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• Either climate data or streamflow data alone is not sufficient to accurately estimate SSL. • Gradient boosting models accurately predict SSL using hydro-climate data. • Hydrological metrics improve the accuracy SSL modeling during model calibration. • The prediction uncertainty of SSL increases with the basin's area. • Average ensemble modeling enhanced the accuracy of models in rivers. Machine learning (ML) models have the potential to improve the accuracy of Suspended Sediment Load (SSL) predictions. However, their ability to incorporate climate data to enhance SSL predictions remains underexplored. This study investigates the efficacy of ML models in modeling sediment transport using hydro-climate variables as input data. Boosted decision tree models, including Xgboost, LightGBM, and Catboost, were employed to estimate SSL using hydro-climate variables such as streamflow and precipitation, as well as maximum and minimum temperatures. The models were trained, optimized, and evaluated using either climate/streamflow data or a combination of both, encompassing 47 gauges across the contiguous United States (CONUS) between 1950 and 2022. The results demonstrate that streamflow data alone is insufficient for accurate SSL estimation in all rivers. Consequently, integrating climate data and streamflow data proved effective in predicting SSL at the daily scale across diverse climate zones with commendable accuracy. The models achieved an average Nash-Sutcliffe Efficiency (NSE) of > 0.66, Kling-Gupta Efficiency (KGE) of > 0.67, and Willmott Index (WI) of > 0.83 during the unseen (test) phase. These findings highlight the potential of ML models, particularly when combining climate data with streamflow, to enhance SSL predictions and improve our understanding of sediment transport dynamics. [ABSTRACT FROM AUTHOR]

Hydraulic geometry (HG) has long enabled daily discharge estimates, flood risk monitoring, and water resource and habitat assessments, among other applications. At-many-stations HG (AMHG) is a newly discovered form of HG with an evolving understanding. AMHG holds that there are temporally and spatially invariant (‘congruent’) depth, width, velocity, and discharge values that are shared by all stations of a river. Furthermore, these river-wide congruent hydraulics have been shown to link at-a-station HG (AHG) in space, contrary to previous expectation of AHG as spatially unpredictable. To date, AMHG has only been thoroughly examined on six rivers, and its congruent hydraulics are not well understood. To address the limited understanding of AMHG, we calculated AMHG for 191 rivers in the United States using USGS field-measured data from over 1900 gauging stations. These rivers represent nearly all geologic and climatic settings found in the continental U.S. and allow for a robust assessment of AMHG across scales. Over 60% of rivers were found to have AMHG with strong explanatory power to predict AHG across space (defined as r 2  > 0.6, 118/191 rivers). We also found that derived congruent hydraulics bear little relation to their observed time-varying counterparts, and the strength of AMHG did not correlate with any available observed or congruent hydraulic parameters. We also found that AMHG is expressed at all fluvial scales in this study. Some statistically significant spatial clusters of rivers with strong and weak AMHG were identified, but further research is needed to identify why these clusters exist. Thus, this first widespread empirical investigation of AMHG leads us to conclude that AMHG is indeed a widely prevalent natural fluvial phenomenon, and we have identified linkages between known fluvial parameters and AMHG. Our work should give confidence to future researchers seeking to perform the necessary detailed hydraulic analysis of AMHG. [ABSTRACT FROM AUTHOR]

Direct groundwater discharge delivers nutrients from land and lakebed sediments to the Great Lakes, which impacts lake water quality. Broad spatial distributions of discharging groundwater are often difficult to measure directly. We present high resolution estimates of direct groundwater discharge across 43% of the Great Lakes coastline based on a water budget approach that uses hydroclimatic models and high-resolution hydrographic data available within the United States. We also integrate land use data to identify coastal areas vulnerable to high groundwater-borne nutrient loads. Estimated rates of direct groundwater discharge along the Great Lakes coast are highly variable, but generally are greatest for Lake Erie and Lake Michigan. Almost one-third of Lake Erie’s United States coastline is vulnerable to groundwater sources of nutrients. To assess uncertainties and limitations in our vulnerability analysis, a vulnerable site along Lake Erie was selected for detailed field measurements of direct groundwater discharge rates and nutrient fluxes. Measured discharge rates were significantly lower than water budget-based estimates (354 ± 25 m 3 y −1 m −1 compared to 588 ± 181 m 3 y −1 m −1 ). Dissolved phosphorous concentrations in the lakebed were elevated compared to onshore groundwater, while nitrate concentrations were lower, indicative of a highly reactive sediment-water interface. Some of the measured phosphorus may be locally sourced from desorption of legacy P or mineralization of organic matter in the lakebed, which our vulnerability framework does not include. Much of the land-derived nitrogen may be transformed along groundwater flow paths prior to discharge. While model-based estimates of direct groundwater discharge and vulnerability to nutrient loading are important for managing Great Lakes water quality, direct field observations remain essential for quantifying fluxes. [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]

The Elwha River restoration project, in Washington State, includes the largest dam-removal project in United States history to date. Starting September 2011, two nearly century-old dams that collectively contained 21 ± 3 million m 3 of sediment were removed over the course of three years with a top-down deconstruction strategy designed to meter the release of a portion of the dam-trapped sediment. Gauging with sediment-surrogate technologies during the first two years downstream from the project measured 8,200,000 ± 3,400,000 tonnes of transported sediment, with 1,100,000 and 7,100,000 t moving in years 1 and 2, respectively, representing 3 and 20 times the Elwha River annual sediment load of 340,000 ± 80,000 t/y. During the study period, the discharge in the Elwha River was greater than normal (107% in year 1 and 108% in year 2); however, the magnitudes of the peak-flow events during the study period were relatively benign with the largest discharge of 292 m 3 /s (73% of the 2-year annual peak-flow event) early in the project when both extant reservoirs still retained sediment. Despite the muted peak flows, sediment transport was large, with measured suspended-sediment concentrations during the study period ranging from 44 to 16,300 mg/L and gauged bedload transport as large as 24,700 t/d. Five distinct sediment-release periods were identified when sediment loads were notably increased (when lateral erosion in the former reservoirs was active) or reduced (when reservoir retention or seasonal low flows and cessation of lateral erosion reduced sediment transport). Total suspended-sediment load was 930,000 t in year 1 and 5,400,000 t in year 2. Of the total 6,300,000 ± 3,200,000 t of suspended-sediment load, 3,400,000 t consisted of silt and clay and 2,900,000 t was sand. Gauged bedload on the lower Elwha River in year 2 of the project was 450,000 ± 360,000 t. Bedload was not quantified in year 1, but qualitative observations using bedload-surrogate instruments indicated detectable bedload starting just after full removal of the downstream dam. Using comparative studies from other sediment-laden rivers, the total ungauged fraction of < 2-mm bedload was estimated to be on the order of 1.5 Mt. [ABSTRACT FROM AUTHOR]

Abstract: The capacity of turbidity currents to carry sand and coarser sediment from shallow to deep regions in the submarine environment has attracted the attention of researchers from different disciplines. Yet not only are field measurements of oceanic turbidity currents a rare achievement, but also the data that have been collected consist mostly of velocity records with very limited or no suspended sediment concentration or grain size distribution data. This work focuses on two turbidity currents measured in Monterey Canyon in 2002 with emphasis on suspended sediment from unique samples collected within the body of these currents. It is shown that concentration and grain size of the suspended material, primarily controlled by the source of the gravity flows and their interaction with bed material, play a significant role in shaping the characteristics of the turbidity currents as they travel down the canyon. Before the flows reach their normal or quasi-steady state, which is defined by bed slope, bed roughness, and suspended grain size, they might pass through a preliminary adjustment stage where they are subject to capacity-driven deposition, and release heavy material in excess. Flows composed of fine (silt/clay) sediments tend to be thicker than those with sands. The measured velocity and concentration data confirm that flow patterns differ between the front and body of turbidity currents and that, even after reaching normal state, the flow regime can be radically disrupted by abrupt changes in canyon morphology. [Copyright &y& Elsevier]

