Process-based numerical modelling up and down beach morphological states

Forest roads are a common land use feature with a significant impact on sediment yield and the water sediment transport processes within a watershed, seriously disrupting the safety and stability of the watershed. Previous studies have focused on the sediment production processes within the road prism. However, there has been limited attention given to the transport processes of road-eroded sediment at various scales, which is crucial for understanding the off-site effects of road erosion. This paper reviews research conducted on forest road erosion over the past two decades. It summarizes the mechanisms of sediment production from road erosion and provides a detailed analysis of the transport mechanisms of eroded sediments from roads to streams at the watershed scale. The paper also examines the ecological and hydrological effects, research methods, and control measures related to sediment transport caused by forest road erosion. It identifies current research limitations and outlines future research directions. The findings of this review highlight several key points: (1) Most research on forest road erosion tends to be specific and unilateral, often neglecting the broader interaction between roads and the watershed in terms of water–sediment dynamics. (2) Various research methods are employed in the study of forest road erosion, including field monitoring, artificial simulation experiments, and road erosion prediction models. Each method has its advantages and disadvantages, but the integration of emerging technologies like laser scanning and fingerprint recognition remains underutilized, hindering the simultaneous achievement of convenience and accuracy. (3) The transport processes of forest road-eroded sediment, particularly on road–stream slopes, are influenced by numerous factors, including terrain, soil, and vegetation. These processes exhibit significant spatial and temporal variability, and the precise quantification of sediment transport efficiency to the stream remains challenging due to a lack of long-term and stable investigation and monitoring methods. The establishment and operation of runoff plots and sedimentation basins may help offer a solution to this challenge. (4) Both biological and engineering measures have proven effective in reducing and limiting sediment erosion and transport. However, the costs and economic benefits associated with these regulation measures require further investigation. This review provides a comprehensive summary of relevant research on sediment erosion and transport processes on unpaved forest roads, enhancing our understanding of sediment yield in watersheds and offering valuable insights for reducing sediment production and transport to streams.

Seasonal variation in sediment transport and deposition on a muddy clinoform in the Yellow Sea

Introduction to the special issue ‘Tracer Applications in Sediment Research’

[1] Aeolian processes, involving erosion, transportation, and deposition of sediment by the wind, occur in a variety of environments including coastal areas, semiarid, and arid regions (e.g., cold and hot deserts), agricultural fields, and some planetary bodies, notably Mars and possibly Venus and Titan. Aeolian processes are responsible for the emission, transport, and deposition of dust and formation of areas of sand dunes. [2] This special section contains 14 papers that recognize the distinguished career of Dr. Dale Gillette. The papers are based upon oral and poster presentations given at the Sixth International Conference on Aeolian Research (ICAR VI), which was held at the University of Guelph, Ontario, Canada, 23–28 July 2006 (for a summary of the conference see Lancaster et al. [2006]). A special aspect of ICAR VI was the recognition of the long, multifaceted, and distinguished career of Dale Gillette, known to many for his seminal work on mineral aerosols and wind erosion processes. ICAR VI was the latest in a series of conferences on aeolian processes, sediments, and landforms that started in 1986 in Aarhus, Denmark, followed by conferences in Sandberg, Denmark (1990); Zzyzx, California (1994); Oxford, UK (1998); and Lubbock, Texas (2002). The next ICAR will be held in Argentina in 2010. [3] The papers in this volume were chosen for their close relationships to aspects of Dale Gillette's career and his major scientific contributions, as well as being a reflection of some of the most innovative contemporary approaches to studies of aeolian processes, sediments, and landforms. Many of the papers cite Dale's work and are clearly inspired by the fundamental concepts and approaches that he articulated. Thus, there are papers on dust emissions from disturbed and undisturbed surfaces [e.g., Macpherson et al., 2008] that build on the work of Gillette et al. [1980] as well as field studies of dust events and processes [McGowan and Clark, 2008] that continue and build upon the methodology developed during collaborative work at Owens Lake, California, the major source of mineral dust in the western United States prior to mitigation measures designed to reduce dust emissions [Cahill et al., 1996; Gillette et al., 1997a, 1997b, 1997c]. Further papers document experiments on dust deposition processes [Goossens, 2008] and field studies of dust deposition to soils and ecosystems [Bowker et al., 2008; Goldstein et al., 2008]. [4] Dale Gillette was a pioneer in conceptualizing and quantifying the effects of roughness elements (rocks, vegetation) on wind erosion and sediment transport processes [Gillette and Stockton, 1989; Musick and Gillette, 1990; Raupach et al., 1993; Stockton and Gillette, 1990], and this volume contains a number of papers [e.g., Brown et al., 2008; King et al., 2008; Sutton and McKenna Neuman, 2008; Okin, 2008; Shao and Yang, 2008] that build on the fundamental concepts that Gillette and his colleagues developed. Dale Gillette also maintained a long-term interest in the fundamentals of sediment mobilization and transport by wind [e.g., Gillette and Stockton, 1986; Gillette et al., 1996]; papers in this special section by Rasmussen and Sorensen [Rasmussen and Sorensen, 2008] as well as McKenna Neuman and Sanderson [McKenna Neuman and Sanderson, 2008] provide further understanding of the controls of sediment transport and creative ways in which to model these complex nonlinear processes. Throughout his career, Dale Gillette maintained a strong interest in modeling of aeolian processes. Many of the papers in this volume develop models that can be used to assess aeolian processes and their effects on the environment as well as to understand fundamental controls of the processes [e.g., Okin, 2008]. Although Dale never worked on dunes, the approach of the paper on barchan dune corridors [Elbelrhiti et al., 2008] adopts the approach to modeling advocated by him, being firmly based upon fundamental physical principles. [5] The papers in this volume clearly indicate the diversity and healthy state of aeolian research today. Challenges for the immediate future include the issue of scaling of detailed process studies, such as those reported here, on small spatial and temporal scales to regional and global issues such as the global dynamics of aeolian systems, including for example the contribution of dust deposition to soil development, and the human dimensions of change in aeolian systems. Despite considerable progress in recent years, there still remains a significant gulf between the modeling community and those engaged in field and experimental studies. Dale Gillette provides a stellar example of a person who has been able to bridge this gap and thereby contribute in a unique way to scientific understanding of aeolian processes as well as its application to real-world problems of wind erosion and air quality.

