Controlling Sediment Deposition Research Articles

Herbivores can benefit both plants and their pathogens through selective herbivory on diseased tissue

Abstract Infectious disease can shape community structure, particularly when pathogens affect foundation species. Seagrasses are foundation species that form meadows along coasts worldwide, controlling sediment deposition and biogeochemical cycling while supporting a diverse community of fish and invertebrates. These plants are hosts to wasting diseases that cause necrotic tissue lesions, which could alter seagrass value as food, habitat and mediators of ecosystem processes. However, such biotic interactions and influences on disease dynamics are still not well understood. We investigated whether a common herbivore affected the development of wasting disease on eelgrass. We measured the severity and prevalence of eelgrass wasting disease in a meadow across two summers through repeated field surveys. We assessed the role of the eelgrass herbivore on disease spread and growth using microcosm and mesocosm experiments. We further explored herbivore feeding preferences in a choice trial, which was paired with chemical analysis of plant tissue and analysed using a structural equation model. While the herbivore facilitates the growth of new disease lesions among isolated leaves, on balance they reduce lesion severity by more than 50% in comparison with no‐herbivore controls in field‐realistic settings. This was likely because the herbivore strongly prefers to eat diseased rather than healthy tissue, consuming nearly twice as much lesion area in choice trials. This preference arises from pathogen‐driven changes in the host plant; lesioned tissue requires less force to penetrate than non‐lesioned tissue. Additionally, as lesions increase in size, their polyphenolic concentrations drop, which further increases the magnitude of preference for lesioned tissue. Synthesis: These results suggest that these herbivores could help maintain disease in this system at a high prevalence (by facilitating disease development) but low severity (through preferential consumption), which is consistent with our field observations of nearly 100% prevalence and low severity in a natural bed where herbivore density is high. Describing such multi‐species interactions in marine systems will advance our predictions of future disease states, as current understandings focus primarily on how environmental change contributes to pathogen outbreaks.

Cyclic sediment deposition by orbital forcing in the Miocene wetland of western Amazonia? New insights from a multidisciplinary approach

In the Miocene, a large wetland system extended from the Andean foothills into western Amazonia. This system has no modern analogue and the driving mechanisms are not yet fully understood. Dynamic topography and Andean uplift are thought to have controlled deposition, with allocyclic base level changes driven by eustasy and orbital forcing also playing a role. In this study we investigate the presumed orbital cyclicity that controlled sediment deposition, while also assessing sediment source and biomes in the Miocene wetland. We do this by integrating lithological, palynological, malacological and geochemical data from the Los Chorros site (Amazon River, Colombia), and by placing our data in a sequence stratigraphic framework. In this sequence biostratigraphic evaluation, the Los Chorros succession is visualized to be composed of a series of flood-fill packages, with a rapid initial flood, marine-influenced conditions at the time of maximum flood, followed by a longer regressive infill phase. Based on the palynology we could differentiate local vegetation, such as palm swamps, from regional origin such as terra firme vegetation (non-flooded Amazonian forest) and Andean montane forest, while from sediment geochemistry we could separate local and regional sediment sources. At the times of flooding, oligotrophic and eutrophic aquatic conditions alternatively characterized the wetland, as is shown by the presence of algae, floating ferns, and mollusc assemblages, while intervening subaquatic debris points to proximal submerged lowlands. In the lower 20 m of the section, marine influences are intermittently evident and shown by short-lived maxima of mangrove pollen, foraminiferal test linings, dinoflagellate cysts, coastal mollusc species, and an episodic decline in terrestrial biomarkers. The upper 5 m of the section is characterized by floodplain forest taxa with a diversity in tropical rain forest taxa and relatively few lacustrine indicators. These marine, mangrove, and lacustrine indicators suggest that the outcrops at Los Chorros represent predominant marine-influenced lacustrine conditions during periods of sea level highstand. The sequence biostratigraphic evaluation further points to eight 41 kyr obliquity-driven depositional cycles, with rapid phases of transgression. Mangrove elements would have colonised within the timeframe of each sea level rise. Based on this relative age constraint and comparison to regional records, deposition likely took place prior to the 13.8 Myr global sea level fall, and most likely during the period just after 14.5 Ma, between Middle Miocene Climatic Optimum (MMCO; 17–14 Ma) and Middle Miocene Climate Transition (MMCT; 14.7–13.8 Ma). Palynological evidence further suggests that to the west, surface elevation ranged from ~1000 up to ~3500 m and hosted protoparamo vegetation, the oldest yet reported and in agreement with predictions from molecular studies. In contrast, contemporaneous sites to the northeast of the wetland consisted of fluvial and cratonic formations, as shown by their Nd and Sr isotopic sediment signature. In summary, our data lead to an improved understanding of how geological and astronomical mechanisms controlled the floral and faunal distribution and controlled sediment deposition in western Amazonia during the middle Miocene. As Miocene conditions strongly contrast with modern western Amazonia, our data provide an important context for the deep time history and evolution of the modern western Amazon rainforest. • We used a sequence biostratigraphic approach to evaluate cyclic deposition in the Miocene wetland of Western Amazonia. • Repeated flood-fill packages were deposited just after 14.5 Ma, during the Middle Miocene Climatic Optimum. • Local vegetation was formed of mangroves, palm and fern swamps, and terra firme lowland. • Molluscs and algae reflect changing salinity, nutrient levels, and water depths. • Sediments and sporomorphs point at the Andes as principal sediment source, with the Amazon craton as additional supplier. • In the mid-Miocene the Andes already had elevations of up to 3500 m and hosted a protoparamo.

