Suspended Sediment Variability Research Articles

Drivers of annual suspended sediment and nutrient yields in tributaries to Lake Erie

Abstract In the early 2000s, harmful algal blooms and hypoxia returned to Lake Erie following a period of ecosystem recovery from the late 1980s through the 1990s. This corresponds to a drastic increase in dissolved reactive phosphorus loads and flow-weighted mean concentrations in the major tributaries to the Western Lake Erie Basin. However, there is substantial variability in suspended sediment and nutrient yields across Lake Erie tributaries. It is well known that agricultural and urban land uses lead to increased watershed sediment and nutrient yields, especially in the absence of proper management practices. Yet attributes such as watershed soil types and slope can also affect yields. We examined the influence of watershed land use, hydrology, soil type, and slope on annual nutrient and sediment yields from tributaries to Lake Erie monitored as part of the Heidelberg Tributary Loading Program. A minimum of one sample and, during storm runoff, up to three samples a day are analyzed for all major nutrients and suspended sediments. The 5-year average annual yields across these watersheds exhibited distinct geographic patterns from west to east, with high suspended sediment but lower nutrient yields from the eastern most tributaries (Cuyahoga, Old Woman Creek, Huron) and the lowest sediment along with lower nutrient yields from the western most tributaries (Raisin, Tiffin, Lost). The Maumee, Portage, Sandusky, along with select subwatersheds tended to have intermediate sediment yields with high nutrient yields. Altogether, the % cultivated crops and poorly drained soil in the watershed increased nutrient yields whereas a higher % slope and lower % pasture increased sediment yields. These patterns highlighted unique regional differences that can help guide management decisions for these watersheds that ultimately would improve the health of Lake Erie.

Temporal and spatial variability of suspended sediment rating curves for rivers draining into the Ethiopian Rift Valley

AbstractQuantification of suspended sediment dynamics is a proxy for the intensity of soil erosion processes in a catchment. However, direct measurement of suspended sediments is difficult. Long‐term‐based discharge‐suspended sediment relationships often fail to provide sufficiently accurate results due to the temporal variations in sediment supply. This study evaluates temporal variations in suspended sediment‐discharge relations for six stations in two selected catchments within the Gamo Highlands in the southern Ethiopian Rift Valley. During a three‐year period (2018–2020), discharge was monitored at a 10‐min interval using a TD‐diver, while 1938 samples of suspended sediment concentration were taken at specific events. Observed suspended sediment concentration varied between 0.04 and 130 kg m−3 for discharge ranging between quasi‐zeros to 339 m3 s−1. The results show that pooled annual datasets lead to unsatisfying sediment rating curves and large errors in estimated sediment load. However, stratification of the data into three rainy season periods strongly improved the performance of the sediment rating curves. The development of a vegetative cover throughout the rainy season largely controls sediment supply from hillslopes to the river channel and hence the shape of the sediment rating curves. Furthermore, localized bank erosion and gully head dynamics also lead to important interannual changes in sediment rating curves within one river system, as well as between different rivers. Thus, attention should be given to possible errors due to high temporal and spatial variability while using discharge‐suspended sediment relations to quantify sediment load.

Satellite assessment of coastal plume variability and its relation to environmental variables in the Sofala Bank

Monthly composites of remote sensing reflectance at 555 nm wavelength (Rrs555) from ocean color imagery of the MODIS sensor onboard the Aqua platform were used to characterize the spatial and temporal variability of coastal plume in the Sofala Bank and its relation to river discharge, local rainfall, and wind speed. To achieve the objective, maps of monthly composites of Rrs555 over the Sofala Bank were inspected and statistical analysis was performed, including correlation, analysis of variance, and wavelet coherence between environmental variables and both plume area and Rrs555. Climatology of Rrs555 revealed that both plume dispersion and Rrs555 values are higher during June to December and lower during January to May. A positive correlation (r = 0.77) between wind speed and monthly time series of Rrs555, and a negative correlation between the Zambezi river discharge (r = −0.21) and rainfall (r = −0.67) with Rrs555 were found. These results suggest that variation of suspended matter in the Sofala Bank is mainly controlled by erosion and re-suspension by winds rather than the input of terrigenous matter by the Zambezi River discharge and rainfall, assuming that Rrs555 can be a valid proxy for the inorganic suspended matter. The southern portion of the Sofala Bank (i.e., near the mouths of the Pungue and Buzi Rivers) presented higher values of Rrs555 if compared to the center region near Zambezi river mouth and the northern region near Licungo river mouth. The higher Rrs555 values in the southern region might be associated with higher re-suspension rates due to increased tide mixing, dredging activities, and the shallower nature of bathymetry in the southern region. The dominance of wind in controlling the variability of suspended sediments and the eventual relatively greater contribution of Pungue and Buzi River than the Zambezi in supplying sediments could represent an evidence of weakening of Zambezi River supply of sediments, a process that might have started after damming the Zambezi Catchment.

