# Effects of Different Aboveground Structural Parts of Grass Strips on the Sediment-Trapping Process
###### Abstract  
Grass strips can decrease erosion, trap sediment in silt-laden water flowing downhill, and control nonpoint source pollution. Determining the effects of different parts of grass strips on silt-laden overland flow will improve our understanding of sediment trapping by grass strips with different structures. Sediment trapping by grass strips was studied using a 5\({}^{\circ}\) slope, 30 L min\({}^{-1}\) m\({}^{-1}\) flow rate, 120 g L\({}^{-1}\) sediment concentration, and different aboveground components of grass strips (complete grass, removed green grass, and removed green and withered grass). The whole overland flow process was monitored. Meanwhile, the runoff sediment samples at the outlet were collected and measured. Sediment trapping by aboveground grass parts was quantified at different stages. Of the soil bed surface, green grass, and withered grass, the soil bed surface dominated sediment trapping in the initial stage of the sediment-trapping process, contributing about 90% of total sediment deposition in the first 5 min. As the sediment-trapping process continued, the effect of the soil bed surface weakened, and the green grass played a major role at the later stage of sediment trapping. The ratio of the soil bed surface, green grass, and withered grass contributions to total sediment deposition at the stable stage of the experiments was approximately 3:5.2. The results will help assess the effects of vegetation restoration on sediment transport in entire watersheds. grass strips; sediment trapping; silt-laden flow; aboveground; grass strip structure 25 May 2021 6 July 2021 6 July  
will change mainly because deposited sediment will affect the roughness of the grassland and the resistance of the grassland to overdland flow [7; 12]. Resistance to overdland flow will be provided by all types of soil surface roughness, including vegetation, small stones, bumps, and small granules on the soil surface. The roughness of a hillslope can therefore be considered to be a composite roughness similar to riverbed roughness [13]. Since the rough elements are superimposed, the flow shear forces exerted on different rough elements in the same region can also be superimposed [14]. [PERSON] et al. performed simulated rainfall experiments on natural pasture containing shrubs and grass strips in the western United States and found, from the stackable principle for hillslope resistance, that the effective Darcy-Weisbach resistance factor \(f_{e}\) can be divided into four parts, each part representing the contribution of certain surface characteristics to overdland flow resistance [4; 15], as shown in Equation (1). \[f_{e}=f_{rs}+f_{rr}+f_{gc}+f_{pb} \tag{1}\]  
where \(f_{rs},f_{rr},f_{gc}\), and \(f_{pb}\) are the resistances of soil, microtopography, surface cover (including the small gravels and litter that may exist on some hillslope), and standing vegetation, respectively. [PERSON] et al. used a 5 m long and 0.38 m wide trough to conduct the experiments of _Pintus tabulaeformis_ litter covering conditions with 7 gradients in the range of 0-70% [16]. Compared with [PERSON] et al. under the conditions of artificial stem mulching with nine gradients in the range of 0-30% in the same trough [17], the results show that the effect of stem on the kinetic energy of the overdland flow is stronger than that of litter. Stable beds unaffected by erosion or deposition have often been used to study the effects of vegetation and bed roughness on the overdland flow [16; 18]. Real soil slopes have been used to study interactions between vegetation cover, erosion, and overdland flow [19; 20]. These studies were mainly focused on vegetation improves interception, increases infiltration, reduces soil erosion, and weakens sediment transport capacity of overdland flow. Under natural conditions, the inflow of a field will usually carry sediment, and the conditions will vary according to the soil and precipitation characteristics uphill. Erosion or deposition may occur when silt-laden water flows into a vegetation area.