Numerical modeling of the effects of water flow, sediment transport and vegetation growth on the spatiotemporal patterning of the ridge and slough landscape of the Everglades wetland

The history of investigations of channel change consequent upon river regulation is traced from the late 1960s until the present. The associated sediment transport and depositional processes are also reviewed. Conveniently the approaches adopted historically have fallen into three basic groups, these are: (1) analyses of the changes in channel networks as evident in adjustments to hydraulic geometry related to catchment area; (2) analyses concerned with sediment transport processes and channel adjustments at the reach scale (typically utilizing regime‐type concepts), and finally; (3) more recent attempts at an integrated approach utilizing holistic concepts of channel change over extended time periods.A major conclusion drawn from this review is that each reservoir‐catchment system is unique, producing singular responses that cannot easily be integrated into a basic general model except at a facile level. The continuing lack of complete theoretical models of channel adjustment is a hindrance in predicting regulation effects and may be related to limited understanding of such factors as sediment supply dynamics and bank collapse mechanisms. Emphasis is placed on: the importance of the aggregational as well as the well‐known degradational response of channels below dams; the recognition of suitable temporal frameworks; the potentially destabilizing effect of rare large floods; and the local effects of unregulated tributary inflows. In addition more sophisticated theory and analysis needs applying to the transport and subsequent deposition of suspended sediments in gravel‐beds whilst the three‐dimensional facies relationships of regulated river alluvial suites need clarification in the light of recent initiatives concerning the sedimentary architecture of other alluvial systems.