Towards an Integrated Observational System to Investigate Sediment Transport in the Tidal Inlets of the Lagoon of Venice

An observation system integrating satellite images, in situ water parameters and hydrodynamic measurements was implemented in a tidal inlet of the Venice Lagoon (Northern Adriatic Sea, Italy). The experimental infrastructure was developed to autonomously investigate suspended sediment dynamics in the two channels of the Lido inlet in relation to the longshore currents in the littoral zone and the tidal circulation along the lagoon channel network. It provided time series of turbidity at the surface, water flow and acoustic backscatter, which was converted into turbidity along the vertical column during different tidal phases and meteo-marine conditions. Accurate turbidity maps were derived from Sentinel-2 (Copernicus) and Landsat 8 (NASA) satellites. Long-term in situ data from field surveys enabled the calibration and intercalibration of the instrumental setup and validation of satellite-derived products. Time series from the instrumental network were analyzed in order to evaluate the temporal variability of suspended sediment in relation to tidal phases and the different meteo-marine conditions. The integration of available datasets with satellite images also permitted the testing of the methodology for a 3-D reconstruction of the suspended sediment pattern in calm sea conditions, under the effect of the sole hydrodynamical forcing. Remotely sensed data provide a synoptic distribution of turbidity in the inlet area allowing the analysis of the surficial patterns of suspended sediment and the inferring of information on the transport processes at different spatial scales. In calm sea conditions, the results show that the transport is driven by tidal currents with a net seaward transport related to a larger export of materials from the northern basin of the Lagoon of Venice. During typical northeasterly storms, materials mobilized on the beaches and in the shoreface are transported into the inlet and distributed into the lagoon channel network, following the flood tidal currents and determining net import of materials. The multitude of information provided by this system can support research on aquatic science (i.e., numerical simulations) and address end-user community practices. The ecosystem management will also benefit operational purposes, such as the monitoring of morphological transformations, erosion processes and planning of coastal defense in the future scenarios of sea level rise. The developed approach will also help to understand how the regulation of the inlet flow introduced by the operation of the flood barriers will affect the fluxes of particles and, in the long term, the lagoon morphodynamics.

Light Limitation and Depth-Variable Sedimentation Drives Vertical Reef Compression on Turbid Coral Reefs

Turbid coral reefs experience high suspended sediment loads and low-light conditions that vertically compress the maximum depth of reef growth. Although vertical reef compression is hypothesized to further decrease available coral habitat as environmental conditions on reefs change, its causative processes have not been fully quantified. Here, we present a high-resolution time series of environmental parameters known to influence coral depth distribution (light, turbidity, sedimentation, currents) within reef crest (2–3 m) and reef slope (7 m) habitats on two turbid reefs in Singapore. Light levels on reef crests were low [mean daily light integral (DLI): 13.9 ± 5.6 and 6.4 ± 3.0 mol photons m–2 day–1 at Kusu and Hantu, respectively], and light differences between reefs were driven by a 2-fold increase in turbidity at Hantu (typically 10–50 mg l–1), despite its similar distance offshore. Light attenuation was rapid (KdPAR: 0.49–0.57 m–1) resulting in a shallow euphotic depth of <11 m, and daily fluctuations of up to 8 m. Remote sensing indicates a regional west-to-east gradient in light availability and turbidity across southern Singapore attributed to spatial variability in suspended sediment, chlorophyll-a and colored dissolved organic matter. Net sediment accumulation rates were ∼5% of gross rates on reefs (9.8–22.9 mg cm–2 day–1) due to the resuspension of sediment by tidal currents, which contribute to the ecological stability of reef crest coral communities. Lower current velocities on the reef slope deposit ∼4 kg m2 more silt annually, and result in high soft-sediment benthic cover. Our findings confirm that vertical reef compression is driven from the bottom-up, as the photic zone contracts and fine silt accumulates at depth, reducing available habitat for coral growth. Assuming no further declines in water quality, future sea level rise could decrease the depth distribution of these turbid reefs by a further 8–12%. This highlights the vulnerability of deeper coral communities on turbid reefs to the combined effects of both local anthropogenic inputs and climate-related impacts.

