Suspended Sediment Concentration Measurements Research Articles

Relationships between basin area and sediment yield upstream Shiroro reservoir, north-central Nigeria

Sediment yield and basin area relationship in a watershed is a very crucial factor in Best Management Practices (BMPs) and reservoir sustainability. Therefore, the study was conducted to examines the suspended sediment concentration (SSC) of the four sub-watersheds of Kaduna watershed north-central Nigeria to aid the dam sustainability and BMP within the watershed. Water samples were collected bimonthly for 8 months (March-October 2018) and subjected to laboratory analysis for SSC and turbidity measurements. With the aid of ArcSwat2012, the watershed was delineated into four sub-watersheds, soil and land-use were classified for a proper understanding of the watershed. The findings demonstrated an inverse relationship between the size of the sub-watersheds and SSC. The smallest Dinya sub-watershed (1%) contributes approximately 25% (3781.5mg/l) of the SSC while the largest Kaduna (80%) contributes approximately 26% (3889mg/l), Sarkinpawa (11%) and Gutalu (8%) contributes approximately 26% (3844mg/l) and 23% (3444mg/l) of SSC respectively. The highest average turbidity was recorded in Sarkinpawa sub-watershed, followed by Dinya, Gutalu, and Kaduna. The SSC and turbidity results followed the rainfall pattern while the regression results for the four sub-watersheds shows a good level of linearity between SSC, rainfall and turbidity, Therefore, it is recommended that sediment management practice is to be carried out along sub-watersheds Dinya and Sarkinpawa and Gutalu to reduce the high rate of sediment influx into the reservoir from these smaller sub-watersheds. Also, detail study of the smaller sub-watersheds is highly recommended for a better understanding of the factors responsible for high sediment generation in these sub-watersheds. Keywords : basin area, best management practice, Kaduna watershed, suspended sediment concentration (SSC), Shiroro reservoir, relationship.

Evaluation of along-channel sediment flux gradients in an anthropocene estuary with an estuarine dam

While estuarine dams can develop freshwater resources and block the salt intrusion, they can result in increased sediment deposition in the estuary. The mechanism of increased sediment deposition in an estuary with an estuary dam is not well understood. To fill this knowledge gap, 7 ADCP measurements of flow and suspended sediment concentration (SSC) were collected along-channel in an estuary with an estuarine dam over a neap-spring cycle. Flow and SSC were used to calculate the sediment flux and sediment flux gradients, which in turn were decomposed into mean-flow fluxes (which occur on timescales longer than a tidal cycle) and correlation fluxes (which occur on the tidal timescale). Then the fluxes were compared with the external forcing to determine the relative importance of tides, dam discharge, and waves in driving the fluxes. The results indicated that the cumulative sediment fluxes at all stations were directed landward. The along-channel sediment flux gradient was negative, which indicated deposition along the channel. The landward mean-flow fluxes were dominant in the deep portion of the channel near the estuary mouth, whereas landward correlation fluxes were dominant in the shallow portion of the channel near the estuarine dam. The tides were the dominant forcing driving the sediment fluxes throughout the estuary. Waves and dam discharge were locally important forcing however. In particular, the dam discharge resulted in seaward mean-flow fluxes for 7 km seaward of the estuarine dam. This distance corresponded approximately to a tidal excursion seaward from the dam. It was the distance a freshwater mass discharged during an ebb tide could propagate before the currents returned landward during the following flood tide. Overall, the along-channel sediment flux gradient in an estuary with an estuarine dam was different from a similar estuary without an estuarine dam because the mean-flow fluxes in the inner estuary are forced by episodic dam discharge which was limited in seaward extent by the tidal excursion. This imposed a limitation for the seaward mean-flow fluxes which counteract the landward mean-flow and correlation fluxes due to the tides. With restricted seaward flushing, the tides could dominate, which could in turn result in increased depositional rates for an estuary with an estuarine dam.

