# Effects of Different Aboveground Structural Parts of Grass Strips on the Sediment-Trapping Process
## 3 Results and Discussions
### Resistances to Overland Flow Provided by the Grass Strips
The soil bed surface played a dominant role in the initial stage (the first 5 min) of the sediment-trapping process, contributing \(\sim\)90% of the sediment trapping that occurred. During the sediment-trapping process, the effect of the soil bed surface became weaker as the deposited sediment coverage increased. Later, the soil bed surface contributed only \(\sim\)30% of the sediment trapping that occurred in the first 50 min. In addition, the soil bed surface contributed 31.10% of \(R(t)\) in the first 50 min and 30.03% of \(R(t)\) in the first 60 min, indicating that the soil bed surface had little effect between 50 and 60 min. The contribution of soil bed surface to \(R(t)\) was mainly due to the sediment trapped in the first 20 min. [PERSON] et al. performed a simulated rainfall experiment in a grassland area at the Renjiatai forest farm in Fuxian County, Ziwuling Forest Region, China [37]. The experiment lasted 31 min. The total contribution of stems, branches, and litter to sediment trapping was 44.6% and the contribution of the soil bed to sediment trapping was 55.4%. At 30 min in our study, the contribution of both green and withered grass was 54.8%, and the contribution of the soil bed surface was 45.2%, which were similar to the contributions found by [PERSON] et al. [37]. As shown in Figure 8, the main factors affecting the cumulative amount of sediment trapped \(R(t)\) changed through the sediment-trapping process. The soil bed surface played an important role in the first 30 min, and green grass was dominant after 40 min. Between 5 and 40 min, the contribution of the soil bed surface to \(R(t)\) decreased from 93.29% to 35.49%, and the contribution of green grass increased from 2.73% to 40.50%. This indicates that the main structural part contributing to sediment trapping changed from the soil bed surface to green grass. The contribution of withered grass was only 3.98% in the initial stage of sediment trapping but gradually increased to 28.53% at 30 min and then decreased to 21.26% at 60 min. The contribution of withered grass was always between the contributions of green grass and the soil bed surface. The rapid increase in the contribution of green grass and withered grass was mainly caused by the soil bed surface becoming covered with deposited sediment and the resistance of the soil bed surface to overland flow gradually weakening, making the resistance provided by green and withered grass become  
Figure 7: Cumulative amount of sediment trapped \(R(t)\) plotted against time for the different grass strip treatment experiments. Note: The solid lines indicate the mean values for the repeated experiments, and the upper and lower horizontal lines indicate the upper and lower limits of the measurements. gradually more prominent. As shown in Figure 7, when sediment trapping occurred for long enough, the contributions of the different components tended to become stable after 50 min. The contributions of the different aboveground parts of the grass strips to \(R(t)\) during the sediment-trapping process changed (either increasing or decreasing), but the overall sediment-trapping efficiencies of the grass strips continually decreased until a stable state was reached.