Total Sediment Volume Research Articles

Sediment Deposition Following Construction of a Breakwater Harbor: Point Judith Harbor of Refuge, Rhode Island, USA

Breakwaters are a common shoreline protection structure, often trapping sediment as the incoming wave energy is reduced. Quantifying the dynamics and volume of these sediment sinks within a coastal system is an important step toward understanding the sediment budget for a particular coastal area. This study examines the volume of sediment deposited within the breakwater enclosed Point Judith Harbor of Refuge (Rhode Island, United States of America (USA)) in the late 19th century using seismic reflection profiles, bathymetric mapping, and isotopic analysis of core sediment. Geophysical profiles show a district seismic facies up to 4 m thick above the ravinement surface, particularly in the western and central portion of the harbor. Century-scale bathymetric changes revealed shoaling of a similar magnitude, and isotopic data support the deposition of this sediment package within the 20th century. The total volume of sediment within the harbor exceeds 5.0 × 106 m3, with an estimated sand volume of 3.6 × 106 m3. The results show that the harbor is a substantial sediment sink for the Rhode Island South Shore and provide the basis for future studies of the sediment budget for this shoreline.

Quantity and distribution of methane entrapped in sediments of calcareous, Alpine glacier forefields

Abstract. Aside from many well-known sources, the greenhouse gas methane (CH4) was recently discovered entrapped in the sediments of Swiss Alpine glacier forefields derived from calcareous bedrock. A first study performed in one glacial catchment indicated that CH4 was ubiquitous in sediments and rocks and was largely of thermogenic origin. Here, we present the results of a follow-up study that aimed at (1) determining the occurrence and origin of sediment-entrapped CH4 in other calcareous glacier forefields across Switzerland and (2) providing an inventory of this sediment-entrapped CH4, i.e., determining the contents and total mass of CH4 present, and its spatial distribution within and between five different Swiss glacier forefields situated on calcareous formations of the Helvetic nappes in the Central Alps. Sediment and bedrock samples were collected at high spatial resolution from the forefields of Im Griess, Griessfirn, Griessen, Wildstrubel, and Tsanfleuron glaciers, representing different geographic and geologic regions of the Helvetic nappes. We performed geochemical analyses on gas extracted from sediments and rocks, including the determination of CH4 contents, stable carbon-isotope analyses (δ13CCH4), and the determination of gas-wetness ratios (ratio of CH4 to ethane and propane contents). To estimate the total mass of CH4 entrapped in glacier-forefield sediments, the total volume of sediment was determined based on the measured forefield area and either literature values of mean sediment thickness or direct depth measurements using electrical resistivity tomography. Methane was found in all sediments (0.08–73.81 µg CH4 g−1 dry weight) and most rocks (0.06–108.58 µg CH4 g−1) collected from the five glacier forefields, confirming that entrapped CH4 is ubiquitous in these calcareous formations. Geochemical analyses further confirmed a thermogenic origin of the entrapped CH4 (average δ13CCH4 of sediment of −28.23 (± 3.42) ‰; average gas-wetness ratio of 75.2 (± 48.4)). Whereas sediment-entrapped CH4 contents varied moderately within individual forefields, we noted a large, significant difference in the CH4 content and total CH4 mass (range of 200–3881 t CH4) between glacier forefields at the regional scale. The lithology and tectonic setting within the Helvetic nappes appeared to be dominant factors determining rock and sediment CH4 contents. Overall, a substantial quantity of CH4 was found to be entrapped in Swiss calcareous glacier forefields. Its potential release and subsequent fate in this environment is the subject of ongoing studies.