Analysis of Suspended Sediment Variability in a Large Highly Turbid Estuary Using a 5‐Year‐Long Remotely Sensed Data Archive at High Resolution

AbstractSpatial variability of surface suspended particulate matter (SPM) concentration in the Gironde estuary and their relationships with environmental forcing are investigated through high spatial resolution multispectral data collected from July 2013 to August 2018 by the Operational Land Imager (Landsat‐8/OLI) and MultiSpectral Instrument (Sentinel‐2/MSI). A principal component analysis using the T‐mode orientation is applied to the discontinuous multiannual time series composed of 41 remotely sensed images. The three first principal components (PC1, PC2, and PC3) explain 65.7% of the total variance. The SPM distribution associated with PC1 and PC2 exhibits a privileged along‐estuary direction of the oscillation modes, while the spatial patterns of PC3 are clearly dominated by lateral oscillations opposing channels and shoals. The main environmental factors affecting the SPM distribution are identified by the analysis of their temporal patterns. The tidal range and the daily river discharge control the spatial patterns of PC1 and PC2, while the tidal cycles and the wind speed are significantly correlated with PC3. Furthermore, the analysis in the along‐estuary and lateral directions shows marked longitudinal and transverse SPM gradients and a strong control of bathymetry on the SPM spatial distribution. For the first time, we highlight that the maxima of surface residual turbidity are located on the shoals regardless of the environmental (tidal and hydrological) conditions. Compared to previous studies, usually based on single‐point in‐water column measurements, these results provide a novel and complementary description of the spatial variability of SPM. They are useful to validate sediment transport numerical models, but also may improve our understanding of suspended sediment dynamics in estuarine systems governed by an estuarine turbidity maximum.

Spatio‐temporal variability of suspended sediments in rivers and ecological implications of reservoir flushing operations

AbstractHigh suspended sediment concentrations during reservoir flushing are known to be harmful to biota in downstream river stretches. Therefore, it is common practice to set legal concentration limits for upstream reservoir management operations such as flushings or controlled drawdowns. However, as shown by measurements, there is a considerable spatio‐temporal variability of suspended sediment concentrations both in the longitudinal profile of rivers and in river cross‐sections. To consider this variability in management operations, SED‐FISH—a three‐dimensional modelling approach—was developed to study this variability in a wider context by upscaling cross‐sectional measurements of suspended sediments to high‐resolution three‐dimensional information on the reach scale in an alpine river. The resulting patterns of suspended sediment concentrations were integrated over their respective time of occurrence for various scenarios in order to calculate severity of harmful impacts for target fish species. The modelling results identified refugial habitats with reduced negative impacts in near‐bank zones even for relatively high suspended sediment concentrations in the centre of the river. Moreover, a substantially larger variability of both suspended sediment concentrations and associated harmful impacts was found for a winding riverbed morphology as compared with a straight reach. Both these findings and the developed modelling tool could assist in establishing individual case‐based concentration limits for reservoir management operations in the future and should also be taken into account when planning river regulation or restoration measures.

Patterns and drivers of spatio-temporal variability of suspended sediment in the Waikato lakes, New Zealand

ABSTRACTQuantifying and interpreting variability in ecological systems allows us to better understand the driving forces that determine ecosystems functioning. We utilised earth observation-based remote sensing to determine total suspended sediment (TSS) concentrations for 109 lakes over 16 years. The coefficient of variation (CV) was used to quantify variability of TSS at three temporal scales (monthly, annual and long-term) and at the horizontal spatial scale. CV values varied between 0.14 and 1.09. Drivers of observed variability patterns were explored using five lake morphological and catchment characteristics. Lake area was the most important variable to predict variability of TSS. De-vegetated lakes displayed significantly higher TSS concentrations than vegetated lakes; however, aquatic vegetation was found to moderate only spatial variability of TSS. As spatio-temporal variability can be assumed to drive key ecosystem functions, determining characteristic variability patterns for various attributes should be a prerequisite when setting management goals and developing monitoring regimes.