Scale breaks of suspended sediment rating in large rivers in Germany induced by organic matter

Abstract. Understanding the transport of suspended sediment and associated nutrients is of major relevance for sustainable sediment management aiming to achieve healthy river systems. Sediment rating curves are frequently used to analyze the suspended sediments and their potential sources and sinks. Here we use more than 750 000 measurements of suspended sediment concentrations (SSCs) and discharge (Q) collected at 62 gauging stations along 19 waterways in Germany based on the suspended sediment monitoring network of the German water and shipping authority, which started in the 1960s. Furthermore, we analyze more than 2000 measurements of the loss on ignition (LOI) of suspended matter at two stations along the rivers Moselle and Rhine to provide a proxy for the relative contributions of mineral load and organic matter. SSC and LOI are analyzed in terms of the power-law rating curve to identify discharge-dependent controls of suspended matter. Our results indicate that for most studied gauging stations, rating coefficients are not constant over the full discharge range, but there is a distinct break in the sediment rating curve, with specific SSC–Q domains above and below this break. The transition of the rating exponent likely results from increased supply of mineral suspended sediments from hillslope erosion at high flow and a shift of the organic matter sources from aquatic biomass-derived organic matter (i.e., high % LOI) at low flow, to mineral-associated organic matter with low % LOI eroded from hillslopes at higher flow. Based on these findings we developed a conceptual rating model for large (>10 000 km2) and low-turbidity (SSC < 1000 mg L−1) rivers separating the mineral and organic fraction of the suspended matter in German waterways. This model allows evaluating the sources of the mineral and organic fraction of the suspended matter and facilitates new insights into the first-order control of discharge on the quality and quantity of suspended sediments.

Sediment Delivery to a Tidal Marsh Platform Is Minimized by Source Decoupling and Flux Convergence

AbstractSediment supply is a primary factor in determining marsh response to sea level rise and is typically approximated through high‐resolution measurements of suspended sediment concentrations (SSCs) from adjacent tidal channels. However, understanding sediment transport across the marsh itself remains limited by discontinuous measurements of SSC over individual tidal cycles. Here, we use an array of optical turbidity sensors to build a long‐term, continuous record of SSC across a marsh platform and adjacent tidal channel. We find that channel and marsh concentrations are correlated (i.e., coupled) within tidal cycles but are largely decoupled over longer time scales. We also find that net sediment fluxes decline to near zero within 10 m of the marsh edge. Together, these results suggest that large sections of the marsh platform receive minimal sediment independent of flooding frequency or channel sediment supply. Marsh‐centric, as opposed to channel‐centric, measures of sediment supply may better characterize marsh platform vulnerability.

Toward Improved Accuracy of Remote Sensing Approaches for Quantifying Suspended Sediment: Implications for Suspended‐Sediment Monitoring

AbstractBecause of the high logistical and financial costs of direct measurements of riverine suspended sediment, remote sensing is increasingly used to supplement the direct‐observation record. The accuracy of this method is poorly constrained, and its potential as a tool for understanding river sediment transport is thus limited. We introduce and apply global‐scale methods for estimating depth‐integrated suspended‐sediment concentrations (SSCs) using Landsat 5 and 7 satellite imagery calibrated with 134,697 in situ SSC measurements. We account for river‐to‐river variability in the relationship between water optical properties and SSC by (a) categorizing rivers using unsupervised K‐means clustering and/or (b) correcting calibration estimates for individual rivers using local in situ measurements of SSC, suspended‐sediment grain size, and percent organic carbon (POC). In the absence of site‐specific in situ SSC measurements, clustering rivers reduces the average relative error of SSC estimates from 97% to 73%. We show that as few as five site‐specific in situ measurements combined with our algorithm further reduces average relative error to 49% and average relative at‐a‐station bias in SSC to 7%. Little additional improvement in accuracy or bias is gained by including measurements of percent sand or POC of the suspended sediment. Since only modest additional accuracy is gained after ~5–10 paired in situ SSC measurements and satellite observations, sampling campaigns should prioritize limited sampling at diverse locations rather than intensive sampling at a limited number of sites. In addition, we publish standalone calibrations for 151 rivers made solely with in situ SSC measurements local to those sites.

