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The study evaluated climate change impact on water flows and nutrient loads to surface water bodies in Lithuania by applying the SWAT model. Seven RCM and GCM combinations were selected and RCP4.5 and RCP8.5 climate change representative concentration pathways were selected for the study. The study concluded that an annual and winter increase in most river water flows are expected. The change will be driven by rising precipitation, mainly in the regions where it is already high. Less snow would result in less surface runoff, substituted by increased lateral and groundwater flows because of more water percolating through the soils. As a result, water flows could be expected to increase by 9.7% for RCP4.5 and by 35.4% for the RCP8.5 climate scenario by the end-century. Whereas sediment transport and phosphorus loads would tend to decline a little bit (median results are -11.4% and -5.6% respectively for the RCP4.5 scenario, -13.3% and -7.4% for the RCP8.5 by the end of century). Conversely, temperature driven nutrient mineralization and increased leaching are expected to cause a significant increase in nitrogen loads (by 23.1% for the RCP4.5 scenario and by 64.4% for the RCP8.5 by the end of century). Overall, it could be concluded that climate change related hydrometeorological and water quality changes were found to be the most profound for the end-century RCP8.5 climate change scenario. [ABSTRACT FROM AUTHOR]

Above average precipitation from October 2018 through July 2019 in the Maumee River (R.) Basin resulted in 29% of cropland left fallow, providing a glimpse of potential effects from decreased nutrient application. Ongoing monitoring at 15 water-quality sites on the Maumee R. upstream from Defiance enabled comparison with 2017, which was hydrologically similar to 2019 in precipitation and streamflow. In 2019, nitrate (as nitrogen; NO 3 -N) for March-July was significantly less than previous years (2015–2018), but the response for phosphorus (P) was more complicated. Relative to 2017, total P (TP) was lower at 7 of 15 sites, but higher at 7, reflecting higher suspended sediment (SS). Dissolved P (DP) was generally lower, but less different than NO 3 ; DP was higher at 3 sites. DP-P:NO 3 -N was generally higher in 2019, DP-P:TP was lower, and there was less TP relative to SS. Overall, less P was in the system in 2019. However smaller streams showed a large range of difference between 2019 and 2017 for all constituents, indicating variability in land management and physiography. In contrast, all constituents were lower in 2019 in larger (>5000 km2) streams, including the Maumee R. near Defiance, where the difference in NO 3 (−37%) exceeded that for TP (−16%), DP (−10%), and SS (−20%). Differences in these relations among N, P, and SS indicate that P was available from legacy sources that are more difficult to distinguish during typical agricultural production years and that some material from 2019 was stored in the system upstream from the largest sites. [ABSTRACT FROM AUTHOR]

Since the 1950s, Moenkopi Wash, in Arizona, United States, has been transformed from a relatively wide river with little riparian vegetation, to a narrow, heavily vegetated river that is less than half of its former width. We analyzed a ∼95-years-long instantaneous-discharge record, an extensive sediment-transport record, oblique and aerial photographs, historical channel surveys, and historical stage-discharge rating relations to determine the primary mechanisms responsible for this transformation. Frequent, large floods dominated the early part of the discharge record between 1926 and 1940. A dramatic ∼30 % decrease in annual mean discharge, and ∼27 % decrease in the mean of the partial-duration flood series occurred in 1941. This decline did not result in widespread channel change but provided an opportunity for vegetation to establish along the channel margins. Widespread channel narrowing began after a second decline in mean and peak discharge in 1956 at which time the channel banks became heavily vegetated. Between 1952 and 2019, the river channel narrowed by 57–59 %. Approximately 2–4 m of bed aggradation occurred at most study sites. As the channel narrowed and became more vegetated, large floods maintained the narrower channel width but did not cause rewidening. Suspended-sediment transport data illustrate the sediment trapping effects of vegetation that lead to channel narrowing; suspended-sand concentrations decline, thereby indicating sediment deposition, as vegetation becomes progressively inundated during floods. Furthermore, dense channel-margin and floodplain vegetation provide increased roughness, resulting in flood-peak attenuation and alteration of hydrograph shape. Vegetation expansion causes positive feedbacks whereby sediment deposition during floods is exacerbated by the roughness and sediment-trapping effects of vegetation leading to further narrowing. These positive feedbacks have reduced sediment delivery to the Little Colorado River downstream. Channel widening is not likely to occur unless there are very large floods that exceed the erosional threshold of the channel-margin vegetation, or unless large-scale vegetation removal efforts are undertaken. • Vegetation plays a stronger role than hydrology alone in causing channel change. • Channel change was caused by biogeomorphic feedbacks associated with vegetation. • Channel narrowing began as vegetation trapped sediment during a low flow period. • Biogeomorphic feedbacks caused flood attenuation and reduced flood-peak discharge. • Biogeomorphic feedbacks reduced sediment delivery to downstream rivers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Climate and human contributions to NPP were 62% and 38% in Loess Plateau. • Precipitation contributed to NPP much than temperature in 2000–2020. • The feedback of GTGP to NPP and climate was higher in second decade. • GTGP brings environmental benefits (river sediment, PM 2.5 , dust weather). Net primary productivity (NPP) has been the subject of numerous studies, but the qualitative and comparative study on NPP that considers human activities, climate change, and their interactions is still insufficient. The Grain for Green Program (GTGP) was established in the Loess Plateau since 1999, could be used as a reference study. The temporal and spatial patterns, change trend, and driving factors of vegetation NPP were analysed in Loess Plateau using data derived from GLASS NPP (the Global Land Surface Satellite Product), meteorology, atmospheric quality, hydrology and land use by correlation and improved residual trend analysis from 2000 to 2020. After GTGP implementation, the climate and human contributions to vegetation NPP were 62 % and 38 %. NPP increased at a rate of 6.3 g C m−2 a−1 from 2000 to 2020, which was higher in 2010–2020 (6.9 g C m−2 a−1) than it was in 2000–2010 (5.7 g C m−2 a−1). The same trend was followed by the contribution of climate change to NPP between 2010 and 2020 (70.6 %) and 2000–2010 (65 %). The GTGP core area was mostly where the vegetation NPP rising zone was located. From the original bare land in the desert area, 4442 km2 of vegetation grew and increased the NPP (68.7 g C m−2). Under the warm–humid climatic trend, the climate factors contributed to NPP more in grasslands (40 %) compared to woodlands (29 %) and precipitation (33 %) was more sensitive than temperature (12.7 %). Consequently, sediment transport, PM 2.5 and dusty weather decreased significantly. In conclusion, although climate change has a greater impact on vegetation, human activities have enhanced the impact faster in the first decade, which benefit and profit from the environment finally. [ABSTRACT FROM AUTHOR]

The MARSSIM landform evolution model has been used successfully over the past three decades to simulate sediment transport on the surface of Mars. The model relies on an advection–diffusion relation that has been used to describe the difference in scale efficiency and profile concavity in landscapes. Beyond this, MARSSIM has also been used to simulate groundwater flow, eolian transport, and impact cratering. We first describe the history of the model in the published literature, followed by an in-depth analysis of the physical theory on which it is based. We review the successes and limitations of the current model and how these have been addressed. Other parts of the model included in the source code have been rarely used, so we also investigate new applications in these areas. Finally, we propose a modification to the model that would allow for an integrated system of precipitation, infiltration, and groundwater flow, and provide a practical example on a simulated cratered terrain similar to those found in past MARSSIM studies. We find that the introduction of an integrated model has noticeable effects on erosion patterns within the simulation domain compared to cases of either complete infiltration or complete runoff. • MARSSIM is a powerful computational tool for understanding early Mars hydrology. • Model parameterizes an advection–diffusion relation to simulate sediment transport. • Modification of current model allows groundwater infiltration from runoff. • Addition of infiltration represents distinct landform evolution scenario for Mars. [ABSTRACT FROM AUTHOR]

