Sediment concentration and hydraulic characteristics of rain-induced overland flows in arid land soils

Abstract

Purpose Rain-induced overland flow involves the detachment of soil particles by raindrop impact and the transportation by the resultant overland flow. The purpose of this study was to investigate the relationship between sediment concentration and different hydraulic parameters including flow depth, flow velocity, shear stress, stream power, and unit stream power. The effects of soil particle size distribution, rain intensity, and slope steepness on measured sediment concentration in rain-induced sheet flow were also examined. Materials and methods Two arid land soils with different particles size distributions (D 2mm and D 4.75mm ) were subjected to simulated rains using a detachment tray under infiltration conditions. Two rain intensities of 57 and 80 mm h −1 were simulated on slope gradients ranging from 0.5 to 20 %, resulting in rain-induced overland flows. After pre-wetting each soil, the sediment-laden overland flow was sampled at several time intervals (2, 5, 15, 20, 30, and 40 min) and the sediment concentration was determined. Different hydraulic parameters including flow depth, flow velocity, shear stress, stream power, and unit stream power were measured. The hydraulic parameters were used to model the sediment concentration, and the model performance was evaluated. Results and discussion The result showed that the measured sediment concentration was greater in the higher rainfall intensity and at steeper slopes. With increasing slope steepness, sediment concentration increased from 4.3 to 15.5 kg m −3 and from 3.8 to 12.5 kg m −3 for soils D 2mm and D 4.75mm , respectively. There was a direct relationship between sediment concentration and the rain-induced flow velocity, shear stress, stream power, and unit stream power. Nevertheless, the values of sediment concentration increased as flow depth decreased on steeper slopes. Also, sediment concentration was lower in the soil containing larger aggregates than in the finer soil. The hydraulic parameters tended to overestimate low amounts of sediment concentration and underestimate high values. Conclusions In general, the accuracy of the hydraulic parameters in predicting sediment concentration was: flow velocity > stream power > shear stress > unit stream power > flow depth. Flow velocity was the best predictor of sediment concentration with a linear relationship, whereas the other parameters showed nonlinear relationships. This study revealed that rain-induced sediment concentration at small scales can be modeled precisely on the basis of the flow velocity parameter.

Aggregate breakdown and surface seal development influenced by rain intensity, slope gradient and soil particle size

“…In other words, the higher the rain intensity introduced on soil D max 4.75 mm, the greater amounts of finer particles were produced. Nevertheless, because of higher infiltration rate of this soil, the stream power of generated flow seems not to be enough to transport and move out all the predetached materials from the test area (Arjmand Sajjadi and Mahmoodabadi, 2015). This finding implies that the redistribution of particles or aggregates on the surface of eroding soil depends on aggregate size distribution as well as rain intensity and the resultant flow stream power.…”

“…Also, the measurement of average drop size was done using the stain method (Arjmand Sajjadi and Mahmoodabadi, 2015). The average (± standard deviation) drop sizes for the rain intensities of 57 and 80 mm h −1 were 2.2 ± 0.08 and 2.5 ± 0.09 mm with the coefficient of uniformity of 86 and 80 %, respectively.…”

“…The washed sediment was collected from the central test area of the tray. On two sides of the test area a buffer section was provided so the soil was not only lost by splash but could also be returned from the buffer area (Arjmand Sajjadi and Mahmoodabadi, 2015). Different parts of the applied detachment tray are shown in Fig.…”

The transport of aggregates associated with soil organic carbon under the rain‐induced overland flow on the Chinese Loess Plateau

“…In previous studies, hydraulic flow characteristics, including hydraulic shear stress, flow depth, flow velocity and stream power, were found to be closely related to the transport of sediment particles and OC in loessial soil sediments Liu et al, 2018). In soil loss models, hydraulic flow characteristics are usually used to quantify flow detachment, sediment transport capacity and soil loss (Trout and Neibling, 1993;Zhang et al, 2003;Arjmand Sajjadi and Mahmoodabadi, 2015). However, the internal relationships between hydraulic factors and SOC distribution in sediments have not been well studied.…”

Hysteretic sediment fluxes in rainfall‐driven soil erosion: Particle size effects

“…Several studies investigated the factors and processes responsible for these loops in order to interpret or determine the distribution of sediment sources within a catchment [Seeger et al, 2004;Smith and Dragovich, 2009;Yeshaneh et al, 2014]. The difficulty of interpretation at these scales is that there are complications arising from spatial and temporal variability in climate [Ghahramani and Ishikawa, 2013;Arjmand Sajjadi and Mahmoodabadi, 2015;Dai et al, 2016], soil types [Keesstra et al, 2014;Rodrigo Comino et al, 2016], land use [Cerd a et al, 2009;Prosdocimi et al, 2016], topography [Ghahramani et al, 2012], catchment connectivity [Ghahramani and Ishikawa, 2013;Marchamalo et al, 2015;Masselink et al, 2016], channel storage and bank erosion [Buendia CHERAGHI ET AL.…”