Search

• The runoff, sediment load and runoff erosion power decreased significantly. • Compared with runoff, runoff erosion power-sediment relationship is better. • The power function of runoff erosion power and sediment is better than linear. • Erosion in particular geographic locations responds strongly to runoff erosion power. In recent years, the acceleration of urbanization in the Yangtze River Economic Belt (YREB) has brought about problems such as soil erosion, ecosystem degradation and decline in ecological service functions. Therefore, this paper selects the Fujiang River Basin (FRB) in Upper Yangtze River (UYR), and analyzes the relationship between runoff erosion power (REP) and sediment transport (ST) on the basis of analyzing the variation characteristics of hydrological elements. Based on SWAT model, a variety of scenarios are set up to quantitatively analyze the impact of different land use changes on runoff and ST and REP in the basin. The results indicated that: (1) The annual precipitation in FRB from 1960 to 2018 did not change significantly, while the annual runoff, annual ST and annual REP decreased significantly. Compared with runoff and runoff depth, the relationship between sediment transport modulus (STM) and REP is the best, especially the power function between them is better than the linear function. (2) The results of the evaluation indexes of the simulation results of the SWAT model based on the measured runoff and sediment data from 2008 to 2018 are pass and above, that is, the simulation results are considered reliable. (3) Under the five scenarios of conversion of sloping farmland to forest, conversion of dry land to paddy field and conversion of grassland to bushland and forest land, the runoff and ST in the basin decreased but the overall range was small. The simulation results of SWAT model show that the erosion of specific areas in the basin shows the greatest degree of weakening with the decrease of REP. [ABSTRACT FROM AUTHOR]

• Length dependent rill erosion processes seemed to be different on gentle slopes. • Equilibrium sediment transport was reached on the rills >7 m length under Q L. • Rolling of coarse particles affected by flow rates and rill length was evidenced. • Continuous head-cuts formation along long rills was an important affecting process. • Steady C and Dr of the 1-m-rill deviated from the Foster-Meyer conceptual model. Understanding the dynamic mechanisms of rill erosion is vital for accurately modeling of soil erosion. In this research, rill erosion was experimentally studied using different rill lengths. A flume, 11 m long and 0.2 m wide adjusted to 3% slope, was used for constructing rectangular rills of 0.05 m width and six different lengths (1 to 12 m). The experiments were carried out on a clayey calcareous soil from a semiarid region under two flow rates of Q L = 0.025 and Q H = 0.045 L s−1. Temporal sediment concentrations (C) were measured at the rill outlet for 40 min and the sediment size distribution (PSD) was recorded twice during each test. The common decreasing trend of C was affected by both flow rate and rill length. The formation of head-cuts along the bed of long rills was an important erosion process affecting C and PSD. The compiled data were used to determine the exponential models' parameters of both C and soil detachment rate based on the steady, unsteady, and event-average values. While, the equilibrium sediment transport occurred by increasing rill length beyond 7 m under Q L , the tested rills under Q H were not sufficiently long for the flow to reach its maximum transport capacity at the gentle slope used and for the calcareous soil tested. Based on the sediment PSD, the selective transport of coarse particles was evidenced. Selectivity transport was affected by rill length reached its maximum at the rill length of 7 m. The findings provides better understanding of rill erosion processes for calcareous soils on gentle slopes in semiarid regions. Further research is needed for better understanding of the rill erosion processes on short gentle slopes to provide experimentally supports for the existing theoretical concepts of rill erosion models. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Brazilian semiarid is the most densely populated dry region in the world. • Sediment source apportionment was quantified in a semiarid ephemeral catchment. • The combination of conventional and alternative tracers improved source discrimination. • Our results may gain high visibility given the climate change projections for the semiarid regions. The Brazilian semiarid is the most densely populated dry region in the world. Although climate change projections underline the need for the creation of integrated strategies to protect water resources in the semiarid, sediment source apportionment data remain scant for this environment. Accordingly, we evaluated sediment source contributions in one of the most relevant Brazilian semiarid catchments by combining geochemical and colour tracer properties. In doing so, we explored the applicability of colour tracers as a low-cost alternative to the use of time-consuming and costly properties, such as geochemical tracers. Two source classification schemes were used based on environmentally contrasting regions within the catchment (upper, middle and lower catchment parts) and land use (Caatinga biome - natural vegetation, unpaved roads, and channel banks). Suspended sediments (SS) and bed sediments (BS) were used as target sediment. A total of 660 individual source material samples were collected and composited. Geochemical and colour tracers were measured on the source and target sediment samples and used as potential fingerprints to discriminate and quantify the sediment source contributions. The geochemical tracers provided weak source discrimination based on land use. However, combining geochemical and colour tracers improved the final outputs. Using the MixSIAR model, the lower catchment contributed more sediment than the other regional sources. The Caatinga (SS = 49 %; BS = 47 %) contributed more sediment than channel banks (SS = 35 %; BS = 39 %). Overall, our results suggest that the recovery and conservation of the Caatinga vegetation and the stabilization of channel banks, especially in the lower catchment part, are critical for improving sediment supply control in the semiarid study basin. More studies are needed to evaluate the conservative behaviour of colour tracers in ephemeral rivers. [ABSTRACT FROM AUTHOR]

