Amount Of Suspended Sediment Research Articles

Estimation of suspended sediment concentration from turbidity measurements using artificial neural networks

Suspended sediment concentration (SSC) is generally determined from the direct measurement of sediment concentration of river or from sediment transport equations. Direct measurement is very costly and cannot be conducted for all river gauge stations. Therefore, correct estimation of suspended sediment amount carried by a river is very important in terms of water pollution, channel navigability, reservoir filling, fish habitat, river aesthetics and scientific interests. This study investigates the feasibility of using turbidity as a surrogate for SSC as in situ turbidity meters are being increasingly used to generate continuous records of SSC in rivers. For this reason, regression analysis (RA) and artificial neural networks (ANNs) were employed to estimate SSC based on in situ turbidity measurements. The SSC was firstly experimentally determined for the surface water samples collected from the six monitoring stations along the main branch of the stream Harsit, Eastern Black Sea Basin, Turkey. There were 144 data for each variable obtained on a fortnightly basis during March 2009 and February 2010. In the ANN method, the used data for training, testing and validation sets are 108, 24 and 12 of total 144 data, respectively. As the results of analyses, the smallest mean absolute error (MAE) and root mean square error (RMSE) values for validation set were obtained from the ANN method with 11.40 and 17.87, respectively. However these were 19.12 and 25.09 for RA. It was concluded that turbidity could be a surrogate for SSC in the streams, and the ANNs method used for the estimation of SSC provided acceptable results.

MARINE SEDIMENT CHARACTERISTICS AT KARIMUN JAVA SEA BASED ON STRATIGRAPHIC PROFILE ANALYSIS, TOTAL SUSPENDED SOLID (TSS) AND GRAIN-SIZE ANALYSIS (GRANULOMETRY)

A sedimentology survey was conducted during “Pelayaran Kebangsaan” research activities with a marine vessel of "Baruna Jaya VIII" in Karimun Java Sea. The objectives of the research were to determine the characteristics of marine water and its sediment, which are important control for coral reef growth in the study area. The survey acquired samples of Total Suspended Sediment (TSS) and gravity coring. Several analyses were then carried out on those samples; TSS analysis to determine the amount of suspended sediments in sea water that reflect the water quality for marine ecology, stratigraphic profile and sediment thickness pattern analyses to determine the sources of sediment, and grain-size analysis based on granulometry to determine deposition energy and grain-size distribution in the area. Those analyses were both conducted on-board Baruna Jaya VIII research vessel and P2O LIPI laboratory in Jakarta. The results showed that in Java Sea nearby Karimun Java Islands, the sediment supply came from the surrounding islands. Two sedimentary units were found in this area. The first units has thickness of tens centimeter from sea bed surface. It is characterized by grayish green color, grain size variation from clay to coarse sand, soft or low density and abundance with shells. The second unit is located beneath the first one, indicated by sharp contact. It is characterized by brownish color, higher density resembling the density of rock, less compacted and can be broken easily by hand, with occasionally thin carbon lenses or remnant of decomposed vegetation, and less shell or fossil At sea surface, TSS distribution shows value between 0.018 and 0.034 gr/l, with average of 0.025 gr/l, whereas at near bottom sea, it ranges between 0.024 and 0.030 gr/l, with average value of 0.027 gr/l. The granulometry shows that more than 50% of sediment is characterized by the abundance of grain size greater than 3 phi. It suggest that sea water around Karimun Java Islands was clear and the current was relatively calm. These conditions were relatively stable for a long time span. Those sea characteristics were important for successful growth of coral reefs and its complementary marine biotas. However, further studies and researches based on chemical and physical characteristics of sea water, and plankton and microbiology variation and abundances are necessary to confirm those presuppositions.Keywords: total suspended solid, gravity coring, stratigraphic profile, granulometry, Karimun Java Sea