A Holistic Modeling Approach to Project the Evolution of Inlet-Interrupted Coastlines Over the 21st Century

Approximately one quarter of the World’s sandy beaches, most of which are interrupted by tidal inlets, are eroding. Understanding the long-term (50-100 year) evolution of inlet-interrupted coasts in a changing climate is therefore of great importance for coastal zone planners and managers. This study therefore focuses on the development and piloting of an innovative model that can simulate the climate-change driven evolution of inlet-interrupted coasts at 50-100 year time scales, while taking into account the contributions from catchment-estuary-coastal systems in a holistic manner. In this new model, the evolution of inlet-interrupted coasts is determined by: (1) computing the variation of total sediment volume exchange between the inlet-estuary system and its adjacent coast, and (2) distributing the computed sediment volume along the inlet-interrupted coast as a spatially and temporally varying quantity. The exchange volume, as computed here, consists of three major components: variation in fluvial sediment supply; basin (or estuarine) infilling due to the sea-level rise-induced increase in accommodation space; and estuarine sediment volume change due to variations in river discharge. To pilot the model, it is here applied to three different catchment-estuary-coastal systems: the Alsea estuary (Oregon, USA), Dyfi estuary (Wales, UK), and Kalutara inlet (Sri Lanka). Results indicate that all three systems will experience sediment deficits by 2100 (i.e. sediment importing estuaries). However, processes and system characteristics governing the total sediment exchange volume, and thus coastline change, vary markedly among the systems due to differences in geomorphic settings and projected climatic conditions. These results underline the importance of accounting for the different governing processes when assessing the future evolution of inlet-interrupted coastlines.

Climatic and anthropogenic impacts on the decrease of sediment discharge to the Mediterranean coast from the largest river of Maghreb

The current study focuses on the issue of the decrease in sediment discharge to the Mediterranean Sea by the largest river in Algeria, the Wadi Cheliff (i.e. Cheliff River). This study clarifies the effect of climatic and anthropogenic factors on the changes in the sedimentary dynamics of the Cheliff River discharging to the sea. The data used (rainfall, water discharge, and sediment discharge) concern the Sidi Bel Attar gaging station on the Cheliff River, only 18 km from discharge to the Mediterranean Sea. A power-type statistical regression model was used to fill the 74.2% gap in Suspended Solids (SS) measurements in the establishment of a SS database for the period 1951–2012. The study results show that the transport of suspended sediment discharged to the sea is about 487 t/km2/yr. Statistical tests of breaks highlight that rainfall decreased by 26% and that water and sediment input to the sea declined from 74% to 63% for the period of 1981–2012. The correlation analysis shows a decrease in the contribution of rainfall on sediment and water input at the outlet equal to 77.9% and 77.8%, respectively, during the period of 1980–2012, compared to the period of 1968–1980. However, the double mass method reflects the contribution of factors other than rainfall to the decrease of sediment input to the sea. These other factors mainly include large dams, which intercepted about 71% of the total volume of sediment discharged to the sea during the period of 1968–2010. In addition the contribution of large dams to the reduction of sedimentary input to the sea is more important than that of the decrease in rainfall. The management of large dams also contributes to the increase in the sediment deficit to the sea through the prioritization of interception of sediment at the expense of releases, for socio-economic purposes, 68.4% of the Cheliff River discharge is diverted for human use. This has led to an increase in the mean water bed level at bankfull downstream, where the Cheliff River gave up 51% of its width to the floodplain between 1996 and 2009. In the light of the scarcity of sediment transport data in North Africa and in many other areas, the current study provides a reference framework for other studies: providing useful information for the study of the transfer of sediment from land to sea, and the links with the socio-economic needs.

Origin of the Baltic Sea basin by Pleistocene glacial erosion

ABSTRACT The present marine Baltic Sea basin (BSB) occupies an eroded Proterozoic intra-cratonic basin on the Fennoscandian shield. Competing models propose a Neogene fluvial origin, with later modification by glacial erosion, or a much younger development, with overdeepening beneath the Fennoscandian Ice Sheet (FIS). We test these alternatives using a first order source to sink sediment budget for the catchment of the BSB. Best estimates derived from geomorphic and cosmogenic nuclide evidence suggest depths of erosion over the last 1 Ma of 20 m in basement and 40 m in sedimentary rocks that surround the BSB. As the BSB has been overdeepened below a regional base level provided by the shallow Darss Sill at the boundary with the Kattegat, erosion of the BSB may be interpreted as glacial in origin, without a fluvial component. The estimated total volume of source area erosion is 30,628 km3 of which 87% is derived from the present BSB. Sediment volumes in the sink area within the limits of maximum Pleistocene glaciation are estimated at a minimum of 37,629 km3, after correction for local erosion, porosity, and carbonate losses. Marine Isotope Stage 12 and younger sediments account for 87% of the total Pleistocene sediment volume in the sink in Poland. Although significant uncertainties remain, the sediment budget is consistent with erosion of the BSB entirely by the FIS, mainly when the ice sheet reached its maximum extent and thickness during the Middle and Late Pleistocene glaciations.

