Maximum Suspended Sediment Concentration Research Articles

Simulating the near-field dynamic plume behavior of disposed fine sediments

Projections of the effects of fine sediment disposals, relevant for managed estuaries and tidally influenced coastal areas, are typically based on numerical far-field models. For an accurate consideration of the disposal itself, near-field models are often needed. The open source near-field model, PROVER-M, simulates the relevant processes of the physics based, dynamic behavior of disposed fine sediments in coastal waters and is applied in this study. First, new small scale laboratory experiments of instantaneous disposals are presented, documenting the dynamic behavior of fine material disposed in shallow waters. Second, results of the PROVER-M model are shown for disposals in three different settings: (1) a field-scaled study complementary to the laboratory set-up, (2) a parametric study of sequentially varied model input and (3) a far-field model coupling for estimation of the PROVER-M impact. By comparing results of the laboratory experiments to the PROVER-M model, the physical behavior of PROVER-M is successfully validated. The impact of the ambient setting and dredged material parameters is evaluated by the PROVER-M simulations, where the results show non-linear, complex interdependencies of the input parameters on disposal properties in dependence of ambient site conditions and material composition. In this context, limits of the model application are assessed and critically discussed. Finally, an exemplary coupling to a far-field model based on a real set of disposals in the tidally influenced Weser estuary (Germany) illustrates the potential impact of PROVER-M for assessing far-field suspended sediment concentration (SSC), with increased maximum SSC values of up to 10%.

Simulating liquefaction-induced resuspension flux in a sediment transport model

Wave-induced liquefaction is a geological hazard under the action of cyclic wave load on seabed. Liquefaction influences the suspended sediment concentration (SSC), which is essential for sediment dynamics and marine water quality. Till now, the identification of liquefaction state and the effect of liquefaction on SSC have not been sufficiently accounted for in the sediment model. In this study, we introduced a method for simulating the liquefaction-induced resuspension flux into an ocean model. We then simulated a storm north of the Yellow River Delta, China, and validated the results using observational data, including significant wave heights, water levels, excess pore water pressures, and SSCs. The liquefaction areas were mainly distributed in coastal zones with water depths less than 12 m, and the simulated maximum potential soil liquefaction depth was 1.39 m. The liquefaction-induced SSC was separated from the total SSC of both liquefaction- and shear-induced SSCs by the model, yielding a maximum liquefaction-induced SSC of 1.07 kg·m−3. The simulated maximum proportion of liquefaction-induced SSC was 26.2% in regions with water depths of 6–12 m, with a maximum significant wave height of 3.4 m along the 12 m depth contour. The erosion zone at water depths of 8–12 m was reproduced by the model. Within 52.5 h of the storm, the maximum erosion thickness along the 10 m depth contour was enhanced by 33.9%. The model is applicable in the prediction of liquefaction, and provides a new method to simulate the SSC and seabed erosion influenced by liquefaction. Model results show that liquefaction has significant effects on SSC and seabed erosion in the coastal area with depth of 6–12 m. The validity of this method is confined to certain conditions, including a fully saturated seabed exhibiting homogeneity and isotropic properties, small liquefaction depth, residual liquefaction dominating the development of pore pressures, no influence by structures, and the sediment composed of silt and mud that experiences frequent wave-induced liquefaction.

Dynamic behaviors of suspended sediment and chlorophyll-a in intertidal flats under episodic meteorological events

Intertidal flats are important shallow-water habitats and buffers against coastal erosion. Strong, short-lasting meteorological events, such as storms and rainfall, are the main mechanisms of transporting (in)organic materials and sediments. Two in-situ mooring systems were installed simultaneously in the tidal channel and mudflat of Jeungdo, Korea, to understand the dynamic behaviors of suspended sediment and chlorophyll-a (chl-a) under the episodic events. During fair-weather periods with a distinct tidal cycle, the sediment in the mudflat was resuspended during the flood and then advected to the tidal channel during the ebb. The maximum suspended sediment concentration (SSC) and chl-a under storm event were approximately 9 and 2 times higher than those under fair-weather periods, respectively. Under rainfall event, the maxima were approximately 7 and 1.2 times higher than fair-weather, suggesting that sediment and microphytobenthos were highest resuspended by the meteorological events. In addition, a time lag (∼ 1.5 h) between SSC and chl-a occurred in the tidal channel during ebb tide with a rainfall event. During the post-rainfall periods, the SSC and chl-a increased, showing a positive relationship with the bed shear stress, suggesting that the rainfall event could reduce sediment stabilization.