MARINE SEDIMENT CHARACTERISTICS AT KARIMUN JAVA SEA BASED ON STRATIGRAPHIC PROFILE ANALYSIS, TOTAL SUSPENDED SOLID (TSS) AND GRAIN-SIZE ANALYSIS (GRANULOMETRY)

<p>A sedimentology survey was conducted during “Pelayaran Kebangsaan” research activities with a marine vessel of "Baruna Jaya VIII" in Karimun Java Sea. The objectives of the research were to determine the characteristics of marine water and its sediment, which are important control for coral reef growth in the study area. The survey acquired samples of Total Suspended Sediment (TSS) and gravity coring. Several analyses were then carried out on those samples; TSS analysis to determine the amount of suspended sediments in sea water that reflect the water quality for marine ecology, stratigraphic profile and sediment thickness pattern analyses to determine the sources of sediment, and grain-size analysis based on granulometry to determine deposition energy and grain-size distribution in the area. Those analyses were both conducted on-board Baruna Jaya VIII research vessel and P2O LIPI laboratory in Jakarta. The results showed that in Java Sea nearby Karimun Java Islands, the sediment supply came from the surrounding islands. Two sedimentary units were found in this area. The first units has thickness of tens centimeter from sea bed surface. It is characterized by grayish green color, grain size variation from clay to coarse sand, soft or low density and abundance with shells. The second unit is located beneath the first one, indicated by sharp contact. It is characterized by brownish color, higher density resembling the density of rock, less compacted and can be broken easily by hand, with occasionally thin carbon lenses or remnant of decomposed vegetation, and less shell or fossil At sea surface, TSS distribution shows value between 0.018 and 0.034 gr/l, with average of 0.025 gr/l, whereas at near bottom sea, it ranges between 0.024 and 0.030 gr/l, with average value of 0.027 gr/l. The granulometry shows that more than 50% of sediment is characterized by the abundance of grain size greater than 3 phi. It suggest that sea water around Karimun Java Islands was clear and the current was relatively calm. These conditions were relatively stable for a long time span. Those sea characteristics were important for successful growth of coral reefs and its complementary marine biotas. However, further studies and researches based on chemical and physical characteristics of sea water, and plankton and microbiology variation and abundances are necessary to confirm those presuppositions.</p><p>Keywords: total suspended solid, gravity coring, stratigraphic profile, granulometry, Karimun Java Sea</p>

Sudden Clearing of Estuarine Waters upon Crossing the Threshold from Transport to Supply Regulation of Sediment Transport as an Erodible Sediment Pool is Depleted: San Francisco Bay, 1999

The quantity of suspended sediment in an estuary is regulated either by transport, where energy or time needed to suspend sediment is limiting, or by supply, where the quantity of erodible sediment is limiting. This paper presents a hypothesis that suspended-sediment concentration (SSC) in estuaries can suddenly decrease when the threshold from transport to supply regulation is crossed as an erodible sediment pool is depleted. This study was motivated by a statistically significant 36% step decrease in SSC in San Francisco Bay from water years 1991–1998 to 1999–2007. A quantitative conceptual model of an estuary with an erodible sediment pool and transport or supply regulation of sediment transport is developed. Model results confirm that, if the regulation threshold was crossed in 1999, SSC would decrease rapidly after water year 1999 as observed. Estuaries with a similar history of a depositional sediment pulse followed by erosion may experience sudden clearing.

NUMERICAL SIMULATIONS OF SEDIMENT TRANSPORT INDUCED BY THE 2004 INDIAN OCEAN TSUNAMI NEAR KIRINDA PORT IN SRI LANKA

Numerical simulations of sediment transport induced by the 2004 Indian Ocean tsunami near Kirinda port in southeastern Sri Lanka is carried out and the relationships between the tsunami-induced flow and sediment transport are discussed. The results show two clear relationships. The first one is that the local scour occurs and a large amount of suspended sediment is generated around the head of breakwaters when the tsunami-induced flow passes through there. The second one is that the suspended sediment is deposited near vortex centers due to a secondary flow.

