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• A method for 3-D river networks extraction was proposed based on multi remote sensing. • A module for recognizing and retrieving cross section morphology was established. • An improved hydrological model was developed to enhance the simulation performance. Many rivers originating from mountainous areas cannot be adequately measured in the field to obtain sufficient basic data due to the challenging terrain, which poses difficulties for conducting relevant research such as hydrodynamic and sediment transport simulations, fluvial material fluxes. This study utilized a combination of 71 river cross sections extracted from multisource remote sensing data and 34 cross sections measured by hydrological stations between 2010 and 2018 to generate generalized cross sections for all river orders in the middle reaches of the Yellow River. By integrating the generalized cross sections, river surfaces, and traditional DEM river network, a comprehensive 3-D river network has been established to provide a more accurate representation of the morphological changes along the river channel. To tackle the challenge of simulating runoff in data-deficient areas, the Digital Yellow River Integrated Model (DYRIM), a potent distributed hydrological model, was enhanced by incorporating geometric parameters derived from a 3-D river network into almost all input parameters that can be obtained from multi-source remote sensing. This enhancement enabled the model to accurately simulate runoff in representative data-deficient rivers of the Loess Plateau. The Nash Efficiency coefficients for the simulated runoff exhibited improvement of 23% compared to previous studies, surpassing 0.8 for the period between 2010 and 2018. Additionally, the simulated errors for flow velocity and water depth were 7% and 9% respectively. This approach can provide essential data for the simulation of hydrological processes and improving hydrological models, as well as technical methodologies for related research such as sediment transport simulations and river carbon emissions. [ABSTRACT FROM AUTHOR]

Highlights • This study analyzed the intensive fluctuations of runoff and sediment load at the upper Yellow River, which has not yet been studied clearly before. • Temporal variations in runoff and sediment load were discerned in terms of changing trend, abrupt change year, and multi-periods from the full measured datasets of all hydrological stations. • Impact of human activities on the hydrological variations was evaluated based on comparison of the measured and the reconstructed time series. Abstract Operations of amount of large and medium reservoirs have remarkably changed runoff and sediment loads, and consequently affected the fluvial processes intensively on the upper Yellow River. In this study, time series of runoff and sediment transport rates of four major hydrological stations on the upper Yellow River were used to analyze temporal and spatial variations of runoff and sediment loads. Mann-Kendall test and wavelet analysis were applied to analyze the datasets. Temporal variations in runoff and sediment loads were discerned in terms of changing trend, abrupt change year, and multi-periods from the time series. Additionally, a time series of runoffs was reconstructed based on a modeling scenario removing impact of reservoir impoundment and water diversion to indicate the status without human disturbances. Comparison of the measured and reconstructed datasets was conducted to evaluate the impact of reservoir impoundment and water diversion on hydrological variations. The measured runoff and sediment loads showed obvious decreasing trends due to impoundment and water diversion. However, the reconstructed runoffs regarded as only affected by climate change showed no significant changing trend at a 95% confidence level, confirming that, instead of climate change, human activities played the most important roles in variations. The measured datasets indicated that the reservoir construction and operation caused an abrupt change in runoff in 1986, while the reconstructed datasets indicated another abrupt change in 1995. Wavelet transform analysis distinguished the multi-periodical features of the time series. The first, second, and third dominant periodicities of the measured runoffs were 25–27, 16, and 8 years, respectively, whereas the first three dominant periodicities of the reconstructed runoffs were 26–31, 12, and 7 years, respectively. It was indicated that the high-frequency periodicities of runoffs decreased while the low-frequency periodicities increased, owing to reservoir impoundment and water diversion. [ABSTRACT FROM AUTHOR]

Soil and water loss from farmland causes land degradation and water pollution, thus continued efforts are needed to establish mathematical model for quantitative analysis of relevant processes and mechanisms. In this study, an approximate analytical solution has been developed for overland flow model and sediment transport model, offering a simple and effective means to predict overland flow and erosion under natural rainfall conditions. In the overland flow model, the flow regime was considered to be transitional with the value of parameter β (in the kinematic wave model) approximately two. The change rate of unit discharge with distance was assumed to be constant and equal to the runoff rate at the outlet of the plane. The excess rainfall was considered to be constant under uniform rainfall conditions. The overland flow model developed can be further applied to natural rainfall conditions by treating excess rainfall intensity as constant over a small time interval. For the sediment model, the recommended values of the runoff erosion calibration constant ( c r ) and the splash erosion calibration constant ( c f ) have been given in this study so that it is easier to use the model. These recommended values are 0.15 and 0.12, respectively. Comparisons with observed results were carried out to validate the proposed analytical solution. The results showed that the approximate analytical solution developed in this paper closely matches the observed data, thus providing an alternative method of predicting runoff generation and sediment yield, and offering a more convenient method of analyzing the quantitative relationships between variables. Furthermore, the model developed in this study can be used as a theoretical basis for developing runoff and erosion control methods. [ABSTRACT FROM AUTHOR]