Response of runoff-sediment processes to vegetation restoration patterns under different rainfall regimes on the Loess Plateau

Vegetation restoration dominates the changes of land surface and then results in the reduction of runoff and sediment yield within a catchment. This study investigated the responses of runoff and sediment yield to vegetation restoration patterns under different rainfall regimes in the paired catchments: Yangjiagou (0.87 km2) with afforestation restoration (Y-AR) and Dongzhuanggou (1.15 km2) with natural restoration (D-NR) on the Loess Plateau. A total of 133 and 164 measured flood events, respectively, were selected to access this investigation in the two catchments during 1954–1965 and 2005–2017. Compared with natural restoration, the benefits of annual runoff and sediment reduction by afforestation reached 60.4 % and 75.1 %, and the high-flow events (peak discharge: 0.1–27.1 m3/s) reduced by 78 %. The 190 erosive rainfall events were categorized into three rainfall regimes, including long-duration and low-intensity (LDLI), short-duration and heavy-intensity (SDHI), short-duration and low-intensity (SDLI). Under each rainfall regime, the flood events in the D-NR had sharply risen with high discharge and sediment peaks, whereas the events had relatively flattened hydrographs and sedigraphs with low peaks in the Y-AR. Hysteresis analysis suggested that anticlockwise and eight-shaped (or more complex) anticlockwise loops were the dominant types in the Y-AR and D-NR, respectively. The power regression model indicated good relationships for rainfall-runoff and rainfall-sediment under regimes LDLI and SDHI in the Y-AR, whereas it was slightly worse in the D-NR. By contrast, afforestation significantly reduced discharge peak and maximum suspended sediment concentration of SDLI events by 59.6 % and 46 %, respectively. Afforestation played a critical role in the difference in runoff-sediment yield processes between the two restoration patterns through the direct vegetation cover and increased ET (evapotranspiration) and soil properties changes. The findings could provide valuable insights on hydrological responses to different vegetation restoration patterns and improve the understanding for watershed management on the Loess Plateau.

Rainstorm sediment events in heterogeneous karst small watersheds: Process characteristics, prediction modeling and management enlightenment

Frequent rainstorms caused by climate change are causing significant stresses and impacts on karst zones and even global hydrological systems. However, few reports have focused on rainstorm sediment events (RSE) based on long series, high-frequency signals in karst small watersheds. Present study assessed the process characteristics of RSE and analyzed the response of specific sediment yield (SSY) to environmental variables using random forest and correlation coefficients. Management strategies are then provided based on revised index of sediment connectivity (RIC) visualizations, sediment dynamics and landscape patterns, and modeling solutions for SSY are explored through the innovative use of multiple models. The results showed that the sediment process showed high variability (CV > 0.36), and the same index had obvious watershed differences. Landscape pattern and RIC show highly significant correlation with mean or maximum suspended sediment concentration (p<0.01, |r|>0.235). Early rainfall depth was the dominant factor affecting SSY (Contribution = 48.15 %). The hysteresis loop and RIC infer that the sediment of Mahuangtian and Maolike mainly comes from downstream farmland and riverbeds, while Yangjichong comes from remote hillsides. The watershed landscape is centralized and simplified. In the future, patches of shrubs or herbaceous plants should be added around the cultivated land and at the bottom of the sparse forest to increase the sediment collection capacity. The backpropagation neural network (BPNN) is optimal for modeling SSY, particularly for running the variables preferred by the generalized additive model (GAM). This study provides insight into understanding RSE in karst small watersheds. It will help the region to cope with future extreme climate change and develop sediment management models that are consistent with regional realities.