Monitoring of seasonal variability and movement of suspended sediment concentrations along the Thiruvananthapuram coast, southern India, using the Landsat OLI sensor

Abstract. Studies on suspended sediment concentrations at a seasonal scale play a vital role in understanding coastal hydrodynamic processes in an area. Assessment of spatio-temporal changes in suspended sediments in nearshore areas has gained complexity due to the utilization of conventional methods; this issue can be successfully solved nowadays using multi-temporal remotely sensed images with the help of advanced image processing techniques. The present study is an attempt to demonstrate the model algorithm used to extract suspended sediment concentrations using Landsat 8 OLI (Operational Land Imager) sensor images. The study was executed in a near-offshore area of the Thiruvananthapuram coast, southern India, and focused on the extraction of suspended sediment concentrations and their seasonal variability during pre-monsoon and post-monsoon periods. The OLI images were pre-processed to obtain the actual reflectance using the FLASSH module of the ENVI v5.5 software. The generic model developed herein is designed to compute the spectral reflectance variability between coastal water and suspended sediments and to differentiate the spatial accumulation of the suspended sediment concentrations from the coastal water at the pixel scale. Maximum (0.8 % in near-infrared bands) and minimum (0.6 % in blue bands) spectral reflectance indicates the occurrence of suspended sediments in the coastal water. The model-derived results revealed that the suspended sediment concentration gradually decreased with increasing depth and distance from the shoreline. Higher sediment concentrations accumulated at lower depths in coastal water due to wave and current action that seasonally circulated the sediments. This higher concentration of the suspended sediment load was estimated to be 0.92 mg L−1 at the shallow depths (<10 m) of the coastal waters and 0.30 mg L−1 at a depth of 30 m. Seasonal variability of suspended sediments was observed in a north–south direction during the pre-monsoon; the reverse was noted during the post-monsoon period. The spatial variability of suspended sediments was indirectly proportional to the depth and distance from the shoreline, and directly proportional to offshore wave and littoral current activity. This study proves that the developed model coupled with the provided computational algorithm can be used as an effective tool for the estimation of suspended sediment concentrations using multi-temporal OLI images; furthermore, the output may be helpful for coastal zone management and conservation planning and development.

Suspended Sediment Variability at the Solimões and Negro Confluence between May 2013 and February 2014

This study focuses on the confluence of two major rivers of the world, the Solimões River (white waters) and Negro River (black waters). Surface suspended sediment samples (SSC) and spectroradiometer taken along transverse profiles at 500 m intervals over a distance of 10 km, as well as satellite images (MODIS) during the hydrological year, were used to follow suspended sediment variability. In January and February, the confluence is dominated by white waters from the Solimões River in the two banks, and in June and July in the right bank by black waters from the Negro River and in the left bank by clear waters from the Solimões River. We found that indirect tools, such as reflectance obtained by spectrometer or MODIS images, can be used to determine surface suspended sediments in a contrasting zone.

Estuarine Suspended Sediment Dynamics: Observations Derived from over a Decade of Satellite Data

Suspended sediment dynamics of Corpus Christi Bay, Texas, USA, a shallow-water wind-driven estuary, were investigated by combining field and satellite measurements of total suspended solids (TSS). An algorithm was developed to transform 500-meter Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite reflectance data into estimated TSS values. The algorithm was developed using a reflectance ratio regression of MODIS Band 1 (red) and Band 3 (green) with TSS measurements (n=54) collected by the Texas Commission on Environmental Quality for Corpus Christi Bay and other Texas estuaries. The algorithm was validated by independently collected TSS measurements during the period of 2011-2014 with an uncertainty estimate of 13%. The algorithm was applied to the period of 2002-2014 to create a synoptic time series of TSS for Corpus Christi Bay. Potential drivers of long-term variability in suspended sediment were investigated. Median and IQR composites of suspended sediments were generated for seasonal wind regimes. From this analysis it was determined that long-term, spatial patterns of suspended sediment in the estuary are related to wind-wave resuspension during the predominant northerly and prevalent southeasterly seasonal wind regimes. The impact of dredging is also apparent in long-term patterns of Corpus Christi Bay as concentrations of suspended sediments over dredge spoil disposal sites are higher and more variable than surrounding areas, which is most likely due to their less consolidated sediments and shallower depths requiring less wave energy for sediment resuspension. This study highlights the advantage of how long-synoptic time series of TSS can be used to elucidate the major drivers of suspended sediments in estuaries.