Summary: The large Mississippi River flood in 2011 was notable in the lowermost Louisiana, USA reach for requiring operation of several flood control structures to reduce stress on artificial levees: the largest diversion went through the gated Bonnet Carré Spillway, which was opened for 42days in May and June. The removal of approximately 20% of the total flood discharge from the river provided an opportunity to examine the impact of large water diversion on the sediment transport capacity of large rivers. Boat-based, acoustic and water and bed sampling surveys were conducted in the Mississippi River channel adjacent to the Spillway immediately prior to the opening of the structure, at full capacity, and immediately following (June 2011) and 1year after (June 2012) closure. The surveys were designed to examine (1) elevation change of the channel bed due to scour or aggradation of sediment, and (2) suspended and bedload transport variability upriver and downriver of the Spillway. The results indicate that approximately 9.1million tons of sand were deposited on the channel bed immediately downriver of the water exit pathway and extending at least 13km downriver at a rapidly and progressively reducing magnitude per river kilometer. The surficial deposit was of finer grain size than the lateral sand bars in the channel upriver of the structure. We argue the deposit was largely delivered from suspension derived from the observed deflation of lateral bars upstream of the diversion point, rather than from sand arriving from the drainage basin. Approximately 69% of the 2011 flood deposit was removed from the 13km downstream reach between June 2011 and June 2012. We conclude that the source of the channel deposit was the reduction in stream power, and, thus, in the sediment transport capacity of the Mississippi, associated with the water withdrawal. The re-entrainment of this material in the following flood year indicates the system rapidly re-establishes an equilibrium to pre-opening conditions. Future diversions in the river for coastal restoration will have to address this issue to maintain a deep draft navigation channel in the Mississippi River. [Copyright &y& Elsevier]

Summary: Estimates of mean annual watershed sediment discharge, derived from long-term measurements of suspended-sediment concentration and streamflow, often are not available at locations of interest. The goal of this study was to develop multivariate regression models to enable prediction of mean annual suspended-sediment discharge from available basin characteristics useful for most ungaged river locations in the eastern United States. The models are based on long-term mean sediment discharge estimates and explanatory variables obtained from a combined dataset of 1201 US Geological Survey (USGS) stations derived from a SPAtially Referenced Regression on Watershed attributes (SPARROW) study and the Geospatial Attributes of Gages for Evaluating Streamflow (GAGES) database. The resulting regional regression models summarized for major US water resources regions 1–8, exhibited prediction R 2 values ranging from 76.9% to 92.7% and corresponding average model prediction errors ranging from 56.5% to 124.3%. Results from cross-validation experiments suggest that a majority of the models will perform similarly to calibration runs. The 36-parameter regional regression models also outperformed a 16-parameter national SPARROW model of suspended-sediment discharge and indicate that mean annual sediment loads in the eastern United States generally correlates with a combination of basin area, land use patterns, seasonal precipitation, soil composition, hydrologic modification, and to a lesser extent, topography. [Copyright &y& Elsevier]

Abstract: The ability to predict the effects of dam removal in highly sediment-filled systems is increasingly important as the number of such dam removal cases continues to grow. The cost and potential impacts of dam removal are site-specific and can vary substantially depending on local conditions. Of specific concern in sediment-impacted removals is the volume and rate of reservoir deposit erosion. The complexity and potential accuracy of modeling methods used to forecast the effects of such dam removals vary substantially. Current methods range from predictions based on simple analysis of pre-dam channel geometry to sophisticated data-intensive, three-dimensional numerical models. In the work presented here, we utilize data collected from past dam removals to develop an additional tool for predicting the rate and volume of sediment deposit erosion. Through the analysis of sediment, discharge, deposit, removal timeline, channel, and watershed data, in conjunction with post-removal monitoring data from a wide range of dam removal projects, some significant trends in the evolution of reservoir deposits following dam removal can be seen. Results indicate that parameters such as median grain size, level of cohesion, spatial variability of the deposit, and removal timeline are among the most influential factors in determining the rate and volume of sediment erosion. By comparing local conditions of dams and reservoirs slated for removal with those of past removals, we hope that predictions of the rate and volume of sediment deposit erosion can be usefully constrained. [Copyright &y& Elsevier]

Abstract: Echo Park Lake is a small lake in Los Angeles, CA listed on the USA Clean Water Act Section 303(d) list of impaired water bodies for elevated levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in fish tissue. A lake water and sediment sampling program was completed to support the development of total maximum daily loads (TMDL) to address the lake impairment. The field data indicated quantifiable levels of OCPs and PCBs in the sediments, but lake water data were all below detection levels. The field sediment data obtained may explain the contaminant levels in fish tissue using appropriate sediment–water partitioning coefficients and bioaccumulation factors. A partition-equilibrium fugacity model of the whole lake system was used to interpret the field data and indicated that half of the total mass of the pollutants in the system are in the sediments and the other half is in soil; therefore, soil erosion could be a significant pollutant transport mode into the lake. Modeling also indicated that developing and quantifying the TMDL depends significantly on the analytical detection level for the pollutants in field samples and on the choice of octanol-water partitioning coefficient and bioaccumulation factors for the model. [Copyright &y& Elsevier]

Abstract: The channel head, defined as the upstream boundary of concentrated water flow and sediment transport between definable banks, represents the transition from hillslope processes to fluvial processes. The ability to delineate the location along a slope at which channels initiate is important for understanding hydrologic and geomorphic processes governing headwater streams. Studies demonstrating an inverse relationship between either contributing drainage area (A) and local valley slope (θ) or basin length (L) and θ for channel heads come primarily from regions with humid climates. Seventy-eight channel heads were mapped in the headwaters of rivers in the semiarid Colorado Front Range. Multiple field sites were chosen to account for variability from aspect and elevation. Surface topographic parameters were measured in the field and analyzed to test the hypothesis that surface processes control channel initiation in this region. Although simple linear regressions indicate a poor inverse relationship between A and L and no relationship between L and θ, multiple regressions indicate that surface topographic parameters explain over half the variability in the location of channel heads. This suggests that surface processes exert an influence on channel initiation, but do not explain as much of the variability as observed in previous studies from wetter regions. A threshold of erosion necessary to initiate a channel was observed at ~10,000m2 for A, although values as high as 600,000m2 were mapped for some channel heads. Variation within the study area correlated with elevation, which is a proxy for differences in volume and type of precipitation; sites at lower elevation with less precipitation, but more intense convective rainfall, tend to have smaller contributing area and basin length. Aspect did not influence surface topographic parameters. We interpret the results to reflect surface and subsurface influences on channel initiation. Nearly 70% of the mapped channel heads coincide with constrictions created by weathered bedrock knobs, suggesting that local factors strongly influence channel initiation once the threshold for contributing area is exceeded. Field-mapped channel head locations plot at or downslope from the inflection point of a regional slope–area curve generated from 10m DEMs, although some extend well downslope into the region assumed to be dissected by alluvial channels. Most actual drainage areas for channel initiation are thus an order of magnitude larger, and plot in a significantly different portion of the slope–area graph, than would result from the widespread practice of assuming channel heads are located at the gradient reversal in such curves. [Copyright &y& Elsevier]

Abstract: The modern Great Basin of the interior western United States is characterized by surface winds with considerable spatial and temporal variabilities. Wind records from the second half of the 20th century for 12 Great Basin localities, analyzed with standard aeolian-sediment transport methods developed elsewhere in the world, reflect this complexity. The drift potential (DP) for aeolian deposits is generally moderate (DP 200–400) in the western Great Basin and weak (DP<200) in the central Great Basin where winds are predominantly west-southwesterly. DP is relatively high (DP>300) at the eastern edge of the Great Basin where the dominant prevailing wind direction is south-southwesterly. Both DP and resultant drift direction (RDD) are consistent with synoptic meteorological observations of the evolution of cold fronts in the Great Basin. Meteorological observations show that effective winds to produce dunes are most commonly the result of late winter–early spring cyclogenesis. There has been considerable temporal variability of DP in the latter half of the 20th century. Most of the Great Basin has experienced decreasing wind strength since 1973, consistent with recent studies of wind strength in North America and elsewhere. Dune morphology matches both localized RDD and temporal variations in DP reasonably well in the Great Basin. The results demonstrate that local topography can have an important influence on wind directionality, thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record. [Copyright &y& Elsevier]

