Suspended Sediment Concentration Patterns Research Articles

Deep learning insights into suspended sediment concentrations across the conterminous United States: Strengths and limitations

Suspended sediment concentration (SSC) is a crucial indicator for aquatic ecosystems and reservoir management but is challenging to predict at large scales. It is unclear whether SSC is predictable using macroscopic environmental attributes and forcings. This study tested the feasibility of deep-network-based models to predict daily SSC at basin outlets given only basin-averaged forcings, readily-available physiographic attributes, and streamflow (from observation or model). We trained long short-term memory (LSTM) deep networks both separately for each of the 377 sites across the conterminous United States (CONUS) (termed “local models”), and on all the sites collectively (Whole-CONUS). The Whole-CONUS and local models presented median coefficient of determination (R2) values of 0.63 and 0.52, respectively. This comparison agrees with previously acknowledged “data synergy” effects for LSTM models, where more data from more sites can help improve predictions overall. Furthermore, the continental-scale analysis provided a wealth of insights about SSC patterns. Both local and Whole-CONUS models tended to be more successful where SSC-streamflow correlations (Rs-q) were high − typically in the humid Eastern US − and with lower SSC. Low Rs-q basins were often found in the arid Southwest with higher SSC. The highly-nonlinear SSC-streamflow relationships seem related to seasonality, basin size, and heterogeneity of land cover and rainfall within the basins, suggesting these basins need to be simulated at higher spatial resolution and may require additional inputs related to SSC induced by seasonality. The Whole-CONUS model also performed well for spatial extrapolation (basins not included in the training dataset, median R2 = 0.55), supporting large-scale modeling efforts. These state-of-the-art results using only minimal inputs suggest data-driven approaches can exploit the natural coevolution of sediment processes and the environment to support sediment modeling.

Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments – Part 2: Suspended sediment dynamics

Abstract. A proper understanding of sediment resuspension and transport processes is key to the morphodynamics of shallow tidal environments. However, a complete spatial and temporal coverage of suspended sediment concentration (SSC) to describe these processes is hardly available, preventing the effective representation of depositional dynamics in long-term modelling approaches. Through aiming to couple erosion and deposition dynamics in a unique synthetic theoretical framework, we here investigate SSC dynamics, following a similar approach to that adopted for erosion (D'Alpaos et al., 2024). The analysis with the peak-over-threshold theory of SSC time series computed using a fully coupled, bi-dimensional model allows us to identify interarrival times, intensities, and durations of over-threshold events and test the hypothesis of modelling SSC dynamics as a Poisson process. The effects of morphological modifications on spatial and temporal SSC patterns are investigated in the Venice Lagoon, for which several historical configurations in the last 4 centuries are available. Our results show that, similar to erosion events, SSC can be modelled as a marked Poisson process in the intertidal flats for all the analysed morphological lagoon configurations because exponentially distributed random variables describe over-threshold events well. Although erosion and resuspension are intimately intertwined, erosion alone does not suffice to describe also SSC because of the non-local dynamics due to advection and dispersion processes. The statistical characterization of SSC events completes the framework introduced for erosion mechanics, and together, they represent a promising tool to generate synthetic, yet realistic, time series of shear stress and SSC for the long-term modelling of tidal environments.

Characterization of suspended sand concentrations in the Yangtze River Estuary and adjacent waters

IntroductionThe study on the distribution characteristics of suspended sediment concentration (SSC) in estuaries is an important subject in the study of estuaries and coasts, which has important theoretical significance and practical value.MethodsIn order to fully understand the characteristics of SSC in the Yangtze River Estuary and its adjacent waters, this paper uses fixed vertical observation data and navigation type large area observation data as data sources to analyze the distribution characteristics of SSC in the Yangtze River Estuary and its adjacent waters under different tidal current states and its vertical profile characteristics. It discusses the impact of tidal current velocity on SSC and the changes of SSC in the Yangtze River Estuary and its adjacent waters from 2018 to 2020. And the applicability of the Rouse and Soulsby formulas in the Yangtze River Estuary and its adjacent waters was verified.ResultsIt was found that the Rouse and Soulsby models have high applicability in the study area, and the prediction accuracy based on the Li’s Soulsby model is higher. This study provides effective support for carrying out marine forecasting, analysis and evaluation, and provides theoretical basis for carrying out analysis of the current situation of estuarine mudflat resources and prediction of the evolution trend. It plays an important role in scientific and comprehensive research and management of mudflat resources in Shanghai.DiscussionHowever, this study only explored the characteristic patterns of SSC in the Yangtze River Estuary and its adjacent waters based on field observations, but SSC is a more complex water environment parameter that is influenced by a variety of factors. The effects of salinity, temperature and wind speed should be considered in subsequent studies.

