough apart to allow for an appreciable friction head loss (roughly 0.5 or more feet) between cross sections. Depending upon river characteristics, this could be as little as 100 to 200 feet or more than 200 yards. This is a judgement call. If space permits, it is better to . locate the sections further apart than necessary than to find that there is a convergence problem once you are working up the results. 3.2.2.2 Cross sections should be perpendicular to the majority of the flow. In selecting the "perpendicular", try to reconstruct the flow lines at peak discharge and set the cross section at right angles to the main channel flow, rather than at right angles to the high water marks. On a straight and uniform reach the cross section will be at right angles to both the main flow lines and the high water marks. On curved or non uniform cross section reaches, there may be some angular variation from perpendicular between the cross section and the high water marks. 3.2.2.3 The cross section should not contain any islands or divided flow. 3.2.2.4 The cross section should be representative of the reach and should not contain any unusual f\,atures. 3.2.2.5 Enough points should be taken in each cross section to adequately define major slope breaks, changes in flow characteristics or changes in roughness. Typically 6 to 12 points are sufficient to define a cross section. They would include end points, top of bank, edge of bed on both sides and any slope breaks in the flood plain or on the stream banks. 3.2.2.6 The cross section should not contain any area which may have experienced zero or reverse flow at the peak. 1-4 syslem lOr orYCifl1.!IIIY III'" "'V"'''' """'''' IIV''''.,.