Abstract: The majority of water and sediment discharge from the small, mountainous watersheds of the US West Coast occurs during and immediately following winter storms. The physical conditions (waves, currents, and winds) within and acting upon the proximal coastal ocean during these winter storms strongly influence dispersal patterns. We examined this river–ocean temporal coherence for four coastal river–shelf systems of the US West Coast (Umpqua, Eel, Salinas, and Santa Clara) to evaluate whether specific ocean conditions occur during floods that may influence coastal dispersal of sediment. Eleven years of corresponding river discharge, wind, and wave data were obtained for each river–shelf system from USGS and NOAA historical records, and each record was evaluated for seasonal and event-based patterns. Because near-bed shear stresses due to waves influence sediment resuspension and transport, we used spectral wave data to compute and evaluate wave-generated bottom-orbital velocities. The highest values of wave energy and discharge for all four systems were consistently observed between October 15 and March 15, and there were strong latitudinal patterns observed in these data with lower discharge and wave energies in the southernmost systems. During floods we observed patterns of river–ocean coherence that differed from the overall seasonal patterns. For example, downwelling winds generally prevailed during floods in the northern two systems (Umpqua and Eel), whereas winds in the southern systems (Salinas and Santa Clara) were generally downwelling before peak discharge and upwelling after peak discharge. Winds not associated with floods were generally upwelling on all four river–shelf systems. Although there are seasonal variations in river–ocean coherence, waves generally led floods in the three northern systems, while they lagged floods in the Santa Clara. Combined, these observations suggest that there are consistent river–ocean coherence patterns along the US West Coast during winter storms and that these patterns vary substantially with latitude. These results should assist with future evaluations of flood plume formation and sediment fate along this coast. [Copyright &y& Elsevier]

Abstract: This paper details the historical coastal evolution of the Columbia River littoral cell in the Pacific Northwest of the United States. Geological data from A.D. 1700 and records leading up to the late 1800s provide insights to the natural system dynamics prior to significant human intervention, most notably jetty construction between 1885 and 1917. All reliable surveys, charts, and aerial photos are used to quantify decadal-scale changes at the three estuary entrances and four sub-cells of the littoral cell. Shoreline, bathymetric, and topographic change over three historical intervals—1870s–1920s, 1920s–1950s, and 1950s–1990s—are integrated to provide an understanding of sediment-sharing relationships among the littoral cell components. Regional morphological change data are developed for alongshore segments of approximately 5km, enabling comparisons of shoreline change to upper-shoreface and barrier volume change within common compartments. The construction of entrance jetties at the Columbia River (1885–1917) and Grays Harbor (1898–1916) has profoundly affected the evolution of the littoral cell, and has accentuated the morphological coupling between the inlets, ebb-tidal deltas, shorefaces, and barriers. The jetties induced erosion of the inlets and offshore migration of ebb-tidal deltas. The change in boundary conditions at the entrances enabled waves to rework the flanks of ebb-tidal deltas and supply enormous quantities of sand to the adjacent coasts. Over several decades the initial sand pulses have been dispersed alongshore up to tens of kilometers from the estuary entrances. Winter waves and coastal currents produce net northward sediment transport across the shoreface while summer conditions tend to induce onshore sediment transport and accumulation of the upper shoreface and barriers at relatively high rates. Historical shoreline progradation rates since jetty construction are approximately double the late prehistoric rates between 1700 and the 1870s. Erosion rates of the mid- to lower shoreface to the south of the jettied estuary entrances have typically been greater than the accumulation rates of the upper shoreface and barrier, suggesting that the lower shoreface has been an important source of littoral sediments over decadal and longer time scales. Until recent decades, sediment supply from the ebb-tidal delta flanks and lower shoreface has largely masked the decline in Columbia River sediment supply resulting from flow regulation and dredging disposal practices. With the contemporary onset and expansion of coastal erosion adjacent to the jettied estuary entrances, proper management of dredged sediment is imperative to mitigate the effects of a declining sediment budget. [Copyright &y& Elsevier]

Abstract: Previous investigations suggest that contaminant transport from the large Kennebec/Androscoggin watershed is an important large-scale process in mid-coast Maine. To investigate this phenomenon, we determined the concentrations of Cd, Cr, Cu, Ni, Pb, Sn and Zn in the surface sediments of 47 stations in the tidal Kennebec/Androscoggin system. Most stations exhibited elevated metal concentrations. Highest levels were found in the main stem of the system. Distribution patterns lead to the conclusion that metals enter the system from the watershed and are transported to the nearshore Gulf of Maine. The coarse-grained, ebb tide dominated flow prevents the accumulation of contaminants in the estuary. This supports the hypothesis of that the Kennebec and Androscoggin watersheds are sources for contaminants observed in the nearshore Gulf of Maine. [ABSTRACT FROM AUTHOR]

Abstract: Sediment is an important environmental factor for aquatic ecosystem and oyster productivities of Apalachicola Bay located in Florida, USA. Based on the data analysis in this study, surface wind speed is highly correlated to the turbidity of water column, which results from sediment resuspension and transport in the Apalachicola Bay. In this paper, an application of a 3D sediment transport model to predict the wind-induced sediment transport in Apalachicola Bay is described. The sediment model is coupled with a 3D hydrodynamic module in the Environmental Fluid Dynamics Code (EFDC) model that provides information on estuarine circulation and salinity transport under normal temperature conditions. The hydrodynamic model was calibrated with field observations of water levels and salinity. The sediment transport model solves the transport equation with sources and sinks terms to describe sediment deposition and resuspension. The coupled hydrodynamic and sediment transport models were used to investigate wind-induced total suspended sediments (TSS) resuspension and transport in the bay. For the period June 1–July 30, 2005 two storm events with strong winds gave model results of TSS concentrations that compared well with the field observations. Model simulations reasonably reproduce the sudden increase of sediment concentrations during the storm events. Maximum sediment concentrations in the bay during the two storm events were 10 times or more than those in the pre-storm conditions. Spatial sediment transport from model simulations indicate active sediment resuspension and transport near areas of highly productive oyster beds. The model predictions of TSS and salinity can be used as inputs to an oyster dynamic model (Wang, H., Huang, W., Harwell, M., Edmiston, L., Johnson, E., Hsieh, P., Milla, K., Christensen, J., Stewart, J., Liu, X., 2008. Modeling eastern oyster population dynamics in response to changing environment in Apalachicola Bay, Florida. Journal of Ecological Modeling 211, 77–89) to support the ecological study of oyster growth and mortality in the aquatic ecosystem of Apalachicola Bay. [Copyright &y& Elsevier]

Abstract: The role of fire in shaping steep, forested landscapes depends on a suite of hydrologic, biologic, and geological characteristics, including the propensity for hydrophobic soil layers to promote runoff erosion during subsequent rainfall events. In the Oregon Coast Range, several studies postulate that fire primarily modulates sediment production via root reinforcement and shallow landslide susceptibility, although few studies have documented post-fire geomorphic response. Here, we describe field observations and topographic analyses for three sites in the central Oregon Coast Range that burned in 1999, 2002, and 2003. The fires generated strongly hydrophobic soil layers that did not promote runoff erosion because the continuity of the layers was interrupted by pervasive discontinuities that facilitated rapid infiltration. At each of our sites, fire generated significant colluvial transport via dry ravel, consistent with other field-based studies in the western United States. Fire-driven dry ravel accumulation in low-order valleys of our Sulphur Creek site equated to a slope-averaged landscape lowering of 2.5mm. Given Holocene estimates of fire frequency, these results suggest that fire may contribute 10–20% of total denudation across steep, dissected portions of the Oregon Coast Range. In addition, we documented more rapid decline of root strength at our sites than has been observed after timber harvest, suggesting that root strength was compromised prior to fire or that intense heat damaged roots in the shallow subsurface. Given that fire frequencies in the Pacific Northwest are predicted to increase with continued climate change, our findings highlight the importance of fire-induced dry ravel and post-fire debris flow activity in controlling sediment delivery to channels. [Copyright &y& Elsevier]