Development of regression equation to study the Total Nitrogen, Total Phosphorus and Suspended Sediment using remote sensing data in Gujarat and Maharashtra coast of India

This study focuses on the assessment of the concentration of water nutrients, such as Total Nitrogen and Total Phosphorus, and suspended sediments in the northern Arabian Sea using MODIS Aqua and Terra data. The in-situ data of water nutrient concentration was collected during the period 2002–2010 by COMAPS from the coastal waters of Gujarat and Maharashtra for the development of algorithms as a part of the application of remote sensing for biochemical cycling in the ocean. Multiple regression analysis was used to develop models for the nutrients and suspended sediments and the results showed the strong correlation between the water nutrients under study and suspended sediment variables with the remote sensing data, having the validated R2 value of 0.7472 (Total Nitrogen),0.8744 (Total Phosphorus) and 0.971 (Suspended Sediment) respectively in marine waters. The models helped understand the seasonal variability and were also applied to one of the latest sensor VIIRS, which came up with the same results as those derived from MODIS. Thus the models can be used for the real time monitoring of water quality and for the development of an alert system using remote sensing data from both MODIS and VIIRS sensor systems.

Purus River suspended sediment variability and contributions to the Amazon River from satellite data (2000–2015)

The Purus River is one of the major tributaries of Solimões River in Brazil, draining an area of 370,091km2 and stretching over 2765km. Unlike those of the other main tributaries of the Amazon River, the Purus River's sediment discharge is poorly characterized. In this study, as an alternative to the logistic difficulties and considering high monitoring costs, we report an experiment where field measurement data and 2700 satellite (MODIS) images are combined to retrieve both seasonal and interannual dynamics in terms of the Purus river sediment discharge near its confluence with the Solimões River. Field radiometric and hydrologic measurements were acquired during 18 sampling trips, including 115 surface water samples and 61 river discharge measurements. Remote sensing reflectance gave important results in the red and infrared levels. They were very well correlated with suspended sediment concentration. The values of R2 are greater than 0.8 (red band) and 0.9 (NIR band). A retrieval algorithm based on the reflectance in both the red and the infrared was calibrated using the water samples collected for the determination of the surface-suspended sediment concentration (SSS). The algorithm was used to calculate 16 years of SSS time series with MODIS images at the Purus River near its confluence with the Solimões River. Results from satellite data correlated with in situ SSS values validate the use of satellite data to be used as a tool to monitor SSS in the Purus River. We evidenced a very short and intense sediment discharge pulse with 55% of the annual sediment budget discharged during the months of January and February. Using river discharge records, we calculated the mean annual sediment discharge of the Purus River at about of 17 Mt·yr−1.

Use of spatially distributed time-integrated sediment sampling networks and distributed fine sediment modelling to inform catchment management

Under the EU Water Framework Directive, suspended sediment is omitted from environmental quality standards and compliance targets. This omission is partly explained by difficulties in assessing the complex dose-response of ecological communities. But equally, it is hindered by a lack of spatially distributed estimates of suspended sediment variability across catchments. In this paper, we demonstrate the inability of traditional, discrete sampling campaigns for assessing exposure to fine sediment. Sampling frequencies based on Environmental Quality Standard protocols, whilst reflecting typical manual sampling constraints, are unable to determine the magnitude of sediment exposure with an acceptable level of precision. Deviations from actual concentrations range between −35 and +20% based on the interquartile range of simulations. As an alternative, we assess the value of low-cost, suspended sediment sampling networks for quantifying suspended sediment transfer (SST). In this study of the 362 km2 upland Esk catchment we observe that spatial patterns of sediment flux are consistent over the two year monitoring period across a network of 17 monitoring sites. This enables the key contributing sub-catchments of Butter Beck (SST: 1141 t km2 yr−1) and Glaisdale Beck (SST: 841 t km2 yr−1) to be identified. The time-integrated samplers offer a feasible alternative to traditional infrequent and discrete sampling approaches for assessing spatio-temporal changes in contamination. In conjunction with a spatially distributed diffuse pollution model (SCIMAP), time-integrated sediment sampling is an effective means of identifying critical sediment source areas in the catchment, which can better inform sediment management strategies for pollution prevention and control.