Paleo-facies distribution and sequence stratigraphic architecture of the Oligo-Miocene Asmari carbonate platform (southeast Dezful Embayment, Zagros Basin, SW Iran)

A facies and sequence stratigraphic analysis was made of the Oligo-Miocene Asmari carbonate platform situated in the east and southeast of the Dezful Embayment (Zagros Basin, SW Iran). This study provides new paleofacies and depositional sequence distribution models for the eastern part of the Dezful Embayment and discusses the impact of the factors controlling sediment deposition being eustatic sea-level changes and tectonic processes. The petrographic study reveals that the variations in facies cover three depositional settings, e.g. open marine, lagoon and tidal flats. In total, six depositional sequences (DS) were identified within the sedimentary sequence of the Asmari Formation. DS1 and DS2 were deposited during the Rupelian (Oligocene) within deeper open marine platform settings. Sediments forming DS3 and DS4 were deposited during the Chattian in a carbonate platform environment within an open lagoon to protected lagoon setting. The Miocene DS5 and 6 sequences, Aquitanian and Burdigalian in age, were deposited in shallower environments compared to other DS's, within protected lagoon to tidal flat settings. A comparison with the sedimentary development in other parts of the Dezful Embayment showed that the deposition of the Asmari strata started earlier (Early Rupelian) in the eastern, south-eastern and north-eastern part of the basin. In the western and central parts of the Dezful Embayment it began in the Late Rupelian or even Rupelian/Chattian. The eastern and south-eastern parts of the Dezful Embayment displayed a platform margin setting during the Rupelian while the north-eastern and central areas showed a basin setting. During the Early Chattian, clastic sediments originating from the Arabian Plate were deposited in the west, southwest, northwest and centre of the basin in response to a sea-level lowstand. The two very thin sandstone units occurring in the Late Aquitanian succession across the west of the Bibi Hakimeh oilfield are the only sandstone layers related to a sea-level lowstand throughout E/SE of the Dezful Embayment. During the Chattian the sediments in the eastern parts of the Dezful Embayment were deposited in a proximal inner ramp setting, and corals and coralline red algae (mainly Lithophyllum sp. and Lithothamnion sp.) dominated the carbonate platform in the east, while imperforate benthic foraminifera (e.g. Peneroplis sp., Archaias sp.) and rare perforate benthic foraminifera (e.g. Neorotalia sp., and Amphistegina sp.) were the most frequent sediment contributors in the southeast of the basin (Bibi Hakimeh area). At the same time, sedimentation occurred on a distal inner to mid-ramp settings through the central areas of the Dezful Embayment. A eustatic fall in sea-level and tectonic processes resulted in the isolation of the basin. During the Aquitanian two exposure horizons formed in the western and central Dezful Embayment basin while the eastern part only displays one. During the Burdigalian, sedimentation in the entire Dezful Embayment occurred within an innermost, very shallow ramp setting. The current study shows that sea-level fluctuations and sometimes combined with regional tectonic processes controlled the variability in platform geometry and paleofacies distribution of the Oligo-Miocene sediments across the basin.