Abstract: The Muleshoe Dunes, an east–west trending dunefield on the border separating Texas and New Mexico, consist of two distinct components: a white (carbonate rich) component and an overlying pink (quartz rich) component. The pink component exhibits significant spatial variation in redness. The reddest sands, in the western part of the dunefield, decrease in redness towards the east. This gradient is thought to result from abrasion of an iron-rich, red clay coating as the sediments were transported eastward by Late Quaternary aeolian processes. The effects of aeolian abrasion on the spectral signature and surface texture of the sediments were examined using laboratory abrasion experiments. Changes in spectral reflectance of abrasion samples from the laboratory were compared to field samples that were abraded naturally because of sediment transport. The changes resulting from increased time of abrasion are similar to those observed with increased distance downwind in the dunefield. These results suggest that downwind abrasion can explain the pattern of dune colour in the Muleshoe Dunes, although this does not preclude other possible causes. [Copyright &y& Elsevier]

[Display omitted] • We proposed a method for fine-tuning stochastic modeling of sediment yield. • Underlying characteristics of sediment transport are used to tune the model. • Various stream regimes are examined to estimate/predict sediment yield. • Various ecoregions are investigated across the conterminous United States. • The effect of watershed properties on the sediment yield process is studied. Sediment transport is a major contributor to a non-point source of pollution impacted by various factors that are modulated by climatic changes and anthropogenic influences. Quantifying and disentangling the contribution of these factors to sediment yield at large scales and across different flow regimes has not been fully explored. Here we present a framework to fine-tune a stochastic sediment yield model by classifying discharge and Suspended Sediment Load (SSL) observations based on the underlying governing processes in unregulated streams with various hydrological regimes. This stochastic model, rooted in copula theory, constructs a joint distribution between discharge and SSL storm events using historical time series of observations, classified based on seasonality, hysteresis patterns, and hydrograph components of the sediment transport processes. We include hydrological, land use, and geological properties of the watersheds to describe and discuss the effects of different factors on applying the underlying dynamics to enhance sediment yield estimation/prediction accuracy. We evaluated the proposed method on 67 streams across the United States. Our results show significant improvements in sediment yield modeling performance. [ABSTRACT FROM AUTHOR]

Abstract: A pseudo-two-dimensional numerical model of estuarine phytoplankton growth and consumption, vertical turbulent mixing, and idealized cross-estuary transport was developed and applied to South San Francisco Bay. This estuary has two bathymetrically distinct habitat types (deep channel, shallow shoal) and associated differences in local net rates of phytoplankton growth and consumption, as well as differences in the water column''s tendency to stratify. Because many physical and biological time scales relevant to algal population dynamics decrease with decreasing depth, process rates can be especially fast in the shallow water. We used the model to explore the potential significance of hydrodynamic connectivity between a channel and shoal and whether lateral transport can allow physical or biological processes (e.g. stratification, benthic grazing, light attenuation) in one sub-region to control phytoplankton biomass and bloom development in the adjacent sub-region. Model results for South San Francisco Bay suggest that lateral transport from a productive shoal can result in phytoplankton biomass accumulation in an adjacent deep, unproductive channel. The model further suggests that turbidity and benthic grazing in the shoal can control the occurrence of a bloom system-wide; whereas, turbidity, benthic grazing, and vertical density stratification in the channel are likely to only control local bloom occurrence or modify system-wide bloom magnitude. Measurements from a related field program are generally consistent with model-derived conclusions. [Copyright &y& Elsevier]

A prominent vector of aquatic invasive species to coastal regions is the discharge of water, sediments, and biofilm from ships’ ballast-water tanks. During eight years of studying ships arriving to the lower Chesapeake Bay, we developed an understanding of the mechanisms by which invasive microorganisms might arrive to the region via ships. Within a given ship, habitats included ballast water, unpumpable water and sediment (collectively known as residuals), and biofilms formed on internal surfaces of ballast-water tanks. We sampled 69 vessels arriving from foreign and domestic ports, largely from Western Europe, the Mediterranean region, and the US East and Gulf coasts. All habitats contained bacteria and viruses. By extrapolating the measured concentration of a microbial metric to the estimated volume of ballast water, biofilm, or residual sediment and water within an average vessel, we calculated the potential total number of microorganisms contained by each habitat, thus creating a hierarchy of risk of delivery. The estimated concentration of microorganisms was greatest in ballast water≫sediment and water residuals≫biofilms. From these results, it is clear microorganisms may be transported within ships in a variety of ways. Using temperature tolerance as a measure of survivability and the temperature difference between ballast-water samples and the water into which the ballast water was discharged, we estimated 56% of microorganisms could survive in the lower Bay. Extrapolated delivery and survival of microorganisms to the Port of Hampton Roads in lower Chesapeake Bay shows on the order of 1020 microorganisms (6. 8×1019 viruses and 3. 9×1018 bacteria cells) are discharged annually to the region. [Copyright &y& Elsevier]

Summary: Bed-load measurements collected at the Las Vegas Wash, a gravel-bed stream near Las Vegas, Nevada, were used to study selective transport of sand and gravel in uni-modal or weakly bi-modal river sediment. Measurements showed that size selectivity in a sediment mixture decreases as shear stress increases. Transport of variously sized sediment particles approaches equal mobility as the transported bed load is composed approximately of the same size particles as surface-bed material. Consequently, a hiding function was derived to account for the increase or reduction in reference shear stress for an individual size class in a sediment mixture as compared with that in an uniformly sized sediment. An empirical equation for determining fractional bed-load transport rate was then formulated by correlating the dimensionless, fractional bed-load transport rate with the dimensionless bed-shear stress. This equation indicated that the hiding function depends not only on the size of individual size class but also on the flow depth used to quantify the magnitude of shear stress. The present study contributes to the body of knowledge used in predicting selective transport of sediment mixtures in gravel-bed streams. [Copyright &y& Elsevier]

Abstract: Recent research on the Mississippi margin indicates notable seasonal variation in seabed dynamics. During years with minimal tropical-system activity, sediments initially deposited from late spring to early fall are remobilized by wind-driven currents and wave energy during extra-tropical weather systems in the winter. This research reveals the profound significance of tropical cyclones on Louisiana Shelf sedimentation. The amount of material delivered to and advected across the shelf by recent tropical cyclones is considerably larger than that related to winter storm systems. In Fall 2004, the river-dominated shelf of Louisiana was impacted by three tropical systems in less than a month, including Hurricane Ivan. Ivan, with maximum sustained winds in excess of 74ms−1 (144 knots) and a minimum measured central pressure of 910mbar, was the eighth most intense Atlantic hurricane on record at the time. In order to assess the impact these tropical systems had on the continental margin west of the Mississippi delta, seabed samples were collected from box cores in October 2004 and analyzed for particle-reactive radionuclides 234Th, 7Be, and 210Pb. Radiochemical data and observations from X-radiographs indicate event-driven sediment deposits ranged from 4 to 30cm on the shelf and 2–6cm in the Mississippi Canyon. These deposits exhibit distinct radiochemical signatures and differ visually and texturally from the underlying sediment. The well-developed physical stratification and graded nature of the deposits observed in core X-radiographs suggests that the sediment could have been deposited from sediment-gravity flows. Inventories of 7Be and 7Be/234Thxs ratios reveal this series of cyclones transported considerably more material to the outer shelf and slope than periods of minimal tropical-system activity. When compared to seasonal depositional rates created by winter storms, tropical-cyclone-related event deposits on the middle and outer shelf are up to an order of magnitude greater in thickness. The number and thickness of these event deposits decrease with distance from the delta and suggest that only the most severe tropical systems are likely capable of redistributing significant quantities of sediment to more distal portions of the shelf and slope. These severe-event-driven deposits may account for as much as 75% of the sediment burial budget on decadal time scales within Mississippi Canyon. Higher than average tropical cyclone activity, predicted by the National Hurricane Center over the next decade, may be the major mechanism controlling sediment transport and deposition on the Mississippi River continental shelf and in Mississippi Canyon. [Copyright &y& Elsevier]