Abstract The paper focuses on the generation of floods as a principal soil threat and on soil erosion as an additional soil threat on arable lands of hillslope areas. As the most important component of floods causing the degradation of soils on arable lands, surface runoff is analysed in this study. The protective effect of crop management on the generation of surface runoff and sediment transport on arable lands is estimated on a plot and slope scale. The site of the case study, which is located in the Myjava river basin in western Slovakia, is a hilly agricultural field with an area of 29 ha; it is characterised by arable soil, extreme erosion processes, and muddy floods. Field rainfall simulation experiments were combined with physically-based modelling for studying the formation of surface runoff under various soil covers. The field experiments consisted of simulating runoff generation from artificial rainfalls using the Eijkelkamp rainfall simulator on experimental plots with a focus on estimating the volume of surface runoff, the mass of sediments transported by the surface runoff, and the time to runoff. The volumes of the surface runoff and the values of the time to runoff have been applied in the parameterisation of the SMODERP physically-based hydrological model. The hydrological modelling of the surface runoff on the selected slope profile quantified the protective effect of various soil covers on reducing surface runoff. The outcome of the modelling was the maximum allowed lengths of the slope that represent the crucial values for flood and erosion control. When exceeding these critical values, protective measures, e.g., vegetation strips, should be proposed. Highlights • Protective effect of soil cover on surface runoff on an arable land was studied. • Results of field rainfall simulations were limited; small plot and temporal scale. • 1D - hydrological model was parametrised on the basis of plot measurements. • Winter crop has a high effect on reduction of surface runoff on a hilly arable land. • Higher reduction of surface runoff was evident in the case of lower design rainfall. [ABSTRACT FROM AUTHOR]

In this paper, we examine the effect of vegetation on soil erosion, runoff generation and sediment transport on saline rangeland hillslopes. Rainfall simulations were conducted at a fixed 114 mm/h intensity on 6 m × 2 m erosion plots with varying degrees of vegetation. Plots were grouped into three categories (L, M and H) based on their canopy cover (L: <5%, M: 5–19%, H: >19%) and selected to limit variations in slope across canopy cover groups. Runoff and sediment samples were combined with three dimensional (3D) reconstruction data used to monitor soil surface microtopographic changes. Runoff initiation was significantly delayed on the L plots but cumulative runoff after 20 min of rainfall simulation indicated a positive effect of vegetation on infiltration processes. Cumulative sediment after 20 min of rainfall was similar across vegetation cover categories. The 3D data suggest that vegetation reduced net sediment delivery from the plots by primarily increasing opportunities for deposition while marginally affecting gross soil erosion. Plots with H vegetation cover experienced lower 3D-estimated erosion volumes but average erosion depth on L plots was lower than that on plots with M and H vegetation covers. Lower runoff volumes on M and H plots may have been compensated by greater runoff erosivity on these plots as runoff was concentrated in a narrower inter-patch space compared to L plots. This study highlights the need for an increased integration between traditional runoff measurement techniques and 3D reconstruction methods. [ABSTRACT FROM AUTHOR]

Hydromorphology is a matter of water and sediment. This constitutes the study of hydrological processes, as well as of the soil and streambed erosion processes imperative. This study presents two different models aiming at continuous simulations of hydromorphological processes at the basin scale. The first model is a Composite Mathematical Model (CMM), consisting of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a stream sediment transport submodel. The second model is the GIS version of the Soil and Water Assessment Tool, SWAT. The application of both models results to continuous hydrographs and sediment graphs at the basin outlet. The computed stream discharge and sediment discharge values are compared with field measurements and both models are evaluated, as to their competence of simulating the hydromorphological processes in a basin. The novelty of this research primarily lies in the fact that different ways for producing continuous sediment graphs, are presented. This can be achieved at any stream segment and provides a continuous assessment of the sediment discharge. Additionally, the application of all models is performed at an hourly time step, for long periods of time. This imparts high precision and detail to the hydromorphological study of a basin at the temporal scale. Sediment discharge is a highly nonlinear physical procedure and high levels of disaggregation (subdaily to hourly time steps) incorporate a very high degree of nonlinearity, especially in flooding periods. In this respect, this research highlights the importance of calculating sediment discharge at fine time scales and offers different methodologies to achieve it. Several statistic efficiency criteria were used to evaluate the models' efficiency to simulate the aforementioned processes. As far as the evaluation of CMM is concerned, values for Nash-Sutcliffe Efficiency (NSE), determination coefficient (r 2 ) and Percent BIAS (PBIAS) amount to 0.974, 0.985 and − 10.344, respectively, for water discharge, and 0.647, 0.660 and 12.371, for sediment discharge, whilst regarding the evaluation of SWAT the corresponding values for NSE, r 2 and PBIAS are 0.978, 0.981 and − 5.104, for water discharge, and 0.593, 0.664 and − 37.155, for sediment discharge. It is considered that the efficiency criteria provide satisfying results. [ABSTRACT FROM AUTHOR]

The Colorado River delta is a dramatically transformed landscape. Major changes to river hydrology and morpho-dynamics began following completion of Hoover Dam in 1936. Today, the Colorado River has an intermittent and/or ephemeral channel in much of its former delta. Initial incision of the river channel in the upstream ∼50 km of the delta occurred in the early 1940s in response to spillway releases from Hoover Dam under conditions of drastically reduced sediment supply. A period of relative quiescence followed, until the filling of upstream reservoirs precipitated a resurgence of flows to the delta in the 1980s and 1990s. Flow releases during extreme upper basin snowmelt in the 1980s, flood flows from the Gila River basin in 1993, and a series of ever-decreasing peak flows in the late 1990s and early 2000s further incised the upstream channel and caused considerable channel migration throughout the river corridor. These variable magnitude post-dam floods shaped the modern river geomorphology. In 2014, an experimental pulse-flow release aimed at rejuvenating the riparian ecosystem and understanding hydrologic dynamics flowed more than 100 km through the length of the delta’s river corridor. This small artificial flood caused localized meter-scale scour and fill of the streambed, but did not cause further incision or significant bank erosion because of its small magnitude. Suspended-sand-transport rates were initially relatively high immediately downstream from the Morelos Dam release point, but decreasing discharge from infiltration losses combined with channel widening downstream caused a rapid downstream reduction in suspended-sand-transport rates. A zone of enhanced transport occurred downstream from the southern U.S.-Mexico border where gradient increased, but effectively no geomorphic change occurred beyond a point 65 km downstream from Morelos Dam. Thus, while the pulse flow connected with the modern estuary, deltaic sedimentary processes were not restored, and relatively few new open surfaces were created for establishment of native riparian vegetation. Because water in the Colorado River basin is completely allocated, exceptional floods from the Gila River basin are the most likely mechanism for major changes to delta geomorphology for the foreseeable future. [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]

This paper developed an automatic mesh generator used for simulating real-world problems of hydrological cycles, fluid flow, salinity and thermal transport, sediment and water quality transport, etc. The 2-D overland area was discretized with quadrilaterals based on conformal mapping technique. A position-percent interpolation equation was established to determine nodal vertical-coordinates and match boundaries. For 3-D simulations of subsurface zones, an additional mesh generation method was proposed to create quadrilaterals for filling the empty regions along river reaches and around junctions with storage, ponds or lakes. In order to deal with special storage region with an odd number of boundary nodes, an additional triangle was inserted. Five topological optimization templates were proposed to improve the quality of degenerated elements. This paper proposed the basic algorithms to generate quadrilateral-prism meshes through stretching the quadrilateral mesh along vertical directions based on material domains. Aiming at four types of fractures, corresponding extraction methods were presented to preserve geometric features. In order to accommodate the need for overland and subsurface simulations, 1-D/2-D/3-D correspondence was established between rivers, junctions, ponds, lakes, control structures and finite element meshes. Finally, several realistic hydrologic and geologic examples for meshing multi-domain areas were provided to demonstrate the accuracy and effectiveness of the mesh generator developed in this paper. [ABSTRACT FROM AUTHOR]