Development and evaluation of an automation algorithm for a time-domain reflectometry bridge scour monitoring system

Bridge scour is a major threat to the safety of bridges. There is a high risk of scour-induced damage due to the catastrophic nature of bridge foundation failure. The development of an innovative bridge scour monitoring system is a pressing task for the research community. Such a system needs to be fieldworthy, which is a characteristic assessed in terms of accuracy, ruggedness, and automation. Among these criteria, an automatic signal analysis algorithm is generally a prerequisite for deploying a long-term field monitoring program. This paper describes the development and validation of an algorithm for a scour monitoring system based on the principles of guided radar: time-domain reflectometry (TDR). This algorithm is based on the extension of the classic dielectric mixing model to layered systems. The performance of this algorithm is evaluated using experiments designed to simulate different field scour conditions. These include different types of sediments and the variation of river conditions (i.e., salinity of river water, air entrainment, and amount of suspended sediments). The experiment results indicate that the developed analyses algorithm is robust and accurate for scour-depth estimation under these investigated conditions.

Sediment and Shallow Coastal Water Detection Utilizing MODIS Land Channels over Gulf of Martaban

Application of clear waters (Case 1) algorithm to satellite imagery acquired with Moderate Resolution Imaging Spectroradiometer (MODIS) over turbid coastal waters (Case 2) often results in negative water-leaving radiances over extended areas. Also, the maximum reflectances for ocean color channels are significantly smaller than those for the land channels at similar wavelengths. Because of that, at the bright coastal waters area, ocean color channels (0.488, 0.531 and 0.551 µm) often saturate. The saturation of this channels contribute to the lost of geophysical and biological activities in the data. So, in order to overcome this circumstance, it is reasonable to use MODIS land and atmosphere channels (1 to 7) to derive an algorithm for the detections of turbid and shallow coastal waters area. In order to improve aerosol retrieving algorithm over the ocean, an algorithm to mask out the turbid coastal water area need to be developed. In this paper, a simple algorithm to identify and mask shallow coastal water and high amounts of suspended sediment area in the Gulf of Martaban using MODIS L1B image is suggested and demonstrated. This algorithm uses log10 ratio of two MODIS solar channels that was originally designed for remote sensing over land and cloud properties (band 3 and band 4) centered at 0.47 and 0.55 µm respectively. Shallow coastal water and the area with high amount of suspended sediment are detected by our algorithm have been masked. The result of this algorithm is then evaluated by comparing the masked area with the true color image of the scene.

Sources of Suspended‐Sediment Flux in Streams of the Chesapeake Bay Watershed: A Regional Application of the SPARROW Model1

Brakebill, John W., Scott W. Ator, and Gregory E. Schwarz, 2010. Sources of Suspended‐Sediment Flux in Streams of the Chesapeake Bay Watershed: A Regional Application of the SPARROW Model. Journal of the American Water Resources Association (JAWRA) 46(4): 757‐776. DOI: 10.1111/j.1752‐1688.2010.00450.xAbstract: We describe the sources and transport of fluvial suspended sediment in nontidal streams of the Chesapeake Bay watershed and vicinity. We applied SPAtially Referenced Regressions on Watershed attributes, which spatially correlates estimated mean annual flux of suspended sediment in nontidal streams with sources of suspended sediment and transport factors. According to our model, urban development generates on average the greatest amount of suspended sediment per unit area (3,928 Mg/km2/year), although agriculture is much more widespread and is the greatest overall source of suspended sediment (57 Mg/km2/year). Factors affecting sediment transport from uplands to streams include mean basin slope, reservoirs, physiography, and soil permeability. On average, 59% of upland suspended sediment generated is temporarily stored along large rivers draining the Coastal Plain or in reservoirs throughout the watershed. Applying erosion and sediment controls from agriculture and urban development in areas of the northern Piedmont close to the upper Bay, where the combined effects of watershed characteristics on sediment transport have the greatest influence may be most helpful in mitigating sedimentation in the bay and its tributaries. Stream restoration efforts addressing floodplain and bank stabilization and incision may be more effective in smaller, headwater streams outside of the Coastal Plain.