Abstract: Bryant and Eastern Canyons are located in northwest Gulf of Mexico, and are characterized by a complex sedimentological history related to glacioeustatic cycles, river discharges, and interactions between depositional and halokinetic processes. This study is based on detailed sedimentological analysis from forty-eight long cores from these two canyons. This paper determines the evolutionary history of the canyons and assesses the response of sedimentary processes to morphological, climatic, hydrological, and sea-level changes. During the last glaciation, the upper and middle continental slope was supplied with sediments by low density turbidity currents derived from the depositional segregation (deposition of the coarsest material in the most proximal locations) of large turbidity currents initiated on the outer shelf. The lower continental slope was supplied with sediment by westward flowing bottom currents, originated from the entrainment of the most diluted wash-load and tails of turbidity currents from the Mississippi Fan. Bryant and Eastern Canyon systems were active during the penultimate glaciation, Marine Isotope Stage (MIS) 6, and were supplied with sediments by an ancestral shelf-margin Mississippi River delta. Gravity flows transported enormous amounts of sediment to the continental slope and abyssal plain of the northwest Gulf of Mexico. The sea-level rise at MIS 5 led to confinement of river-sourced sediments to the widespread continental shelf of the northwest Gulf of Mexico, and consequently to the cessation of gravity flows. During the first 40 kyr of MIS 5, salt diapirs transformed the canyons into a network of intraslope basins. The sea level dropped to the mid-shelf during MIS 3 and 4, but never reached the shelf-break, and therefore, river-sourced sediments remained largely confined to the shelf. However, seaward sediment transportation was achieved occasionally through turbidity currents related to sediment failures, storms, and high-river discharges. Four high river discharge events have been identified during this period. The first three were centred at 37, 45, and 53 cal ka BP. The last high river discharge occurred at the end of MIS 3 (29.4-33.2 cal ka BP), and resulted in the deposition of closely-spaced, mud turbidites over the entire continental slope. The Laurentide Ice Sheet (LIS) was restricted north of the upper Mississippi River valley during 60 to ∼30 cal ka BP and therefore, the high river discharge events are interpreted as melt-water events, related to brief southward advancements of the LIS, which resulted in the flooding of Mississippi River. The extensive lowering of sea level during the last glacial maximum (MIS 2) resulted in the almost direct discharge of Mississippi River sediments to the upper continental slope leading to the development of abundant turbidity currents. Eleven wet–dry cycles during this period are defined; they probably originated from episodic subglacial melt-water floods, released from southern parts of the LIS. The last deglaciation event is characterized by the development of a major melt water event at 16.5–13 cal ka BP that resulted in the deposition of distinct, organic-rich sediments. At about 13 cal ka BP, the melt water discharges of the LIS in North America switched from the Mississippi River to either the St. Lawrence or Mackenzie River valleys, causing the domination of hemipelagic sedimentation on the continental slope of the northwest Gulf of Mexico. Isotopic data indicate that melt-water discharges returned to the Mississippi River Valley at ∼11.4 cal ka BP. The absence of any sedimentological indication on the continental slope of the northwest Gulf of Mexico of the return of the melt-water discharges to the Mississippi River is attributed to the confinement of river-sourced sediments on the continental shelf due to the rise of the sea level. [Copyright &y& Elsevier]

Abstract: The formation and spatial evolution of Chandeleur Island, Louisiana, has been investigated extensively during the past several decades. No significant evaluation of the longshore sediment system, which is instrumental in the island''s evolution and morphodynamic maintenance, has been completed. This paper provides the first quantitative description of the longshore transport system that operates along this transgressive, overwash-dominated barrier island system. The net longshore sediment transport system was investigated via the wave refraction model, WAVENRG, which provided estimates of the transport volumes and drift directions alongshore. Surficial samples were collected from the foredune, midtide and step environments in an effort to characterize the sediments along the island and determine if textural or compositional trends have developed in response to a predicted longshore sediment transport system. Data obtained during this research indicate that the longshore transport system along Chandeleur Island is characterized by a bi-directional drift system, with drift directed both north and south from a nodal point located in the south-central portion of the barrier island. Analysis of the predicted transport volumes indicates that the degree of wave refraction, and therefore the breaker angle, is more instrumental in controlling the alongshore volume rate of sediment transport than the breaker wave heights. Additionally, a larger magnitude of sediment transport is predicted in the southern portion of the barrier, which is in a greater state of deterioration than the north and central portion of the island. This apparent contradiction indicates that factors such as a variable subsidence rate along the island are contributing to the alongshore geomorphology. No significant textural or compositional trends were identified alongshore. This absence of granulometric trends is attributed to the lack of variability of the sediments that comprise the barrier and the frequency of overwash events which occur on this low-profile island. [Copyright &y& Elsevier]

Summary: River-training structures, such as spur dikes, are effective engineered methods used to protect banks and improve aquatic habitat. This paper reports the development and application of a two-dimensional depth-averaged hydrodynamic model to simulate suspended sediment concentration distribution in a groyne field. The governing equations of flow hydrodynamic model are depth-averaged two-dimensional Reynold’s averaged momentum equations and continuity equation in which the density of sediment laden-flow varies with the concentration of suspended sediment. The depth-averaged two-dimensional convection and diffusion equation was solved to obtain the depth-averaged suspended sediment concentration. The source term is the difference between suspended sediment entrainment and deposition from bed surface. One laboratory experiment was chosen to verify the simulated flow field around a groyne, and the other to verify the suspended sediment concentration distribution in a meandering channel. Then, the model utility was demonstrated in a field case study focusing on the confluence of the Kankakee and Iroquois Rivers in Illinois, United States, to simulate the distribution of suspended sediment concentration around spur dikes. Results demonstrated that the depth-averaged, two-dimensional model can approximately simulate the flow hydrodynamic field and concentration of suspended sediment. Spur dikes can be used to effectively relocate suspended sediment in alluvial channels. [Copyright &y& Elsevier]

Abstract: Channel pattern effectively stratifies the dynamics of rivers and floodplains in forested mountain river systems of the Pacific Northwest, USA. Straight channels are least dynamic, with relatively slow floodplain turnover and floodplains dominated by old surfaces. Braided channels are most dynamic, with floodplain turnover as low as 25 years and predominantly young floodplain surfaces. Island-braided and meandering channels have intermediate dynamics, with moderately frequent disturbances (erosion of floodplain patches) maintaining a mix of old and young surfaces. Return intervals for the erosion of floodplains increase in the order of braided, island-braided, meandering, and straight (8, 33, 60, and 89 years, respectively). A threshold for the lateral migration of a channel occurs at a bankfull width of 15–20 m. The most likely mechanism underlying this threshold is that larger channels are deep enough to erode below the rooting zone of bank vegetation. Above this threshold, channels not confined between valley walls exhibit channel patterns distinguishable by slope and discharge, and slope–discharge domains can be used to predict channel patterns. Meandering and braided patterns are most consistently identified by the model, and prediction errors are largely associated with indistinct transitions among channel patterns that are adjacent in plots of slope against discharge. Locations of straight channels are difficult to identify accurately with the current model. The predicted spatial distribution of channel patterns reflects a downstream decline in channel slope, which is likely correlated with a declining ratio of bed load to suspended load. Ecological theory suggests that biological diversity should be highest where the intermediate disturbance regime of island-braided channels sustains high diversity of habitat and successional states through time. [Copyright &y& Elsevier]