The transfer of sediments through the landscape (sediment connectivity) depends on hydrological conditions. This study aimed at assessing changes in sediment sources engendered under extreme drought. A sediment budget model that considered hillslope sediment connectivity was applied to the Latrobe River catchment (South-east Australia) in a relatively normal period (1990–1996) followed by part of the ‘Millennium Drought’ (1997–2005). Bayesian inference was applied to optimize monthly streamflow and calibrate sediment parameters against mean annual specific sediment yields at ten monitoring stations. In 1990–1996, assessed sediment yield at the outlet was 68 kt/y; 60% of sediments originated from net hillslope erosion and 40% from streambank erosion. In 1997–2005, sediment yield decreased to 13 kt/y, 27% from net hillslope erosion against 65% from streambank erosion. During the drought, both hillslope gross erosion and hillslope sediment connectivity decreased dramatically. Streambank protection is of the utmost importance under all hydrologic conditions and especially during drought periods. [ABSTRACT FROM AUTHOR]

Despite the increased sophistication of numerical models and field techniques for investigating wave-induced nearshore sediment transport and ensuing beach morphological response, there remains a significant demand for large-scale laboratory experiments to address this research topic. Here, we describe the Barrier Dynamics II Experiment ( BARDEX II ), which involved placing a near prototype-scale sandy barrier in the middle of the Delta Flume in the Netherlands and subjecting the structure to a range of wave, tide, and water level conditions. A unique aspect of the experiment was the presence of a lagoon behind the barrier, as often occurs in natural barrier settings, providing a convenient means to experimentally manipulate the groundwater hydrology within the barrier. The overall aim of the BARDEX II was to collect a large-scale data set of energetic waves acting on a sandy beach/barrier system to improve our quantitative understanding and modeling capability of shallow water sediment transport processes in the inner surf, swash, and overwash zone. In this paper, we introduce BARDEX II and provide a detailed description of the experiment, including the experimental design, instrumentation, test program, and data set, as well as presenting some examples of the morphological and hydrodynamic data set. We also reflect objectively on the strengths and weaknesses of the data set. This paper serves as an introduction to a special issue of Coastal Engineering , solely devoted to the results of BARDEX II . [ABSTRACT FROM AUTHOR]

A dynamic landscape evolution modelling platform (CLiDE) is presented that allows a variety of Earth system interactions to be explored under differing environmental forcing factors. Representation of distributed surface and subsurface hydrology within CLiDE is suited to simulation at sub-annual to centennial time-scales. In this study the hydrological components of CLiDE are evaluated against analytical solutions and recorded datasets. The impact of differing groundwater regimes on sediment discharge is examined for a simple, idealised catchment, Sediment discharge is found to be a function of the evolving catchment morphology. Application of CLiDE to the upper Eden Valley catchment, UK, suggests the addition of baseflow-return from groundwater into the fluvial system modifies the total catchment sediment discharge and the spatio-temporal distribution of sediment fluxes during storm events. The occurrence of a storm following a period of appreciable antecedent rainfall is found to increase simulated sediment fluxes. [ABSTRACT FROM AUTHOR]

Summary Sediment concentration ( SC )–water discharge ( Q ) relations in rivers are typically governed by multiple and relatively complex processes. Due to hysteresis effects, sediment discharges can differ for similar or equivalent water discharges, which causes scatter in empirical datasets and may decrease the predictive power of SC rating curves. Such hysteresis effects must therefore be understood and accounted for to make dependable predictions for river system management. The overall objectives of this study are to develop modelling approaches suitable for reproducing and predicting hysteresis effects at larger scales and to investigate the possible contribution of in-channel processes (erosion and deposition) to sediment concentration hysteresis loops. To investigate relevant field-scale conditions, we develop a one-dimensional dynamic sediment transport model of the downstream Tuul River (northern Mongolia), investigating in-channel processes along a 141 km stretch during a hydrological year. The results show that the present modelling approach can reproduce both anti-clockwise and clockwise hysteresis effects. Importantly, in-channel processes alone can cause considerable anti-clockwise hysteresis effects without being reinforced by catchment processes such as hillslope erosion. Such specific contributions from in-channel processes introduced data scatter into the sediment rating curves, decreasing their R 2 -values from unity to approximately 0.5 to 0.6. More generally, possible changes in the number or magnitude of high-flow events, caused by climatic or other anthropogenic factors, could influence total sediment deposition, which was primarily found to occur during relatively short high-flow events. Such potential changes also have important implications for the possible spreading of polluted sediments. [ABSTRACT FROM AUTHOR]

An important part of planning for the rehabilitation of a mine site is the design of stable final landforms for waste rock dumps or spoil piles. Whilst able to be assessed over the short-term (years to decades), the longer term behaviour (centuries to millennia) of such landscapes is not within any meaningful human time frame of observation. Predictive numerical models, therefore, form an important tool with which current landscape behaviour and longer term trajectory can be assessed. However, an important issue associated with the use of models is the ability to assess the reliability and accuracy of the model. Here the SIBERIA and CAESAR-Lisflood Landscape Evolution Models (LEMs) are used to simulate and assess the geomorphic stability of a conceptual rehabilitated landform of the Ranger uranium mine in the Northern Territory, Australia, for a simulated period of up to 1000 years. Utilising both models in this study enabled an independent assessment of likely landscape processes and evolution as well as each model. Results show that SIBERIA and CAESAR-Lisflood produce erosion rates and patterns that are broadly similar. At millennial time scales, short-term processes such as gullying appear to be the dominant erosion features in the proposed landforms and may produce substantial erosion in terms of size and amount of hillslope material eroded and transported downslope. Vegetation was found to have a major effect on the erosion potential of the landform surface. Overall both models produce very similar results. [ABSTRACT FROM AUTHOR]

The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in March 2011 resulted in the deposition of large quantities of radionuclides, such as 134 Cs and 137 Cs, over parts of eastern Japan. Since then high levels of radioactive contamination have been detected in large areas, including forests, agricultural land, and residential areas. Due to the strong adsorption capability of radiocesium to soil particles, radiocesium migrates with eroded sediments, follows the surface flow paths, and is delivered to more populated downstream regions and eventually to the Pacific Ocean. It is therefore important to understand the transport of contaminated sediments in the hydrological system and to predict changes in the spatial distribution of radiocesium concentrations by taking the land-surface processes related to sediment migration into consideration. In this study, we developed a distributed model to simulate the transport of water and contaminated sediment in a watershed hydrological system, and applied this model to a partially forested mountain catchment located in an area highly contaminated by the radioactive fallout. Observed discharge, sediment concentration, and cesium concentration measured from June 2011 until December 2012 were used for calibration of model parameters. The simulated discharge and sediment concentration both agreed well with observed values, while the cesium concentration was underestimated in the initial period following the accident. This result suggests that the leaching of radiocesium from the forest canopy, which was not considered in the model, played a significant role in its transport from the catchment. Based on the simulation results, we quantified the long-term fate of radiocesium over the study area and estimated that the effective half-life of 137 Cs deposited in the study area will be approximately 22 y due to the export of contaminated sediment by land-surface processes, and the amount of 137 Cs remaining in the catchment will be reduced to 39% of the initial total within 30 y after contamination. This study provides a perspective on the transport of suspended sediments and radiocesium in catchments with similar land use and radiocesium contamination. [ABSTRACT FROM AUTHOR]

Tropical river systems, wherein much of the drainage basin experiences tropical climate are strongly influenced by the annual and inter-annual variations of the Inter-tropical Convergence Zone (ITCZ) and its derivative monsoonal winds. Rivers draining rainforests and those subjected to tropical monsoons typically demonstrate high runoff, but with notable exceptions. High rainfall intensities from burst weather events are common in the tropics. The release of rain-forming aerosols also appears to uniquely increase regional rainfall, but its geomorphic manifestation is hard to detect. Compared to other more temperate river systems, climate-driven tropical rivers do not appear to transport a disproportionate amount of particulate load to the world's oceans, and their warmer, less viscous waters are less competent. Tropical biogeochemical environments do appear to influence the sedimentary environment. Multiple-year hydrographs reveal that seasonality is a dominant feature of most tropical rivers, but the rivers of Papua New Guinea are somewhat unique being less seasonally modulated. Modeled riverine suspended sediment flux through global catchments is used in conjunction with observational data for 35 tropical basins to highlight key basin scaling relationships. A 50 year, daily model simulation illuminates how precipitation, relief, lithology and drainage basin area affect sediment load, yield and concentration. Local sediment yield within the Amazon is highest near the Andes, but decreases towards the ocean as the river's discharge is diluted by water influxes from sediment-deprived rainforest tributaries. Bedload is strongly affected by the hydraulic gradient and discharge, and the interplay of these two parameters predicts foci of net bedload deposition or erosion. Rivers of the tropics have comparatively low inter-annual variation in sediment yield. [ABSTRACT FROM AUTHOR]