The effect of air bubbles on optical backscatter sensor measurements under plunging breaking waves

Accurate suspended sediment concentration measurements are key to understand and quantify the sediment transport patterns in the surf and swash zones. One of the most widely used instruments to collect suspended sediment concentrations is the Optical Backscatter Sensor (OBS). However, the OBS is known to give erroneous readings when deployed in bubbly environments like the surf zone. The present study aims to quantify the influence of an aerated wave breaking environment on the OBS sediment concentration measurements. Experiments are performed in a large wave flume, which ensures full air entrapment under plunging breaking waves, and avoids scale effects that could affect the volume of entrapped air, the air bubble penetration depth and the residence time of air bubbles in the post-breaking turbulent eddies. OBS measurements are obtained at 66 locations along a fixed bed profile for 14 regular breaking wave conditions. In the absence of suspended sediment particles, OBS voltage measurements are used as a proxy for air bubble content. The presented OBS results show peaks up to 1.49 V (31% of the OBS measurement range, corresponding to 16 g/l for sediment with d50 = 0.25 mm) produced by air bubbles in the most energetic tested wave breaking conditions, while the maximum time-averaged value obtained is 0.48 V (10% of the OBS measurement range, corresponding to 5 g/l). The results highlight the importance of considering the presence of air bubbles where OBS are deployed to measure suspended sediment concentrations. A good correlation is found between the breaker depth index and the air bubble distribution and two predictive formulas are derived to forecast the area of air bubble influence in the surf zone.

Profile of Suspended Sediment Concentration in Submerged Vegetated Shallow Water Flow

AbstractThe vertical distribution pattern of the fine suspended sediment concentration (SSC) plays an important role in the aquatic ecosystem of shallow water. To investigate the SSC profile in submerged vegetated river flow, a series of indoor flume experiments was conducted. Glass spherical balls of three different diameters (40, 77, and 90 μm) with a uniform specific gravity of 2.5 were used for the model sediments. A set of sampling devices was designed for the simultaneous measurements of SSCs at multipoints along a vertical line. Experimental results show that the SSC profile was re‐distributed in the vegetated region, gradually forming a new equilibrium pattern in the overcanopy flow layer with its maximum occurring near the canopy top. From this maximum point near the canopy top, the suspended sediment formed a dynamic balance between upward turbulent diffusion and downward gravitational settling. Meanwhile, the momentum diffusivity was observed to linearly decrease upward from the maximum‐SSC elevation toward the water surface, thereby allowing us to deduce an empirical negative linear formula. Based on the convection‐diffusion equilibrium mechanism and with assistance of the empirical formula of flow momentum diffusivity, a new form of the Rouse formula was derived for the overcanopy flow layer. In general, this equation agrees well with the measured data. Some undercalculated deviations appear in the well‐above canopy zone due to the upskewed turbulence and the weak upward secondary flow. This deviation decreases with increasing sediment diameter. The bed deposition mainly comes from the deep part of canopy‐occupied flow layer.

Effect of Wave, Current, and Lutocline on Sediment Resuspension in Yellow River Delta-Front

Historically, the Yellow River in China discharges > 1 × 109 ton/yr sediment to the sea, and has formed a large delta in the western Bohai Sea. Its river mouth is characterized by an extremely high suspended sediment concentration (SSC), up to 50 g/L. However, the hydrodynamic factors controlling the high suspended sediments in the Yellow River estuary are not well understood. Here, we conducted two hydrodynamic observations and SSC measurements in the winter and spring low-flow seasons of 2014–2015 and 2016–2017 under five sea conditions, including calm-rippled, smooth-wavelet, slight, moderate, and rough, in the Yellow River Delta-front during the observation period. Under calm-rippled conditions, the contribution of currents to the total resuspended sediment concentration (RSC) was 77.7%–100.0%. During the smooth-wavelet and slight periods, the currents’ contribution decreased as low as 30% and 3.0% of the total RSC, respectively. Under moderate and rough-sea conditions, waves accounted for at least 70% and 85% of the total RSC, respectively. The results indicate that 20 cm-thick lutoclines were created after a significant increase in the wave height to a peak value followed by a decrease. When the SSC is over 3 g/L and hydrodynamic conditions could not break the lutoclines, the flocculent settling of suspended sediment changes to hindered settling in the Yellow River Delta. Under hindered settling, the settling velocity decreases, and the resuspended sediments remains in the lutoclines and their lower water layers. This study reveals different controlling factors for the high SSC near a river-influenced delta, and helps us get a better understanding of a delta’s resuspension and settling mechanisms.