Causes and consequences of the streambed restructuring of the Koiavgan Creek (North Caucasus, Russia)

The restructuring of the lower reach of the Koiavgan Creek channel (the right bank tributary of the Djankuat River) occurred on 1 July 2015 after continuous rainfall with a total precipitation amount of 227 mm. This led to the breakthrough of the Djankuat Glacier lateral moraine. The lower reach of the creek channel was initially formed at the junction of the bedrock slopes and lateral moraine and descended sharply at the end of the moraine to a wide glacial valley of the Djankuat River. The part of the channel from the end of the moraine line to the creek’s outlet in the bottom of the glacial valley had a height difference of 125 m at a distance of about 250 m. The active landslide has been recorded in the place of future breakthrough based on interpretation of 2014 summer satellite image. The linear erosion began to form on the wall of the disruption. Thermokarst processes probably also contributed to this breakthrough. The total volume of sediment eroded during the breakthrough and for four years after is 156 500 m3. The breakthrough has formed the largest sediment cone 300 meters wide and more than 200 m long in the bottom of the Djankuat River valley.

Sulfur Cycling and Mass Balance at Meridiani, Mars

AbstractThe Opportunity rover was sent to Meridiani Planum, Mars, to investigate aqueous processes as inferred from orbiter observations of hematite. While the rover found the source of the hematite signal, it also identified abundant bedrock enriched in SO3 on average by >20 wt% throughout its >40‐km traverse. Geological mapping and orbiter data show that the layered sulfate deposits occur over ~4 × 105 km2, an area larger than Germany. Multiple scenarios for formation of the sediment and sulfur sources in the Meridiani sulfate‐rich bedrock have been proposed, including groundwater upwelling in a playa environment, volcanic ash, ice deposits, and fluvial input. Mass balance calculations show that none of the existing scenarios as currently portrayed can account for the total sediment volume and sulfur mass in the Meridiani region. Thus, after 14 Earth years of rover observations, there are still fundamental questions that remain regarding formation mechanisms of the sulfate‐rich bedrock.

Initiation and runout characteristics of debris flow surges in Ohya landslide scar, Japan

The characteristics of debris flows (e.g., velocity, discharge, kinematic energy) are highly dependent on surges incurring abrupt changes to flow height, velocity, and boulder concentration. Therefore, understanding the initiation and runout characteristics of surges is essential when planning debris flow mitigation. Monitoring performed using 10 time-lapse cameras (TLCs) in Ohya landslide, central Japan, where debris flows occur frequently due to mobilization of storage (i.e., talus cone and channel deposits), allowed us to obtain data on a series of surge processes, from initiation to termination, which occurred during each debris flow event. We also analyzed temporal changes in the spatial distribution of storage in the debris flow initiation zone, associated with sediment supply from hillslopes and evacuation of sediment by the occurrence of debris flows, through periodic measurements of topography using unmanned aerial vehicles (UAVs). Debris flow surges were mainly induced by repetitive mass movement of storage through the erosion of channel deposits by overland flow, sliding of channel deposits, and sediment and water supply from channel banks and tributaries. Development of a spontaneous wave on the flow surface was not an important formation process of surges in the Ohya landslide. Many debris flow surges initiated at channel sections with deep storage (>2 m in depth), located <30 m below a junction with a tributary, when the maximum 10-min rainfall intensity exceeded 5 mm. Partly saturated flow, which has an unsaturated layer in its upper part, was the predominant flow type in the steep initiation zone, while fully saturated flow was predominant in the gentle transportation and deposition zones. Flow type often changed as the surges descended. Partly saturated flow was predominant when the volume of storage in the initiation zone was large, whereas fully saturated flow was predominant when the volume of storage was small. When we compared debris flows with similar total sediment volume, travel distance was long when fully saturated flow with high flow mobility was predominant because of the small volume of storage in the initiation zone. The volume of storage also affected flow path avulsion on the debris flow fan by controlling the flow mobility of surges. Consequently, the spatial distribution and total volume of storage are important factors controlling the initiation location, predominant flow type, and termination location of surges.

