Search

Efficient mitigation of environmental loads from agricultural fields to surface waters requires sufficient knowledge of dominating erosion processes and sediment transport pathways. Computational models are often applied in sediment load assessments but their structure inherently includes assumptions and uncertainties, which can hinder their predictive and explanatory capabilities. In this study, a 3D dual-permeability model was applied with field-scale data from a high-latitude site to investigate sediment balances and structural uncertainties in sediment transport components. The two-year data encompassed hourly records of water flow and sediment concentration composite samples from tillage layer runoff and drain discharge in two adjacent clayey fields with different slopes (1% and 5%). Three model structures with different assumptions of sediment transport pathways were built to test their performance against the data. The simulations demonstrated how different model structures can reproduce the data with varying results on sediment balance. The varying results revealed the importance of flow, erosion, and sediment transport observations from the fields to improve the simulations. Structural uncertainty analysis revealed uncertainties which parameter sensitivity analysis could not describe. Concentration data was shown to include more information about erosion and sediment transport processes than solely the load data. The results suggest that a major part (48–69%) of the detached particles remained in the field and that lateral subsurface transport contributed to load generation (10–21% of total loads) especially in the steeper field. The results demonstrated that the majority (84–87%) of sediment loads occurred via subsurface drain discharge and groundwater outflow with the slope gradient of 1–5%, which suggests that load mitigation measures should also be directed to decrease loads via subsurface transport pathways. The simulations demonstrated how transport processes were controlled not only by water flow but also by soil structure. [ABSTRACT FROM AUTHOR]

• 173 papers related to ephemeral gully erosion in Web of Science were reviewed. • Critical morphological features of ephemeral gully channel were different worldwide. • Topographic, climate, land management, soil, and hydraulics factors were assessed. • Fifteen methodological approaches employed to quantify gully erosion were evaluated. • Complexity of gully channel development and driving force mechanisms were discussed. Although concern for ephemeral gully (EG) erosion has been growing within the research community, knowledge gaps still need to be identified for a state-of-the-art review. This review is based on an extensive search of published literature in the Web of Science database that specifically addressed EG erosion. This review included 173 papers published in 56 scientific journals over the last 30 years. The results indicated that the main EG erosion topics were related to gully erosion processes, factors, methodology, models, and the detrimental effects of EGs. The definition of EG was identical worldwide. There is an urgency to define critical morphological values under different conditions for identifying EG channel locations in fields in order to map and model their development quickly and accurately. Topographic factors have been much more studied than other contributing factors, including climate, land management, soil, and hydraulics. Fifteen different methodological approaches or technologies, which were categorized into four kinds of methods, including field monitoring, modelling, simulation experiments, and review, have been employed to assess and quantify EG erosion. The average soil erosion rate of EGs in 36 publications increased and decreased with increase of slope and catchment areas, respectively, and the number of EGs linearly increased with catchment area. The complexity of the development of EG channels and the driving force mechanisms should also be studied intentionally, e.g., the quantification of soil detachment and sediment transport mechanisms for both surface and subsurface flow during different sub-processes, including gully head advance, sidewall collapse and bed incision. It was concluded that the interactive effects of different contributing factors on EG erosion across various spatio-temporal scales should be further researched. The comprehensive utilization or application of new methods and technologies, e.g., automatic monitoring technologies, artificial intelligence, machine learning algorithms, would be helpful to improve study efficiency and accuracy. The scientific basis of prediction models still needs further development and refinement. This review provides recommendations and suggestions to improve knowledge, prediction, and control of EG erosion. [ABSTRACT FROM AUTHOR]

• The transition from inter-rill to rill erosion was documented using two tracers. • The technique was applied to eight cultivated hillslope soils. • Samples with highest tracer concentrations were selected for textural analysis. • Grain size of paired inter-rill and rill samples were statistically compared. • The lack of statistical consensus may reflect differences in soil properties. Understanding the extent to which textural characteristics of inter-rill and rill-eroded sediment differ across a range of agricultural soils is important in order to more accurately predict sediment transport capacities and thus increase the reliability of erosion models. However, a lack of consensus still exists over how much influence these two mechanisms exert on the physical characteristics of sediment during an erosion event. This communication reports results from a prototype tracing technique using two different artificial radionuclides to compare the grain size composition of inter-rill and rill-eroded sediment from eight different cultivated hillslope soils from southern England. A 1.0 m * 0.2 m * 0.11 m soil box was filled with soil labelled with caesium-134 (134Cs) to a depth of 0.1 m. A second layer of soil labelled with cobalt-60 (60Co) was distributed across the first soil layer, to a depth of 0.01 m, and lightly textured to replicate a fine tilth. The soil box was pitched at a ca. 17% slope (9.5°) and each soil was subjected to ca. 35 mm hr−1 of simulated rainfall until surface runoff was initiated and a rill developed. All runoff-eroded sediment was collected over 90 s intervals, dried and radiometrically assayed. Changes in radiometric signals were used to identify the transition from inter-rill to rill erosion, demarking a shift in sediment-source. Samples recording highest activity of either radionuclide were deemed to contain largest contributions of sediment mobilised by each respective erosion process and were selected for grain size analysis. Grain sizes, measured at 10 percentile intervals, were subjected to a paired-sample statistical analysis to determine whether size-difference was significant. Rill-eroded sediment was significantly coarser than inter-rill eroded sediment for four soils, whereas inter-rill eroded sediment was significantly coarser than rill-eroded sediment for one soil. There was no significant size-difference for two soils, and one soil was omitted from statistical analysis due to excessive contamination by the sub-dominant erosion process. [ABSTRACT FROM AUTHOR]

Runoff and sediment transport are distinctively three-dimensional (3D) processes and occur through overland, tillage layer and subsurface pathways. The objective was to quantify water balance and sediment concentrations in runoff waters and to assess sediment loads via surface runoff and drainflow in a clayey, subsurface drained field section using the FLUSH model. The model can simulate field scale two-dimensional overland flow and 3D unsaturated and saturated subsurface flow, including preferential flow in macropores. The erosive processes, comprised of hydraulic and raindrop splash erosion, occur in the overland domain while suspended sediment is conveyed from the field surface to subsurface drains via preferential transport in macropores in the subsurface domain. The study site, located in southern Finland, is a clayey, subsurface drained field section with an area of 12 ha and an average slope of 2.8%. The growing seasons and the following autumns of two years with distinctly different rainstorm characteristics were modelled. The simulated sediment loads via tillage layer runoff and drainflow were 85 and 117 kg ha-1, respectively in 1988, and 63 and 189 kg ha-1 in 1984. Despite the high precipitation in October 1984 (143 mm), erosion in the field area was low due to minimal surface runoff and consequently minimal hydraulic erosion. The suspended sediment at the site was generated by raindrop impacts and the eroded material was transported to the open ditch through tillage layer flow and subsurface drainflow. The model was able to reproduce the measured sediment concentrations in the main open ditch into which both tillage layer runoff and drainflow are discharged from the field. Spatially distributed erosion simulations facilitate the detection of net erosion and deposition locations in the field and could be used to design intensive measurement campaigns and guide erosion control practices in the future. [ABSTRACT FROM AUTHOR]