Effects of different land-use on suspended sediment dynamics in Sabah (Malaysian Borneo) – a view at the event and annual timescales

Suspended sediment concentrations (SSC) and the duration of high SSC are important for river ecology and water resource conservation. Using annual and storm-event datasets, this paper explores the hypothesis that key suspended sediment variables increase along a land-use disturbance gradient in hilly terrain in Sabah (Malaysian Borneo). Five small (1.7–4.6 km2) catchments of increasing disturbance history – primary forest, old growth virgin jungle reserve, twice-logged forest, multiple-logged forest and mature oil palm – were instrumented from late 2011 with dataloggers and sensors to record river stage, turbidity and rainfall. The oil palm catchment had 4–12 times greater mean discharge-weighted SSC (587 mg L–1), annual sediment yield (1128 t km–2 y–1), median event peak SSC, and duration of SSC above 1000 mg L–1 than in the other catchments. The multiple-logged catchment (last logged around 2004) has SSC characteristics close to values for primary forest, possibly due to increased ground protection against erosion afforded by low understorey regrowth and/or depletion of erodible sediment by multiple logging episodes. Results demonstrate that in hilly terrain even heavily logged rainforest has high value in safeguarding water quality and reducing erosion, whereas oil palm requires careful land management, especially of road runoff and ground cover.

Assessing controls on cross‐shelf phytoplankton and suspended particle distributions using repeated bio‐optical glider surveys

AbstractCharacterizing the space/time variability of bio‐optical properties is essential to understand the mechanisms that control cross‐shelf phytoplankton and suspended particle distributions in coastal waters. Approximately 400 high‐resolution cross‐shelf sections of bio‐optical properties collected with an oceanographic glider in the coastal Santa Barbara Channel, California, revealed complex relationships among optical properties and environmental conditions. Surface waves were found as a proximate control on suspended sediment variability for both inner and midshelves. Increases in phytoplankton abundances attributed to horizontal advection and upwelling events were observed only on episodic time scales. The lack of all‐encompassing linear relationships between environmental forcings and changes in cross‐shelf phytoplankton highlights the challenge of decoupling bio‐optical signals from their controlling processes in coastal zones where phytoplankton distributions are patchy, and where nearshore and offshore phytoplankton populations and suspended sediments often occupy the same portion of the water column. Clear relationships between runoff and productivity were not observed. Temporal variability of suspended particles and phytoplankton distributions were roughly independent from each other during stratified conditions. Synchronous increases in phytoplankton and suspended sediments were observed when associated with strong upwelling events that may induce mixing and promote productivity. The repeated glider sections illustrated many processes regulating phytoplankton and particle transport in the innershelf and showed the difficulty in establishing general connections between high‐frequency changes in optical properties and potential environmental forcings in a complex coastal environment.

Remote monitoring of sediment dynamics in a coastal lagoon: Long-term spatio-temporal variability of suspended sediment in Chilika

We present a comprehensive analysis of sediment dynamics in a coastal lagoon by synthesizing various remote sensing datasets. The goal of the study was to monitor and analyze the spatio-temporal variability of total suspended sediment (TSS) concentration and associated environmental forcings in Chilika Lagoon, the largest brackish water lagoon in Asia. Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance cloud free data was used to calibrate a TSS model. MODIS daily 250 m surface reflectance (MOD09GQ) and 8-day composite products (MOD09Q1) were chosen because they are atmospherically corrected and available for free thus making them widely applicable for frequent monitoring of environmental phenomena. Three variants of Miller and McKee (2004) TSS model were recalibrated to establish the relationship between in situ TSS and surface reflectance value in band 1 (Rrs at 645 nm). A significant relationship (R2 = 0.91; n = 54; p < 0.001) was obtained between in situ TSS and MODIS Rrs (645 nm) using a polynomial model. The other two models, exponential and linear, showed comparatively low R2 (0.77 and 0.73 respectively). Accuracy of the models were assessed by comparing the field measured TSS with MODIS derived TSS. Based on R2 values, validation analysis (RMSE = 2.64 mg/L), and residual trend, the polynomial model was found to be the best performing TSS model with an estimation range of 6.5 mg/L – 200 mg/L. The model was then implemented to derive weekly time-series TSS maps of Chilika Lagoon for 14 years (2001–2014). Marked seasonal and inter-annual variations in TSS distribution were observed in different sectors (northern, central and southern) of the lagoon. It was found that the TSS variability is primarily driven by three factors: monsoon effect (precipitation and runoff), wind-driven bottom re-suspension, and river discharge into the lagoon. Further analysis of the relationship between MODIS derived time-series TSS and meteorological parameters revealed that the variability of TSS in the northern sector is highly correlated with precipitation and runoff, whereas, TSS dynamics in southern sector is mainly governed by wind induced re-suspension events. The applicability of the TSS model was demonstrated by analyzing the impact of a recent category-5 cyclone, Phailin, which showed a significant increase in TSS concentration in the lagoon. This is the first of its kind study to comprehensively examine the long term TSS dynamics of Chilika, moreover, the model developed in this research was implemented in various coastal lagoons and estuaries around the world and was proven effective in quantifying TSS.

