Sediment trapping efficiency of slit check dam in laboratory experiment and field observation

Introduction
This study used time-lapse photography to record the slit check dam in Huisun experimental forest, Nantou, Taiwan, and set series scale-model in lab. On July 13 2013, typhoon Soulik landed in North Taiwan and caused heavy rain totaling up to 550mm and caused debris flow to occur at Law-Dow River within the test site and the slit check dam got buried.
The study purposes are to research sediment trapping efficiency of slit check dam with different types of removing transverse beam and interaction with landslide induced by heavy rainfall.

Experiment Installed

This study measured the actual size of field channels and modular steel check dam, and used a 1/25 scaled model to prepare four kinds of  experiment sediment with grain size of 4.50 cm, 2.84 cm, 2.07 cm, and 1.52 cm respectively for the grain sizes distribution of debris flow.

To analyze the influence of sediment trapping efficiency between modular steel check dam with and without transverse beams, in the case of a dam with transvers beams, a dam module installed four transverse beams. This experiment was made against two kinds of modular steel check dam with and without transverse beams, matching four discharges. To quantify the differences between with and without transvers beams the two experiment designs; we used the block ratio to define.

Figure 2. Instructions of  laboratory experiment

Figure 4. Photos of laboratory experiment(RS1) and field record 

Results and Discussion

The result of experiment showed both of slit check dam and slit check dam with steel, the trapping efficiency declined with discharge increasing. Furthermore, we find similarity between laboratory experiment(RS1) and field event by particle size analysis. In the field the sediment d95 is 0.7m  in upstream of slit check dam and d95 is 0.6m  in the slit check dam.  By compression ratio(1:25), we find it closed to the laboratory experiment result that the sediment in upstream d95 is 2.939cm and in the slit check dam d95 is 2.7cm.

Figure 5.  Relation of trapping efficiency and discharge in experiment 

Figure 6. Grain size accumulation curve

Figure 7. History events in Law-Dow River(Typhoon Mindulle) 

Conclusion

The result of experiment showed that slit check dam and slit check dam with steel could reduce rate of sediment discharge and total sediment discharge, and improve sediment trapping efficiency after installing transverse beams. By comparing history events, the  slit check dam can reduce damage and impact caused by landslide.