Sediment modeling of a large-scale basin supported by remote sensing and in-situ observations

Sediment models are important for estimating soil erosion, sediment transport, and deposition at different scales and for disparate scenarios; however, the availability of in-situ measurements may not be sufficient for the appropriate evaluation of model performance. For this reason, this study investigated how surrogate data (water quality [WQ] and remote sensing) could be used as a proxy for suspended sediment concentration (SSC) in order to evaluate the performance of a large-scale erosion and sediment transport model. To achieve this, the daily SSC was simulated, using the Large Scale Sediment Model (MGB-SED), a semi-distributed and conceptual model in which the Modified Universal Soil Loss Equation (MUSLE) is used to estimate sediment yield and an advection-diffusion equation is used to route suspended loads along rivers. Four experiments were performed that compared simulated SSC against: (1) in-situ SSC; (2) turbidity; (3) total suspended solids (TSS); and (4) surface spectral reflectance (SSR). Correlation analysis showed that r-values above 0.5 were found in 62%, 91%, 89% and 83% of the SSC, turbidity, TSS and SSR stations, respectively. Spatially, the model was evaluated in smaller drainage areas, using WQ data. Temporally, the number of SSR observations was greater than the number of in-situ measurements, allowing a better analysis of the temporal dynamics of the simulated SSC. Also, the SSR data improved the spatial coverage and could be employed for even large-scale, ungauged basins. These results bring a new perspective to the application of sediment models in poorly or ungauged basins, since surrogate data can improve the spatial and temporal suspended sediment coverage when compared to traditional SSC measurements, which is a common issue in large-scale sediment modeling.

Remote Sensing Monitoring on Spatial Differentiation of Suspended Sediment Concentration in a River-Lake System Based on Sentinel-2 MSI Imaging:A Case for Shengjin Lake and Connected Yangtze River Section in Anhui Province

Carrying out monitoring of suspended sediment concentration in river and lake systems is of great significance for understanding the laws of sediment transport in water and formulating policies on water environmental control. Taking Shengjin Lake and the connected Yangtze river section in Anhui province as the study area, band reflectance of a Sentinel-2 MSI sensor is simulated according to field spectral datasets, and the retrieval model is established by statistical regression from the synchronized suspended sediment concentration measurements. Then, the retrieved results from 28 scene MSI images during 2017-2019 are used to analyze the spatiotemporal variation of suspended sediment concentration in rivers and lakes, and the influence of water level variation on their spatial differentiation is also discussed. The results show that:① The retrieval model established by the ratio of the sixth band to the third band of the MSI sensor is suitable for high-turbidity water type, with high accuracy (R2=0.863, RMSE=22.211 mg·L-1). ② Spatially, the suspended sediment concentration near the lake entrances, northwestern parts of the upper and middle lake areas, and the lower lake is relatively higher, and that of Shengjin Lake is lower than that of the Yangtze River overall except for in summer. Temporally, the suspended sediment concentration in Shengjin Lake is relatively lower in summer and higher in other seasons, while the connected Yangtze River section exhibits the opposite intra-annual variation. ③ The water level, which is caused by the connectivity of rivers and lakes under the influence of the sluice, is the key factor affecting the spatial differentiation of suspended sediment concentration in the river and lake system. The suspended sediment concentration in Shengjin Lake contributes to the Yangtze River in dry and normal water periods, and that in the normal water period is more significant. In contrast, during the flood period, the correlation between suspended sediment concentration in the Yangtze River and that in Shengjin Lake is not obvious.

Application of time domain reflectometry to high suspended sediment concentration measurements: Laboratory validation and preliminary field observations in a steep mountain stream

The dielectric constant around a sensor was measured with a time domain reflectometry (TDR) system and used to calculate the volumetric sediment concentration (SC) of stream water and deposition on a streambed. The measurements of various SCs in laboratory experiments demonstrated that the TDR system proposed in this study had an accuracy of 0.01 m3 m−3 for practical uses, and that the measured concentrations were not sensitive to particle size. The vertical SC distributions were measured at heights of 17–37 cm in a steep mountain stream. The resulting SCs at the various heights increased by 0.01–0.07 m3 m−3 at the time of peak stream discharge during an extreme storm with a return period of approximately 12 years. After extreme precipitation, the SC of the lowest probe increased rapidly from approximately 0 to 0.4 m3 m−3. This was followed by rapid increases in the SCs at the other heights, indicating deposition around each probe. The TDR measurement system, with its straightforward calibration procedure, effectively measured deposition and a high-concentration layer above the deposited layer even during the storm event.