Alternating patterns of cross-shelf suspended sediment transport in the northern East China Sea in winter

Suspended sediment transport across the continental shelf is a key process for the materials exchange between coastal seas and the deep ocean. The cross-shelf transport through the Yangtze Shoal in the northern East China Sea (ECS) exhibits a unique pattern, which is characterized by alternations between high and low values in suspended sediment concentration (SSC). This study is conducted to reveal the underlying mechanisms and their effects on sediment fluxes. Surface SSC retrieved from GOCI data are combined with in situ observations of concentration and particle sizes of suspended sediment to study the temporal and spatial variations of the SSC in the Yangtze Shoal. Additionally, a numerical model for examining ocean circulation based on the FVCOM is established to display the hydrodynamic feature in the study area. The alternating SSC pattern is closely related to the topography of three ridges and two troughs. High SSC with fine particle size can be found over the ridge, while low SSC is detected at the surface layer of water in the trough. Even during the flood and ebb tides, this alternating pattern of high and low SSCs does not change, except for the expansion and contraction of coverage areas of high SSC. The high SSC near the tidal ridge should have resulted from the combined effect of resuspension and upwelling since the stronger bottom shear stress and a surface divergence that may induce an upwelling can be found in this area. Combined with the simulated current, the sediment transport flux between ridges and troughs is estimated. The sediment flux in the ridge is substantially increased than that in the trough, especially during the flood maximum and ebb maximum time. The contribution of suspended sediments from the Yangtze Shoal to the Southwestern Cheju Island Mud (SCIM) is relatively small during the normal weather in winter. However, cross-shelf transport can be remarkably strengthened by strong northerly winds in winter. This work puts forward a detailed cross-shelf transportation process induced by topography.

Identification, extraction and interpretation of multi-period variations of coastal suspended sediment concentration based on unevenly spaced observations

Suspended sediment concentration (SSC) is an important indicator for coastal morphodynamics and health, exhibiting significant periodic variations at multiple timescales in response to various cyclic forcing factors. Identification of key periods and the extraction of corresponding amplitudes and phases can greatly aid effort to characterize the representative portrayal of SSC, which contributes to further physical interpretation. Remote sensing missions are intended to satisfy the retrieval of long-term SSC variations. However, the unevenly spaced characteristic and low effective sampling rates of the retrieved time series would hamper the extraction and interpretation of the feature changes. Here, we retrieved a 9-year SSC time series in a coastal tidal basin of Jiangsu coast, China, based on hourly GOCI satellite images from 2011 to 2019, and applied the Lomb-Scargle periodogram with the phase-folded method to extract their periodic information. On the basis of the unevenly spaced data with effective rate of 6.9%, the semidiurnal, diurnal, fortnightly, and seasonal cycles were successfully identified as the main periods, with amplitudes of 33.1, 23.4, 54.1, and 71.4 mg/L, respectively. In accordance with investigations into phase lags between SSC and forcing factors, we found that the unimodal SSC pattern at the semidiurnal timescale was induced by flood dominance, while the diurnal inequality of water level and wave intensity accounts for the SSC variation at the diurnal timescale. Tidal ranges vary consistently with the SSC in the fortnightly scale while background wave dominates the SSC variation in the seasonal timescale, the latter resulting in the seasonal difference in semidiurnal and fortnightly SSC cycles. The annual semidiurnal SSC variations experience a regime shift from 2014 to 2016, which is in consistency with the sequential reclamation. The research presents a typical application of long-term unevenly spaced observations into coastal SSC, and the proposed methodology can be extended to similar studies aiming at uncovering the mechanism of SSC variations at multiple timescales.

