Document Type : Research Article
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Abstract
Flash flood is due to rapid precipitation in arid and semi-arid areas. This flood is example of unsteady flow which has hydrograph with little time duration and high discharge. Investigation behavior of these floods is very important on sediment transport and characteristics streams. In this research evaluated the effect of flash floods on bed load transported to downstream. The input hydrographs are symmetric and Asymmetric triangles. Time duration of hydrograph was selected 90 second and constant and the maximum discharge were changed 6.58 to 16.18 l/s. The median size of particles is 2.5 mm; three bed slopes 0.005, 0.01 and 0.02 were select in these experiments. The results show that a temporal lag was found between the flow hydrographs peak and the sediment hydrograph peak. The temporal lag was found to be about equal to 5 - 11% of flow hydrograph duration. Also bed slope and maximum discharge of hydrograph are effect on upstream erosion and transportation of sediment to downstream. Since increases the bed slope from 0.005 to 0.01 increased 50% bed load transported and with two times the slope it show increase 400% in bed load transported. Bed load transported to downstream with symmetric triangle hydrographs more than symmetric triangle hydrograph.
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