• Physically based 2D hydrodynamic and sediment transport model, CCHE2D. • High resolution mesh, topography photogrammetry, experimental landform evolution. • Watershed hydrology, raindrop soil detachment, displacement, erosion and transport. • Distributed solution, tilled watershed, cornfield tillage ridge and furrow morphology. • Simulated runoff, sediment transport, landform evolution; channel network analysis. Soil and gully erosion is a critical threat to sustainable agricultural land management and productivity. Soil erosion by rain splash, sheet runoff, and concentrated flow are complex problems conditioned by the combined interactions of soil physical properties, hydrology, human activity, landscape topography, and climate. Effective management of erosion processes driven by rainfall and surface runoff requires a combined effort of field observation, physical experimentation, and numerical simulation. A physically-based hydrodynamic numerical model, CCHE2D with updated raindrop erosion effects, is applied to simulate landscape evolution processes as a result of raindrop impact and overland flow. The numerical model simulates a thin layer of runoff and concentrated flow over complex terrains, and predicts sediment transport due to raindrop splash detachment, transport and soil surface erosions. Soil erosion and landform evolution simulations due to rainfall are presented for an experimental landscape and a tilled large scale agricultural field. Photogrammetric field data were collected using an unmanned aerial system (UAS) following planting and subsequent rainstorms. Numerical simulation results agreed well with the observed experimental soil surface topography, sediment yield, and drainage network developments. The simulated soil and gully erosion in the tilled field also agreed well with observations. This research successfully demonstrates how high resolution spatial and temporal topographic measurements in experimental and field landscapes can be simulated and interrogated by 2D physically-based hydrodynamic and morphodynamic models. The accurate predictions of tillage field and gully erosion process in agriculture watersheds with complex tillage conditions also indicated the usefulness of the model for studying soil and landscape degradation. [ABSTRACT FROM AUTHOR]

• Linkage between soil surface microrelief and overland flow was examined. • Differently oriented wheel tracks served as water flow paths or as sediment sinks. • Increase of surface connectivity after a rain was shown by functional connectivity. • Structural connectivity showed reorganization of the surface runoff pathways. Although wheel tracks cover only a small portion of the surface of agricultural fields, their effect on surface runoff and sediment transport is substantial. Wheel tracks change the microrelief of the soil surface, and influence how the surface is further altered by rainfall and runoff. This study presents a plot-scale microrelief analysis of a tilled surface with wheel tracks under simulated rainfall. Digital elevation models of the microrelief with 1 cm spatial resolution were obtained using the Structure from Motion method. The random roughness, the structural connectivity, and functional connectivity were calculated for before-rainfall and after-rainfall soil surface conditions. The experiments were carried out on inclined, freshly-tilled plots (8 m long, 2 m wide). The wheel tracks were created by four passages of machinery in the slope direction (SWT) and in the contour-line direction (CWT). The experiments were compared to reference plots without wheel tracks (NWT). The wheel tracks increase water and sediment connectivity if they are oriented in slope-wise direction. Microrelief analysis shows that SWT drains water from the surrounding soil. The soil surface adjacent to SWT can also become more connected with the wheel track, due to changes in microrelief introduced by rainfall and runoff. The calculated higher connectivity in the SWT plot corresponded to the measured increased sediment loads. This suggests faster overland flow and therefore shorter flow pathways on the soil surface microrelief. CWT leads to a decrease in the water and sediment connectivity compared to the NWT and SWT plots. Although the surface runoff can overflow the CWT, the network of flow paths results in decreased flow velocity and a slower sediment transport rate. However, the CWT effect is not permanent, and declines as the wheel tracks become silted with the deposited sediment. It is shown that detailed microrelief data provide relevant information for a study of the changes in flow routing in a tilled agricultural field with the presence of a wheel track. SWT accelerates the runoff and especially the sediment transport. During a rainfall event, the hydraulic connection between the wheel track and the surrounding soil increases dramatically. CWT reduces the surface runoff and also the sediment transport. In the long term, rainfall events and surface runoff alter the microrelief connectivity, causing the soil surface to be more hydraulically connected, irrespective of the wheel track orientation. This study demonstrates the effect of wheel tracks on water and sediment transport. The results draw attention to the importance of appropriate soil protection measures, as a bare unprotected surface microrelief exposed to rainfall leads to increased sediment connectivity. [ABSTRACT FROM AUTHOR]

