Now go to Table 1 to determine the gradient class for the segment. Record the gradient class on the map. When you have determined gradient class for each of your segments, you may find that two adjacent segments are in the same gradient class. Estimate Channel Confinement for Each Segment Channel confinement means how much space is available on the valley floor for the channel move move laterally, develop a floodplain, develop meanders, etc. Channel confinement is defined as the ratio of the channel bankfull width to the width of the modern floodplain.
Bankfull width is the width of the channel at the point at which overbank flooding begins.
Overbank flow commonly occurs as flows reach the 1.5-year recurrence interval level. Channel confinement is difficult to determine from topographic maps, because channel bankfull width is not shown accurately on maps, except for very large rivers. Confinement classes are presented in in the table below. See Figure 2 for an example of how to apply the map criteria. Moderately confined M Floodplain width is 2 to 4x channel width Channel is relatively straight, and crossing contours are U-shaped.