Effective discharge ( Q e ) for suspended sediment transport in the alluvial reaches of the Ganga River in the western Ganga plains (WGP) has been computed using ‘analytical’ and an alternative ‘magnitude–frequency’ approach. Thirty years of mean monthly discharge data from various sites of the Ganga River have been assessed, and the abundance of discharge occurrence has been determined. Our analysis shows that less than 40% of the flow causes effective sediment transport in the Ganga, and this can be considered as the effective discharge for suspended sediment transport. Alternatively, 50% of the sediment load for all studied sites is moved by a discharge varying between 14 and 40% of the total discharge. Effective discharges calculated over the period of record are well below the bankfull discharges ( Q b ). A few events are close to the bankfull level, but with a high return period (RI > 40 years), and therefore, not effective to transport most of the available sediments. Our computation shows that the mean annual discharge (RI = 2.33 yrs) can transport only 0 to 10% of the total available sediments. The computation of effective discharge also provided important insights to understand the linkage between hydrology and channel morphology. Sediment storage and removal processes, which are reflected in sediment budget, cause changes in cross-sectional area/channel bathymetry at various sites but the channel margins are not affected. A high ratio of bankfull to effective discharge ( Q b / Q e ) forces the flow lines to be concentrated to the thalweg position and channels are incised. Our study also implies that incision and aggradation of the river valley during a relatively long period are caused by changes in effective discharge. We argue that the valley incision and filling episodes in the western Ganga plains at Late Quaternary timescales in response to monsoonal fluctuations were primarily affected by changes in the effective discharges of the rivers. [ABSTRACT FROM AUTHOR]

Sediment-discharge hysteresis loops are frequently analyzed to facilitate the understanding of sediment transport processes. Hysteresis patterns, however, are often complex and their interpretation can be complicated. Particularly, quantifying hysteresis patterns remains a problematic issue. Moreover, it is currently unknown how much data is required for analyzing sediment-discharge hysteresis loops in a given area. These open questions and challenges motivated us to develop a new method for quantifying suspended-sediment hysteresis. Subsequently, we applied the new hysteresis index to three suspended-sediment and discharge datasets from a small tropical rainforest catchment. The datasets comprised a different number of events and sampling sites. Our analyses show three main findings: (1) datasets restricted to only few events, which is typical for rapid assessment surveys, were always sufficient to identify the dominating hysteresis pattern in our research area. Furthermore, some of these small datasets contained multiple-peak events that allowed identifying intra-event exhaustion effects and hence, limitations in sediment supply. (2) Datasets comprising complete hydrological years were particularly useful for analyzing seasonal dynamics of hysteresis. These analyses revealed an exhaustion of hysteresis on the inter-event scale which also points to a limited sediment supply. (3) Datasets comprising measurements from two consecutive gauges installed at the catchment outlet and on a slope within that catchment allowed analyzing the change of hysteresis patterns along the flowpath. On the slope, multiple-peak events showed a stronger intra-event exhaustion of hysteresis than at the catchment outlet. Furthermore, exhaustion of hysteresis on the inter-event scale was not evident on the slope but occurred at the catchment outlet. Our results indicate that even small sediment datasets can provide valuable insights into sediment transport processes of small catchments. Furthermore, our results may serve as a first guideline on what to expect from an analysis of hysteresis patterns for datasets of varying quality and quantity. [ABSTRACT FROM AUTHOR]

Abstract: To better understand instream suspended sediment delivery and transformation processes, we conducted field measurements and laboratory experiments to study the natural function of spatial and temporal variation, sediment particles, stable isotopes, particle size, and aspect ratio from tributary to mainstream flows of the Sukhaya Elizovskaya River catchment at the beginning of and during snowmelt. The Sukhaya Elizovskaya River is located in the Kamchatka Peninsula of Russia and is surrounded by active volcanic territory. The study area has a range of hydrological features that determine the extreme amounts of washed sediments. Sediment transported to the river channels in volcanic mountainous terrain is believed to be strongly influenced by climate conditions, particularly when heavy precipitation and warmer climate trigger mudflows in association with the melting snow. The high porosity of the channel bottom material also leads to interactions with the surface water, causing temporal variability in the daily fluctuations in water and sediment flow. Field measurements revealed that suspended sediment behaviour and fluxes decreased along the mainstream Sukhaya Elizovskaya River from inflows from a tributary catchment located in the volcanic mountain range. In laboratory experiments, water samples collected from tributaries were mixed with those from the mainstream flow of the Sukhaya Elizovskaya River to examine the cause of debris flow and characteristics of suspended sediment in the mainstream. These findings and the geological conditions of the tributary catchments studied led us to conclude that halloysite minerals likely comprise the majority of suspended sediments and play a significant role in phosphate adsorption. The experimental results were upscaled and verified using field measurements. Our results indicate that the characteristics of suspended sediment and river discharge in the Sukhaya Elizovskaya River can be attributed primarily to the beginning of snowmelt in volcanic tributaries of the lahar valley, suggesting a significant hydrological contribution of volcanic catchments to instream suspended sediment transport. Daily fluctuations in discharge caused by snowmelt with debris flow were observed in this measurement period, in which suspended sediment concentration is ~10mg/l during nonflooding periods and ~1400mg/l when flooding occurs. The oxygen and hydrogen isotope measurements, when compared with Japan, indicated that the Kamchatka region water is relatively lightweight, incorporating the effects of topography; and the water from the beginning of the snowmelt is relatively lightweight when compared with water from the end of the snowmelt. The trend line of isotopes from the beginning of the snowmelt was defined by a slope of 6.88 (n =12; r 2 =0.97), significantly less than that of isotopes from the snowmelt (8.72). The sediment particles collected during the snowmelt were round in shape caused by the extreme flows and high discharge. The shape of the sediment particles collected at the beginning of the snowmelt, assumed to be fresh samples from the hillslope, was sharper caused by the relatively small discharge by moderate snowmelt. Finally, the relationship between river discharge and suspended sediment concentration was indicated. The results are compared with mountainous rivers of Japan and Malaysia. A new diagram is proposed to describe the relationship between suspended sediment concentration and river discharge. [Copyright &y& Elsevier]

Abstract: The Lower Mekong River has been an important research topic for at least 15years, notably in the fields of hydrology, fluvial geomorphology, and the impact of dams. Recent papers refer mostly to the impact of the Lancang chain of hydroelectric dams constructed on the Chinese section of the river. Among the pending scientific questions are (1) the upstream–downstream variations in the concentration and yield of suspended sediment and (2) the relative importance of sand in the total yield. The general consensus among the scientific community is that the relative importance of sand in suspended load is not the main scientific concern despite its extensive presence in the Mekong River channel, as noted by geomorphologists, and despite its extreme importance for the stability of the delta shoreline in Viet Nam. This paper contradicts the general consensus. Its objective is to present new information on the processes of sand transport in the Lower Mekong channel. Imagery, field observations, sampling on the river banks, and grain size analysis of sand deposits have been carried out between Chiang Sean (downstream of the Chinese border) and the delta. The C–M image technique served to discriminate between the various transport processes (bedload and different types of suspension). This technique helps in understanding the changing processes responsible for downstream sediment transfer in river channels. The results of this study are the following. [(1)] Discrepancies in the values of annual suspended-sediment load detected by different gauging stations have not yet been satisfactorily explained. The CM image technique indicates that grain size and the quantity of sand transiting in suspension vs. bedload vary from upstream to downstream. [(2)] These upstream–downstream differences may be related to the energy of floods. Energy helps to explain longitudinal variations in the relative importance of the different modes of transport and serves to distinguish between bedload, graded and uniform suspension, and wash load. [(3)] The Mekong is seen as a river carrying mostly silt and clay; however, the results suggest that sand plays a major role in downstream sediment transfer during floods. This result is in line with the large amounts of sand present in the channel. Its relative importance in the total yield must be reassessed, as suggested by Walling (2005, 2008). As may be expected, the role of sand in the stability of the delta shoreline is of prime importance. [Copyright &y& Elsevier]