Comparing in situ turbidity sensor measurements as a proxy for suspended sediments in North-Western European streams

Climate change in combination with land use alterations may lead to significant changes in soil erosion and sediment fluxes in streams. Optical turbidity sensors can monitor with high frequency and can be used as a proxy for suspended sediment concentration (SSC) provided there is an acceptable calibration curve for turbidity measured by sensors and SSC from water samples. This study used such calibration data from 31 streams in 11 different research projects or monitoring programmes in six Northern European countries. The aim was to find patterns in the turbidity-SSC correlations based on stream characteristics such as mean and maximum turbidity and SSC, catchment area, land use, hydrology, soil type, topography, and the number and representativeness of the data that are used for the calibration. There were large variations, but the best correlations between turbidity and SSC were found in streams with a mean and maximum SSC of >30–200 mg/l, and a mean and maximum turbidity above 60–200 NTU/FNU, respectively. Streams draining agricultural areas with fine-grained soils had better correlations than forested streams draining more coarse-grained soils. However, the study also revealed considerable differences in methodological approaches, including analytical methods to determine SSC, water sampling strategies, quality control procedures, and the use of sensors based on different measuring principles. Relatively few national monitoring programmes in the six countries involved in the study included optical turbidity sensors, which may partly explain this lack of methodological harmonisation. Given the risk of future changes in soil erosion and sediment fluxes, increased harmonisation is highly recommended, so that turbidity data from optical sensors can be better evaluated and intercalibrated across streams in comparable geographical regions.

Contrast of fine sediment dynamics between shoals and channels in a microtidal estuary with mixed semi-diurnal tides

Estuaries usually feature complex bathymetries, where shoals and channels are co-existent. Due to the differences in water depth, current, density gradient and therefore stratification, sediment dynamics on the shoal and in the channel demonstrate significant variations. In this study, field measurements were carried out during spring and neap tides in both wet and dry seasons in the Huangmaohai Estuary, a microtidal estuary located in the southwest of the Pearl River Delta. Harmonic analysis was conducted for the timeseries data of current and suspended sediment concentration (SSC) for each deployment. Sediment transport flux was decomposed into an advective component, and tidal pumping fluxes by different tidal constituents. During the neap tides, sediment transport is primarily controlled by the advective flux, whereas during the spring tides, tidal pumping fluxes become comparable to, sometimes even exceeding, the advective one. For a 25-hr period, the M1 component of SSC usually denotes the maximum SSC associated with the highest bottom stress, while the M2 component signifies the two highs of the SSC. The M4 component is generally insignificant. The M1 and M2 components can be induced by both the advection and bottom resuspension. For the resuspension part, the M1 component is mostly induced by tidal velocity asymmetry, while the M2 component is generated by tidal straining effect. Sediment transport at the shoal is mostly controlled by the advective flux and the tidal pumping due to tidal velocity asymmetry, while that in the channel is dictated by advective transport and the tidal pumping due to tidal mixing asymmetry.

Investigating the effect of biochar application on raindrop-driven soil erosion under laboratory rainfall experiments

Rainfall soil erosion is mainly initiated by raindrop splashing. Many studies have addressed the role of biochar in water and soil conservation; however, the processes and mechanisms of soil erosion via raindrop splashing with biochar application remain unclear. Thus, this study investigated raindrop-driven erosion in a silt loam red soil mixed with different ratios of biochar (i.e., 0, 3 %, and 5 %) and groups with different biochar particle sizes (i.e., <0.5, 0.5–1, and 1–2 mm) under artificial rainfall experiments with a high rainfall intensity (68.5 mm/h). A Hydrus 1D combined Rose soil erosion model was employed to explain the hydro-erosion processes. Our experimental results showed that the maximum suspended sediment concentration (SSC) eroded in the surface runoff increased from 12.77 to 14.15 and 15.41 g/L as the amount of biochar application increased from 0 to 3 % and 5 %, respectively. Owing to the decreased infiltration capability, increased surface runoff volume and SSC resulted in the largest amount of suspended sediment (SS) in the 5 % biochar group. Moreover, the biochar grain size also affected raindrop-driven erosion. The mid-sized biochar (0.5–1 mm) had the highest effect on the SSC and the total amount of SS; however, the finer biochar (<0.5 mm) inhibited SS accumulation. Model simulations indicated that biochar application potentially increased the fraction of erodible particles and soil detachability, thereby enhancing raindrop splash erosion. Given that contaminants could diffuse as solid bound (i.e., soil and biochar) and dissolved forms, the trade-off between decreased leaching and increased surface load, or vice versa, under biochar application requires further research to evaluate the associated environmental transport and fate.