North to South Variations in the Suspended Sediment Transport Budget within Large Siberian River Deltas Revealed by Remote Sensing Data

This study presents detailed suspended sediment budget for the four Siberian river deltas, representing contrasting conditions between Northern and Southern environments. Two of the studied rivers empty their water and sediments into the marine located in the permafrost zone in the Arctic region (Lena and Kolyma), and the other two (Selenga and Upper Angara) flow into Lake Baikal located in the steppe and forest-steppe zone of Southern Siberia. For the first time, these poorly monitored areas are analyzed in terms of the long-term and seasonal changes of spatial patterns of suspended sediment concentrations (SSC) over distributaries systems. Remote sensing reflectance is derived from continuous time series of Landsat images and calibrated with the onsite field measurements of SSC. Seasonal variability of suspended sediment changes over deltas was captured for the period from 1989 to 2020. We identify significant variability in the sedimentation processes between different deltas, which is explained by particularities of deltas networks and geomorphology and the existence of specific drivers—continuous permafrost impact in the North and abundant aquatic vegetation and wetland-dominated areas in the South. The study emphasizes that differences exist between Northern and Southern deltas regarding suspended sediments transport conditions. Mostly retention of suspended sediment is observed for Southern deltas due to sediment storage at submerged banks and marshlands located in the backwater zone of the delta during high discharges. In the Northern (arctic) deltas due to permafrost impacts (melting of the permafrost), the absence of sub-aquatic banks and river to ocean interactions of suspended sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels. These results shine light on the geochemical functions of the deltas and patterns of sequestering various metals bound to river sediments.

Estimation of Suspended Sediment Concentration from Remote Sensing and In Situ Measurement over Lake Tana, Ethiopia

Discharge from basins joining a lake is the main factor determining the lake volume and sediment inflow to the lake. Suspended sediment is an important parameter for describing the water quality of aquatic ecosystems. Lake Tana is an important and the largest lake in Ethiopia for the local ecological system. However, environmental change and anthropogenic activities in the area threaten its water quality. The conventional methods of suspended sediment concentration (SSC) observation are unable to determine and compare spatial and temporal SSC patterns for the lake over a period of years. Remote sensing methods have made it possible to map SSC. The objective of this study is to characterize the spatial and temporal distribution of suspended sediment of Lake Tana using in situ measurement and remote sensing applications and specifically to develop a relationship between in situ and remote sensing observation to retrieve suspended sediment concentration and map the spatal distribution of SSC. This study used MODIS‐Terra and in situ data to characterize the spatial and temporal distribution of SSC in the rainy season. Four sampling campaigns (20 samples per campaign) were carried out on Lake Tana, and the first three sampled campaigns on May 11–13, 2018, June 08–10, 2018, and July 15–17, 2018, were used for calibration of regression models. MODIS‐Terra reflectance in NIR was found best related to in situ water quality data and varies linearly with SSC (r2 = 0.81) and turbidity (r2 = 0.85). Secchi disc depth (SDD) found the best fit for a power relation with NIR band reflectance (r2 = 0.74). The MODIS‐Terra reflectance in red was found to be poorly related to in situ measurements. The relation in NIR reflectance was validated using the LOOCV (leave‐one‐out‐cross‐validation) technique and the fourth sampled data set collected on August 12–14, 2018. Developed models are validated with RMSE of 42.96 mg/l, 14.6 NTU, and 0.17 m, ARE of 23.3%, 27.6%, and 12.4%, and RRMSE of 25.1%, 44.5%, and 29.6% for SSC, turbidity, and SDD, respectively, using LOOCV. The equation was also validated using August 2018 collected data sets with RMSE of 87.6 mg/l, 11.7 NTU, 0.08 m, ARE of 20.8%, 25.9%, and 28.8%, and RRMSE of 17.8%, 20.5%, and 27.9% for SSC, turbidity, and SDD, respectively. Applying the developed regression model, a 10‐year time series of SSC from 2008–2017 for May‐August was estimated and the trend was tested using the Mann–Kendall trend test. It was found that an increasing trend was observed from the period 2008 to 2017. The result shows that satellite data like the MODIS‐Terra imagery could be used to monitor and obtain past records of SSC with the developed equation. The increasing SSC can be reduced by implementing selected management practices in the surrounding watersheds of the lake to reduce nutrient and sediment inflow.