Empirical Orthogonal Function Analysis of Suspended Sediment Concentration in Gulf of Kachchh, India, and Its Tidal Influence

Complexity of the temporal sediment variability within the Gulf of Kachchh is resolved into major modes of variations using empirical orthogonal function (EOF) analysis on sequential OCM derived suspended sediment concentration (SSC) images during spring intermonsoon period of 2011. Variance accounted collectively by the first four modes is around 80% and the principal component (PC) of each mode is correlated with different hydro-meteorological forces influencing the hydrodynamics of the gulf. Hydro-meteorological forces are classified in the order of precedence of influencing the sediment dynamics of the region. PC1 contributing 50% of the total variance is correlated with average of the simulated current velocities between consecutive images, indicating the variation of tides from neap-spring ranges (r2 = 0.86). The ocean state parameters like tidal height, wind speed, and current speed at the time of OCM pass contribute to around 20%, 6%, and 4%, respectively, to the total variability of the temporal dynamics of SSC. The interchange of tides from neap and spring is the major contributor toward the temporal variability of sediment concentration within the gulf, where the sediments are subjected to deposition and resuspension. The gulf being highly tide dominated, the suspended sediment variability also reverberates with the variability of tidal characteristics and subtly with the wind conditions.

Temporal variability of suspended sediment transport and rating curves in a Mediterranean river basin: The Celone (SE Italy)

In the Mediterranean region suspended sediment transport is the predominant process in sediment export in most river basins. The aim of this paper is to analyze suspended sediment variability over a period of 12months in the Celone river, a temporary river located in the Puglia region (SE-Italy), and to evaluate sediment rating curves for estimating suspended sediment concentrations for subsequent load calculations. Similarly to most temporary rivers, the Celone river shows relevant differences among mean daily flows and the extreme instantaneous flows during floods. To take into account these peculiarities, the rating curves were developed as a function of hydrological conditions: high, normal and low flows. Continuous measures of streamflow and frequent samplings of suspended solid concentrations (SSCs) during flood events, normal flow and low flow were used. The plot of the SSC against discharge takes the form of a hysteresis loop. Clockwise, anticlockwise and mixed-shaped loops were observed. Suspended sediment yield was found to be in the range of 250–384tkm−2y−1. The results show that about 94% of the total suspended materials were transported during the high flow regime, while less than 0.1% were under low flow conditions. Moreover, it was observed that 90% of the total annual suspended loads were moved between November to May. Flash floods that occur in summer exhibit the highest values of SSC. The proposed method, which was based on sediment rating curves, has proved to be valuable to generate SSC data for high and normal flows although it tends to underestimate the highest values. It can represent a useful tool for water resource managers who need a quick and inexpensive method, specific for temporary rivers, to evaluate suspended sediment yield.

Evaluation of hydrology, suspended sediment and Nickel loads in a small watershed in Basque Country (Northern Spain) using eco-hydrological SWAT model

Suspended sediment transportation and associated pollutants from catchment to stream networks are responsible for aquatic habitat degradation, reservoir sedimentation and the transportation of sediment bound pollutants. Quantifying suspended sediment loads from lands to watercourses is essential in controlling soil erosion and in implementing appropriate mitigation practices to reduce stream sediment and associated pollutant loads, and hence improve surface water quality downstream.The main objective of this study is to evaluate the temporal variability of hydrology, sediment and nickel loads using Soil and Water Assessment Tool in Oka watershed located in north Spain. Model simulation was completed using 11 years historical records (2001–2009 for validation and 2009–2012 for calibration) of streamflow and suspended sediment concentration (SSC). Thestreamflow, SSC and sediment load estimated from the model were compared with observed data using statistical parameters, which indicates a successful simulation. The annual production of simulated sediments shows variability between 662 and 1515 t, with a mean specific yield of 33 t km−2 y−1. The annual load of nickel simulated ranged from 32 to 72 kg, representing a mean specific of 1.63 kg km−2 year−1. The information obtained from this research is of interest to understand long term interannual variability of suspended sediment and nickel yield.