Rainfall event‐based surface runoff and erosion in small watersheds under dairy and direct‐seeding grain production

AbstractA 3‐year study on erosion and streamflow was conducted in two adjacent paired watersheds that flow into the Passo Real reservoir, one of the largest and most important reservoirs for human water supply and power generation in southern Brazil. The watersheds have similar land use and soil management, but different size and riparian vegetation. The first objective of the study was to monitor and evaluate hydrosedimentological dynamics and effects of riparian vegetation, over a range of rain events, in the two watersheds; the second was to assess the ability of the Limburg Soil Erosion Model (LISEM) to represent these small watersheds in hydrosedimentological terms (runoff and erosion) under individual rain events, in the context of better understanding the role of riparian vegetation and land cover. LISEM is a hydrological model structured on physically based equations that can be used for planning and conservation purposes. Studied rainfall events between 2016 and 2018 had a wide range in total rainfall (10–170 mm), rainfall intensity in 1 h (3–66 mm h−1), stream peak flows (4–5741 L s−1), runoff volume (0.02–40 mm), runoff coefficient (0.1–32%), maximum suspended sediment concentration (20–19 611 mg L−1), and sediment yield (0.002–33.790 Mg km−2). Both watersheds showed a rapid response to rain events with significant runoff generation. Abundance of unpaved roads (often parallel to the slope) promoted high runoff due to channelization effects. South Watershed has 59% more riparian vegetation than North Watershed, but this greater riparian vegetation was not effective in reducing surface runoff and erosion. Furthermore, local adoption of no‐tillage was insufficient to control runoff and sediment yield.

Suspended sediment dynamics in macrotidal turbid Hangzhou Bay during Typhoon Chan-hom

Typhoons are extreme weather events that cause serious social and economic losses in coastal and estuarine areas worldwide. Understanding the impact of typhoons on sediment dynamics is essential for protecting coastal areas from these marine disasters. Hangzhou Bay is macro-tidal, turbid, and frequently affected by strong typhoons. In this study, we established and validated a three-dimensional model coupling waves, current, and sediment to investigate the sediment dynamics in Hangzhou Bay during Typhoon Chan-hom. The results showed that high suspended sediment concentration (SSC) areas during the typhoon were mainly located at the bay head and near the southern shore near the Andong tidal flat. The maximum bottom SSC was at least twice that near the surface. The peak bottom SSC values at the peak flood (6 g/L) were larger than those at the peak ebb (5 g/L) owing to the stronger current velocity at peak flood. The SSC near the northern shore was larger at the peak flood than at other times, and the SSC was high at the southern shore at peak ebb at the cross-section near the Andong tidal flat. The typhoon impacted SSC by changing the bottom stress. SSC was most influenced by wave action, followed by wind stress action, and was least influenced by air pressure action, which contributed 71.3%, 69.9%, and 1.8% to the bottom stress, respectively. Our findings are scientifically important for research on geomorphological evolution and are practically meaningful for coastal management.

Combining sediment fingerprinting and hydro-sedimentary monitoring to assess suspended sediment provenance in a mid-mountainous Mediterranean catchment

Soil erosion and sediment transport are controlled by complex factors promoting variable responses in catchment's erosion rates and sediment yields. To mitigate eventual negative effects derived from altered fluxes, integrated catchment management plans should assess the sediment cascade from upstream erosive processes, sediment mobilization through hillslopes and within the channel, up to downstream sediment yields. This study links hydro-sedimentary dynamics with sediment fingerprinting source ascription in a mid-mountainous Mediterranean catchment during five hydrological years (2013–2018). Soil colour parameters and fallout radionuclides were used as tracers to predict dominant suspended sediment sources using (i) a Bayesian mixing model (MixSIAR) and (ii) an End Member Mixing Analysis (EMMA). MixSIAR suggested that crops were the dominant source in most of the collected samples. EMMA showed similar results, clustering all except one sediment samples close to the crop and channel bank signatures. In addition, a quantitative hysteresis index was calculated and floods were clustered in function of their hydro-sedimentary characteristics. Despite different patterns were associated to each of the four identified clusters (e.g. different sediment loads and maximum suspended sediment concentrations), correlation between sediment origin and hydro-sedimentary variables was not significant due to the little seasonal variation in source type ascription.