Highlights: [•] Certain areas (CSA) are more vulnerable to nutrient and sediment losses. [•] Watershed models are effective tools in identifying locations of CSAs. [•] Model choice can effect CSA locations. [Copyright &y& Elsevier]

• Sediment transport capacity is the dynamic and spatial equilibrium value. • Subsurface hydrology affects sediment size distribution and sediment transport rate. • Fractions of coarse-sized particles increased from saturation to seepage conditions. • Sediment transport capacities increased from free drainage to seepage conditions. Sediment size distribution and sediment load are important factors for the estimation of sediment transport processes. Subsurface hydrologic conditions including drainage, saturation, and seepage can affect the sediment selectivity process and sediment transport, given that downward infiltration under drainage and upward exfiltration under seepage can add one more force on surface particles compared to saturation conditions. The aim of this study was to investigate characteristics of sediment selectivity and transport rates under different subsurface hydrologic conditions in small laboratory flume channels. Series of experiments were conducted with an Opal clay soil under four subsurface hydrologic states ranging from free drainage to 10 cm seepage head conditions with water discharge rates from 0.0003 to 0.0008 m2 s−1 at three slope gradients from 4.56% to 12.17%. Results showed that the fraction of coarse-sized particles increased from saturation to 5 cm and 10 cm seepage head conditions. Compared to saturation conditions, the greater proportion of coarse particles leaving in flow in the free drainage experiments may have been caused by infiltration enhancing the deposition processes and regenerating a coarser surface when reaching the dynamic equilibrium. As slope gradients increased, the subsurface hydrologic impacts decreased on the sediment selectivity process. Both the sediment size distribution and the sediment transport rate changed dynamically and spatially before reaching an equilibrium condition. The determination of sediment transport capacity should consider both dynamic and spatial equilibrium conditions. For the Opal soil, the sediment transport capacity values greatly increased from free drainage to saturation conditions, and the differences between these two subsurface hydrologic conditions increased for greater water discharge rates and slope gradients. From saturation to 5 cm and 10 cm seepage head conditions, the sediment transport capacity values increased slightly, and the differences were stable for the slope gradients and water discharge rates studied. [ABSTRACT FROM AUTHOR]

Abstract: The erosion and transport of sediments allow us to understand many activities of significance, such as crust evolution, climate change, uplift rates, continental processes, the biogeochemical cycling of pollutants and nutrients. The Amazon basin of Peru has contrasting physiographic and climatic characteristics between the Andean piedmont and the plains and between the north and south of the basin which is why there are 8 gauging stations located along the principal rivers of the Andean piedmont (Marañón, Huallaga, Ucayali) and the plain (Marañón, Tigre, Napo, Ucayali and Amazon rivers). Since 2003, the ORE-Hybam (IRD-SENAMHI-UNALM) observatory has performed out regular measurements at strategic points of the Amazon basin to understand and model the systems, behavior and long-term dynamics. On the Andean piedmont, the suspended yields are governed by a simple model with a relationship between the river discharge and the sediment concentration. In the plain, the dilution effect of the concentrations can create hysteresis in this relationship on a monthly basis. The Amazon basin of Peru has a sediment yield of 541 *106 t year−1, 70% comes from the southern basin. [Copyright &y& Elsevier]

Abstract: The Madeira River may contribute nearly half of the Amazon River sediment discharge to the Atlantic Ocean, showing the highest erosion rates in the Amazon Basin. However, few studies have assessed the Madeira River sediment budget and the transport processes occurring in the main stem of the river. In this study, MODIS space-borne sensors were used to analyze the suspended sediment transport processes along the main stem of the Madeira River. Field measurements of suspended sediment concentration, spectral radiometry and granulometry were performed during 10 cruises from 2007 to 2011. The relationship between the spectral reflectance and the surface suspended sediment concentration (SSSC) was analyzed using both field radiometric measurements and satellite data. Ten-day SSSC samples acquired by the HYBAM monitoring network were used to match satellite observations with field measurements performed from 2000 to 2011. Over 900 MODIS images of 6 different locations were processed to monitor the SSSC dynamics in space and time. Satellite reflectance was found to be significantly correlated with the SSSC. However, a seasonal dependency was demonstrated, most likely caused by a variable granulometric distribution along the annual cycle. The ratio between the red and near-infrared bands was found to be free of the seasonal dependency (r = 0.79, N = 282), and a SSSC retrieval model was built from the satellite data using a bootstrap resampling technique. The satellite-retrieved SSSC time series showed excellent accuracy over the 11-year period and at two different stations located 800 km from each other. The satellite data were averaged to analyze the SSSC pattern temporally and spatially along the entire Madeira River, which provided evidence of significant sedimentation and resuspension. The backwater effect caused by the two-to-three-month lag between peak water in the Madeira and Amazon Rivers was used to predict local sedimentation near the Madeira River mouth. Our results facilitated a precise assessment of such sedimentation, which demonstrated an SSSC decrease 400 km upstream from the Madeira–Amazon confluence. [Copyright &y& Elsevier]

Abstract: A range of bed-load sediment transport formulae are used to run fully coupled, morphodynamic simulations of one [1] swash cycle on an erodible plane beach. A system comprising shallow water equations and Exner equation is solved, in which sediment transport rate q is either dependent only on depth averaged velocity (u), or on u and water depth (h). The results are in agreement with equivalent uncoupled results [2] in that all sediment transport formulae considered applied to the event of [1] yield net erosion in the whole of the swash. Consistent with [3], however, full coupling yields significantly less erosion for all the formulae compared to the equivalent uncoupled results. It is shown that differences between uncoupled and coupled approaches (for most formulae) accumulate over the course of the swash event. The main reason for the reduced net erosion is the smaller maximum inundation. It is also shown that including a dependence on h in the bed load sediment transport formula for fully coupled simulations can result in net deposition in the upper swash. Bed shear stress described by a Chezy law is further included in fully coupled simulations to examine net beach change. Much reduced maximum inundation and net offshore sediment transport are predicted both for and . It is shown that although the net sediment flux at the base of the swash under one [1] swash event is still offshore, deposition in the middle or upper swash may be predicted when bed shear stress is included, particularly when the drag coefficient in the backwash is reduced compared to that in the uprush, consistent with some in-situ measurements. The implication is that bed shear stress must be included not just to obtain correct quantitative beach change, but also to obtain correct qualitative beach behaviour. [Copyright &y& Elsevier]

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]

Abstract: This paper uses a multifaceted remote sensing and morphometric approach to investigate if the surface of subcatchments in the Parana Valles area of Mars (20–30°S, 0–20°W) is reflective of hydrology and sediment transport by water. Using digital elevation model (DEM) data obtained from the Mars Orbiter Laser Altimeter (MOLA), three nested subcatchments were examined using a suite of terrestrial geomorphic and hydrologic statistics to determine if their shape and form lies within the known range of fluvial catchment properties on Earth. Further, an examination of statistical accuracy via an innovative pixel-by-pixel solution of two statistics established that despite mineralogical homogeneity confirmed by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral survey, erosion processes were likely to be variable across the study site. The DEM-based methods outlined here can be employed at other sites to investigate geomorphic properties and attributes of the Martian surface. [Copyright &y& Elsevier]

Abstract: A new grid-based model of nutrient dynamics and transport process has been developed within a distributed hydrological modelling framework and integrated with river network module. The key aspect of this development is a process based description of nutrient generation process on the land surface and its related nutrient release with hydrologic runoff and soil erosion. Whereas the conventional modelling uses the event mean concentration method for nutrient dynamics modelling and estimates nutrient loads from catchments to the rivers this study has introduced an export function based release related with flow capacity. The river module solves the dynamic equation for transport and chemical reaction. The model output is available in high spatial and temporal resolution, which was tested and verified applying in two catchment areas from different hydro-climatic backgrounds. The model was able to simulate short term high intensity flood events as well as long term seasonal patterns. The simulated results for most of the nutrient parameters are within acceptable range as reflected by measures of statistical indices and visual interpretation. For example, the R 2 values for different nutrient levels in the Saru River, Japan are within the range of 0.83–0.99 and 0.66–0.87 for calibration and validation, respectively. Similarly, the relative root mean square error (RRMSE) values for different nutrient levels in the Saru River range between 0.06–0.22 and 0.06–0.26 for calibration and validations, respectively. The maximum load of nutrients in each grid was extracted from time series output, analyzed further and presented in two dimensional maps, which showcase the usefulness of the model in decision making process for management of land and maintenance of the in-stream water quality. [Copyright &y& Elsevier]