Effects of herbivorous gastropod grazing on the sedimentation and succession of subtidal macroalgal assemblages

The subtidal zone on cold temperate rocky coasts is an environment exposed to much less physical disturbance than the intertidal, and sediment deposition is continuous. Removal of this sediment by gastropod grazers is therefore presumed to affect the structure of subtidal algal communities. This concept was investigated by evaluating the grazing effects of the dominant herbivorous gastropod Omphalius rusticus by exclusion experiments in the field. Settlement plates of both exclusion and control treatments were placed every month from November 2014, and immersed for 1 mo. Algae colonized from May and tended to increase in biomass toward summer. No marked differences were observed in the algal composition of exclusion and control. Sediment deposition showed no apparent seasonal changes. Cumulative successional plates of both exclusion and control treatments were placed in November 2014, and immersed for 1 to 9 mo. The colonization of algae started in February and the species number peaked earlier in the exclusion and later in the control. Sediment load and algal biomass were high from February to May in the exclusion, and from April to July in the control. Seedlings of Sargassum confusum were found in both plots starting in July. We conclude that O. rusticus constantly removed sediments by its grazing activity and had a large impact on the formation of the macroalgal community by controlling sediment deposition. Its presence delayed the colonization of early-successional turf algal species, but did not affect colonization of late-successional canopy-forming algae such as S. confusum.

Sedimentation Management Strategy in River Estuary for Control the Water Damage in Downstream of Ayung River

The Ayung River Basin is the largest watershed on Bali Island. Ayung River flows from Lake Batur and empties into Padanggalak beach. River estuary is an area of sediment material deposition that will form an alluvial formation. The deposition of sediment at the river estuary is due to the influence of river flow, tidal, and wave action on the beach. Sediments that settle at the river estuary can obstruct water flow to the sea, which can cause backwater and flooding to the mainland. The strategy of controlling sediment deposition in the river estuary is essential to reduce the water damage in the downstream area, which is usually used as a tourism area. Ayung River Estuary is one of the estuaries that experienced a massive deposition; on the other hand, the Ayung River Estuary is widely used as a tourism area. The data used are primary and secondary—primary data obtained by a survey to the location and secondary data obtained from supporting data for analysis. Sedimentation occurs in the Ayung river estuary. It is due to soil type, topography, and hydro oceanographic condition. Besides, changes in the regional functions, such as temple construction, also affect the sedimentation process in the estuary. Sedimentation management strategies that can be carried out for the Ayung River estuary are the first is with the jetty construction method, which begins with the normalization of the downstream river, and the second is maintenance dredging, which is carried out through cooperation between the government and the community. Besides being used as sediment control, the jetty that was built can be developed as a tourist location around the estuary area.

Flexural Rigidity and Shoot Reconfiguration Determine Wake Length Behind Saltmarsh Vegetation Patches

AbstractVegetation patches play an important role in controlling sediment deposition in shallow aquatic environments such as coastal saltmarshes and fluvial systems. However, predicting deposition around vegetation patches is difficult due to the complexity of patch morphology and their dynamic interaction with the flow. Here we incorporate a biomechanical model, parameterized using field data, within a 3‐D computational fluid dynamics model which allows prediction of individual shoot reconfiguration within patches due to flow forcing. The model predicts velocity attenuation and bed shear stresses within the wake of the patch which agree spatially with accretion patterns measured in the field using terrestrial lidar. The model is applied to sparse patches of Suaeda maritima, located in saltmarshes of coastal habitats, to explore the role of (I) shoot distribution, (II) patch geometry, (III) shoot flexural rigidity, and (IV) bulk flow velocity in determining the length of the predicted wake region. We demonstrate that for Suaeda maritima, with intermediate rigidity, the vertical shear layer over the vegetation controls the length of the predicted wake region. Consequently, reconfiguration due to flexural rigidity strongly impacts on wake length, confounding the relationship between patch height and wake length. A simplified model for predicting wake length based on shoot reconfiguration is applied to the simulation data and shows good agreement. The results demonstrate that the observed wake characteristics can be well explained by intraspecific variability in flexural rigidity, thus demonstrating the importance of biomechanical traits in determining flow‐vegetation‐sediment interactions.

Lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins: an example from the Early Cretaceous Jiuquan Basin, Northwestern China

Development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins. However, these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development. This paper documents fan delta deposition alongside an intrabasinal structural high within the Early Cretaceous Xiagou Formation of the Jiuquan Basin, China, using subsurface geological and geophysical data. Deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows. Subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts, suggesting that deposition alongside the structural high is sensitive to lake-level changes. The temporal and spatial distribution of the fan deltas display retrogradational stacking patterns, where fan deltas exhibit a decreasing lateral extent up-sequence until fan delta deposition terminated and was replaced by deposition of fine-grained lacustrine deposits. The retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the Xiagou Formation. Subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation, likely resulting from border fault movements. These data suggest that non-uniform stacking patterns in the lower parts of the Xiagou Formation reflect basin-scale tectonic movements as the dominant control on synrift deposition patterns. However, later stages of Xiagou Formation deposition were characterized by uniform subsidence across the basin, and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault. These observations suggest that basin-scale tectonic movements played a relatively limited role in controlling sediment deposition, and imply a potential change to regional-scale processes affecting fan delta deposition during later synrift stages. Climate change is favored here as the region-scale control on the uniform retrogradational fan delta stacking patterns. This assertion is supported by pollen assemblages, isotope signatures, and organic geochemical analyses, which collectively suggest a change from a humid to semi-arid environment during later synrift stages. We suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin- and regional-scale processes that control rift basin deposition.

Neogene–Quaternary fault reactivation influences coastal basin sedimentation and landform in the continental margin of NE Brazil

We investigate the role of reactivation of Precambrian basement fabric in the tectono-sedimentary and geomorphological evolution of the Paraiba Basin, continental margin of northeastern Brazil, during the Cretaceous, Neogene, and Quaternary. This basin represents part of the last bridge between South America and Africa before the last breakup stage of the South Atlantic rifting in the early Cretaceous. The Paraiba Basin infill is composed of siliciclastic and carbonate Cretaceous units, as well as aeolian, fluvial and marine Quaternary units. We used shuttle radar imagery, aeromagnetic, wellbore and field data. The reduced-to-the-pole magnetic map (RTP) indicates the continuity of the steeply dipping Precambrian basement shear zones beneath the Paraiba Basin. The combined analysis of surface and subsurface data shows that NE–SW and E–W-striking shear zones were subjected to brittle reactivation in the Aptian–Middle Albian during the basin opening and again in the Neogene–Quaternary, forming a system of horsts and grabens along the basin; some of these structures such as the E–W-oriented Pernambuco shear zone present modern-day seismicity. N–S- and mainly NW–SE-striking transfer faults cut across Aptian–Middle Albian to Neogene–Quaternary strata. These four main fault directions control main river channels and alluvial valleys up to 2 km wide. Topographic breaks up to 50 m were created by late reactivation of rift faults, which mark the boundary between horsts and grabens along the basin. In addition, structural data evidence syn-tectonic faulting with vertical offsets up to 80 m in the Cretaceous and up to 70 m in the Neogene–Quaternary. We conclude that shear zones across the study area are long-lived structures that have behaved as weakness zones. Their neotectonic brittle reactivation has controlled sediment deposition and landform development, which continued through the Neogene–Quaternary.

Seasonal variability in turbidity currents in Lake Ohau, New Zealand, and their influence on sedimentation

Layers of sediment that are deposited on the floor of Lake Ohau, New Zealand, offer a means to reconstruct past climate conditions in the Southern Hemisphere at subdecadal and annual resolution. A robust understanding of the modern physical processes that control the influx and dispersal of sediment in the lake is required to reconstruct climate from these sedimentary archives. In this study, water temperature and velocity measurements collected during 2012–13 were analysed to determine the primary physical processes that influence sediment transport in the lake. Sediment input from river inflow occurs throughout the year but exhibits strong seasonal variation. Large inflow events (Q>500m3s–1) that follow strong summer rainstorms trigger high-concentration turbidity currents, which are the main agents for sediment delivery and deposition. During winter, smaller turbidity currents also occur after rain events and contribute to annual sediment accumulation. In addition, large internal waves were observed during the summer and may influence sedimentation. In conclusion, several processes including river inflow, internal waves and convectively driven flows control sediment deposition and accumulation in the Lake Ohau system. We utilise these observations to establish a conceptual model to explain the observed infill stratigraphy in Lake Ohau and guide interpretation of the longer sedimentary record.