Summary River dynamics in cold regions and the physical processes involving ice formation and release remain relatively understudied topics. Current research suggests that anchor ice forms in diurnal cycles and has the potential to move sediments when released from the bed. Given the importance of river ice dynamics, studies are needed to describe the physical processes of anchor ice and its impact on sediment transport. The study presented in this paper investigated in situ anchor ice formation on the Stoke River in Quebec, Canada. In the fall of 2012, we observed multi-day anchor ice formation cycles and release, which usually ended with a small runoff event. During a cycle, there was little or no release of anchor ice, thus allowing its gradual growth as the air temperature remained cold. Surface and anchor ice layers also often merged, leading to the formation of thick ice masses. Sediment transport was monitored using bed particles individually tagged with passive integrated transponders (PIT-tags). Movement of the experimental particles, measured after each multi-day cycle event, ranged from 0.5 to 4 m. Possible transport mechanisms include: (1) anchor ice rafting, (2) ice jam breakup creating a jave with high erosive capacity, (3) flow corridors through anchor ice masses with high erosive capacity, (4) mechanical pushing of particles by drifting ice blocks during ice breakup, and (5) entrainment by flow or drifting ice blocks of anchored ice with strong ice-pebble bonds. Given the coincidental occurrence of anchor ice release and runoff events, it is uncertain which specific mechanism caused the particles to move. This study is a step forward in understanding the behavior of anchor ice processes and ice-related sediment transport. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sediment particles were trapped by grassed filter strip. [•] Synthetic stormwater runoff was made from construction site. [•] The empirical equations were developed from experimental data. [•] The use of the equations can predict the efficiency of sediment traps. [•] New approaches have been proposed to investigate flow and sediment transport. [ABSTRACT FROM AUTHOR]

• This paper presents new data on the intensity fluctuations in natural rainfall. • Literature review demonstrates the importance of intensity profile to rainfall simulation research. • The origin and landsurface process relevance of intensity profile are reviewed. • Recommendations are suggested that could enhance the utility of rainfall simulation research. The temporal sequence of fluctuating rainfall intensities during an event - the intensity profile or 'rainfall pattern' - is known to affect water partitioning at the ground surface and associated erosional processes. There can be large differences in runoff ratios and runoff rates between early-peak and late-peak events, and hence in the depth, speed, and sediment transport capacity of resulting overland flow. Whilst rainfall intensity may fluctuate continually during all IPs in natural rainfall, there is little information on the rates of such intensity fluctuations that can be used to guide the design of rainfall simulation experiments. This review analyses relevant data derived from published high-resolution rainfall records and also from new analyses of data from Australian ground observing stations. Both sources confirm the occurrence of rates of intensity change of greater than 500 mm h−1 min−1. It is suggested that the fluctuating intensities characteristic of natural rainfall need to be employed in rainfall simulation experiments in order to generate results applicable to natural landsurface processes like infiltration or soil removal. Constant-intensity rain, as commonly used in rainfall simulation experiments, lacks both the kinds of rapid intensity fluctuations seen in natural rainfall, as well as any representation of natural intensity profiles. These unrepresentative conditions can result in lower runoff rates and larger proportions of infiltration than when intensity fluctuations are present. There is thus a strong case for changing the design of rainfall simulation to reflect more closely natural intensity fluctuations and intensity profiles and their influence on key surface processes such as overland flow and soil erosion. [ABSTRACT FROM AUTHOR]

Summary: Under the influence of climate and human activities, fluvial systems have natural ability to make adjustments so that the river hydrology, sediment movement, and channel morphology are in dynamic equilibrium. Taking the Changjiang (Yangtze River) for example. In the early stages after the Three Gorges Dam (TGD) began operational ten years ago, the suspended sediment content (SSC) and fluxes in the middle and lower reaches of the river decreased noticeably. At present, they appear to be in a stable state on the decadal scale. Although the river runoff has not shown any trends, the water level in the river decreased appreciably in time. In the meantime, channel down cutting along the thalweg almost existed throughout the river course. The riverbed has turned from depositional before the dam construction to erosional afterwards. In other words, the riverbed had turned from being sediment sinks to sediment sources. In the main channel of the Changjiang between Yichang and Nanjing, a distance of 1300km, the riverbed sedimentation mode displays strong, intermediate, and weak erosion depending on the closeness to the TGD. [ABSTRACT FROM AUTHOR]