Estimating Impacts of Dam Development and Landscape Changes on Suspended Sediment Concentrations in the Mekong River Basin’s 3S Tributaries

The Mekong River Basin (MRB) is undergoing rapid dam development, which is altering the river suspended sediment concentration (SSC). In this study, we used satellite remote sensing records spanning 31 years to detect SSC changes (SSC prediction r2=0.78, RMSE=21.2 mg/L) due to dam development. We focused on the 3S basin of the MRB. We also used satellite data on nighttime lights, which reflect human settlement patterns, and land cover to explain SSC patterns. Our technique allowed for quantification of SSC changes due to dam construction (e.g., +120 mg/L near basin outlet), reservoir sediment trapping (e.g., −108 mg/L), deforestation, and human settlement (e.g., +117 mg/L near impacts). Our technique also demonstrated how the SSC of the 3S rivers compared to that of the Mekong mainstem over time (e.g., from ∼13% to 100% greater). Our comprehensive analyses of SSC records with dam development indicate that SSC changes will continue with ongoing dam and landscape development in the MRB. From a hydrologic perspective, SSC monitoring will be imperative for effective sediment and water management. Our satellite-based approach answers critical sediment needs of improved monitoring and adaptive management throughout the MRB and other global locations for practitioners who are engaged in real-world management of their river basins.

Spatial and temporal patterns of suspended sediment concentrations in the Rhine River

Suspended sediment is a natural and crucial component and plays a crucial role in the hydrological, ecological and geomorphological functioning of the river system. The main objective of this study was to understand the spatial and temporal variation of SSC in Rhine River. This study used daily data of suspended sediment concentration from 1952 to 2016 from SSC model Sutari et al. (submitted manuscript, 2019) and daily data of water discharge collected from International Commission for the Protection of the Rhine (IKSR) and Dutch Rijkswaterstaat from 1995 to 2016 to understand the change of SSC. Analyses of product images suggest that the change of SSC shows a marked increase of about 6 mg/L at Upper Rhine (km 0 to km 435), a gradual increase of about 3 mg/L at Middle Rhine (km 435 to km 735), and is relatively constant at Lower Rhine (km 735 to km 865). Turning to seasonal variation, high SSC is mostly found in winter while low SSC is mostly found in summer. However, another result shows that the SSC tend to be high in June at almost all monitoring stations where the discharge is minimum. Meanwhile, under high discharge condition, the Mosel River gives the most significant contribution of SSC to the Rhine compared to other tributaries due to having a high discharge.

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.

The influence of runoff and wind on the dispersion patterns of suspended sediment in the Zhujiang (Pearl) River Estuary based on MODIS data

Cloud-free moderate-resolution imaging spectroradiometer (MODIS) images of the Zhujiang (Pearl) River Estuary (ZRE) taken between 2002 and 2012 are retrieved and used to study the spatial and temporal patterns of suspended sediment concentrations (SSCs) across the estuary under runoff, wind, and tropical storm conditions. Five typical dispersal patterns of suspended sediments in the estuary are defined: Case I shows generally low SSCs under low dynamics; Case II shows a river-dominant dispersal pattern of suspended sediments from the outlets, particularly from Modaomen, Jiaomen, Hengmen, and others; Case III shows wind-dominant dispersal of high SSCs derived from the west shoal and southwesterly transport under a strong NE wind; Case IV is the combination of relatively large runoff and wind; and Case V is caused by a strong tropical storm with high river discharge and wind, which is characterized by the high SSCs across the entire estuary that are transported eastward by winddriven and buoyancy currents outside the estuary. Runoff is a dominant factor that controls seasonal and annual SSC variations in the ZRE, with the area of high SSCs being largest in the summer and smallest in the spring. The correlation coefficients between the monthly averaged river-suspended sediment discharge and the area of the high SSCs are approximately 0.6. The wind power over the west shoal increases with a wind speed, which induces more sediment resuspension and shows a close relationship between the wind speed and high SSC area.