Mediterranean semi-arid watersheds are characterized by a climate type with long periods of drought and infrequent but high-intensity rainfalls. These factors lead to the formation of temporary flow tributaries which present flashy hydrographs with response times ranging from minutes to hours and high erosion rates with significant sediment transport. Modeling of suspended sediment concentration in such watersheds is of utmost importance due to flash flood phenomena, during which, large quantities of sediments and pollutants are carried downstream. The aim of this study is to develop a modeling framework for suspended sediment transport in a karstic watershed and assess the impact of climate change on flow, soil erosion and sediment transport in a hydrologically complex and intensively managed Mediterranean watershed. The Soil and Water Assessment Tool (SWAT) model was coupled with a karstic flow and suspended sediment model in order to simulate the hydrology and sediment yield of the karstic springs and the whole watershed. Both daily flow data (2005–2014) and monthly sediment concentration data (2011–2014) were used for model calibration. The results showed good agreement between observed and modeled values for both flow and sediment concentration. Flash flood events account for 63–70% of the annual sediment export depending on a wet or dry year. Simulation results for a set of IPCC “A1B” climate change scenarios suggested that major decreases in surface flow (69.6%) and in the flow of the springs (76.5%) take place between the 2010–2049 and 2050–2090 time periods. An assessment of the future ecological flows revealed that the frequency of minimum flow events increases over the years. The trend of surface sediment export during these periods is also decreasing (54.5%) but the difference is not statistically significant due to the variability of the sediment. On the other hand, sediment originating from the springs is not affected significantly by climate change. [ABSTRACT FROM AUTHOR]

Aeolian deposits are frequently used for palaeoenvironmental change studies. Their formation depends on an array of requirements: the supply of material suitable for aeolian transport and favorable conditions of sediment availability and wind strength. In order to infer palaeoenvironmental information from aeolian sand deposits these factors need to be carefully evaluated. We present a study from northern Chinese Hexi Corridor, based on 11 optically stimulated luminescence (OSL) dated sediment sections. These represent interchanging aeolian and alluvial deposits under gravel surfaces and aeolian sand in dune fields interrupted by interdunal flood deposits. Investigations in two subareas reveal contrasting geomorphologic and sedimentary histories: (1) sediment deposition during the Pleistocene–Holocene transition (~ 12 ka) followed by deflation during the Holocene and (2) frequent sediment recycling revealed by a wide spectrum of ages throughout the Holocene. The late glacial sediment pulse recorded in the western Hexi Corridor is attributed to high sediment supply, generated by efficient (peri-)glacial sediment production during glacial times in the adjacent Qilian Shan (< 5700 m asl) and a moisture increase inducing the reworking of those (glacio-)fluvial deposits during the Pleistocene–Holocene transition. The absence of a powerful reworking agent preserved these late glacial deposits in the western Hexi Corridor in contrast to moister eastern parts where Holocene sediment reworking prevailed. Geomorphological and hydrological preconditions of the subareas are discussed and reveal the controlling influence of fluvial processes on sand supply for the aeolian system. While a perennial drainage is missing in the drier western part, the Hei River drainage is fed by higher monsoonal precipitation in the central Hexi Corridor. It maintains a sediment recycling system and has ensured a sufficient sediment supply throughout the Holocene. The study promotes closer consideration of the fluvial influence on aeolian archives in palaeoenvironmental studies from central Asian and other drylands. [ABSTRACT FROM AUTHOR]