Summary: The impact of rainfall characteristics on runoff generation and soil erosion are not fully understood despite their importance. In this study, a series of laboratory experiments, systematically considering different rainfall intensities, durations, moving directions, rainfall positions, and no-rainfall intervals, were conducted to investigate the impacts of rainfall characteristics on runoff generation and soil erosion. Significant differences, including hydrograph, sediment graph, soil water content, and infiltration depth (depth of wetting front), were observed. The following conclusions are drawn for the studied rainfall characteristics and soil from this study: (1) when compared with moving upstream rainfall scenarios (MURSs), moving downstream rainfall scenarios (MDRSs) can generally be characterized by hydrographs with a later rise and higher runoff peak for most of the rainfall events; (2) surface sealing changes the infiltration pattern so that MURS generally produce more total runoff than MDRS, and for some rainfall events MDRS generate lower runoff peak than MURS, which is different from what has been widely reported; (3) with the increase in the runoff peak, the erosion peak increases first and then decreases, indicating a switch from transport-limited erosion to detachment-limited erosion; (4) the increase ratio of underground water content for MURS is lower than MDRS; (5) rainfall duration is an important factor in soil crack occurrence. Not only does this study expand the understanding of hydrologic response and erosion, it also provides an important database for the hydrology community. [Copyright &y& Elsevier]

Summary: The Universal Soil Loss Equation (USLE) is the most widely used and misused prediction equation in the world. Although it was designed to predict long-term average annual soil loss, it has the capacity to predict event soil losses reasonably well at some geographic locations and not well at others. Its lack of capacity to predict event erosion is highly influenced by the fact the event rainfall–runoff factor used in the USLE and its revisions (RUSLE, RUSLE2) does not consider runoff explicitly. While including direct consideration of runoff in the event rainfall–runoff factor improves the capacity to predict event erosion when runoff is measured, that capacity is reduced by inaccurate runoff prediction methods. Even so, the predictions may be better than when the traditional event rainfall–runoff factor is used if the rainfall–runoff model used to predict runoff works reasonably well. Direct consideration of runoff in the rainfall–runoff factor may improve the ability of the model to account for seasonal effects. It also enhances the ability of the model to account for the spatial variations in soil loss on hillslopes which result from spatial variations in soil and vegetation. However, the USLE model will not provide a capacity to account for deposition taking place on concave hillslopes unless it is coupled with an appropriate sediment transport model, as in done in RUSLE2. Changing the basis of the event rainfall–runoff factor has consequences on a number of the other factors used in the model, in particular new values of the soil erodibility factor need to be determined. Using runoff values from cropped areas is necessary to account for differences in infiltration capacities between vegetated and tilled bare fallow areas, but requires re-evaluation of the crop factors. [Copyright &y& Elsevier]

• Frequency analysis and wavelet reconstruction techniques are suitable for the analysis of non-linear and non-stationary processes of badlands catchments. • Intra-annual and annual time scales are led by climatological characteristics of the catchment site. • Multi-year sediment yield response is linked with the intrinsic sediment storage/depletion cycle of the catchment. A long-term database with information on precipitation, discharge and sediment yield dynamics was analyzed to characterize the temporal structure response of a catchment in a humid mountain badland area. Due to the non-linearity and non-stationary nature of the data, a combination of frequency analysis and wavelet reconstruction techniques were initially used to determine the dominant time scales of the precipitation, discharge and sediment yield. Within the full spectrum of time scales, the spectral frequency analysis could distinguish the dominant ones governing the overall trend of the time-series. Furthermore, the temporal multiresolution wavelet technique enabled accurate de-noising of the hydrometric and sediment time-series, by filtering out the high frequency intermittent processes superimposed on the main signal. Geomorphological metrics were subsequently applied to the filtered data and link to the temporal structure of the catchment response. The combined frequency-geomorphological analysis provides a physical explanation of the complete temporal structure of the catchment response to precipitation. This analysis features components from intra-annual, annual and multi-year scales. Intra-annual and annual time scales are led by climatological characteristics of the catchment site (seasonal rainfall patterns of a mountain Pyrenean catchment). The multi-year response related to the sediment yield reveals the importance of the sediment storage/depletion cycle in the catchment: although the main driver of the sediment yield is the discharge, weathering processes and sediment storage are also major control factors. Therefore, correct management of the catchment requires the combined multi-temporal response of water and sediment fluxes to be controlled. The temporal spectral analysis herein outlined provides a detailed analysis of the long-term temporal structure of databases and can be accepted as an adequate tool for catchment management in terms of flood forecasting or reservoir operation. [ABSTRACT FROM AUTHOR]