Quaternary fault control on the coastal sedimentation and morphology of the São Francisco coastal plain, Brazil

The role of neotectonic faulting in shaping topography and controlling sediment deposition has been increasingly documented along the stable continental margin of South America, but the level of the present-day tectonic stability of this margin is still a matter of debate. This paper presents an investigation of the effects of Quaternary fault reactivation on the São Francisco coastal plain (SFCP). This feature is a 56-km long progradational coastal plain located in the Sergipe–Alagoas Basin along the continental margin of Brazil. The SFCP is bounded on the west by a system of normal faults striking N–S to NE–SW. The horst that bounds this plain is capped by the Miocene Barreiras Formation and Quaternary debris-flow and fluvial deposits, whereas the graben is filled with braided stream deposits and sandy beach-ridge sediments. The faulting contributed to the generation of accommodation space for the deposition of coastal sediments on the plain. These processes started with the reactivation of Cretaceous faults during the Miocene. During the Quaternary, fault reactivation and associated soft-sediment deformation occurred between 82 and 8.3ka, with minor pulses between 1700 and 60calyrBP. Several faults along this margin are tectonically active and may represent the onshore continuation of gravitational collapses that have been documented offshore along the continental shelf and slope.

Bed thickness distributions on Mars: An orbital perspective

AbstractStudies on Earth show that sedimentary bed thickness and bed thickness distributions record information about the processes controlling sediment deposition. High‐resolution digital terrain models (DTMs) such as those derived from the High Resolution Imaging Science Experiment (HiRISE) now provide the opportunity to quantify bed thickness properties on Mars over several orders of magnitude, down to the submeter scale. This study uses HiRISE DTMs and visible images to measure bed thickness distributions at 10 deposits on Mars, with the aim of determining whether statistical techniques can provide useful criteria for distinguishing sedimentary depositional processes. Basic statistics, including mean thickness and range, are examined, as are histograms, cumulative frequency plots, and log‐log plots. Statistical tests interrogate these deposits for thinning or thickening upward trends and the presence of normal, lognormal, and exponential distributions. Although there are challenges associated with these methods, the statistical analysis of bed thickness, coupled with morphological and mineralogical interpretations, has the potential to be a powerful tool for characterizing and classifying sedimentary rocks on Mars. In particular, bed thickness statistics are particularly well suited for examining changes in sediment supply and accommodation within Martian sedimentary sequences.

Influence of Wind-Driven Inundation and Coastal Geomorphology on Sedimentation in Two Microtidal Marshes, Pamlico River Estuary, NC

Marsh sediment accumulation is predominately a combination of in situ organic accumulation and mineral sediment input during inundation. Within the Pamlico River Estuary (PRE), marsh inundation is dependent upon event (e.g., storms) and seasonal wind patterns due to minimal astronomical tides (<10 cm). A better understanding of the processes controlling sediment deposition and, ultimately, marsh accretion is needed to forecast marsh sustainability with changing land usage, climate, and sea level rise. This study examines marsh topography, inundation depth, duration of inundation, and wind velocity to identify relationships between short-term deposition (tile-based) and long-term accumulation (210Pb and 137Cs) recorded within and adjacent to the PRE. The results of this study indicate (1) similar sedimentation patterns between the interior marsh and shore-side marsh at different sites regardless of elevation, (2) increased sedimentation (one to two orders of magnitude, 0.04–4.54 g m−2 day−1) within the interior marsh when the water levels exceeded the adjacent topography (e.g., storm berm), and (3) that short-term sea level changes can have direct effects on sediment delivery to interior marshes in wind-driven estuarine systems.