Particle size characteristics of suspended sediment transported in meltwater from the Gangotri Glacier, central Himalaya — An indicator of subglacial sediment evacuation

Proglacial meltwater streams draining out of the Himalayan glaciers carry considerable amounts of suspended sediment, with a variety of particle sizes, because of the supraglacial, englacial, and subglacial debris, as well as formation of sediments from erosion by the movement of the ice. This paper examines particle size transported in the proglacial meltwater stream of Gangotri Glacier for seven consecutive melt seasons (May–October, 2000–2006) in order to provide information on (i) temporal variations in the particle size distribution, (ii) texture and mineralogy of the sediments, and (iii) origin and evacuation pattern of the sediments. Our results indicate dominance of silt size (0.002–0.06 mm) particles (71%) followed by sand size (0.06–0.6 mm) particles (24%) and clay size (< 0.002 mm) particles (5%) during the melt season, with increased variation as melt season progresses. The sediment contains quartz, feldspar, mica, illite, and kaolinite minerals, which represent a poor to poorly sorted fraction with a coarse to fine skewed textural distribution. Overall, this study indicates a subglacial evacuation pattern of the suspended sediment based on (i) size classification, (ii) higher percentage of coarser particles toward the end of the melting season, (iii) symmetrical to positively skewed with a kurtosis of mesokurtic to platykurtic texture, and (iv) a less-rounded shape of particle size. Our result on the evolution of meltwater pathways indicates a progressively better interconnected drainage system with advancing melt season. The evolution of meltwater pathways also demonstrates complex behavior of the glacial system and the need for a better understanding of sediment availability and contribution.

The effect of weathering in the Buyukmelen River basin on the geochemistry of suspended and bed sediments and the hyrogeochemical characteristics of river water, Duzce, Turkey

The Buyukmelen River is expected to be a water source that can supply the drinking water needs of Istanbul until 2040. The drinking and utility water needs of Istanbul are to transport water from the Buyukmelen River to Istanbul via pipeline and pump it into the Alibeykoy and Omerli reservoirs when their water levels drop. The Buyukmelen River is located in the province of Duzce in 170 km east of Istanbul and its water basin is approximately 2250 km 2. The Buyukmelen River flows muddy in the rainy season and into the Black Sea. The chemical compositions of natural waters alter due to interaction with geological formations, physical and chemical weathering of various rocks and the effects of mining and agricultural production. A research was conducted at the Buyukmelen River basin to determine the effects of hydrological processes. Therefore, the samples of rocks, soil, stream water, suspended and bed sediment were collected from the Buyukmelen River basin. Geochemical and water chemistry analyses of samples were performed at ALS Chemex laboratories, Canada. The bed sediments contain quartz, calcite, plagioclase, amphibole and clay minerals. The clay minerals in the suspended and bed sediment samples are kaolinite, smectite and illite. The water samples collected from the Aksu, Kucukmelen, Asarsu and Ugursuyu streams and the Buyukmelen River in winter (December 2005) and summer (June 2006) periods are rich in Ca and HCO 3 ions. The ions most abundant in rainfall sample are HCO 3 and Na. The ion compositions of surface waters have increased due to the weathering of limestone, agglomerate and volcanic sandstones, light acidic rainfall, semi-arid Black Sea climate in the Buyukmelen basin. The suspended sediment amount of the Buyukmelen River in the rainy season (December 2005) is 174 mg/l. According to the water contamination regulation of Turkey, the Buyukmelen Rivers belongs to quality class 4 based on Al ion and to quality class 3 based on Fe ion in winter period, and to quality class 2 based on Mn concentration in summer period. Chemical index of alteration (CIA) indices observed in the suspended and bed sediments (average of 55) suggest that their source area underwent moderate degrees of chemical weathering processes. According to Upper Continental Crust (UCC) values, the suspended sediment was rich in elements such as Fe 2O 3, CaO, MgO, MnO, TiO 2, P 2O 5, V, Cr, Co, Cu, Zn, As, Cd, Sb, Hg and Pb. The element concentrations of the suspended sediments were related to size fractionation, mainly of clay content. The mentioned enrichment was contributed by agglomerate, basalt, volcanic sandstone and graywacke from rocks in the study area. Source of ions such as Al, Fe, Mn, Ba, Cr, Co, Cu, Ni, Ti and Hg and major in the Buyukmelen River is interaction with rocks such as the agglomerate, basalt, andesite, volcanic sandstone and graywacke. As suggested by Singh et al. (2005), before weathering of some rocks in the Buyukmelen River basin, it was determined that they were graywacke and literanite based on the geochemistry of the suspended and bed sediments.