Influences of conservation measures on runoff and sediment yield in different intra-event-based flood regimes in the Chabagou watershed

The Loess Plateau in China has suffered severe soil erosion. To control soil erosion, extensive conservation measures aimed at redistributing rainfall, hindering flow velocity and intercepting sediment were implemented on the Loess Plateau. To accurately evaluate the combined effect of conservation measures in the Chabagou watershed, this study classified intra-event-based floods into four regimes via cluster and discriminant analyses. Regime A was characterized by short flood duration and low erosive energy, regime B was characterized by short flood duration and high erosive energy, regime C was characterized by long flood duration and low erosive energy, and regime D was characterized by long flood duration and high erosive energy. The results indicated that peak discharge (qp), runoff depth (H), mean discharge (qm), and runoff erosion power (E) decreased by 75.2%, 56.0%, 68.0% and 89.2%, respectively, in response to conservation measures. Moreover, area-specific sediment yield (SSY), average suspended sediment concentration (SCE), and maximum suspended sediment concentration (MSCE) decreased by 69.2%, 33.3% and 11.9%, respectively, due to conservation measures. The nonlinear regression analysis revealed a power function relationship between SSY and E in both the baseline (1961–1969) and measurement period (1971–1990) in all regimes. Conservation measures reduced sediment yield by not only reducing the runoff amount and soil erosion energy but also transforming the flood regime, for example, transforming a high-sediment-yield regime into a low-sediment-yield regime. Moreover, conservation measures altered the SSY-E relationship in regime A, whereas no obvious difference in regime B or C/D was observed between the measurement period and the baseline period. This study provides a better understanding of the mechanism of runoff regulation and the sediment yield reduction under comprehensive conservation measures in a small watershed on the Chinese Loess Plateau.

Sediment transport, turbidity, and dissolved oxygen responses to annual streambed drawdowns for downstream fish passage in a flood control reservoir

Sediment transport, turbidity, and dissolved oxygen were evaluated during six consecutive water years (2013–2018) of drawdowns of a flood control reservoir in the upper Willamette Valley, Oregon, USA. The drawdowns were conducted to allow volitional passage of endangered juvenile chinook salmon through the dam's regulating outlets by lowering the reservoir elevation to a point where the historical streambed was exposed and transported water and sediment through the reservoir dam. Sediment loads during the drawdown were highest in the first year of monitoring, with a computed value of 40,200 metric tons over a 5-day drawdown, followed by 5 years of lower sediment loads and lower sediment transport rates, suggesting that much of the stored sediment within the reservoir thalweg was transported out of the reservoir in the early years of the consecutive drawdowns. Suspended sediment concentrations (SSC) computed using turbidity and streamflow data resulted in maximum SSC at the onset of the drawdowns, with the highest computed values occurring during the water year 2017 drawdown at 17,500 mg/L (turbidity = 2,990 FNU), and average drawdown SSC values ranging from 654 to 3,950 mg/L for the six years of monitoring. Computed SSC were on the lower range of concentrations that could be harmful to out-migrating juvenile salmon published in other studies. High amounts of particulate organic matter and sand-sized material in drawdown SSC samples affected relations between turbidity and SSC, requiring the use of multiple surrogate regression models over short time frames. Dissolved oxygen minimum values were recorded in two of the monitoring years, with a minimum value of 0.71 and 3.4 mg/L recorded at the onset of the drawdowns in water years 2016 and 2018, respectively. Dissolved oxygen values below 4 mg/L lasted for 1 h, suggesting a rapidly expressed chemical oxygen demand. The response of suspended sediment loads and SSC highlight the site-specific nature of reservoir drawdowns, and the need for evaluation of expected sediment responses for drawdowns being considered at other locations.

Suspended sediment dynamics and associated hydro-meteorological interrelations in east rathong glacier, eastern himalaya, india

The records of suspended sediments and associated hydro-meteorology of the glacierized catchments are very limited in Sikkim Himalaya. Therefore, we carried out the first-ever estimate of suspended sediment transport from the meltwater stream of East Rathong Glacier for June-September during three consecutive melt seasons (2013–2015). These records were used to estimate the suspended sediment concentration (SSC), load (SSL), yield (SSY) and erosion rate (ER). The daily mean SSC was 105.75, 84.20, and 91.51 mg/l during melt seasons of 2013–2015 respectively. The monthly mean SSC of the combined melt season of 2013–2015 was 92.72, 107.14, 105.93 and 60.46 mg/l for June-September, respectively. The observation shows that July-August contributed to maximum SSC, accounting 70.45% of total SSC. Similarly, the monthly mean SSL for June-September was 55.64, 69.61, 65.75 and 25.72 tons, respectively. We observed high variability in SSL (CV = 0.54) than SSC (CV = 0.38) since the estimation of SSL depends on both discharge (Q) and SSC. The relationship between monthly mean SSC and Q was highly significant (R2 = 0.98) than daily SSC and Q (R2 = 0.25) due to reduced variability on a monthly scale. Further, mean SSY in the catchment was high during peak melting season (July-August), which substantially reduced during the end of the melting season. We estimated the mean SSY of 281.93 ton/yr km2 during the combined melt season (2013–2015). The average ER for the East Rathong Glacier basin was 1.04 mm/yr, which is lower than the ER of most of the Himalayan glaciers. We observed significant meteorological control of Tmean, Tmax and Rainfall in the transportation of suspended sediments from meltwater stream at a monthly scale. These in-situ based records on dynamics of suspended sediment and associated hydro-meteorological parameters are relevant for the planning and management of freshwater resources and planning for hydropower projects under a changing climate.