GlobSed: Updated Total Sediment Thickness in the World's Oceans

AbstractWe present GlobSed, a new global 5‐arc‐minute total sediment thickness grid for the world's oceans and marginal seas. GlobSed covers a larger area than previously published global grids and incorporates updates for the NE Atlantic, Arctic, Southern Ocean, and Mediterranean regions, which results in a 29.7% increase in estimated total oceanic sediment volume. We use this new global grid and a revised global oceanic lithospheric age grid to assess the relationship between the total sediment thickness and age of the underlying oceanic lithosphere and its latitude. An analytical approximation model is used to mathematically describe sedimentation trends in major oceanic basins and to allow paleobathymetric reconstructions at any given geological time. This study provides a much‐needed update of the sediment thickness distribution of the world oceans and delivers a model for sedimentation rates on oceanic crust through time that agrees well with selected drill data used for comparison.

Effects of Extreme Dust Storm in Agricultural Areas (Poland, the Greater Lowland)

The article aims to present extreme aeolian processes observed in April 2011 in the fields of the Szamocin municipality in Pojezierze Wielkopolskie (the Great Poland Lakeland). Aeolian erosion of cropland was fostered by strong wind with gusts exceeding 15 m·s−1. The erosion was related to the movement of a deep barometric low from the Norwegian Sea over western Russia (Joachim barometric low). Geomorphological mapping of accumulated sandy aeolian covers was conducted. Morphometric measurements of aeolian covers were made considering their spatial distribution and the thickness of sediments that build them. Samples were collected from sediments to analyze grain size and the volume of deposited sediments was calculated. According to grain size analysis the accumulated fine-grained mineral material was well, moderately well and moderately sorted. The thickness of aeolian covers exceeded the thickness of covers presented in Polish literature so far. Calculations of the total volume of mineral sediment derived from small areas covered with aeolian erosion (a few hectares each) indicate significantly greater volumes than those provided in publications from other research areas in Poland. The described dust storms did not cause much damage in Poland. At the same time (8 April) in northern Germany, a dust storm led to a severe collision on the A19 highway. Eight people died in car accidents and dozens suffered serious injuries.

The quality of sediment in shallow water bodies – Long-term screening of sediment in Czech Republic. A new perspective of nutrients and organic matter recycling in agricultural landscapes

The results of long-term screening of sediments from the Czech Republic from 2011 to 2017 are presented, more than 80% of the samples of which were taken from fishponds. The total sediment volume of Czech Republic fishponds is estimated to be 197 mil. m3. Quality of the sediment is impacted by numerous factors. Sediment may be used for land application, etc., as long as it abides with legislation limits. All results from our database, containing some 200 sites, have been compared with the Decree regulating the conditions for the application of sediments on agricultural land.We have evaluated toxic metals (As, Pb, Zn, Cu, Hg, Cd), organic pollutants (C10–C40, BTEX, PAH, PCB, DDT) and nutrient volume. The assessment of results reveal the average concentrations of evaluated metals to have the following ranking: Zn > Cu > Pb > As > Cd > Hg. The most frequent excesses of the limit listed in Decree No. 257/2009 Sb. were reported for cadmium (21 sites, i.e. 13.2%). In the case of organic pollutants, the worst pollutant exceeded the limits for 7.2% of sites. DDT volume values were all below the threshold. The ratio between available nutrients and overall nutrient volume was: 0.5% P; 1.3% N; 48.1% Na; 20.4% Mg; 5.8% K; and 65.7% Ca.