Abstract: Factors that control the routing and storage of sediments in the Appalachian region are poorly understood. This study involves a comparative geomorphic analysis of three watersheds underlain by sandstones and shales of the Acadian clastic wedge. These areas include the Fernow Experimental Forest, Tucker County, West Virginia; the North Fork basin, Pocahontas County, West Virginia; and the Little River basin, Augusta County, Virginia. GIS-based analyses of surficial map units allow first-order approximation of sediment-storage volumes in valley bottoms. Estimates of volumes are examined in tandem with morphometric analyses and the distribution of bedrock channels to make inferences regarding controls on sediment-transport efficiency in the central Appalachians. The Fernow and North Fork areas are characterized by V-shaped valleys with mixed reaches of alluvial-bedrock channels distributed throughout the drainage network. In contrast, the Little River valley is notably wider and gravelly alluvial fill is abundant. Comparator watershed parameters for the Fernow, North Fork and Little River areas include, respectively: (1) basin area=15.2 km2, 49.3 km2, 41.5 km2; (2) basin relief=0.586 km, 0.533 km, 0.828 km; (3) drainage density=4.2 km−1, 3.3 km−1, 4.7 km−1; (4) ruggedness=2.5, 1.7, 3.9; (5) Shreve magnitude=139, 287, 380; (6) total valley-bottom area (km2)=0.76 km2, 1.86 km2, 3.09 km2; (7) average hillslope gradients=17.2°, 18.4°, 22.1°; (8) total debris-fan surface area=0.113 km2, 0.165 km2, 0.486 km2; and (9) debris-fan frequency=2.0 km−2, 1.0 km−2, 2.8 km−2. The storage volumes in valley bottoms were estimated using map polygon areas and surface heights above channel grade. The Little River contains significantly higher sediment volumes in floodplain, terrace and fan storage compartments; total volumes of the valley bottoms are approximately twice that of the Fernow and North Fork areas combined. Unit storage volumes for the Fernow, North Fork and Little River are 5.2×104 m3 km−2, 5.5×104 m3 km−2 and 1.6×105 m3 km−2, respectively. A conceptual model postulates that valley-width morphometry and style of delivery from hillslopes are the primary factors controlling the efficiency of sediment transport. Steep, debris-flow-prone hillslopes at the Little River deliver high volumes of gravelly sediment at magnitudes greater than transport capacity of the channel. Patterns of stream power are complex, as low-order tributaries are under capacity and high-order tributaries over capacity with respect to sediment load. Aggraded alluvial fill insulates valley-floor bedrock from vertical erosion and valley widening dominates. Expansion of the valley width creates a positive response via increased storage capacity and lower unit stream power. Conversely, the Fernow and North Fork are characterized by diffusive mass movement on hillslopes with incremental bedload transport to higher-order tributaries. Rates of hillslope delivery are balanced by the rate of channel export. Mixed alluvial-bedrock reaches provide the optimal channel configuration for active incision of the valley floor. Low expansion of valley width promotes high unit stream power and processes of vertical erosion. The model implies that the Fernow and North Fork have been more effective at sediment transport during the Late Quaternary. Given similar climatic and tectonic settings, variation in bedrock lithofacies is likely the primary factor modulating the efficiency of sediment transport. [Copyright &y& Elsevier]

Abstract: Recent studies regarding the climate variability in South America during the 20th century, revealed the existence of climate cycles that influenced the hydrologic conditions in the Paraná River basin, one of the largest in the continent. How that variability affected the channel morphology of this river in its middle reach is quantitatively analyzed in this paper. The link between climate, hydrology and channel morphology is obtained through the computation of effective discharge. This discharge implicitly synthesizes the point hydrologic and bed sediment transport changes in an alluvial stream during a relatively long period. The results were obtained studying, with increasing detail, two channel reaches 373 km and 25 km long, respectively. The analysis involved the processing of more than 180 bathymetric charts, satellite images and hydraulic and sedimentologic data recorded in the Paraná River since the very beginning of the 20th century. A rather detailed description of the treatment made with this information is given in the paper. It is shown that three periods of different effective discharges fairly well correlated with reported climatic fluctuations occurred during the last 100 years, i.e. two periods of high discharges (at the century beginning and from 1970 till present) and another of relatively low discharges between 1930 and 1970. Morphologic parameters of the main channel, such as mean width, thalweg sinuosity, braided index and aspect ratio, increased or decreased in correspondence with those variations. In transitional channels (between meandering and braided) like the Paraná River, careful study of the thalweg behavior is a key issue, if a proper approach to the dynamic of morphologic processes operating on the whole channel is intended. Finally, on the basis of theoretical (extreme hypotheses approach) and empirical results, it is suggested that the Paraná River main channel would not be adjusted to the present high values of effective discharge. Thus, larger erosion of banks (channel widening) and increases in the other cited morphologic characteristics will occur if those values persist. [Copyright &y& Elsevier]

Abstract: This paper presents an overview of tropical river systems around the world and identifies major knowledge gaps. We focus particularly on the rivers draining the wet and wet–dry tropics with annual rainfall of more than 700 mm/year. The size of the analyzed river basins varies from 104 to 6×106 km2. The tropical rivers across the globe drain a variety of geologic–geomorphologic settings: (a) orogenic mountains belts, (b) sedimentary and basaltic plateau/platforms, (c) cratonic areas, (d) lowland plains in sedimentary basins and (e) mixed terrain. All of them show clearly high but variable peak discharges during the rainy season and a period of low flow when rainfall decreases. Some tropical rivers show two flood peaks, a principal and a secondary one, during the year. We computed the intensity of floods and discharge variability in tropical rivers. The relationship between sediment yield and average water discharge for orogenic continental rivers of South America and Asia was also plotted. Insular Asian rivers show lower values of sediment yield related to mean annual discharge than continental orogenic rivers of Asia and South America. Rivers draining platforms or cratonic areas in savanna and wet tropical climates are characterized by low sediment yields. Tropical rivers exhibit a large variety of channel form. In most cases, and particularly in large basins, rivers exhibit a transition from one form to another so that traditional definitions of straight, meandering and braided may be difficult to apply. In general, it is more useful to apply the terminology of single and multi-channel systems or complex anabranching systems at least for selected regional segments. Present-day knowledge of tropical systems and its potential application to improve interpretation of older alluvial sequences and facies models are briefly discussed. Human impact and river management issues including land use changes, mining, dams, interbasin water transference as well as flood hazards are some of the daunting problems in tropical river basins today. [Copyright &y& Elsevier]

Agricultural practices dominate over climatic variability in determining temporal variability in dust blowing on cropland in the USA. Farming operations that increase wind erosion and dust emissions include plowing, leveling beds, planting, weeding, seeding, fertilizing, mowing, cutting, baling, spreading compost or herbicides and burning fields. Methods of controlling sediment loss include planting windbreaks and special crops to alter wind flow; retaining plant residue after harvesting; tilling soil to bury erodible particles, create aggregates that resist entrainment, and increase surface roughness; improving farm equipment; and stabilizing soil surfaces using water or commercial products. Government programs prescribe air quality standards, provide education programs, and cost-share and incentive payments to assist farmers in controlling erosion and dust production. Problems continue because farmers do not consider wind erosion a significant problem. Dust events have nevertheless decreased in some areas, indicating that improved management practices may be effective where accepted by farmers. [Copyright &y& Elsevier]

Parent materials greatly influence soil development and the distribution of soils on the southeastern US Coastal Plain. We examined the physical, chemical, and mineralogical properties of 11 pedons in a 1-ha plot on the Upper Coastal Plain of Georgia, USA. Uniformity of parent materials was assessed by sand grain size characteristics. The soils have sandy epipedons of variable thickness and argillic horizons of variable texture. Six of the pedons also have kandic horizons. They are classified (US Soil Taxonomy) in Psammentic, Grossarenic, Arenic, and Typic subgroups of Paleudults and Kandiudults. Loamy pedons possess argillic horizons with two distinct increases in clay and greater differences between eluvial and illuvial horizons than sandy pedons. The upper boundary of the argillic horizon is approximately parallel to the present geomorphic surface, suggesting that it is associated with the contemporary surface. Discontinuities, identified by changes in sand grain size ratios and plots of the third (skewness) and fourth (kurtosis) moments of sand grain distribution, roughly correspond to the bottom of the solum. Our data suggest that there are both eolian and fluvial components in the solum, whereas subjacent horizons are completely derived from fluvial deposits. Sandier pedons have greater gibbsite/kaolinite ratios, possibly because greater permeability has enhanced leaching and Si loss. Our data suggest parent materials largely control soil distribution over this plot. [Copyright &y& Elsevier]