Coastal dunes have received growing attention in recent years because of the ecosystem services they provide and the high anthropic pressure that they have historically been subjected to and continue to endure. Such pressure especially affects arid dune fields where any changes are more noticeable due to their natural dynamics. The aim of this paper is to analyze the relationship between the degradation of an arid aeolian sedimentary system (El Médano, Tenerife, Spain) due to historical long-term land uses and its subsequent biogeomorphological evolution. The methodology combines historical sources (historical documents, aerial and common photographs and oral sources) and current ones (orthophotos, LiDAR data and field work). In order to analyze the response of the system to these uses, 8 plots were chosen in which 3 different historical land uses had resulted in the total or partial elimination of the vegetation and landforms. Biogeomorphological variables were measured on 461 nebkhas in these plots. The main results show that the historical land uses studied in this paper (aerodrome , aggregate extraction and crop cultivation) modified the entire system, with changes observed in the topography, vegetation cover and sediment availability for transport. Changes in topography and distance from shore were important factors in its recovery capacity. This research contributes to our understanding of the different aeolian sedimentary dynamics that can be detected in the same dune field (especially with nebkha landforms) and is of particular importance for making appropriate environmental management decisions to facilitate the recovery of the ecosystem. • Aggregate extractions on the foredune have an irreversible impact. • Different environmental patterns in a dunefield are responses to historical land uses. • Distance to the coast acts as a main factor in system recovery. • Historical land uses modify the natural gradients of the system. • Biogeomorphological patterns in 461 nebkhas were analyzed. [ABSTRACT FROM AUTHOR]

Aeolian sand movement contributes to evolution of surface landforms on Earth and Mars, as well as on Venus and Titan. Most natural landforms in arid regions are molded by wind with a general feature of unsteadiness. Many researches have improved our cognition of saltation in unsteady flow, but it is probably true that this issue is not yet fully analysed. In this paper, we conducted three-dimensional numerical simulations of wind-blown sand under unsteady wind conditions. The trajectories of sand particles are simulated by using a Lagrangian model. Particle motion, particle-bed interaction and wind modification have been taken into account. Results indicate that the characteristics of sand transport in unsteady and steady wind conditions profoundly differ; the sediment transport in unsteady conditions is significantly enhanced and increases with the amplitude of the sinusoidal wind fluctuations; the time series of sediment transport reveals a sine-like variation which lags behind the variation of the wind with a time delay of about 1 s (response time of saltation to wind variation). In unsteady conditions, sand transport shows an 'overshoot' which is embodied in the initial wave of the sediment transport. The impact of unsteady sediment transport should be paid more attention in future Aeolian research. Our work undertakes the key point by conducting three-dimensional numerical simulation of solid particles over unsteady wind conditions. Corresponding to different amplitudes and frequencies, the sediment transport rate reveals a sine-like variation, and the average sediment transport rate of unsteady flow is greater than that of uniform one. Unlabelled Image • 3D numerical simulations of wind-blown sand under unsteady wind are conducted in terms of LES. • Characteristics of unsteady wind have an impact on sediment transport and particle velocity. • The first wave crest of sediment transport is affected by wind period. [ABSTRACT FROM AUTHOR]