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B. Hydrogeomorphology <br />Indicator 3. Floo~lpl~ain Connection ranrllnundntion. <br />The likelihood that the stream will be able to escape its bank and flow over the floodplain dur- <br />ing typical high flow events can be measured by the ratio of the height between the channel <br />bottom and the first terrace that indicates the boundary of the floodplain itself and the distance <br />between the channel bottom and its first bank (banlcfull location; see Figures 1 and 2). <br />To calculate the floodplain-banlcfull ratio, choose three random but representative points along <br />the entire study reach. Use a laser level (or a survey instrument if available) to measure the dis- <br />tance between the bottom of the channel and bairlcfi~ll (in the example in Figure 2, this would <br />be 1.2 feet). Then measure the distance or height of the beginning or closest part of the floo <br />plain to the channel, and the channel bottom (1.8 feet in this example). Next, divide the flood- <br />plain depth by banlcfull depth. For Figure 2, 1.8 divided by 1.2 gives 1.5. Use the scoring scale <br />in Figure 3 to determine the score to put on the Score Sheet for this location. lii this example, <br />the observed ratio of 1.5 leads to a score of 2. Repeat the measurements at two additional repre- <br />sentative locations along the reach, and then take the mean of the three ratios to calculate the <br />final score for this indicator. The final score indicates the level of connectivity between the <br />stream and its floodplain; a high ratio (and low indicator score) shows less potential for over- <br />bankflooding. <br />Figure 1: Idealized cross section of small and medium sized streams and their associated floodplains in the <br />American Southwest. The scour zone. which is flooded during periods of peals runoff in most y~e lrs. is also called <br />the Lower Riparian Zone (LRZ), and is used for one of the vegetation transects in this protocol (LRZ transect). <br />The areas of the floodplain that are outside of the scour zone are flooded only during increasingly rarer and <br />increasingly- higher flow events. The edge of the first terrace closest to the stream channel marks the inside edge of <br />the Upper Riparian Zone (TJRZ) as used in this protocol, and a second vegetation transect (URZ transectj is estab- <br />lished along this edge. Ilhirh°ntiot~ U~, Heidi St~ell <br />17 <br />