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<br />A. The following figure summarizes hydraulic factors affecting stream stability, <br />Each factor is summarized below. <br /> <br />1, Design flow <br /> <br />a. The term "design flow" should be avoided because bridge <br />crossings cannot typically be designed for a unique flood <br />event <br /> <br />b, In reality, a range of events should be examined to determine <br />which design conditions is most advantageous, ilnsofar as <br />costs and risks are concemed. <br /> <br />c. If a design flood is designated, it should be that ,event that <br />causes the greatest stress to the crossing, <br /> <br />2. Bed configurations in sand-bed streams <br /> <br />Bed configurations are important because many streams flow on <br />sand beds for the greater part of their length and nearly all large <br />rivers have sand beds. <br /> <br />a. Bedfonns include ripples, dunes, plane bed, and ;antidunes. <br /> <br />Bedform condition influences water surface condition, <br /> <br />NOTES: <br /> <br />3.8 <br />