During the late Holocene, sediment deposition on the lowland Cosumnes River floodplain, CA has depended on factors that varied temporally and spatially, such as basin subsidence, sea level rise, flow, and sediment supply from both the Sacramento River system and from the Cosumnes River system itself, and anthropogenic changes. Through field investigations and analyses of historical maps, bridge core logs, and sediment size distributions, we link hydrogeomorphic processes to three stages of floodplain sedimentation on the lowland Cosumnes River. Stage I (1000–200 YBP) combined late Holocene pre-disturbance flood basin overflow and anastomosing river processes deposited spatially variable sediment consisting of gray–blue clay (87% clay) interlayered with relatively thin coarser sediment. Pre-disturbance Holocene deposition rates of up to ∼3.0 mm/year kept pace with sea level rise and tectonic basin subsidence. Stage II (200 to ∼10 YBP) anthropogenic disturbances caused a rapid increase in floodplain sedimentation rates up to 25 mm/year between 1849 and ∼1920, and deposited a relatively coarser reddish-brown sandy clay (∼40% clay) layer that overlies the basin deposits. Between ∼1920 and 1990 AD, sedimentation was greatly limited on the lower Cosumnes floodplain because levees inhibited connectivity between both the Sacramento and Cosumnes River systems and the Cosumnes floodplain. During this stage, the density of channel segments in the anastomosing river floodplain decreased by 30% as agricultural activities filled secondary channels and leveled floodplain topography. During Stage III (∼10 YBP to the present), post-rehabilitation floodplain sand splay complex sediment deposited after 1998 AD resulted from intentionally breaching levees to promote habitat at the Cosumnes River Preserve. The splay complex is dominated by medium to very coarse sand with finer intervening layers. The post-rehabilitation splay complex overlies the older basin deposits in a generally upward coarsening sequence that reflects depositional processes and land use changes that continue to affect the lowland Cosumnes River floodplain. [Copyright &y& Elsevier]

Equal-mobility transport (EMT) of bed load is more evident than size-selective transport during near-bankfull flow events in a small, step-pool channel in the Ouachita Mountains of central Arkansas. Bed load transport modes were studied by simulating five separate runoff events with peak discharges between 0.25 and 1.34 m3/s (1.0- to 1.6-year recurrence intervals) in a natural channel using controlled releases from a storage tank. EMT occurrence was investigated using four different bed load relationships suggested by previous research. With each of these approaches, the relationship of a given bed load characteristic (Dmax, distribution percentile, displacement distance and skewness) to some independent factor (τc*, τ and grain size) was assessed to determine which transport mode was evident. Regression models derived using combinations of these four relationships with different datasets provide seven separate tests. Five of the seven tests indicate that EMT occurred or was predominant. Several reasons may explain the apparent contradictory results, but the confounding effects of changes in the structural arrangements of bed material prior to or during the events seem particularly important. [Copyright &y& Elsevier]

Historical aerial photographs and topographic survey sheets are used to establish a 70-year shoreline history (1926–1996) for Kailua Beach, Oahu, Hawaiian Islands. The shoreline has migrated seaward over this period at an average rate of 0.5 m/yr, with a maximum net accretion along the beach of 58.7 m and a maximum net erosion of −13.2 m. Net accretion has taken place even while sea levels have risen on the order of 0.1 m. Semi-annual and monthly beach profile surveys (1995–1999) at seven transects reveal short-term variations of shoreline position, sand volume, and beach shape. A relationship between beach width and corresponding sand volume fluctuations, established from the beach profile data, is applied to the historical shoreline change data to establish a history of sand volume fluctuations. Results show that Kailua has experienced a net accretion of 673 000 m3 of sand over the period 1926–1996, with average annual rates of volume change varying between 6.8 m3/m/yr and −0.1 m3/m/yr. The most recent period (1989–1996) shows a net volume increase of 41 000 m3. Given the lack of sand inputs at the ends of the beach, exchange with offshore deposits is a likely mechanism for long-term accretional trends. Seasonal fluctuations in Kailua Beach morphology dominate the variability with a response to seasonal wave state that varies along the length of the beach in magnitude and sign. At least four alongshore zones are observed, with the first and third zones exhibiting high/low sand volumes during the summer/winter, and the second and fourth zones exhibiting opposite behavior with high/low volumes during the winter/summer. Although seasonal sand accumulation varies along the beach, the overall beach profile is largely maintained. Moreover, changes in sand volume occur in phase over the subaqueous and subaerial sections of the beach. This behavior suggests that longshore rather than cross-shore sand transport is important at annual time scales. A simple seasonal transport pattern is proposed to account for these observed fluctuations, which depends in part on the topography of the offshore reef. [Copyright &y& Elsevier]

Sediment of Ostrich Bay, an arm of Dyes Inlet on Puget Sound, was historically contaminated with ordnance compounds from an onshore US Navy facility. An initial recommendation for a sediment cover to mitigate benthic risks was followed by studies of sediment transport and deposition to determine whether contaminated sediment from Dyes Inlet or other offsite sources in Puget Sound may contribute to Ostrich Bay impacts. A Sediment Trend Analysis (STA®) identified net sediment transport pathways throughout the bay and inlet by examining changes in grain size distributions in multiple adjacent samples. Results indicated that fine-grained sedimentary material transports into and deposits throughout the Dyes Inlet system, with no erosion or transport out of Ostrich Bay. Echinoderm larvae mortality bioassay results were elevated in fine-grained sediments of both Ostrich Bay and Dyes Inlet. Ordnance compounds were undetected, and although sediment mercury concentrations were elevated at 0.48–1.4 mg/kg in both waterbodies, the relationship with toxicity was weak. Results of the studies and sedimentation modeling indicate that impacted sedimentary material deposits throughout the Dyes Inlet/Ostrich Bay system from unknown sources and will prevent natural recovery of Ostrich Bay as well as negate long-term effectiveness of active remedial measures. Stakeholders have recognized that remediation of the bay can be achieved only after the toxicity of depositing sediment decreases. [Copyright &y& Elsevier]

In describing suspended sediment conditions in the lower Chesapeake Bay, VA, USA, this paper reports and develops methods for distinguishing multiple particle populations in the bottom boundary layer of estuaries in general. In addition, a novel application of the acoustic Doppler velocimeter (ADV) is shown to estimate in situ particle fall velocity at a single point without affecting the ambient turbulence. In situ estimates of suspended sediment concentration from ADV, optical backscatter, and laser in situ scattering and transmissometry (LISST) instruments are compared with gravimetrically determined mass concentrations from pumped water samples. In this environment, acoustic backscatter from the ADV proved to be the best estimator of mass concentrations due to its apparent insensitivity to the size or density of muddy aggregates. The concentration estimates and the relative sensitivities of the instruments to particle size and density combined with size distribution information from the LISST reveal the characteristics of multiple particle populations in the bottom boundary layer. Two rapidly settling sediment populations are suggested with similar fall velocities but distinct critical erosion stresses. A slowly settling background population is also identified whose concentration varies over meteorological time scales. Fall velocities are estimated analytically from a balance of settling and diffusive flux gradients using two methods, one employing Reynolds concentration flux, and the other estimating eddy diffusivity using the von-Karman Prandtl equation. Comparison of the local change and advective terms in the solute transport equation to the magnitude of the settling term suggests that a balance between the settling and resuspension term is a good first order approximation at this site, validating the indirect method for estimating settling velocity. Single elevation estimates of fall velocity using the ADV to estimate Reynolds concentration flux produced the best estimates of fall velocity which are on the order of 1 mm/s. [Copyright &y& Elsevier]

We combine direct observations, longer-term wave data, and model calculations to characterize resuspension and transport of fine-grained, effluent-affected sediment on the Palos Verdes shelf. Near-bed waves, currents, and suspended sediment concentrations were monitored during the winter of 1992–93 with a bottom tripod and current-meter mooring at a 63-m-deep site. Wave conditions that winter were moderate (∼2 year recurrence interval), and mean current was alongshelf to the northwest; currents were not significantly correlated with wave conditions. Seven wave events during the winter (December–March) produced near-bed wave orbital velocities at the study site in excess of 14 cm s−1, the observed threshold for significant resuspension. Three of these events occurred during the bottom tripod deployment and are characterized by the highest persistent suspended sediment concentrations in the tripod record. Suspended sediment flux was alongshelf to the northwest for 5 of the 6 wave events for which current data were available; one event occurred during low southeast currents. Measured suspended sediment concentration and grain size generally agree with values that were calculated using a shelf sediment transport model with no adjustment of parameters from values determined for two muddy sites on the northern California shelf. We extend our seasonal observations to a period of almost 2 decades by applying the observed thresholds for wave-driven resuspension to near-bed wave conditions calculated from NDBC Buoy 46025 surface wave data. An average of 10 resuspension events per year, with an average duration of 1.6 days, were identified at a water depth of 60 m; the number of events dropped to 3 per year at 90 m, beyond the shelf break. For the majority of these events, calculated net suspended sediment flux is toward the northwest (alongshelf) at an average rate of 140 kg m−1 h−1; about a third of the events have net southeastward flux at an average rate of 30 kg m−1 h−1. The calculated thickness of the resuspended surface layer of the bed was less than 1 cm for all events at 60 m. [Copyright &y& Elsevier]