Coral community changes in response to a high sedimentation event: A case study in southern Hainan Island

A high sedimentation event caused by dredging and dumping of sediment was recorded on Xiaodonghai Reef in Yulin Bay, southern Hainan Island, China. Significantly high sedimentation and constant light shading were observed during the sediment dumping event (SD Event). Using long-term video transects, we quantified coral community changes and responses to the SD Event between 2008 and 2010. The SD Event caused severe coral mortality on Xiaodonghai Reef at a depth of 6 m, while corals at 3 m were less affected. Total live coral cover at 6 m decreased from 54.3% to 14.8%, and Diploastrea heliopora replaced Galaxea fascicularis as the dominant coral species at 6 and 9 m. The density of juvenile corals also declined after the SD Event, especially for the genera Galaxea and Platygyra. However, the density of juvenile Porites and Pocillopora spp. slightly increased. Monitoring for 11 months after the SD Event indicated no recovery of coral communities on Xiaodonghai Reef. Long-term video transect data also revealed that mean live coral cover dramatically declined, from 30.5% in 2008 to 9% in 2010, while the dominant corals in Yulin Bay shifted to more tolerant coral species, such as massive Porites spp. and D. heliopora. The rapid coral community degradation in Yulin Bay between 2008 and 2010 was probably caused by high sediment deposition resulting from intensive dredging and land-clearing activities. These results highlight the necessity for an integrated watershed management to control sediment deposition on near-shore coral reefs.

The influence of Late Cretaceous tectonic processes on sedimentation patterns along the northeastern Arabian plate margin (Fars Province, SW Iran)

Abstract During the Late Cretaceous the northeastern margin of the Arabian plate (Zagros–Fars Area) was characterized by significant variations in sedimentary facies, sedimentation patterns and accommodation space, and by shifting depocentres. A succession of events recording the evolution of the region from a passive to an active margin is documented by the study of eight outcrop sections and one well. This new study uses new age dating (benthic and planktonic foraminifers, nannoplankton and radiolarian biozonations and strontium isotope stratigraphy). The new observations provide a detailed overview of the response of the sedimentary system to changes in the tectonic regime related to obduction processes. These changes are very well shown in regional cross-sections and palaeogeographical maps. Three tectono-sedimentary phases are recognized indicating the evolution from a passive to an active margin: Phase I (Late Albian to Cenomanian, before obduction) comprises three depositional third-order sequences comparable with those of the other parts of the Zagros and Arabian plate. This interval is composed of shallow-water platform carbonates and intra-shelf basins. The platform facies consists of rudist and benthic foraminifer-dominated assemblages, whereas the intra-shelf basins contain an ‘ Oligostegina ’ facies. Eustatic sea-level variations and local differential subsidence controlled sediment deposition during this phase. Phase II (Turonian to Late Campanian, obduction phase) is characterized by major changes in depositional environments and sedimentary facies, as a result of obduction and foreland basin creation. It consists of pelagic and platform carbonates in the south, and a foreland basin with obducted radiolarites, ophiolitic and olistoliths or thrust slices in the north. During this phase, large volumes of turbidites and gravity flows with olistoliths were shed from both the SW and NE into the foreland basin. The age of the tectonic slices increases upward through the section, from Early Cretaceous at the base to Permian at the top. Based on various dating methods used on the far-travelled sediments, the depositional age of the radiolarites can be attributed to the Albian–Cenomanian, whereas the planktonic foraminifers are of Santonian to Campanian age. Phase III (Late Campanian to Maastrichtian, after obduction) shows the development of rudist-dominated carbonates in the NE prograding onto the deep basinal facies in the centre of study area. In the extreme NE no sediments of this age have been recorded, suggesting uplift at that time.

Decision support system for optimal reservoir operation modeling within sediment deposition control

Suspended sediment deals with surface runoff moving toward watershed affects reservoir sustainability due to the reduction of storage capacity. The purpose of this study is to introduce a reservoir operation model aimed at minimizing sediment deposition and maximizing energy production expected to obtain optimal decision policy for both objectives. The reservoir sediment-control operation model is formulated by using Non-Linear Programming with an iterative procedure based on a multi-objective measurement in order to achieve optimal decision policy that is established in association with the development of a relationship between stream inflow and sediment rate by utilizing the Artificial Neural Network. Trade off evaluation is introduced to generate a strategy for controlling sediment deposition at same level of target ratio while producing hydroelectric energy. The case study is carried out at the Sanmenxia Reservoir in China where redesign and reconstruction have been accomplished. However, this model deals only with the original design and focuses on a wet year operation. This study will also observe a five-year operation period to show the accumulation of sediment due to the impact of reservoir storage capacity.