Suspended‐sediment sources in an urban watershed, Northeast Branch Anacostia River, Maryland

AbstractFine sediment sources were characterized by chemical composition in an urban watershed, the Northeast Branch Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible land‐based sediment sources and suspended sediment collected from the water column at the watershed outlet during storm events. These tracer concentrations were used to determine the relative quantity of suspended sediment contributed by each source. Although this is an urbanized watershed, there was not a distinct urban signature that can be evaluated except for the contributions from road surfaces. We identified the sources of fine sediment by both physiographic province (Piedmont and Coastal Plain) and source locale (streambanks, upland and street residue) by using different sets of elemental tracers. The Piedmont contributed the majority of the fine sediment for seven of the eight measured storms. The streambanks contributed the greatest quantity of fine sediment when evaluated by source locale. Street residue contributed 13% of the total suspended sediment on average and was the source most concentrated in anthropogenically enriched elements. Combining results from the source locale and physiographic province analyses, most fine sediment in the Northeast Branch watershed is derived from streambanks that contain sediment eroded from the Piedmont physiographic province of the watershed. Sediment fingerprinting analyses are most useful when longer term evaluations of sediment erosion and storage are also available from streambank‐erosion measurements, sediment budget and other methods. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Seasonal patterns of suspended sediment transport in an abandoned farmland catchment in the Central Spanish Pyrenees

AbstractThe suspended sediment response of a small catchment subjected to farmland abandonment and subsequent plant recolonization was studied in relation to its hydrological functioning. The analysis of data over a seven‐year period demonstrated that suspended sediment yield was greatly influenced by the occurrence of intense, low‐frequency events. Greater amounts of suspended sediment were exported during spring, when the catchment was hydrologically more active. Rainfall intensity and baseflow at the start of a flood event had a strong influence on the sediment response, suggesting that several hydrological processes were active within the catchment. SSC (suspended sediment concentration)‐Q hysteretic loop analysis at the event scale aided understanding of the sedimentological and hydrological behaviour of the catchment. During the study period the SSC‐Q loops showed a high degree of seasonality and two main patterns strongly related to catchment wetness were distinguished. When the catchment was dry (mainly during summer and the beginning of autumn) the predominant process was infiltration excess runoff over sparsely vegetated areas close to the main channel. Under these conditions, floods exhibited a counter‐clockwise hysteretic loop and were characterized by a small streamflow response, short duration and high SSC. Under wet conditions (mainly during winter and spring), saturation excess runoff was increasingly dominant over vegetated areas. Under these conditions, floods exhibited a clockwise hysteretic loop, and were characterized by a larger streamflow response, longer duration and higher suspended sediment yield. The lower SSC during the falling stage of the hydrograph is likely to be due to dilution effects related to the contribution of clean water resulting from enlargement of the saturated areas, together with an increase in the baseflow discharge. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Dynamics and spatial variability of near-bottom sediment exchange in the Yangtze Estuary, China