Coastal sediment balance in the eastern part of the Gulf of Riga (2005–2016)

A hurricane known as Ervin or Gudrun travelled over Latvia in 8–9 January, 2005. As a result of severe SW and W winds, as well as lack of sea ice, clearly pronounced changes in the distribution of coastal sediment has been induced. Cross-shore profile leveling at various time instants was used to obtain quantitative estimates of the amount of accumulated sediments. The total volume of sediments eroded from the subaerial part of coastal slope reached 0.8 million m3. This paper represents assessment of consequent changes and coastal slope “rebuilding” success after this storm event. The data indicates lack of significant overall net loss of subaerial sediment volume along the most part of the eastern coast of the Gulf of Riga. Significant primary dune growth and beach accumulation is mostly limited to southernmost part of assessed coastal stretch. Total volume of fine sediments in beach and primary dunes still is 5 % lower than before erosion event of 2005. Erosion vulnerability and total length of coastal sections that are expected to be a subject to future coastal retreat is increasing.

Morphology and pattern of Quaternary sedimentation in the North Sea Basin (52–62°N)

Abstract The Quaternary North Sea Basin, which extends from northwest mainland Europe in the south (52°N) to the Norwegian Sea in the north (62°N), contains a thick (up to 1 km) sedimentary succession that records the changing nature of sediment supply from surrounding land areas during the last c.2.6 Ma. We use an extensive 2D and 3D seismic database to correlate major Quaternary seismo-stratigraphic surfaces and units across the North Sea and reconstruct the broad-scale infill pattern of the entire Quaternary North Sea Basin. The total volume of Quaternary sediments in the North Sea (350 000 km2) is c.140 000 km3, while the area inside the 500 m contour of the base-Quaternary surface has a volume of 109 000 km3. Two largely independent depocentres developed in the North Sea Basin during the early Quaternary: the southern and central sub-basin was infilled by shelf fluvio-deltaic and prodeltaic sediments delivered from the east and south-east, whilst the northern sub-basin was infilled mainly by prograding glacigenic debris-flows deposited from an ice mass centred on the Norwegian mainland. Contour currents were an important mechanism of sediment deposition and reworking, with water circulation in the basin probably occurring in an anti-clockwise direction. Whilst most of the southern North Sea Basin was infilled by around 1.6–1.7 Ma, a depression persisted in the central North Sea until around 1 Ma. The analysis of landforms on 3D seismic data suggests that the Fennoscandian Ice Sheet (FIS) extended intermittently to the palaeo-shelf break in the northern North Sea during the earliest Quaternary and expanded into the central North Sea prior to the excavation of the Norwegian Channel.

Comparative Studies between Urbanization and Dam Settlement Processes

The city of Viamao is located in the metropolitan region of Porto Alegre, in the Rio Grande Sul State, southern Brazil. The Mae d'Agua dam was built in 1962 and, due to the lack of urban planning during the last forty years, received large discharges of sediments and contaminants (organic and/or inorganic). This study aimed to use the geochronology technique using the lead element 210 (210Pb) through the cores of sediments sampled from the Mae D'agua dam and to establish the chronology of the sedimentary layers over the last four decades, in addition to the characterization of the sedimentation processes in the Mae D'Agua reservoir and to size the sediment volumes silted in the reservoir in the current scenario, year 2014 (year of sampling) and thus, to present the total sediment concentrations during the 40-year silting. The sediment column, bathymetry, bibliographical references and GIS resources were used to infer the process of urbanization and sedimentation process of the dam, and representative samples were collected in June 2014, using sediment cores distributed in the dam area. The sediment cores were extracted through the Piston core sampler. With the results obtained, graphs and tables were generated to create the mathematical models and later the sedimentation maps, establishing correlations with the sedimentation geochronology studies during the last four decades (layers of sedimentation generated in each of these periods). There were periods with high sedimentation rates, mainly during the acceleration of the process of urbanization of the basin resulting in a total sediment volume of 44% of the useful volume of the project, which drastically reduces the capacity of the Mae d'Agua dam. Keywords: Urban dams, Sediments, Sedimentation of dams.