Summary: Rapid land use/-cover change has increasingly transformed the hydrological functioning of tropical Andean ecosystems. The hydrological response to forest cover change strongly depends on the initial state of the ecosystem. Relatively little is known about human-disturbed ecosystems where forest plantations have been established on highly degraded land. In this paper, we analyze the impact of forest change on water and sediment fluxes for a highly degraded Andean catchment. Different pathways of land cover change (1963–2007) are observed in the Jadan catchment, with deforestation taking place in remote uplands and recovery and reforestation in the middle and lower parts where agricultural and bare lands are prevalent. Time series analyses of streamflow and rainfall data (1979/1982–2005/2007) show significant shifts in the distribution of rainfall and flow data. Changes in discharge are not resulting from changes in precipitation, as the direction of change is opposite. The removal of native forest for rangeland or croplands (by −20km2) is likely to have contributed to the increase in total annual water yield, through an increase in annual baseflow by 25mm. The observed changes in peakflow are important as the 1st percentile highest flow rates were 54% lower, while the 1st percentile rainfall amounts increased by 52%. The observed decrease in peakflow cannot be explained by clearcut of native forest, but is likely to be related to reforestation of degraded lands as well as spontaneous recovery of vegetation on remaining grazing lands. Over the same time period, a major decrease in specific sediment yields and suspended sediment loads was observed. Although deforestation in the upper parts led to increased landslide activity, this change is not reflected in an increased sediment yield. Small upland rivers are often nearly completely blocked by landslide material, thereby reducing their potential to transport sediment. In contrast, the reduction in estimated erosion is likely to be caused by the reduction of the degraded areas in areal extent as well as to the (partial) recovery of the vegetation in these areas. [Copyright &y& Elsevier]

Abstract: That sediment transport estimates have large uncertainty is widely acknowledged. When these estimates are used as the basis for a subsequent analysis, such as cumulative sediment loads or budgets, treatment of uncertainty requires careful consideration. The propagation of uncertainty is a problem that has been studied in many other scientific disciplines. In recent years, Bayesian statistical methods have been successfully used to this end in hydrology, ecology, climate science, and other disciplines where uncertainty plays a major role—their applications in sediment transport, however, have been few. Previous work demonstrated how deterministic sediment transport equations can be brought into a probabilistic framework using Bayesian methods. In this paper, we extend this basic model and apply it to sediment transport observations collected on the Snake River in Wyoming, USA. These data were used previously to develop a 50-year sediment budget below Jackson Lake dam. We revisit this example to demonstrate how viewing sediment transport probabilistically can help better characterize the propagation of uncertainty in the calculation of cumulative sediment transport. We present the development of probabilistic sediment rating curves that rely on deterministic sediment transport equations and then show how these can be used to compute the distribution of sediment input and output for each year from 1958 to 2007. The Bayesian approach described provides a robust way to quantify uncertainty and then propagate it through to subsequent analyses. Results show that transport uncertainty is quantified naturally in the Bayesian approach, making it unnecessary for modelers to assume some specified error rate (e.g., ±5%) when developing estimates of cumulative transport. Further, we demonstrate that a Bayesian approach better constrains uncertainty and allows sediment deficit and surplus to be examined in terms of quantified risk. [Copyright &y& Elsevier]

Abstract: Fluvial systems in tropical regions are not only the lifeline for modern civilizations there but also form an important continental archive for reconstructing Quaternary palaeoclimates and palaeoenvironments. Tropical rivers drain through a variety of geological and geomorphological settings across the world and have been studied for their hydrology, sediment transport characteristics, facies models, stratigraphic development and flood hazards. This paper presents an overview of the research on tropical rivers globally and identifies major gaps and unanswered research questions. As a part of the IGCP 582 on Tropical Rivers, the participants of this project are continuing to tackle many of these issues. The collection of papers in this special issue is an outcome of this activity and presents new data on processes and alluvial stratigraphy of the tropical rivers from China, India, South America and northern Australia. [Copyright &y& Elsevier]

Abstract: Suspended load dynamics were analyzed for the period 2007–2009 in a semi-meandering cross-section under different hydrological conditions. Samples were collected at four different points of the cross-section. During “low discharges” (≤600 m3/s) suspended load samples were collected at-a-monthly basis, whereas at “high discharges” (>600 m3/s) sampling was conducted intensively (at-a-daily basis during the first stages of the flood event). Results indicated that during low discharges, both organic and inorganic suspended load concentrations tended to be uniformly distributed across the fluvial section; but during high discharges, two distinct areas were found: an area extending from the “Inner-bank” to the “Channel centre” (Area-I) with higher suspended concentrations (organic and inorganic) than those recorded in the “Outer bank” (Area-II). This phenomenon was likely related to the formation of secondary flow velocity cells and the activation of new sources of sediment. In addition, a non-significant relationship between organic suspended load and water flow was observed in the outer-bank. At-a-monthly basis, the analysis of the suspended load showed the existence of an intra-annual cycle of the inorganic concentrations, with a progressive increase from October to March followed by a decrease from March to September. Nevertheless, the organic suspended load did not show any trend, being equally distributed along the year, suggesting that other sources of organic matter besides phytoplankton are predominant. [Copyright &y& Elsevier]

Abstract: Our goal is to develop a model capable to discern the response of a watershed to different erosion mechanisms. We propose a framework that integrates a geomorphic component into the physically-based and spatially distributed TIN-based Real-time Integrated Basin Simulator (tRIBS) model. The coupled model simulates main erosive processes of hillslopes (raindrop impact detachment, overland flow entrainment, and diffusive processes) and channel (erosion and deposition due to the action of water flow). In addition to the spatially distributed, dynamic hydrologic variables, the model computes the sediment transport discharge and changes in elevation, which feedback to hydrological dynamics through local changes of terrain slope, aspect, and drainage network configuration. The model was calibrated for the Lucky Hills basin, a semi-arid watershed nested in the Walnut Gulch Experimental Watershed (Arizona, USA). It is demonstrated to be capable of reproducing main runoff and sediment yield events and accumulated volumes over the long term. The model was also used to study the response of two first-order synthetic basins representative of landforms dominated by fluvial and diffusive erosion processes to a 100-year long stationary climate. The analysis of the resultant slope-contributing area relationships for the two synthetic basins illustrates that the model is consistent with assumed principles of behavior and capable of reproducing the main mechanisms of erosion. [Copyright &y& Elsevier]

Summary: After the Yangtze River was closed by the Three Gorges Project (TGP) in 2003, erosion occurred from the dam site to the river mouth, especially in the middle and lower reaches of the Yangtze River. However, in some local areas of Chenglingji reach which holds the key position for flood management, there is actually deposition in contrast to the expected erosion. In this paper, a one dimensional mathematical model of the river network with sediment transport is used as the tool to simulate flow and fluvial processes. The calculation domain is from Yichang, which is downstream of the dam, to Hankou, the controlling node of flood management, 694km long in total. The model is calibrated based on the field data of hydrology and sediment transport during the period from October 2003 to October 2008. Then the model is utilized to simulate the erosion and deposition of the middle and lower reaches of the Yangtze River in the next two decades, and produce the results of a new river channel after river bed deformation occurs. The typical flood processes of 1954 and 1998 in the Yangtze River basin are used to check the flood management scheme for the research area, and results show that water storage of Three Gorges Reservoir (TGR) and a flood diversion program downstream of the Yangtze River should be taken into consideration. [Copyright &y& Elsevier]