Frequency and intensity of extreme rainfall events is expected to increase. Extreme rainstorms cause redistribution of contaminated sediments which is a significant problem due to the presence of many contaminated sites in heavily populated urban coastal areas. This study evaluates contaminated sediment transport and redistribution in rivers due to extreme rainfall. To do so, a conceptual model that couples hydraulic, sediment and contaminant transport is formulated to predict erosion and deposition of sediments and the transport of adsorbed heavy metals in a river after extreme rainfall.One dimensional energy equation and Manning's equation were used to predict water surface elevations, the sediment continuity equation is used for sediment transport predictions and calculate sediment erosion and deposition, hydrodynamics and sediment transport predictions were linked to predict contaminated sediment transport assuming equilibrium and linear soil-contaminant partitioning. The hydraulic model was calibrated using water surface elevations from USGS. The sediment transport model was calibrated using USGS sediment loads data. Metal concentrations reported by USGS were also used to calibrate contaminant transport model and simulate contaminant-sediment sorption. Lead is used as a model contaminant due to its high sorption on sediment particles. A sensitivity analysis was first carried out to assess the impacts of key parameters on contaminated sediment transport. The approach was then implemented to evaluate the effect of Hurricane Harvey, which hit Texas and Louisiana in 2017, on contaminated sediment transport at the Neches River watershed, one of the most contaminated waterways in Texas, as a case study. The study shows that extreme rainfall events cause substantial transport and redistribution of contaminated sediments in rivers. Redistribution of heavy metals contamination is controlled by transport of fine particles due to their high sorption capacity. This causes significant spreading of contamination after such event as fine particles constitute the majority of transported sediments. Further, the increase in Lead concentrations in surface water and sediments from upstream to downstream the river lasts for long periods after the rain event.

This paper provides a comprehensive review of recent research on the role of vegetation in open channels and its impact on sediment transport and flow dynamics. Vegetation plays a crucial role in influencing flow characteristics and sediment deposition, with factors such as vegetation density, porosity, shape, flexibility, and height significantly affecting flow turbulence and sediment transport. Different vegetation arrangements, including patches, are found to alter sediment deposition rates and turbulence structure. The review examines laboratory, field, and modelling studies that investigate the effects of vegetation characteristics on mass transport and flow behaviour, highlighting the methods used to assess vegetation porosity and sediment transport rates. Additionally, the paper explores the swash-zone dynamics, where high velocities and suspended sediment concentrations contribute to shore line erosion and accretion. Despite limited research in this area, studies in both low-energy reflective beaches and high-energy dissipative beaches have provided insights into sediment transport processes in the swash-zone. These processes, including the role of groundwater influx and out flux, must be considered in any model of sediment transport in the swash-zone. This paper underscores the importance of vegetation and swash-zone dynamics in sediment transport and coastal morphology.

Rill networks have been a focus of study for many decades, but we still lack a complete understanding of the variables that control the spacing of rills and the geometry of rill networks (e.g., parallel or dendritic) on hillslopes. In this paper, we investigate the controls on the spacing and geometry of rill networks using numerical modeling and comparison of the model results to terrestrial‐laser‐scanner‐derived topographic data from rill networks formed in physical experiments. The landscape evolution model accounts for the transport of sediment due to rain splash and fluvial entrainment as well as the deposition of sediment being advected by the overland flow. In order to develop realistic rill networks in the model, we find that it is necessary to incorporate the effects of raindrop impact within the fluvial sediment transport process. Model results are only consistent with those of experiments when raindrop‐aided fluvial sediment transport is accounted for. Dendritic networks are often predicted by the model in cases of high initial topographic roughness and high rates of advective (fluvial) sediment transport relative to diffusive (colluvial) transport. Parallel networks form within numerical experiments in low‐roughness cases under a wide range of relative advective and diffusive transport rates as well as in high roughness cases in which diffusive sediment transport is high relative to advective transport. The transition from dendritic to parallel rill networks is shown to occur gradually rather than being associated with a particular threshold. Finally, based on a balance between diffusive and advective sediment transport processes, we predict that the mean spacing between parallel rills scales with the square root of the ratio of diffusivity to channel erodibility.

Faecal bacteria exist in both free-living and attached forms in estuarine waters. The deposition of sediments can take faecal bacteria out of the water column and to the bed. The sediments can subsequently be re-suspended to the water column, which can then lead to re-suspension of the faecal bacteria of the attached forms back to the water column. Therefore, the fate and transport of faecal bacteria is highly related to the governing sediment transport processes, particularly where these processes are significant, such as the Severn Estuary, UK. However, little attempt has been made to model such processes in terms of predicting the impact of the sediment fluxes on faecal bacteria levels. Details are given of the refinement of a numerical model of faecal bacteria transport, where the sediment transport processes are significant. After testing the sediment-bacteria interaction model favourably against known results in previous study, the model was applied to the Severn Estuary and Bristol Channel, UK, to investigate the impact of suspended sediment fluxes on the corresponding faecal bacteria transport processes. The model predictions have proved to be encouraging, with the results being compared to a traditional faecal bacteria modelling approach, where sediment bacteria interactions were not included. The new model provides improved predictions of faecal bacteria concentrations when sediment transport is included and for the Bristol Channel Severn Estuary it can be seen that the effects of the sediments on the bacterial levels in the water column can be significant.