Modeling the sediment dynamics in the gulf of Urabá, colombian Caribbean sea

The potential of the gulf of Urabá to hold a multi-purpose port motivated a sediment dynamics study to describe the seasonal sediment concentration patterns in this tropical region. Challenges addressed in this study include a complex three-dimensional flow pattern in a tropical estuary and the lack of in-situ measurements. To overcome such challenges, this study completed: (i) Measurements of suspended sediment concentrations during two climatic seasons and an extreme event (2010–2011); (ii) Definition of boundary conditions from global databases; (iii) Qualitative analysis of sediment concentrations from satellite imagery; and (iv) integration of the previously mentioned steps to build a process-based 3D sediment transport model. Seasonal patterns of suspended sediment concentrations were identified and corroborated by the agreement between model results, satellite imagery and field measurements. During the calm rainy season, the Atrato River turbid plume extends northward and dominates the sediment dynamics in the gulf. On the other hand, during the dry season and extreme events, bed transport is enhanced and the river's plume and the littoral drift shift southwards.

Deriving spatial and temporal context for point measurements of suspended-sediment concentration using remote-sensing imagery in the Mekong Delta

Rivers are a major supplier of sediment to the open oceans, but observations of sediment dynamics are limited in downstream reaches where significant amounts of sediment can be trapped. Point observations of riverine properties are the usual method for estimating processes and building predictive models. Although point observations provide extensive data at one location for a short duration, they do not easily provide larger spatial or temporal context. Remote-sensing has the capability to provide this context if imagery values can be translated into riverine properties. In this paper, we present a demonstration of using a combined data set of remote-sensing imagery and in situ observations to derive spatial maps of suspended-sediment concentration (SSC) in the Mekong Delta as conditions change from high-flow (Sep 2014) to low-flow (Mar 2015), and to estimate a decadal change in SSC from 1987 to 2016. Using a test set of coincident in situ observations of SSC with multi-spectral remote-sensing imagery, we develop a six parameter empirical model using ratios of reflectivity that generates a root-mean-squared error (RMSE) for the test set of 0.038g/l. Using these models, we generate large-scale spatial maps of SSC and extract the spatial changes in SSC within the Dinh An and Tran De distributary channels as conditions change from high- to low-flow. We determine the SSC patterns within this region that correspond to high-, intermediate- and low-flow conditions and show that these patterns exist during Sep–Oct (high-flow), Nov–Jan (intermediate-flow), and Feb–Mar (low-flow). We show that during high-flow the SSC values throughout the region are increased, and there is a gradual increase in SSC from the upstream channel regions of the study area to the offshore plumes consistent with the intrusion of a salt wedge. We also show that during low-flow there is an unique increase in SSC in the upstream channel regions, consistent with this being the region of opposing river and tidal-inflow currents. The decadal analysis indicates a decrease in SSC from 1987 to 2016 throughout the Mekong Delta of 1% per year starting in 2001.

Parameterization of wind turbine impacts on hydrodynamics and sediment transport

Monopile foundations of offshore wind turbines modify the hydrodynamics and sediment transport at local and regional scales. The aim of this work is to assess these modifications and to parameterize them in a regional model. In the present study, this is achieved through a regional circulation model, coupled with a sediment transport module, using two approaches. One approach is to explicitly model the monopiles in the mesh as dry cells, and the other is to parameterize them by adding a drag force term to the momentum and turbulence equations. Idealised cases are run using hydrodynamical conditions and sediment grain sizes typical from the area located off Courseulles-sur-Mer (Normandy, France), where an offshore windfarm is under planning, to assess the capacity of the model to reproduce the effect of the monopile on the environment. Then, the model is applied to a real configuration on an area including the future offshore windfarm of Courseulles-sur-Mer. Four monopiles are represented in the model using both approaches, and modifications of the hydrodynamics and sediment transport are assessed over a tidal cycle. In relation to local hydrodynamic effects, it is observed that currents increase at the side of the monopile and decrease in front of and downstream of the monopile. In relation to sediment transport effect, the results show that resuspension and erosion occur around the monopile in locations where the current speed increases due to the monopile presence, and sediments deposit downstream where the bed shear stress is lower. During the tidal cycle, wakes downstream of the monopile reach the following monopile and modify the velocity magnitude and suspended sediment concentration patterns around the second monopile.