A conceptual model is presented for the northern Monterey Bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf. Data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine-grained sediment introduced into Monterey Bay. The principal sources of the fine sediment are the three rivers that enter Monterey Bay: the San Lorenzo, Pajaro and Salinas rivers. Accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion, and also are high relative to other documented mud accumulations of the west coast continental shelves. [Copyright &y& Elsevier]

Identification of fluvial-to-marine transitions is often problematic in Neoproterozoic and Cambrian strata due to the absence of diagnostic, physical, and/or biogenic sedimentary structures. This study highlights the identification of a fluvial-to-marine transition in a post-rift setting. Siliciclastic sediments of the Early Cambrian Hardyston Formation, in eastern Pennsylvania, are assigned into four facies associations (FA A–D), within which a fluvial-to-marine transition can be delimited. The lowermost subdivision, FA A, consists typically of thick-bedded, fining-upward beds of structureless, pebbly conglomerate that grade into structureless sandstone. Within the uppermost FA A, structureless sandstone is replaced by trough and planar, cross-stratified sandstone. FA A is best interpreted as deposits of a bedload-dominated, braided fluvial system. FA B consists of densely packed Skolithos burrows, thick-bedded, normally graded sandstone with rare poorly preserved tabular-planar and trough cross-beds near its upper boundary. Sedimentary structures in FA B are analogous to those found in a shoreface setting. Normally graded beds reflect deposition from waning storm-induced flow, with structured sandstone recording possible fair-weather or post-storm reworking. The fluvial–marine transition lies at the abrupt change from FA A to FA B and is identified by vertical changes from: (1) feldspathic to quartz sandstone, (2) fluvial bar to shoreface storm deposits, and (3) nonbioturbated to bioturbated strata. Additionally, heavy minerals are concentrated along the boundary. FA C is composed of trough cross-stratified conglomerate and sandstone with paleocurrents interpreted as shore-parallel and offshore-directed marine currents. FA C represents a marginal-marine setting reflecting a gradation from FA B to FA D, including characteristics of both Skolithos of FA B and a number of sedimentary structures indicative of FA D. FA D consists of offshore-directed, tabular-planar and trough cross-stratified quartz sandstone separated by thin siltstone–mudstone beds. Some tabular-planar cross-stratified beds contain obliquely oriented ripples on siltstone-draped pause planes. Preserved sinuous-crested dunes with superimposed current ripples cap some cross-bed cosets. The presence of tidal currents is inferred to be the mechanism responsible for the formation of FA D in a probable subtidal marine setting. The Hardyston Formation accumulated in response to thermal or jerky subsidence. Aggradational fluvial deposits developed as a result of the initial Sauk trangression. The fluvial–marine transition most probably records the shoreface retreat unconformity. [Copyright &y& Elsevier]

A portable system for bedform-mapping was evaluated in the delta of the lower Sacramento and San Joaquin Rivers, California, from 1998 to 2000. Bedform profiles were surveyed with a two-person crew using an array of four single-beam transducers on boats about 6 m in length. Methods for processing the bedform profiles into maps with geographic coordinates were developed for spreadsheet programs and surface-contouring software. Straight reaches were surveyed every few days or weeks to determine locations of sand deposition, net transport directions, flow thresholds for bedform regimes, and bedform-transport rates. In one channel of unidirectional flow, the portable system was used to record changes in bedform regime through minor fluctuations of low discharge, and through high discharges near channel capacity. In another channel with reversing flows from tides, the portable system recorded directions of net bedload-transport that would be undetectable by standard bedload sampling alone. [Copyright &y& Elsevier]

• Prescribed fire promoted herbaceous growth in bare interspaces. • Litter enhanced infiltration and provided protection against erosion. • Increased vegetation cover altered flow paths and reduced runoff and soil loss. • Reduced soil surface connectivity post-fire improved hydrologic function. • Hydrologic function continues to improve 9 yr after fire. Woody species encroachment into herbaceous and shrub-dominated vegetations is a concern in many rangeland ecosystems of the world. Arrival of woody species into affected rangelands leads to changes in the spatial structure of vegetation and alterations of biophysical processes. In the western USA, encroachment of pinyon (Pinus spp.) and juniper (Juniperus spp.) tree species into sagebrush steppes poses a threat to the proper ecohydrological functioning of these ecosystems. Prescribed fire has been proposed and used as one rangeland improvement practice to restore sagebrush steppe from pinyon-juniper encroachment. Short-term effects of burning on the ecohydrologic response of these systems have been well documented and often include a period of increased hydrologic and erosion vulnerability immediately after burning. Long-term ecohydrologic response of sagebrush steppe ecosystems to fire is poorly understood due to lack of cross-scale studies on treated sites. The aim of this study is to evaluate long-term vegetation, hydrologic, and erosion responses at two pinyon-juniper-encroached sagebrush sites 9 years after prescribed fire was applied as a restoration treatment. Thirty-six rainfall simulation experiments on 6 m × 2 m plots were conducted for 45 min under two conditions: a dry run (70 mm h−1; dry antecedent soils) and a wet run (111 mm h−1; wet antecedent soils). Runoff and erosion responses were compared between burned and unburned plots. Overall, increases in herbaceous cover in the shrub-interspace areas (intercanopy area between trees) at both sites 9 years post-burn resulted in runoff- and erosion-reduction benefits, especially under the wet runs. While the initially more degraded site characterized by 80% bare ground pre-burn, registered a higher overall increase (40% increase) in canopy cover, greater post-fire reductions in runoff and erosion were observed at the less degraded site (57% bare ground pre-burn). Runoff and erosion for the wet runs decreased respectively by 6.5-fold and 76-fold at the latter site on the burned plots relative to control plots, whereas these decreases were more muted at the more degraded site (2.5 and 3-fold respectively). Significant fragmentation of flow paths observed at the more-degraded site 9 years post-fire, suggests a decreased hydrologic connectivity as a mechanism of runoff and erosion reduction during post-fire recovery. [ABSTRACT FROM AUTHOR]

This paper summarizes the findings of a workshop convened in the United States in 2018 to discuss methods in coastal and estuarine modeling and to propose key areas of research and development needed to improve their accuracy and reliability. The focus of this paper is on physical processes, and we provide an overview of the current state-of-the-art based on presentations and discussions at the meeting, which revolved around the four primary themes of parameterizations, numerical methods, in-situ and remote-sensing measurements, and high-performance computing. A primary outcome of the workshop was agreement on the need to reduce subjectivity and improve reproducibility in modeling of physical processes in the coastal ocean. Reduction of subjectivity can be accomplished through development of standards for benchmarks, grid generation, and validation, and reproducibility can be improved through development of standards for input/output, coupling and model nesting, and reporting. Subjectivity can also be reduced through more engagement with the applied mathematics and computer science communities to develop methods for robust parameter estimation and uncertainty quantification. Such engagement could be encouraged through more collaboration between the forward and inverse modeling communities and integration of more applied math and computer science into oceanography curricula. Another outcome of the workshop was agreement on the need to develop high-resolution models that scale on advanced HPC systems to resolve, rather than parameterize, processes with horizontal scales that range between the depth and the internal Rossby deformation scale. Unsurprisingly, more research is needed on parameterizations of processes at scales smaller than the depth, including parameterizations for drag (including bottom roughness, bedforms, vegetation and corals), wave breaking, and air–sea interactions under strong wind conditions. Other topics that require significantly more work to better parameterize include nearshore wave modeling, sediment transport modeling, and morphodynamics. Finally, it was agreed that coastal models should be considered as key infrastructure needed to support research, just like laboratory facilities, field instrumentation, and research vessels. This will require a shift in the way proposals related to coastal ocean modeling are reviewed and funded. • Standards are needed for I/O, benchmarks, coupling/nesting, grids, and validation. • Methods for robust parameter estimation and uncertainty quantification are needed. • Models should resolve scales between the depth and the Rossby deformation scale. • Models for bottom drag, wave breaking, and air–sea interactions should be improved. • Improved sediment transport, nearshore circulation, morphodynamics models are needed. [ABSTRACT FROM AUTHOR]