Fluvial and oceanographic influences on suspended sediment dispersal in the Magdalena River Estuary

The Magdalena River is the main contributor of fresh water and sediment to the Caribbean Sea. Hydrological inputs from the Magdalena River are 10,287 and 4068 m3 s−1 at high and low flows, respectively. Sediment delivery from the Magdalena River is among the largest in the world, with 142 × 106 t yr−1 of transported suspended matter. We used MODIS images to develop a regional model and assess the spatial and temporal variability of suspended sediment concentration at the mouth of the Magdalena River, map the extent of the turbidity plume using its morphometric properties, and identify the main fluvial and oceanographic factors associated with plume variability. We analyzed monthly average suspended sediment concentration data for the period 2003–2017. MODIS images were calibrated with in situ measurements of suspended sediment concentrations in surface waters of the study area. A finite mixing model was used to identify turbidity thresholds and define areas within the plume. Calculated suspended sediment concentrations indicate high turbidity in the Magdalena River mouth (178.6 ± 78.7 mg L−1), values that are of the same order of magnitude as those measured in the Yangtze, Huang He and Amazon River mouths. Calculated plume areas (diffuse, solid and mixing) and their shapes suggest that the Magdalena River plume has a limited area, related to conditions such as wind speed and direction, streamflow, and sediment transport. Calculated areas and shapes demonstrate the ability to generate a near-field area, which indicates the presence of a clear convergence front. The data also emphasize the importance of sediment transport from the Magdalena River to the Caribbean Sea. Such fluvial transport is important in the biogeochemistry of estuarine systems, especially in turbid estuaries, where there is marked variability in the distribution of sediment in surface waters.

Compositional dynamics of suspended sediment in the Rhine River: sources and controls

PurposeInformation on the geochemical composition of suspended sediments in rivers is crucial to identify sediment source type or area. In large river basins, however, the relation between sediment composition and its controlling factors is often obscured. This study aims to assess and improve the conceptual understanding on the factors and mechanisms that control the composition of suspended sediments in the River Rhine, one of the large European rivers, and to identify the dominant source types of elements.Materials and methodsWe performed log-linear regression analysis and principal component analysis (PCA) on bi-weekly monitoring data of suspended sediment composition, supplemented with daily measurements of suspended sediment concentrations (SSC) and discharge at the Lobith monitoring station near the German-Dutch border for the period 2011–2016.Results and discussionThe statistical analyses show a consistent grouping of elements that display contrasting temporal variation or different responses to increased discharge. The contrasting behaviour also becomes manifest in the results from the PCA. A first component that explains about the half of the total variance in the entire dataset reflects the variation in clay content in the suspended sediment. A second component reflects anthropogenic pollution and explains about a quarter of the total variance. A third component probably reflects variation in sediment provenance.ConclusionsThe majority of the temporal variation in suspended sediment composition can be attributed to variations in grain size (clay content), organic matter content, and anthropogenic pollution. Only a minority of the variation can be attributed to variations in the contributions from different upstream source areas. This variation represented by the third and higher components from the PCA can potentially be used for sediment provenance analysis.

An integrated optic and acoustic (IOA) approach for measuring suspended sediment concentration in highly turbid environments

Accurate measurement of suspended sediment concentration (SSC) in highly turbid environments has been a problem due to optical or acoustic signal saturation and attenuation. The saturation returns a limited measurement range, and the attenuation raises an ambiguity problem that a low optical or acoustic output could mean a low or a high SSC. In this study, an integrated optic and acoustic (IOA) approach is proposed to (i) overcome the ambiguity problem; (ii) increase the measurement range to high SSC values; and (iii) obtain high-resolution SSC profiles. The IOA approach is a combination of Argus Suspension Meter (ASM), Optical Backscatter Sensor (OBS) and Acoustic Doppler Velocimeter (ADV). In this approach, the ASM-derived SSC is preferred because of its lowest relative error, followed by OBS and ADV. The ASM can produce high-resolution (1 cm interval) SSC profiles when it is not saturated (usually SSC < 9 g/L). When ASM is saturated, the SSC is recovered by OBS. Since the ambiguity problem is solved, the measurement range of OBS and ADV can be extended up to 300 g/L. The best way to use an ADV, however, is to have a rough estimation first and assist in the OBS conversion, because its estimates contain large uncertainty. To further mitigate the impact of sediment particle size on SSC retrieval, we suggest the usage of in-situ sediment samples for sensor calibration. The IOA approach was verified in the Yangtze Estuary which is a highly turbid system. Comparison of the IOA approach outputs against water sampling results demonstrates the reliability of the IOA approach with a relative error of 17–34%. The observed high SSCs were up to 63 g/L. The field data show that high SSCs were confined in the benthic layer (within 2 m above the bed) in the wet season under a high river discharge, whereas the suspension was better mixed throughout the water column in the dry season. • A combination of ASM, OBS and ADV resolves the ambiguity problem of two possible SSC values for an OBS or ADV output. • The integrated optic and acoustic (IOA) approach enlarges the measurement range of OBS and ADV to 300 g/L. • The IOA approach provides high-resolution (1 cm) SSC profiles by ASM. • The IOA approach was successfully applied in the Yangtze Estuary with SSC > 10 g/L.