Modelling the potential effects of Oil-Sands tailings pond breach on the water and sediment quality of the Lower Athabasca River

Within the Oil-Sands industry in Alberta, Canada, tailings ponds are used as water recycling and tailings storage facilities (TSF) for mining activities. However, there could be possible circumstances under which a sudden breach of an embankment confining one of the TSFs may occur. Such a tailings pond breach would result in a sudden release of a huge volume of Oil Sands process-affected water (OSPW) and sediment slurry containing substantial amount of chemical constituents that would follow the downstream drainage paths and subsequently enter into the Lower Athabasca River (LAR). This study investigates the implications of OS tailings release on the water and sediment quality of the LAR by simulating the fate of sediment and associated chemicals corresponding to a hypothetical breach and release scenarios from a select set of tailings ponds using a two-dimensional hydrodynamic and constituent transport model. After predicting the total volume, time evolution and concentration of sediment and associated chemicals (metals, polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs)) reaching the LAR, the transport and deposition of these materials within the study reach is simulated. The results show that, depending on tailings release locations, between 40 and 70% of the sediment and associated chemicals get deposited onto the river bed of the 160 km study reach while the rest leaves the study domain during the first three days following the release event. These sediment/chemicals deposited during the initial spill may also have long-term effects on the water quality and aquatic ecosystem of the river and the downstream delta. However, care has to be taken in interpreting the results as further analysis has shown that the outcomes of such model simulations are very sensitive to the various underlying assumptions as well as the values assigned to some model parameters representing the physical properties of the tailings material.

Combining field monitoring and aerial imagery to evaluate the role of gully erosion in a Mediterranean catchment (Tunisia)

The objective of this study was to address the role of gully erosion on sediment delivery at the catchment scale by assessing the contribution of gullies to the total sediment yield at the outlet of the Kamech (Cape Bon, Tunisia), which is a small cultivated catchment in the Mediterranean environment. The methodology was based on the long-term analysis of the evolution of gully volume, and the total volume of sediment that reached the catchment outlet. The evolution of gully volume was assessed by field surveys and image analysis. The total volume of sediment was calculated using intensive field monitoring of the runoff and erosion in the reservoir at the catchment outlet. The contribution of gullies to the total flux of sediment that reached the catchment outlet was estimated to be less than 30%. This means that siltation of the reservoir was mainly due to erosion processes other than gully erosion, i.e., topsoil erosion processes such as rill and interrill erosion in cropland areas. This result was consistent with a previous independent estimation of the apportionment of gully and topsoil erosion sources conducted at the same site using the fingerprinting approach. Therefore, the study confirms that, even in a heavily eroded agricultural catchment area with a dense network of gullies, gully erosion nevertheless accounted for less than 30% of the total erosion balance. The results also showed that the cumulated gully length has decreased in the last fifty years, thus revealing the declining role of gullies. However, the decrease in gully activity could not be linked to an isolated factor. Complementary observations, such as the appearance of vegetation in the permanent gullies and the decrease in the percentage of active gullies, showed that the degree of hydro-sedimentary connectivity in the Kamech catchment has probably entered a decreasing phase. We also analysed the potential use of historical aerial images for studying gully erosion. We found that these images were useful for calculating accurate ortho-photography but failed to provide a DEM with the precision required to measure the historical volume of gullies.

Impact of relative sea-level changes since the last deglaciation on the formation of a composite paraglacial barrier