Spatio-temporal patterns of soil erosion and suspended sediment dynamics in the Mekong River Basin

Understanding of the distribution patterns of sediment erosion, concentration and transport in river basins is critically important as sediment plays a major role in river basin hydrophysical and ecological processes. In this study, we proposed an integrated framework for the assessment of sediment dynamics, including soil erosion (SE), suspended sediment load (SSL) and suspended sediment concentration (SSC), and applied this framework to the Mekong River Basin. The Revised Universal Soil Loss Equation (RUSLE) model was adopted with a geographic information system to assess SE and was coupled with a sediment accumulation and a routing scheme to simulate SSL. This framework also analyzed Landsat imagery captured between 1987 and 2000 together with ground observations to interpolate spatio-temporal patterns of SSC. The simulated SSL results from 1987 to 2000 showed the relative root mean square error of 41% and coefficient of determination (R2) of 0.89. The polynomial relationship of the near infrared exoatmospheric reflectance and the band 4 wavelength (760–900nm) to the observed SSC at 9 sites demonstrated the good agreement (overall relative RMSE=5.2%, R2=0.87). The result found that the severe SE occurs in the upper (China and Lao PDR) and lower (western part of Vietnam) regions. The SSC in the rainy season (June–November) showed increasing and decreasing trends longitudinally in the upper (China and Lao PDR) and lower regions (Cambodia), respectively, while the longitudinal profile of SSL showed a fluctuating trend along the river in the early rainy season. Overall, the results described the unique spatio-temporal patterns of SE, SSL and SSC in the Mekong River Basin. Thus, the proposed integrated framework is useful for elucidating complex process of sediment generation and transport in the land and river systems of large river basins.

Statistical characterization of spatiotemporal sediment dynamics in the Venice lagoon

AbstractCharacterizing the dynamics of suspended sediment is crucial when investigating the long‐term evolution of tidal landscapes. Here we apply a widely tested mathematical model which describes the dynamics of cohesive and noncohesive sediments, driven by the combined effect of tidal currents and wind waves, using 1 year long time series of observed water levels and wind data from the Venice lagoon. The spatiotemporal evolution of the computed suspended sediment concentration (SSC) is analyzed on the basis of the “peak over threshold” theory. Our analysis suggests that events characterized by high SSC can be modeled as a marked Poisson process over most of the lagoon. The interarrival time between two consecutive over threshold events, the intensity of peak excesses, and the duration are found to be exponentially distributed random variables over most of tidal flats. Our study suggests that intensity and duration of over threshold events are temporally correlated, while almost no correlation exists between interarrival times and both durations and intensities. The benthic vegetation colonizing the central southern part of the Venice lagoon is found to exert a crucial role on sediment dynamics: vegetation locally decreases the frequency of significant resuspension events by affecting spatiotemporal patterns of SSCs also in adjacent areas. Spatial patterns of the mean interarrival of over threshold SSC events are found to be less heterogeneous than the corresponding patterns of mean interarrivals of over threshold bottom shear stress events because of the role of advection/dispersion processes in mixing suspended sediments within the lagoon. Implications for long‐term morphodynamic modeling of tidal environments are discussed.

Conversion to drip irrigated agriculture may offset historic anthropogenic and wildfire contributions to sediment production

This study is an investigation into the roles of wildfire and changing agricultural practices in controlling the inter-decadal scale trends of suspended sediment production from semi-arid mountainous rivers. In the test case, a decreasing trend in suspended sediment concentrations was found in the lower Salinas River, California between 1967 and 2011. Event to decadal scale patterns in sediment production in the Salinas River have been found to be largely controlled by antecedent hydrologic conditions. Decreasing suspended sediment concentrations over the last 15years of the record departed from those expected from climatic/hydrologic forcing. Sediment production from the mountainous headwaters of the central California Coast Ranges is known to be dominated by the interaction of wildfire and large rainfall/runoff events, including the Arroyo Seco, an ~700km2 subbasin of the Salinas River. However, the decreasing trend in Salinas River suspended sediment concentrations run contrary to increases in the watershed's effective burn area over time. The sediment source area of the Salinas River is an order of magnitude larger than that of the Arroyo Seco, and includes a more complicated mosaic of land cover and land use. The departure from hydrologic forcings on suspended sediment concentration patterns was found to coincide with a rapid conversion of irrigation practices from sprinkler and furrow to subsurface drip irrigation. Changes in agricultural operations appear to have decreased sediment supply to the Salinas River over the late 20th to early 21st centuries, obscuring the influence of wildfire on suspended sediment production.