Abstract: Flood water in an alluvial channel (or river) conveys suspended sediments from upstream to downstream, and entrains bed materials along with flood currents. Morphological changes on channel/river bed trend to reduce the conveyance capability of channel, and then to affect water stages and discharges. It is therefore necessary to quantify the influence of sediment transport on variations of water stages for the purpose of best flood water management in alluvial rivers. This paper presents a simulation-based optimization model to systematically investigate optimal control of flood stages for various geometries and sediment properties in alluvial channels. This integrated system consists of a well-established one-dimensional river flow model and a non-uniform/non-equilibrium sediment transport model, as well as an adjoint model for determining the sensitivity of objective function. Flood control is demonstrated by operating a single floodgate and multiple gates to withdraw flood waters from alluvial channel. The optimal withdrawal hydrographs for scheduling the floodgate opening operations are obtained under the constraints of objective water stages applied to target reaches. It is found that the influence of morphological changes on flood control becomes significant under certain hydrological and morphological conditions, and varies with the installation of control structures. This preliminary study shows that this simulation-based optimization model is effective to facilitate best management of flood and sediment transport and design of control structures in alluvial channels/rivers. [Copyright &y& Elsevier]

Summary: This study explores the influence of rainfall and runoff production on wash load sediment transport in a low-order, ephemeral watershed in southeast Arizona. Wash load concentrations measured at the watershed outlet generally decreased throughout a runoff event and were better correlated with the rainfall intensity and the rainfall volume that fell within the 6min (the watershed’s ‘time of concentration’) before the sediment concentration was measured than with the runoff discharge. The difference between the rainfall volume per unit time and the runoff discharge was primarily due to infiltration and transmission losses, processes that reduce runoff volume but do not appear to affect the wash load concentration within the runoff. Infiltration and transmission losses are significant in this watershed and vary considerably in space and time but are generally described by an inverse relationship between the runoff coefficient and drainage area. Runoff coefficients vary amongst runoff events and are correlated to the peak rainfall intensity during each event. Results indicate that wash load concentrations are set by the sediment entrainment processes occurring on the hillslopes (e.g., rainsplash, Hortonian overland flow) and do not greatly fluctuate as water is routed through the watershed. This suggests that wash load concentration may be better predicted by metrics of rainfall than flow discharge in certain environments. Using rainfall as a predictor of wash load could be useful for estimating sediment fluxes in semiarid regions where flow discharge is often difficult to monitor and sediment transport concentrations can be high (i.e., >10,000mgL−1). [Copyright &y& Elsevier]

Summary: The Soil and Water Assessment Tool (SWAT, 2005) was used to simulate discharge and sediment transport at daily time steps within the intensively farmed Save catchment in south-west France (1110km2). The SWAT model was applied to evaluate catchment hydrology and sediment and associated particulate organic carbon yield using historical flow and meteorological data for a 10-years (January 1999–March 2009). Daily data on sediment (27months, January 2007–March 2009) and particular organic carbon (15months, January 2008–March 2009) were used to calibrate the model. Data on management practices (crop rotation, planting date, fertiliser quantity and irrigation) were included in the model during the simulation period of 10years. Simulated daily discharge, sediment and particulate carbon values matched the observed values satisfactorily. The model predicted that mean annual catchment precipitation for the total study period (726mm) was partitioned into evapotranspiration (78.3%), percolation/groundwater recharge (14.1%) and abstraction losses (0.5%), yielding 7.1% surface runoff. Simulated mean total water yield for the whole simulation period amounted to 138mm, comparable to the observed value of 136mm. Simulated annual sediment yield ranged from 4.3tkm−2 y−1 to 110tkm−2 y−1 (annual mean of 48tkm−2 y−1). Annual yield of particulate organic carbon ranged from 0.1tkm−2 y−1 to 2.8tkm−2 y−1 (annual mean of 1.2tkm−2 y−1). Thus, the highest annual sediment and particulate carbon yield represented 25 times the minimum annual yield. However, the highest annual water yield represented five times the minimum (222mm and 51mm, respectively). An empirical correlation between annual water yield and annual sediment and organic carbon yield was developed for this agricultural catchment. Potential source areas of erosion were also identified with the model. The range of the annual contributing erosive zones varied spatially from 0.1 to 6tha−1 according to the slope and agricultural practices at the catchment scale. [Copyright &y& Elsevier]

Summary: There are a number of landscape evolution models now developed to the stage where they can be routinely used for both geomorphic evaluations and quantification of soil erosion rates and processes when subject to the action of rainfall and runoff. These models have considerable advantages over traditional modelling approaches as they remove the need to manually determine slope length and angle and because they can also determine both erosion and deposition. A further advantage of digital elevation based models is that they dynamically adjust the landscape in response to erosion and deposition, thus producing a better representation of slope length and angle over the duration of the simulation. A recent advance is that these models now have the ability to employ spatially variable hydrological and erosion parameters, the spatial distribution of soil particle size at user defined soil depths as well as several different flow direction algorithms. While these options are available in these models, minimal evaluation of these hydrological and geomorphological functions has taken place to assess whether they are correct. This study evaluates the well known SIBERIA and CAESAR models for their ability to predict landscape form and erosion for a grassland catchment in South-East Australia under similar rainfall conditions. The results demonstrate that both models predict similar hillslope form as well as erosion rates over a 1000-year modelled period. They also predict erosion rates within the range of independently determined field measured data using environmental tracers at decadal time scales for the site and region demonstrating the models are reliable in the setting examined here. [ABSTRACT FROM AUTHOR]

Abstract: Soil erosion is a significant concern when considering regional environmental protection, especially in the Yellow River Basin in China. This study evaluated the temporal-spatial interaction of land cover status with soil erosion characteristics in the Longliu Catchment of China, using the Soil and Water Assessment Tool (SWAT) model. SWAT is a physical hydrological model which uses the RUSLE equation as a sediment algorithm. Considering the spatial and temporal scale of the relationship between soil erosion and sediment yield, simulations were undertaken at monthly and annual temporal scales and basin and sub-basin spatial scales. The corresponding temporal and spatial Normalized Difference Vegetation Index (NDVI) information was summarized from MODIS data, which can integrate regional land cover and climatic features. The SWAT simulation revealed that the annual soil erosion and sediment yield showed similar spatial distribution patterns, but the monthly variation fluctuated significantly. The monthly basin soil erosion varied from almost no erosion load to 3.92t/ha and the maximum monthly sediment yield was 47,540 tones. The inter-annual simulation focused on the spatial difference and relationship with the corresponding vegetation NDVI value for every sub-basin. It is concluded that, for this continental monsoon climate basin, the higher NDVI vegetation zones prevented sediment transport, but at the same time they also contributed considerable soil erosion. The monthly basin soil erosion and sediment yield both correlated with NDVI, and the determination coefficients of their exponential correlation model were 0.446 and 0.426, respectively. The relationships between soil erosion and sediment yield with vegetation NDVI indicated that the vegetation status has a significant impact on sediment formation and transport. The findings can be used to develop soil erosion conservation programs for the study area. [ABSTRACT FROM AUTHOR]

Abstract: We hypothesise that stream sediment elemental composition can predict mean and minimum concentrations of alkalinity, Ca and Mg in the river water throughout a river network. We tested this hypothesis for the River Derwent catchment in North Yorkshire, England, by using 6years of water chemistry data from the Environment Agency and a digital elevation model to flow path-weight British Geological Survey (BGS) sediment element concentration data. The predictive models for mean concentrations were excellent for Ca and alkalinity, but less good for Mg, and did not require land use data inputs as stream water sediment composition seems to reflect all aspects of the riparian zone soil system. Predictive model forms were linear. Attempts to predict minimum values for Ca and alkalinity also were less satisfactory. This probably is due to variations in hydrological response times to individual precipitation events across the catchment. [ABSTRACT FROM AUTHOR]