This study was conducted to examine the spatial variations in the exchange between near-bottom suspended and sea-bottom sediments in the Yangtze Estuary and adjacent region, as well as to explore the fate of suspended sediments in the study area. The relationship between the sand, silt, and clay contents of the sediments was analyzed by log-ratio analysis, which revealed a non-linear function for selective deposition and a wide range of grain-size distributions in the estuary. This finding does not conform to the nearly constant clay/silt ratios reported for other tidal basins around the world, due to non-linear sediment mixing under complex hydrodynamic conditions. The sediment exchange processes in the Yangtze Estuary were quantified based on the principle of mass balance. The average grain-size distribution of near-bottom suspended sediments from the estuary showed that approximately 49% of the riverine sediments accumulated in the mouth bar area, while the rest, which is primarily composed of fine-grained sediments, is transferred to the outer estuary and deposited in the form of flocs. The spatial distribution of the sediment exchange ratios demonstrated that small amounts of suspended sediment were deposited onto the seabed of the upper estuary (exchange ratio < 0.1), because the fine-grained suspended sediments in this region were transported to the mouth bar area by the ebb-dominated tidal flow. The sediment exchange ratios in the outer estuary also showed very low values (<0.1) due to the oceanic currents offshore that prevented the diffusion of riverine sediments further seaward. Intensive sediment exchange occurred in the inner estuary due to the sand-mud mixing which was controlled by bidirectional tidal flows. In addition, a high sediment exchange ratio occurred in the muddy area (>0.8) seaward of the river mouth, which implies that this is the present-day depocenter of Yangtze mud. The sediment exchange rates obtained by combining the dimensionless exchange ratios and bulk sediment accumulation rates, were found to be 2–3 cm/yr in the muddy depocenter, which extends to the south of the river mouth (from 122° E to 123° E longitude, at 31° N latitude).

The changes in the lower Drava River water level, discharge and suspended sediment regime

Massive construction on the Drava River basin and on the river itself during the last centuries, as well as recent climate change and/or variability, has caused many different and possibly dangerous changes to its hydrological and ecological regime. Since 1975, numerous hydrotechnical works have been carried out on the 60-km long section of the Drava River from the Slovenian–Croatian border to the River Mura mouth. Three hydrotechnical power plants with three reservoirs and three long inlet and outlet canals have been built. Changes in water level, discharge and suspended sediment yield along the Drava River measured in Croatia, downstream of the three Croatian reservoirs, during the last 30–130 years are presented. The investigation focuses on changes that have occurred during the last thirty-odd years, caused by the anthropogenic influences on the Drava River watercourse and its catchment in Croatia and Hungary, and probably by climate change or variability. Methods of rescaled adjusted partial sums, statistical tests, as well as regression and correlation analyses are used to explain changes in water level, discharge and suspended sediment yield. There is evidence in the time series of decreases in the minimum, mean and maximum annual water levels, and minimum and mean discharges on the lower part of the Drava River. One of the main objectives of this study was to examine the effect of dams and reservoirs operation on the changes in the downstream suspended sediment regime. The amount of suspended sediment has been greatly reduced, which can cause serious consequences.

Estimation of annual suspended sediment yield from a Japanese cypress ( Chamaecyparis obtusa) plantation considering antecedent rainfalls