Water Surface Temperature and Suspended Sediment Concentration (SSC) Retrieval from Landsat Imagery, Northwest Territories, Canada

This paper presents water surface temperature retrieval using Landsat thermal band and meteorological ancillary data. The algorithms were tested using Landsat-5/7/8 imagery acquired at different study sites along the Slave River and Mackenzie River of the Northwest Territories (NWT), Canada. By comparing the retrieved temperatures with in situ water temperatures, in-depth validation of one reliable retrieved technique was successfully demonstrated. The method yielded a mean absolute error (MAE) in the range of 1.00–1.38 °C, over 7 validation locations in a 2-year observation period. This paper also presents a method to estimate suspended sediment concentration (SSC) in the Slave River region using Landsat-8 imagery. The numerical relationships between in situ SSC measurements and water-leaving reflectance in visible and near-infrared (NIR) bands were investigated through regression fitting. The SSC estimation results using the retrieved models were analyzed and validated, the NIR model was found to generate the smallest estimation errors with a MAE of 7.98 mg/L using leave-one-out (LOO) uncertainty assessment. An operational web-based tool for water surface temperature and SSC mapping based on the algorithms validated during this study has been developed to address additional monitoring requirements of the NWT communities. The design and implementation of this tool is also described.

Sediment deposition and coral smothering.

Dredging in the marine environment to create and maintain safe, navigable shipping channels, and subsequent disposal of the material at sea in dredge material placement sites (spoil grounds) can generate large quantities of suspended sediment that can impact upon epibenthic marine communities. For sensitive taxa such as hard corals, understanding the mechanisms of mortality and the spatial scale over which these occur is critically important for impact prediction purposes, management of dredging using zonation schemes, and also public perception. We describe the sediment deposition field from suspended sediment falling back out of suspension created around a large (7.6 Mm3) 1.5-year capital dredging project on a reef, using data from 2 weekly repeat observations of >500 individually tagged corals at multiple locations from 0.2–25 km from the dredging. The observations were supported by concurrent in situ measurements of proxy suspended sediment concentrations, underwater light, and sediment deposition (using optical backscatter sensors), and before and after surveys of seabed particle size distributions (PSDs). The distance at which 90% of the effect (from maximum to minimum) had dissipated (ED10) was 20 km away from the dredging for suspended sediment concentrations (estimated via nephelometry), and underwater light (measured using PAR sensors) associated with turbid plumes, 14 km for sediment deposition (measured using optical backscatter sensors) and 4.6 km for changes seabed clay and silt content (PSD analysis). The ED10 for smothering of corals (the build-up of pools of loose sediment on the surface that could not be removed by self-cleaning) occurred much closer still at 3–3.3 km or (0.5–0.6 km for an ED50). Smothering was common on encrusting and foliose forms where sediments accumulated in hollows and massive hemispherical forms where surface undulations (bumps) allowed sediments to pool. Smothering was never observed on branching species, even under extreme levels of sedimentation. Sediment smothering resulted in tissue bleaching and partial mortality (lesion formation), but if sediments were removed (by currents) bleached areas regained pigmentation over weeks and there was regrowth/reparation of lesions over weeks and months even before the dredging was completed. Overall sedimentation tolerance was highly related to coral morphology and surface inclination and the ability to avoid smothering by having uninterrupted downhill pathways for sediment transport across the colony.