: A long-term goal of our sediment transport and deposition investigations is to link sediment-transport processes to the formation and preservation of event beds in sediment deposits. The general aim of this project is to investigate how forcing processes affect the sediment-transport dynamics that act to import or export fine-grained sediment in shallow-water regions with fine-grained sediment supply. We strive to understand how the delicate balance of ebb and flood sediment fluxes is maintained to create tidal flat and mangrove complexes, and distributary shoals and islands within tidal rivers. All of these environments are characterized by variable bathymetry and variable seabed stability, and our goal is to answer the question: How do the processes that control the transfer of fine-grained sediment, e.g., tidal (semidiurnal, fortnightly), riverine and other seasonal (winds/waves, precipitation temperature, and biological) processes influence the transport pathways, seabed erosion/deposition, and morphological development in shallow tidal systems? Understanding the transfer and transformation of sediment between terrestrial source and marine sink is essential for knowledge of global carbon budgets, landform evolution, and interpreting the stratigraphic record. Sediment is eroded, transported, and trapped via a myriad of processes along the continuum from terrestrial to oceanic environments. These processes are driven by the varying degrees of fluvial, wave, and tidal influence in each environment. At present, we are completing our studies on unvegetated tidal flats, and are ramping up our focus on sedimentary phenomena in relatively unstudied components within the source-to-sink framework: the connection between the tidal river and the subaqueous delta on the inner continental shelf, and sediment sinks within vegetated/mangrove shoreline complexes. Our overall hypothesis is that sediment-transport signals (magnitude, grain size, pathways) are modulated.

This study investigates bed load sediment transport dynamics in selected areas of Punatsangchhu River, focusing on rock type identification, their association with topography, grain size distribution, and factors influencing bed load transport rates. 1D numerical sediment transport modeling was also done in HEC-RAS 6.3.1 using the discharge data of four years from 2020 to 2023. Bed load sediment samples were collected from 55 plots laid systematically 500 meters apart along the river. Results reveal Granite as the predominant rock type, reflecting the region's geological complexity shaped by Himalayan tectonics. Significant associations between rock types and topography, particularly for Granite Boulder, highlight the complex interplay of topographic factors shaping sediment distribution. Bed load transport rates vary across sediment roundness and river reach types, with round particles exhibiting higher rates and riffles displaying greater transport than pools. Regression analysis confirms the significant influence of river velocity and bed slope on transport rates, emphasizing the importance of hydraulic factors in sediment transport processes. The output from HEC-RAS revealed the highest sediment concentration in this valley during the late summer months directly aligning with the higher flow in these seasons. During these years, critical bed changes in some of the cross-sections were also observed. RS 12521 has witnessed the highest deposition rate of about 2.5 meters and similarly, RS 7006 has witnessed the highest erosion rate of about 2.3 meters. Likewise, the profile plot of the river reveals a series of erosion and deposition processes during this time window, affecting the riverbed and consequently channel morphology.

Small-scale sediment scouring and siltation laws in the evolution trends of fluvial facies in the Ningxia Plain Reaches of the Yellow River (NPRYR)

The present study discusses flood hazard characteristics in the lower reaches of the West Rapti River based on the results obtained from field surveys and numerical computations using depth averaged 2-D numerical models for flood flow and associated sediment transportation. To evaluate the inundation process with sediment erosion and deposition in the floodplain, a new erosion term was introduced into the mass conservation equations for suspended sediment and bed sediment. The results obtained from numerical computations indicated that field data on the spatial distributions of depths for inundation, and sediment erosion and deposition can be evaluated by the numerical model. Thus, numerical predictions were performed for the inundated areas, and the accumulated volumes of sediment erosion/deposition for floods with return periods of 50, 100, and 200 years, as a step towards damage assessment and risk assessment due to floods with active sediment transportation in the floodplains.

The effects of bioturbation on sediment transport on an intertidal mudflat