Japanese cypress ( Chamaecyparis obtusa) is one of the most common plantation species in Japan. In most Japanese cypress plantations, closure of the forest canopy hinders understory growth because of insufficient management practices. Thus leaf litter barely covers the soil surface. Such plantations are vulnerable to surface erosion triggered by rainfalls, and could yield large amounts of suspended sediment (SS). However, few studies have investigated the annual SS yield. This study aimed to develop a modified model of SS yields, and to accurately estimate and characterize the annual SS yield from a Japanese cypress plantation. For this, hydrological surveys were conducted for 5 years, and stream water was sampled weekly as well as sequentially at 15–60 min intervals in each of 14 rain events in a small forested watershed of Japanese cypress. The root mean square error (RMSE) and the annual SS yield estimates were obtained using three different equations: the rating curve derived from instantaneous SS concentration versus stream discharge relationship (SSC − Q equation); the rating curve derived from cumulative SS yield versus cumulative specific discharge relationship (∑SS − ∑ Q equation); and the multiple regression of cumulative SS yield expressed as functions of cumulative specific discharge and antecedent rainfalls (∑SS − ∑ Q × AR equation). The ∑SS − ∑ Q × AR equation is a modified model considering the effects of antecedent rain history on the SS yield. The parameters in each equation were determined by a nonlinear least square method. Of the three equations, the RMSE was the highest using the SSC − Q equation. Although the ∑SS − ∑ Q equation and the ∑SS − ∑ Q × AR equation gave similar RMSE values, the SS yields extrapolated by the ∑SS − ∑ Q equation would be overestimated. Thus, the 5-year average of annual SS yield estimated by the ∑SS − ∑ Q equation was three times larger than that estimated by the ∑SS − ∑ Q × AR equation. These results indicate that the ∑SS − ∑ Q × AR equation more accurately estimates the annual SS yield, compared with the other two equations. The results also suggest that antecedent rain history, as well as stream discharge, should be considered for appropriately estimating the annual SS yield. The annual SS yield estimated by the ∑SS − ∑ Q × AR equation was the largest among 25 undisturbed forested watersheds, except for two watersheds dominated by sandstone. Our results suggest that the annual SS yield is greater from a Japanese cypress plantation under current management practices than from other undisturbed forests.

새만금 해역에서 연직 1차원 퇴적물 확산모델 검증

The sediment resuspension and diffusion model is an integral part of a sediment transport and morphologic change model. We examined a vertical one-dimensional sediment resuspension and diffusion model using field data collected at about 10-m depth off the Saemangeun 4 th dike. The field data include waves, currents and suspended sediment concentration near the bed for about a day in May, 2007. The suspended sediment concentration obtained from the 1D model overestimated the observation about two orders of magnitude with single grain size and multiple grain sizes. The incorporation of the bed armoring effect, which adjusts the amount of suspended sediment with the available bed sediment, improved the agreement between the model and observation within a factor of two.

Effects of sediments on larval settlement of abalone Haliotis diversicolor

The effects of deposited sediments on the settlement of the abalone Haliotis diversicolor Reeve were examined through both field observations and a laboratory experiment. Occurrences of newly settled post-larvae (shell length < 500 μm) and the amount of suspended and deposited sediments were monitored at two stations (Stns 1 and 2), which experienced different sediment deposition conditions, located at Nagai on the coast of Sagami Bay, Japan. Quantities of suspended sediments at the two stations varied considerably during the survey period, but no significant difference was detected between the stations. Mean volume densities of sediments deposited on cobbles were significantly higher at Stn 2 than at Stn 1. Densities of newly settled post-larvae from the 2001 to 2004 cohorts were significantly higher at Stn 1. A laboratory experiment was conducted to assess the effects of sediment quantity and quality on larval settlement. Two substances with different physical properties, kaolin and clamshell powder, were used as sediments. Larvae were subjected to four different sediment treatments with crustose coralline algae (CCA) substrates; thin and thick treatments for both kaolin and clamshell powder. Negative (without CCA) and positive (with CCA) controls without sediments were also established. The rate of metamorphosis decreased as sediment thickness increased in both the kaolin and clamshell powder treatments. Larvae in the kaolin treatments appeared to be trapped by the kaolin, and most could not metamorphose successfully. There were no trapped larvae in the clamshell powder treatments. The results indicate that the quantity and physical properties of sediments deposited on substrata affect the settlement and behaviour of larval abalone. Experimental results suggest that the lower densities of newly settled post-larvae observed at Stn 2 may have been a result of larger quantities of deposited sediments, which reduced the availability of suitable substrate for larval settlement.