Recent sedimentation patterns within the central Atchafalaya Basin, Louisiana

Sediment deposition and storage are important functions of forested bottomlands, yet documentation and interpretation of sedimentation processes in these systems remain incomplete. Our study was located in the central Atchafalaya Basin, Louisiana, a distributary of the Mississippi River and contains the largest contiguously forested riparian wetland in North America, which suffers from high sedimentation in some areas and hypoxia in others. We established 20 floodplain transects reflecting the distribution of depositional environments within the central Basin and monitored general and local sediment deposition patterns over a three-year period (2000-2003). Deposition rate, sediment texture, bulk density, and loss on ignition (LOI, percent organic material) were determined near or just above artificial markers (clay pads) located at each station per transect. Transect mean sedimentation rates ranged from about 2 to 42 mm/yr, mean percent organic material ranged from about 7% to 28% ,m ean percent sand (. 63 m) ranged from about 5% to 44%, and bulk density varied from about 0.4 to 1.3. The sites were categorized into five statistically different clusters based on sedimentation rate; most of these could be characterized by a suite of parameters that included hydroperiod, source(s) of sediment-laden water, hydraulic connectivity, flow stagnation, and local geomorphic setting along transect (levee versus backswamp), which lead to distinct spatial sedimentation patterns. Sites with low elevation (long hydroperiod), high hydraulic connectivity to multiple sources of sediment-laden water, and hydraulic damming (flow stagnation) featured the highest amounts of sediment trapping; the converse in any of these factors typically diminished sediment trapping. Based on aerial extent of clusters, the study area potentially traps 6,720,000 Mg of sediment annually, of which, 820,000 Mg represent organic materials. Thus, the Atchafalaya Basin plays a substantial role in lowland sediment (and associated contaminant) storage, including the sequestration of carbon. Findings on local sedimentation patterns may aid in management of flow to control sediment deposition and reduce hypoxia.

Sediment facies and hydrodynamic setting: a study in the south western Baltic Sea

This study aims at investigating the relationship between sedimentary facies and hydrodynamic setting by applying statistical analysis of sedimentological data and hydrodynamic modelling. The facies description bases on a dataset of grain-size analysis of surface sediments of the southwestern Baltic Sea. The facies is described by the grain-size parameters median, sorting, and skewness – parameters of a distribution function fitting the grain-size data. The function was derived from a formula proposed by Tauber (1995). The three grain-size parameters were mapped for the southwestern Baltic Sea area applying ordinary kriging (Journel and Huijbregts 1978). The study area was subdivided into uniform facies regions using the concept of regionalized classification after Harff and Davis (1990). The near-bottom hydrodynamic conditions controlling sediment deposition are represented by the average kinetic current energy, the average kinetic wave energy, and the average current vector derived from results of numerical modelling covering a period of 1 year (Rietz et al. 2000). Transport pathways in the southwestern Baltic Sea were postulated based on the directions of the average current vectors which are assumed to be the preferred directions for clastic material transport. A comparison of the hydrodynamic conditions at selected test locations along the preferred transport pathways with the granulometric facies reveals the common case of a direct genetic dependency between the surface sediment facies and the recent hydrodynamic setting. An exception occurs within the Pomeranian Bight. Results indicate that the sediments of this area have not been accumulated under the present-day conditions which supports the findings of Wehner (1990) reporting a glacio-fluviatile late Pleistocene genesis of the sediments there.