Insights on the Impacts of Hydroclimatic Extremes and Anthropogenic Activities on Sediment Yield of a River Basin

Streamflow and sediment flux variations in a mountain river basin directly affect the downstream biodiversity and ecological processes. Precipitation is expected to be one of the main drivers of these variations in the Himalayas. However, such relations have not been explored for the mountain river basin, Nepal. This paper explores the variation in streamflow and sediment flux from 2006 to 2019 in central Nepal’s Kali Gandaki River basin and correlates them to precipitation indices computed from 77 stations across the basin. Nine precipitation indices and four other ratio-based indices are used for comparison. Percentage contributions of maximum 1-day, consecutive 3-day, 5-day and 7-day precipitation to the annual precipitation provide information on the severity of precipitation extremeness. We found that maximum suspended sediment concentration had a significant positive correlation with the maximum consecutive 3-day precipitation. In contrast, average suspended sediment concentration had significant positive correlations with all ratio-based precipitation indices. The existing sediment erosion trend, driven by the amount, intensity, and frequency of extreme precipitation, demands urgency in sediment source management on the Nepal Himalaya’s mountain slopes. The increment in extreme sediment transports partially resulted from anthropogenic interventions, especially landslides triggered by poorly-constructed roads, and the changing nature of extreme precipitation driven by climate variability.

PENDEKATAN MODEL KOMPUTASI UNTUK PENANGGULANGAN SEDIMENTASI PELABUHAN AKIBAT PENGARUH MUARA SUNGAI: STUDI KASUS PELABUHAN TANJUNG MAS SEMARANG

Shoaling due to sedimentation process leads to the problem of port operation, where ships have a problem to navigate inside the port. The problem of the operation can lead to the reduction of the profit margin for the port. This paper discusses the engineering solution to solve the sedimentation problem because of the estuary inflow. In order to analyze the sedimentation behavior, computational model deploys as a tool for the assessments. The simulation results are validated by observation data; water level observation one month and current measurement for fifteen days. Simulation results show that the sedimentation in Tanjung Mas port mostly because of estuary inflow in the West and in the East side of the port with maximum suspended sediment concentration around 0,15 kg/m3. Sedimentation problems can be solved both by dredging and refunctioning of the breakwater. In the dredging process, the existing dumping area has an appropriate location since the sedimentation dispersion still in the offshore area. Refunctioning of the breakwater can also reduce the sedimentation effectively, it is shown by morphological model results where siltation process both near the navigation channel and inside the port can be blocked by the structure.

A two-decade record of variations in suspended sediment in the Warta River, a lowland river in western Poland

Fluctuations in suspended sediment concentration (SSC) has been investigated in the Warta River (western Poland), based on data obtained for the period 1961–1980 from three gauge stations located in upstream, middle-stream and downstream areas. Over the two decades, the SSC values demonstrated wide fluctuations and an overall increase at each gauge station. No significant correlation was generally observed between SSC and discharge but high SSC was found to follow low discharge and increasing temperature during the summer seasons in some years. Measurements of SSC and discharge were used to estimate total annual suspended sediment load (SSL). SSL values were found to increase downstream along with an increase in discharge. SSC decreases along the river course. However, when it comes to changes over time, SSL variability was mainly determined by SSC changes. The maximum SSC values were primarily caused by anthropogenic factors: the disposal of mine wastewater upstream, river training works, increased urbanisation and the intensification of sewage disposal. Where the river catchment has been greatly affected by anthropogenic factors, a denudation index calculated solely based on SSC and discharge does not appear to reflect the actual denudation rate, and must be treated with caution.