Summary: Over the past 60years, climate change and human activities in the Huanghe (Yellow River) basin have changed the river system. In particular, construction of large reservoirs and soil-conservation practices within the river basin have reduced sediment flux to the sea by ∼90% and increased the grain size of suspended sediment delivered to the sea (30μm now versus 18μm before in median grain size). Scouring of the channel in the lower reaches has added a new sediment source to those derived from the loess region of the middle reaches. Before construction of the Xiaolangdi Reservoir at the downstream end of the middle reaches, suspended sediment concentrations at station Lijin, the last hydrographic station before the river enters the sea, were high enough (>35kg/m3) in the flood season to offset the density contrast between freshwater and ambient seawater. Thus, hyperpycnal flows developed along the subaqueous slope at the river mouth during the flood season. Observations from two cruises near the Huanghe river mouth, one before and one after the operations of the Xiaolangdi Reservoir, suggest that buoyant hypopycnal plumes, rather than hyperpycnal plumes, have occurred at the river mouth since the dramatic changes in concentration and grain size of suspended sediment discharged to the sea. The rapid decrease of sediment discharge to the sea and the increase of grain size of suspended sediments not only changed the sediment dispersal pattern at the river mouth, but also modified the shoreline and subaqueous slope. The effects of climate change and human activities in the river basin have been transferred along the hydrological pathway to the estuary and delta, and have changed estuarine sediment dynamics and delta morphology. The Huanghe presents an illustrative example of river basin–coastal zone interactions in the context of climate change and human activities. [ABSTRACT FROM AUTHOR]

Abstract: The Red River (China/Vietnam, A=155,000km²) is a typical humid tropics river originating from the mountainous area of Yunnan Province in China. Based on information on daily discharge (Q) and suspended particulate matter (SPM) concentration between 1960–2008 for the SonTay gauging station (outlet of the River and entry to the Delta) provided by the National Institute IMHE-MONRE, the mean annual SPM flux was estimated at 90 Mt/yr, corresponding to a sediment yield of 600t/km²/yr. The temporal variability of annual SPM fluxes (ranging from 24 to 200Mt/yr) is strongly related to the interannual hydrological conditions. However, some years of high water flow were not associated with high sediment fluxes, especially after 1989 when the HoaBinh dam came into operation. Therefore, the median discharge pre- (3389m3/s) and post 1989 (3495m3/s) are similar indicating there was little or no change between both periods. Sediment rating curves (power law-type; SPM=aQb) were fitted for both periods (1960–1989; 1990–2008). The analysis of the pre- and post-1989 sediment rating parameters (a, b) suggests a downshift of b-parameter values after 1989, attributed to a decrease of the sediment supply due to the commissioning of the HoaBinh dam. A single sediment rating curve derived from 1960–1989 data was used to simulate the annual variability of former sediment delivery, generating excellent cumulative flux estimates (error ~1%). In contrast, applying the same rating curve to the 1990–2008 data resulted in systematic and substantial (up to 109%) overestimation. This suggests that the HoaBinh dam reduces annual SPM delivery to the delta by half, implying important metal/metalloid storage behind the HoaBinh dam. [ABSTRACT FROM AUTHOR]

Abstract: Sediment transport in the Ribera Salada stream was estimated from continuous suspended and bedload monitoring between 2005 and 2008. The Ribera Salada basin is a mountainous perennial river in the Southern Pyrenees and is representative of the extensive forestry land use in this upland region. Water and sediment fluxes have been analysed with the aim of determining the thresholds, duration, ranges and relative contributions of the two sediment transport modes (suspended and bedload), and their variability in relation to the basin''s annual hydrology. The stream''s hydrology in the first two sampling years was average in the context of a 10-yr series of the basin, while 2007–2008 can be classified as a wet year. The specific total sediment load during the study period amounted to 12tkm− 2y− 1, a low value compared with similar Mediterranean counterparts. The maximum load (31.5tkm− 2y− 1) was observed during the wettest year of the monitoring programme. During average years most of the total load (>90%) was transported in suspension; consequently, suspended sediment transport is more frequent through time. In contrast, bedload occurs sporadically during floods that exceed certain hydraulic thresholds, corresponding to a flow equalled or exceeded 4% of the time, that yields an average shear stress of ∼35Nm− 2. Under such conditions bedload transport becomes relevant and, if the threshold is frequently exceeded as in relatively wet years such as 2007–2008, may constitute the majority of the total sediment load (74%). This paper provides new evidence of the distinct role of sediment transport modes in stable fluvial environments where only sporadic inputs of surplus energy (flow discharge) determine the dominant mode, magnitude and duration of their respective contribution. [Copyright &y& Elsevier]

Abstract: The effect of geomorphic features and hydraulic conditions on the formation, evolution, and morphology of sediment cluster microforms in an unregulated gravel-bed stream were investigated at field sites on the Entiat River, which drains the eastern slopes of the Cascade Mountains in central Washington state, USA. Sediment clusters were marked, described, and photographed before and after a series of moderate to high discharges over an 18-month period to quantify the evolution of the cluster morphologies. Individual sediment particles were tracked to calculate the range of flows and bed shear stresses that maintain and destroy clusters. Examination of geomorphic settings, channel morphology, and particle size distributions documented the conditions that favor cluster formation. The investigation tested the hypotheses that clusters in this environment delay sediment entrainment and that their morphology and evolution follow a predictable evolution similar to that found in laboratory studies. Clusters formed on gravel bars adjacent to riffles with slopes ≥1%, poor to moderate sorting, and mean and maximum particle size values 1.5 times greater than those associated with noncluster bars. Clusters were more stable under the bimodal sediment size distribution contributed by a tributary alluvial fan and were destroyed with and without anchor clast mobilization at sites where sediment size was more uniform. The six cluster morphologies identified in the field were similar to those in flume studies, but did not follow the same evolutionary cycle over multiple flow events. This contrast was attributed to the flow events resetting the cluster cycle, leading to a high percentage of upstream triangles. The dimensionless critical shear stress required to entrain the mean grain size ranged from 0.06 to 0.08. The hydraulic thresholds and geomorphic features that result in stable vs. mobilized cluster microforms in this setting can serve as a model for regulated rivers and restoration projects aimed at sustaining instream flows to maintain natural sediment transport conditions. [Copyright &y& Elsevier]

Abstract: This study examined spatial and temporal variations in the surface moisture content of a fine-grained beach at Padre Island, Texas, USA. Surface moisture measurements were collected on a 27×24 m grid that extended from the dune toe to the upper foreshore. The grid was surveyed at 2 to 4 h intervals for two tidal cycles, generating 17 maps of the spatial distribution of surface moisture. Simultaneous measurements of air temperature and humidity, wind speed and direction, tidal elevation, and water table elevation were used to interpret observed changes in surface moisture. It was found that the spatial distribution of surface moisture was broadly characterized by a cross-shore gradient of high to low content moving landward from the swash zone. The distribution of surface moisture was conceptualized in terms of three zones: saturated (>25%), intermediate or transitional (5–25%), and dry (<5%). The position of the saturated zone corresponded to the uppermost swash zone and therefore shifted in accordance with tidal elevation. Moisture contents in the intermediate and dry zones were primarily related to variation in water table depth (which was in turn controlled by tidal elevation) and to a lesser extent by evaporation. Signals associated with atmospheric processes such as evaporation were muted by the minimal degree of variation in atmospheric parameters experienced during most of the study period, but were apparent for the last few hours. The observed spatial and temporal variations in moisture content correspond reasonably well with observations of key controlling processes, but more work is needed to fully characterize this process suite. [Copyright &y& Elsevier]

Abstract: The Daly River occupies a mainly undisturbed large catchment in the Australian wet–dry tropics. Concerns about possible increased sediment input to the River from clearing and cropping have motivated this study of fine sediment sources. Using geochemical tracers for both modern sediments and alluvial bench deposits, it is shown that, for the last ~30 years, 89–97% of the fine sediment originates from erosion by gullying and channel change. There is no discernible input of top soil from the cleared land adjacent to the Daly River in the study area. The analysis and OSL dating of the alluvial benches have also provided data on the age of (and inferences about the causes of) bench formation, flood frequency change, sedimentation rate change, and episodes of sand transport. The benches are being destroyed as the channel widens (contributing sediment to the river) and the bed of the Daly appears to be shallowing, both responses to increased overbank flows. The sediment source created by channel widening is almost all the result of hydrologic change, with no discernible role for land use. [Copyright &y& Elsevier]