*4.2. E*ff*ect of Terraces and Vegetation on Sediment Reduction*

We counted the total simulated sediment yield of each event per case, and also calculated the *AR* of vegetation and terraces, and the *RR* of R1, R2, and R3, as shown in Table 7. The average *RR* of R1 for sediment was 13.31% in the 1980s. For the three events in the 2010s, the average *RR* of R1 was 32.22%, the average *RR* of R2 was 24.52%, and the average *RR* of R3 was 53.85%. The average *RR* of R1 in recent years increased by 18.91% over that in the 1980s. The average *AR* of R1 was 449.95 t/km2, and 2850.17 t/km<sup>2</sup> for R2. The results also show that the sediment reduction rate of vegetation was higher than that of terraces, but that terraces could reduce more sediment per unit area. In general, the effectiveness of sediment reduction of R3 was highest. Besides, the sum of *RR*<sup>1</sup> and *RR*<sup>2</sup> was inconsistent with *RR*3. As mentioned previously, the reason might be that when terraces had played the role of sediment reduction, the sediment reducing efficiency of vegetation in the same time zone would be decreased. The assumption that all terraces in the Pianguanhe Basin are of good quality and have the same embankment height may have overestimated the sediment reduction efficiency of terraces.


**Table 7.** The efficiency of sediment reduction by vegetation and terraces in the Pianguanhe Basin.

Annotation: *RR*<sup>1</sup> and *AR*<sup>1</sup> mean the *RR* and *AR* of vegetation, respectively; *RR*<sup>2</sup> and *AR*<sup>2</sup> mean the *RR* and *AR* of terrace, respectively; *RR*<sup>3</sup> means the *RR* of both vegetation and terrace; Difference denotes *RR*<sup>3</sup> minus the sum of *RR*<sup>1</sup> and *RR*2.