Suspended sediment concentration measurement based on optical fiber technology

A novel approach based on optical fiber technology was presented to measure suspended sediment concentration (SSC) in water and A turbidimeter prototypes with a range of propagation lengths was developed in order to test the effect of that variable on accuracy in this study. A series of experimental runs were performed with natural sediments uniformly distributed in water to test the relationship between SSCs, the intensity of the reflected light and the incident light. The detected voltage collected by a modern measurement was introduced as the parameter to characterize the intensity of the light which was confirmed to increase with the sediments added in the case of low SSCs, so it was thought to be useful for measuring the unknown SSCs. The test results indicated that this optical fiber turbidimeter had good stability and sensitivity which could not be affected by water flow disturbance and the measurement range of SSC was determined by the particle size. It was worth noting that an inflection point would appear in the curve of SSCs-Detected voltage as the increase of the SSC and the value of SSC at the inflection point in terms of 10 g l−1 was close to the value of median particle size in terms of µm. Before the inflection point, and there was a positive logarithmic relationship between SSCs and the detected voltage. On the premise of the same SSCs, the detected voltage decreases with the increase of the median particle size. After the inflection point, the SSC is negatively correlated with the voltage value, but the correlation is unstable due to the difference in the particle size. Finally, according to the scattering and absorption principle of light, the calibration of this optical fiber turbidimeter was discussed. The data processing of the measurement is simple and fast, and the density value is directly readable.

Determination of the particle load based on detailed suspended sediment measurements at a hydropower plant

Suspended sediment particles contained in inflows of water systems of hydropower plants (HPPs) cause hydro-abrasive erosion of the hydraulic turbines and structures leading to significant maintenance costs, efficiency reductions, and downtime. Relevant parameters such as suspended sediment concentration (SSC), particle size distribution (PSD), shape, and mineralogical composition were measured with an online multi-frequency acoustic instrument and based on manually taken samples from the end of the sand trap of the Toss HPP in the Himalayan region, India. In the laboratory, the samples were analyzed using the gravimetric method, laser diffraction, turbidity, dynamic digital image processing, scanning electron microscope, petrography analysis, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The online instrument and the samples provided measurement results at a single point. To investigate vertical gradients in concentration and particle sizes, additional samples were collected 9 times at 7 relative water depths. The SSC, most particle sizes, and particle shape were found to be evenly distributed over depth except d90, i.e. the diameter which is not exceeded by 90% of the particle mass. d90 measured at 76% of the water depth was in the range of fine sand and was multiplied by 1.05 to obtain an average value representative for the entire depth. Improved methodologies to quantify both particle shape and size in an analytical model for hydro-abrasive erosion are proposed. Also, the PSD measuring performance of laser diffraction and dynamic imaging was studied and similar values of the median particle sizes were obtained from both instruments. Further, multi-frequency acoustic, turbidity and laser diffraction techniques were found suitable for SSC measurement at the test case HPP.

Evaluation of a simple, inexpensive, in situ sampler for measuring time‐weighted average concentrations of suspended sediment in rivers and streams

AbstractThe accurate measurement of suspended sediment (&lt;200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.

Estimation of Suspended Sediment Concentration by Using Mobile ADCP Instrument

The measurement of suspended sediment concentration (SSC) by using Acoustic Doppler Current Profiler (ADCP) instrument still not widely used in Indonesia. The application of this technology uses sound wave by four direction transducers placed in the vessel, and this ADCP measured the intensity of backscatter from sediment particles. This study is equipped with RD Instruments WorkHorse Mariner 307.2 kHz ADCP, and the water sample collected from Lembeh Strait, North Sulawesi by using van Dorn bottle sampler. Beyond the experimental purpose of this installation, the interest in having wide area data at different tidal condition is that it provides the possibility of determining the effect of tidal to the SSC. The losses of sound signal were corrected to get more accurate results. Simple linear regression analysis performed to obtain the estimates of the SSC. Estimation of SSC of ADCP measurement was then compared with SSC on water analysis in the laboratory, and the result showed that insignificantly different by statistical analysis. From this research, it showed that the concentration of suspended sediment ranged between 60-73 mg L−1 on location near the Port of Bitung, and 50-62 mg L−1 at a location away from the port. The result also observed that the highest concentration is in the region below the water column, and tidal condition was affected the condition of SSC. Based on all analysis, the mobile ADCP can provide a suitable measurement of suspended sediment concentration.