Experimental Investigation of Flash Flood Resulting from Dam-Break on Bed Sediment Transport

Varied flows such as flooding resulting from dam break can happen due to earthquakes, seepage, bombing, overtopping, mistake in design and project performance as well as causing financial damages and human losses. Unsteady flow during flooding events has a high impact on flow field pattern, sediment motion, ecology and also, distribution of contamination in the river. In this study, the impact of various slopes, sediment diameters and unsteady flows with different discharges on sediment transport were carried out at the flume with 12 m length, 0.5 m width and height. In this research, two type of uniform sediment particle with 10 and 15 mm in diameter were spread over the bed of above mentioned flume with slope of 0.01 and 0.02. To build a dam physical model, a mechanical lift-gate was used at 2 m from the upstream inlet of the flume. Potential hydrostatic initial conditions of the fluvial experimental model resulted from dam-break was based on using three water depths of 35, 20 and 12 cm at the gate upstream and one water depth of 3cm at the downstream of the gate. By considering the above mentioned procedures, fluvial flows were produced and have been used with discharge between 0.07 to 0.66 m3/s. The result showed that by increasing the sediment particle size 1.35 times the sediment transport have been reduced by 1/4 for 35 cm upstream water depth and also by increasing the slope by 2 times from 0.01 to 0.023 for sediment with 15 mm and with initial upstream water depth condition was 35, 20 and 12 cm the sediment transport have been increased 3.42, 1.83 and 3.38 times respectively. The above mentioned points show the significance of fluvial flows and their effects on sediment transport and therefore the morphological changes of rivers. Result has been shown that high sediment transport rate and bed evolution was resulting from positive wave head and after that, sediment transport rate have been intensity decreased.