Limiting sediment deposition on roadways: topographic controls on vulnerable roads and cost analysis of planting grass buffer strips

Effective erosion control requires both a sound understanding of the physical context and sufficient motivation on the part of farmers to act, and in Europe this almost inevitably depends on financial subsidies. In south-west France, intense spring and summer storms lead to large scale sediment deposition on roadways, and cleanup costs are a major concern for local authorities. Current erosion control subsidy rates are not sufficient to encourage farmers to limit erosion and reduce cleanup costs. The objective of this study was to define the topographic characteristics which control sediment deposition on roadways in order to compare the cost of planting grass strips along these roads to current cleanup costs. Topographic conditions were characterised by midslope inclination (with a range of from 6 to 8%) and distance of this slope to the road (range of 50–200 m), and these were defined by a combination of field visits, air photos, and GIS techniques. The effect of grass buffer strips on sediment deposition was estimated using the revised universal soil loss equation (RUSLE). The financial benefits of planting grass strips were based on the estimated efficiency of the buffer strips and the length of roads affected according to the topographic conditions. More than 70% of roads requiring regular cleanup occur within 200 m of a midlsope inclination of 6%. Errors in predicting sediment deposition sites according to topography occur mainly when small scale changes in topography are beneath the resolution of the Digital Elevation Model (DEM) or when sediment deposition occurs due to the intersection of talwegs with roads. Modelling the effects of grass strips on soil erosion rates suggests that buffer strips of 12 or 24 m wide reduce sediments leaving the field by 32 and 54%, respectively. Planting grass buffer strips along predicted problem road sections can reduce cleanup costs associated with sediment deposition. Savings in the first year of planting are in the order of about 2% of current estimated cleanup costs (100,000 ) for 12 m wide strips, and this amount increases to almost 35% in subsequent years for 24 m strips. Savings in cleanup costs can be used to increase erosion control subsidies, thereby ensuring a higher level of farmer participation. In addition to reducing sediment deposition on roadways, the grass buffer strips serve as demonstration plots for the farming community. The strategy does not directly eliminate soil degradation upslope, but it is a first step towards better erosion control.

Control of sediment deposition rates in two mid-Atlantic Coast tidal freshwater wetlands

Eustatic sea level rise and rapidly increasing coastal development threaten tidal freshwater wetlands. Sediment deposition is one process that affects their ability to maintain surface elevations relative to adjacent rivers. Sediment dynamics in salt marshes have been studied extensively, but little is known about the factors that control sediment deposition rates in tidal freshwater wetlands. We examined geomorphic, hydrological, and biotic factors that may influence sedimentation in two tidal freshwater wetlands that fell at opposite ends of the riverine–estuarine continuum. Our data demonstrate that sediment dynamics are highly variable among tidal freshwater wetlands, and are influenced by the location of the wetland on the continuum. Sediment deposition was up to 10 times higher during the growing season at the downstream site than the upstream site. Plant density and height were highly correlated with sediment deposition rates at the downstream site ( r≥0.92, p≤0.009) but not at the upstream site. Elevation, flood depth, and flood duration were correlated with deposition rates only when each site/season combination was considered separately. River suspended sediment and surficial floodwater suspended sediment concentrations were significantly higher at the downstream site ( p=0.02 and p=0.04, respectively). These data suggest that vegetation is important in determining sediment deposition rates when river suspended sediment is not limiting, which is not always the case. Longer flood duration increased sediment deposition, but was of secondary importance. Land use and proximity to the turbidity maximum (near the forward extent of the salt water intrusion) appear to be critically important in determining river suspended sediment availability in the tidal freshwater zone of the Mattaponi River, VA.

Acoustical techniques for observing the processes that control the formation of ocean bottom geology

While acoustical methods provide useful techniques for surveying geological properties of the seafloor, acoustical techniques are also useful for examining the processes which create the observable geological properties. The dynamic processes which control sediment deposition and erosion are complex, and understanding these processes requires knowledge of the interactions of the seafloor topography with the hydrodynamics just above the seafloor and the subsequent sediment erosion, transport, and deposition. Observing these interactions requires multi-dimensional systems with high resolution in both space and time. This mini-tutorial talk will review some of the acoustic techniques for observing sediment transport processes which are currently being used. These techniques include acoustic backscatter measurements of suspended sediment concentration, acoustic imaging techniques such as rotary sidescan sonars and rotary pencil beam sonars, and the latest advances in high-resolution Doppler current profiling. Examples of data from these techniques will also be presented to give an overview of the transport processes including sediment transport due to the combined action of both waves and mean currents, sediment transport due to gravitational flows, and the relation between bedform migration and bedload transport.