Abstract:in order to obtain the progress of longitudinal erosion and effects of different factors

we conducted 6 flume tests. The results indicate that: the longitudinal erosion process includes 3 stages. At stageⅠ

the outflow is slow

and the suspended load wastransported to downstream mainly during the process.At stageⅡ

the depth of the breach changed rapidly.The bed load wastransported fiercely due to backward erosion. Atstage Ⅲ

the velocity and rateof outflow decreased

armor layer was formed which protected the sediment under the armor layer from eroding. At last

dynamic equilibrium was achievedbetween the water phase and sediment phase. With inflow rate increasing

the breach time decreases and outflow discharge increases

this leads to greaterstream power and highererosion rate. And the bottom of the breach become smoothly due to large inflow rate. The slope of the erosive characteristics curve becomes larger with the outflow discharge increasing. The shape of erosive curve changes from multi-peak curve to mono-peak curve with downstream slope increasing. The steepslope of downstream also increases the outflow discharge and erosion rate

and decreases the residual height of the dam. The factor J3 which is equal tothe third power of tangent values of the bed slope and downstream slope’s summation

can reflect the stability of soil particles in differentdownstream slopes. The shortcoming of current study is that the effects of material diversity on the dam breaching process was not considered and shall be investigated in the future work.