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<br /> <br />EPHEMERAL STREAMS <br /> <br /> <br />A. Time 1:14 p. m. Upstream view. Bore is covering the small sand island. <br /> <br /> <br />c. Time about 1:14~ p. m. Floating debris typical of rising flood stage can be seen <br />onsur[a.oo. <br /> <br /> <br />E. Time about 1:15Hn p. m. VIew diagonally downstream at agltated and debris. <br />strewn area just behind the bore. <br /> <br />355397-56----2 <br /> <br />5 <br /> <br /> <br />B. Timeabout 1:l4H p. m. Bore advances faster in deep than in shaJlow pB.rtofchannel. <br /> <br /> <br />D. Time about 1:15 p. ill. Vie",' across channel parallel to bore face. Note tha <br />slope of water surface as shown by shadow of vertical hank. <br /> <br />FIGURE 4.-Passage of a small bore in the rising stage of an <br />ephemeral flow in an arroyo channel, Rio Puerco, a t.ributary <br />to the Rio Grande. Location is 8 miles north of Puerco <br />Station, N. Mex.) September 191 1941. Soil Conservation <br />Service photographs. <br /> <br />from the vertical walls and lying crumbled but un- <br />eroded in the channel. This debris is picked up and <br />washed away by subsequent flows and is undoubtedly <br />an important source of debris load. <br />Flash floods in arroyos, therefore, appear to do but <br />insignificant amounts of bank cutting as a, direct result <br />of impingement of flow on the banks. Wetting of the <br />banks, however, results in subsequent collapse of <br />arcuate slabs of alluvium which tumble into the channel <br />to become important additions to the load of later <br />floods. <br />