Lateral circulation and suspended sediment transport in a curved estuarine channel: Winyah Bay, SC, USA

Shipborne vertical profiles of flow and suspended sediment concentration collected on a transect, across a curved, nonsymmetrical estuarine channel are presented. Analysis of the transient cross‐channel momentum balance equation shows that the lateral circulation pattern is controlled by the interaction between centrifugal and lateral baroclinic forcings although those two might not be necessarily in balance as suggested earlier by Seim and Gregg (1997). Instead, differential along‐channel advection and local acceleration appear to influence greatly lateral circulation dynamics. During ebb when the water column is highly stratified, the interaction between centrifugal acceleration and opposite‐directed lateral baroclinic forcing results in weak lateral flows. During flood, lateral flows are dominated by centrifugal acceleration, which is directed toward the outside of the curvature at the mid‐depth because of the nonlogarithmic current profile, and reinforced by lateral baroclinic forcing. This results in strong two‐layer clockwise circulation (looking up‐estuary) during flood. The eastward‐directed bottom currents during ebb deliver only a small amount of suspended sediment from the relatively narrow western shoal to the channel bed. During flood, the west‐directed near‐bed currents deliver a significant amount of sediments from the gentle, broad eastern shoal, which in conjunction with the locally resuspended sediment load promotes the development of the estuarine turbidity maximum. Increased lateral advection of sediments during flood reinforces a tidal asymmetry in the development of turbidity maximum. Decomposition analysis of lateral sediment fluxes averaged over a tidal cycle suggests convergence of sediment toward the center of the channel is driven mainly by the oscillatory tidal component.

Long‐distance nutrient‐transport process in the Changjiang river plume on the East China Sea shelf in summer

Idealized physical and ecosystem numerical models are coupled to investigate the phytoplankton bloom in Changjiang Diluted Water (CDW) on the East China Sea shelf in summer. Special attention is given to the phytoplankton not exhausting nutrients in CDW over a period of a few months in spite of high biological productivity. In the present study, CDW is expressed by a bowl‐shaped three‐layered plume moving on an infinitely deep layer due to ambient eastward currents. This model permits layers outcropping to the sea surface. The simplest ecosystem model composed of the nutrient, phytoplankton, and detritus is coupled with the above physical model. When river plumes contain a large amount of suspended sediment, it is likely that turbid river water prevents sunlight from reaching the lower layer of the plumes. Hence in the ecosystem model for turbid CDW, it is assumed that primary production is completely restricted when a layer is shaded by upper layers. As three‐layered CDW is carried eastward by the ambient currents, lower layers south of the plume outcrop to the sea surface because of the layer‐to‐layer interaction. The nutrient released into the lower layers is used for primary production when it reaches the outcrop area south of the plume, and causes the phytoplankton bloom there. The modeled phytoplankton concentration in the uppermost layer exhibits a similar pattern to that seen in satellite‐derived chlorophyll a images in which a high concentration is observed south of CDW extending eastward.

Case Study for a Cohesive Sediment Transport Model for Matagorda Bay, Texas, with Coupled ADCIRC 2D-Transport and SWAN Wave Models

Tidal current and wave forces are the primary factors causing agitation, suspension, and transport of littoral materials in a bay. This paper presents a study of the circulation patterns of the water and sediment fluxes in a real bay during ordinary natural weather conditions. A coupled hydrodynamic and wave model is developed to support the research. A two-dimensional parallel advanced circulation hydrodynamic model with an extended transport module is used to calculate the water circulation within the bay, while the simulating wave nearshore model is implemented to provide the wave parameter data. The month of March 2003 is selected to represent the test case for the sediment transport model in Matagorda Bay, Tex. The presence of wave action significantly, increases the amount of suspended sediment, and consequently, more deposited sediments occur around the ship channel, where shallow shoals are located. Comparison of the simulated deposited sediments in the Matagorda ship channel with the two selected...