Analysing hydrological and sediment transport regime in two Mediterranean intermittent rivers

Flow and the sediment regime affect water quality and nutrient delivery in all river systems and are fundamental in sustaining the river ecosystem. This study aims to identify the most relevant factors affecting the flow regime and the suspended sediment transport in two Mediterranean intermittent rivers: the Búger (Spain) and the Carapelle (Italy). A set of hydrological indicators were used to characterize and classify the flow regime. High-resolution data, streamflow and suspended sediment concentration were used to quantify runoff and sediment yields at different temporal scales (annual, monthly, event). Rainfall, streamflow and sediment variables were used at the event scale to assess the rainfall-runoff-suspended sediment relationship through the Pearson correlation matrix. Hysteresis analysis provided information on sediment source dynamics. In the Búger River, the high degree of flow intermittence was mainly due to the presence of carbonate lithology and forest land use at headwaters promoting low values of runoff coefficient (2–10%) and specific suspended sediment yield (SSY; 0.5–46 t km−2 y−1). In the Carapelle River, the high values of annual runoff coefficient (14–35%), together with low flow intermittence and SSY (89–745 t km−2 y−1) were related to clay and flyschoid lithology. Most of the annual sediment yield (SY, t) was transported during floods. In Búger, SSY and maximum suspended sediment concentration (SSCmax, g l−1) were checked against runoff, peak discharge and antecedent rainfall. In Carapelle, SSY and SSCmax were checked against the amount and intensity of rainfall. The catchment size and the spatial distribution of rainfall, land uses and lithology played important roles in the flow regime, suspended sediment transport and hysteretic behaviour. Characterization of the flow regime linked to its main physical drivers improved understanding of the hydrological response and sediment transport variability of intermittent rivers. This study provided valuable insights into water resource management, improving the prediction of spatial patterns and of the intensity of sediment transport in river basins.

Investigation of Ship-Induced Hydrodynamics and Sediment Suspension in a Heavy Shipping Traffic Waterway

In order to investigate the complex hydrodynamics and associated sediment movement resulting from the ship passages in heavy shipping traffic waterways, field measurements were performed in a heavy shipping traffic waterway. Based on the collected waves, flow velocity and water turbidity data, the analyses of the ship-induced hydrodynamics and associated sediment suspension phenomena were conducted. The low-frequency primary wave and high-frequency secondary wave were more pronounced for a barge and yacht in the wave structure, respectively, and contributed more to the flow velocity fluctuations and the bottom shear stress. The ship-induced bottom shear stress can cause significant suspended sediment concentration increase, and there is a correlation between the maximum suspended sediment concentration and maximum ship-induced drawdown height, which can provide a reference for the waterway management.

Monsoon driven waves superpose the effect from macro-tidal currents on sediment resuspension and distribution

Sediment transport processes in remote tropical and macro-tidal estuaries are typically understudied due to costly instrumentation requirements, access difficulties and extreme weather conditions. Dry season sediment transport in Darwin Harbour (DH), northern Australia, is governed by a flood dominated tidal asymmetry. However sediment transport processes during active moonson in Darwin Harbour are poorly understood. We monitored turbidity and suspended sediment concentration (SSC) using sea bed moorings at more than seven locations in Darwin Harbour over two (Australian summer monsoon) seasons. We compared our results with sea surface elevation, wind, river discharge, wave height and period, and ocean currents recorded over the same period. We found that the maximum SSC (330 mgL−1) correlated with a peak in significant wave height (>1.3 m) and consistently strong (∼7.5 ms−1) long lasting (25–29 days) north to northwesterly winds. A striking feature of this study was that the maximum SSC coincided with neap tides and unusually low rainfall runoff for the first active monsoon in the study period. This contradicts the common misconception that peak SSC during monsoons should occur during periods of high rainfall runoff. The peak SSC was six times the peak during normal conditions of spring tides, and was the result of significant wave heights associated with northwesterly wind driven ocean swell. Wind driven northwesterly waves therefore superpose tidal dominance for sediment resuspension during the observed active monsoons, which occur regularly (1–4 times per year). Following the active monsoon, flood tidal dominance returns and causes a landward spread of SSC through the process of tidal pumping. We strongly recommend wave modelling be included in future port developments and infrastructure projects in Darwin Harbour.