Using a seismic array to study sediment redistribution after dam breaching

Abstract

In the case of dam breaches in natural rivers, there is a lack of systematic studies understanding how the changes in the river bed elevation. This study aims to understand the characteristics of erosion and deposition along the river channel. Two field-scale dam breach experiments were conducted in Landao Stream, which is a tributary of Beigang River, length about 1,952 km and average altitude 1,200 meters. The total length of the experiment area is 280 m, and the average slope is 6.3°. Experiment I is a case of single dam and Experiment II is single dam with spur dike. In Experiment I, a seismic array of 20 stations was installed along the left and right banks of the river. In Experiment II, a seismic array of 12 stations was first deployed along the center of the river channel with station spacing distances of 10 m. Then, a seismic impact experiment was carried out to obtain the associated seismic parameters for seismic physical models. After the impact experiment, the seismometers were reinstalled on the left and right banks of river. For each experiment, the surveys of sediment grain size distribution and digital elevation model were conducted before and after experiment, which can provide information on erosion and deposit of river bed. Additionally, the water level, surface flow velocity, time-lapse photos, and temporal changes in beach shape were also monitored during experiment. With the available data of fluvial measurements, topographic changes in riverbeds, grain size survey, and seismic parameters, our study suggested that the riverine seismic signals can record the ground motions caused by water flow, sediment transport, and debris flow. Results of a series of time-frequency analysis presented the additional information about the erosion and sedimentation of river bed. Finally, our proposed mechanisms based on seismic physical models (e.g., turbulent flow, bedload saltation, and debris flow) will be discussed with the previous results of numerical simulation. Our results demonstrated that the riverine seismic signals of seismic array can effectively and immediately quantify downstream sedimentary erosion and deposition characteristics after the dam breaching.