SSC Analysis of South Maharashtra Coast: A Case Study from Vengurla Coastal Region

Suspended sediment transport plays a major role in many coastal, estuarine and offshore engineering applications. The transport of suspended sediment influences the constructions of harbours, constructions of coastal power stations and refineries, safety of offshore platforms and pipelines, erosion and accretion of beaches, quality of the water and many other applications. To understand the suspended sediment transport pattern along South Maharashtra coastal region, a case study was conducted at Vengurla coastal waters. In order to do that, the sea water samples at 6 transects (18 stations) were collected for analysis of suspended sediment concentration (SSC) during pre-monsoon and post-monsoon periods. The results showed that during post monsoon, the SSC pattern at surface, mid and bottom layers having 10-20mg/l, 10-19mg/l and 50-60mg/l respectively. But during the pre-monsoon, the respective layers show 5-20mg/l, 4-15mg/l and 70mg/l of SSC concentration. In addition, Ocean Colour Monitor (OCM) satellite images were analyzed in the same study area to know the SSC distribution pattern. In Vengurla, post-monsoon, the SSC values of surface coastal waters ranging from 5-15mg/l from OCM satellite images and also SSC is compared with OBS 5+ profiles. In this paper, the SSC distribution pattern of both seasons is narrated and the validations of SSC using OCM satellite data are also discussed.

Retrieval of coastal ocean currents using MCC technique on satellite imagery for supplementing altimeter derived currents

Abstract. Maximum Cross Correlation (MCC) technique have been used to derive coastal currents from sequential OCM derived suspended sediment concentration (SSC) maps and the MCC currents are integrated with the Ocean surface current analysis-Real time (OSCAR) ocean currents along the coastal regions of the Southern India. OSCAR currents are mainly depended on the oceanographic measurements from the satellite altimeter which have limitations in the coastal region and in representing the mesoscale properties dominating the coastal ocean. Sequential pair of atmospherically corrected and georeferenced OCM image is used to derive SSC, along the southern coast of India. Maximum Cross-Correlation (MCC) method is applied on the sequential time lapsed images of OCM for matching the suspended sediment dispersion patterns. The MCC technique involves computing of cross-correlation coefficients and identifying correlation peaks. The spatial change of the sediment pattern occurs due to the advection by the currents and the extent of the change corresponds to the speed and direction of the current. From the first image, template window is selected, which is searched in the second image within large region defined as the search window. The movement of the SSC pattern is calculated based on the maximum cross correlation in successive images. Error statistics are calculated between the spatially coherent MCC vectors and OSCAR currents. Based on statistical analysis, an error threshold of 30 degree for current direction and 0.06m/sec for current speed was given to MCC currents and MCC currents beyond the error limit are rejected, while the MCC current within the error limit is merged with the OSCAR ocean currents. The merging of MCC currents has spatially enhanced the OSCAR currents. MCC method is significant in calculating the coastal currents and its mesoscale properties, which dominate the coastal surface flow field and can be used in supplementing the OSCAR ocean currents. Merging of both the currents, have effectively resulted in preparing contiguous maps of coastal ocean currents.

Modelling-based assessment of suspended sediment dynamics in a hypertidal estuarine channel

We investigate the dynamics of suspended sediment transport in a hypertidal estuarine channel which displays a vertically sheared exchange flow. We apply a three-dimensional process-based model coupling hydrodynamics, turbulence and sediment transport to the Dee Estuary, in the north-west region of the UK. The numerical model is used to reproduce observations of suspended sediment and to assess physical processes responsible for the observed suspended sediment concentration patterns. The study period focuses on a calm period during which wave-current interactions can reasonably be neglected. Good agreement between model and observations has been obtained. A series of numerical experiments aim to isolate specific processes and confirm that the suspended sediment dynamics result primarily from advection of a longitudinal gradient in concentration during our study period, combined with resuspension and vertical exchange processes. Horizontal advection of sediment presents a strong semi-diurnal variability, while vertical exchange processes (including time-varying settling as a proxy for flocculation) exhibit a quarter-diurnal variability. Sediment input from the river is found to have very little importance, and spatial gradients in suspended concentration are generated by spatial heterogeneity in bed sediment characteristics and spatial variations in turbulence and bed shear stress.