Comprehensive onshore-offshore surficial and sub-surface mapping of a composite barrier (combination of prograded, aggraded, and/or transgressive segments) have provided a better understanding of the (i) mechanisms responsible for the formation and development of coastal barrier systems, (ii) relationships and interactions among individual parts of those systems, and (ii) the overall stratigraphic framework of subaerial and subaqueous segments of the barriers. Here, we investigate these facets of barrier evolution through integration of stratigraphic data from subaqueous high-resolution seismic and subaerial ground-penetrating radar, sedimentology (terrestrial cores and seafloor surface samples), and merged topographic and bathymetric mapping of the Miquelon-Langlade Barrier (northwest Atlantic Ocean, south of Newfoundland). This barrier system has two open coasts and evolved in a paraglacial setting, influenced by the reworking of glaciogenic sediment (glacial moraines) in a regime of complex sea-level changes. The barrier stratigraphic sequence is placed within the context of a shifting period from shoreline transgression to one of regression; the resulting sedimentary units reflect the isolated position of the Saint-Pierre-and-Miquelon Archipelago distal from continental influence. Seismic profiles reveal the position of the lowstand shoreline, located 20–25 m below modern sea level, further refining the existing lowstand model of southern Newfoundland. Continuous onshore-offshore subsurface geophysical mapping of the barrier allows for the identification of the relative positioning of distinct sedimentary units interpreted as subaerial barrier (beaches, dunes, spit), shoals, and shoreface deposits, and allows for estimation of the total barrier sediment volume (235 × 106 m3) and its relative subaqueous (90%) and subaerial (10%) components. Moreover, it reveals the three distinct morphological units comprising the Holocene barrier: (i) central, regressive, swash-aligned beach-ridge plains developed atop both thin (westward-prograding) and thick (eastward-prograding) shoreface deposits, (ii) drift-aligned, elongating spits located in the northwest and northeast of the island, and (iii) a transgressive barrier located adjacent to the northwest spit, pinned on its landward side to parabolic sand dunes, and currently experiencing erosion and limited overwash. Finally, this study places evolution of this system in the framework of paraglacial barrier evolutionary typology.

True Volumes of Slope Failure Estimated From a Quaternary Mass‐Transport Deposit in the Northern South China Sea

AbstractSubmarine slope failure can mobilize large amounts of seafloor sediment, as shown in varied offshore locations around the world. Submarine landslide volumes are usually estimated by mapping their tops and bases on seismic data. However, two essential components of the total volume of failed sediments are overlooked in most estimates: (a) the volume of subseismic turbidites generated during slope failure and (b) the volume of shear compaction occurring during the emplacement of failed sediment. In this study, the true volume of a large submarine landslide in the northern South China Sea is estimated using seismic, multibeam bathymetry and Ocean Drilling Program/Integrated Ocean Drilling Program well data. The submarine landslide was evacuated on the continental slope and deposited in an ocean basin connected to the slope through a narrow moat. This particular character of the sea floor provides an opportunity to estimate the amount of strata remobilized by slope instability. The imaged volume of the studied landslide is ~1035 ± 64 km3, ~406 ± 28 km3 on the slope and ~629 ± 36 km3 in the ocean basin. The volume of subseismic turbidites is ~86 km3 (median value), and the volume of shear compaction is ~100 km3, which are ~8.6% and ~9.7% of the landslide volume imaged on seismic data, respectively. This study highlights that the original volume of the failed sediments is significantly larger than that estimated using seismic and bathymetric data. Volume loss related to the generation of landslide‐related turbidites and shear compaction must be considered when estimating the total volume of failed strata in the submarine realm.

Reservoir sedimentation impact downstream in a semi-arid basin with greenhouses cultivation

This work analyzes the loss of storage, in a medium-term basis, of Beninar reservoir (Almería, Spain) built in a semiarid watershed and its consequences downstream. The reservoir, in the Adra river basin (Southern Spain), was designed to supply water for the irrigation of more than 28.000 hectares of greenhouses. Its storage volume, that was initially of 68 hm3 in 1984, has been reduced approximately to half. The total sediment volume arrived to the reservoir during the last 32 years is 6,8 hm3, of which 1,68 hm3 are estimated to come from fluvial contributions. The results remark the torrential nature of rainfall events for generating large sediment contributions and highlights the importance of taking into account these types of events. The total loss of storage is especially relevant from two points of view 1) reduction of flood abatement due to sedimentation and structural problems of dam, which has left only 2 hm3 of regulation capacity and 2) loss of water volume which is essential to improve the water quality of the overexploited and salinized aquifers which supply the greenhouses downstream. Beninar reservoir is a key infrastructure to preserve a competitive price of water for greenhouse cultivation.

Reply to the comment by M. Genge and M. Van Ginneken on paper entitled “Unmelted cosmic metal particles from the Indian Ocean”

Reply to the comment by M. Genge and M. Van Ginneken on paper entitled “Unmelted cosmic metal particles from the Indian Ocean”