The Experts below are selected from a list of 108 Experts worldwide ranked by ideXlab platform
Dinesh Chandra Shaha - One of the best experts on this subject based on the ideXlab platform.
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Spatiotemporal variation of Van der Burgh's coefficient in a Salt Plug estuary
Hydrology and Earth System Sciences, 2017Co-Authors: Dinesh Chandra Shaha, Yang-ki Cho, Bong Guk Kim, Sampa Rani Kundu, M. Rafi Afruz Sony, M. Faruqul IslamAbstract:Abstract. Salt water intrusion in estuaries is expected to become a serious global issue due to climate change. Van der Burgh's coefficient, K, is a good proxy for describing the relative contribution of tide-driven and gravitational (discharge-driven and density-driven) components of Salt transport in estuaries. However, debate continues over the use of the K value for an estuary where K should be a constant, spatially varying, or time-independent factor for different river discharge conditions. In this study, we determined K during spring and neap tides in the dry ( 750 m−3 s−1) seasons in a Salt Plug estuary with an exponentially varying width and depth, to examine the relative contributions of tidal versus density-driven Salt transport mechanisms. High-resolution salinity data were used to determine K. Discharge-driven gravitational circulation (K ∼ 0.8) was entirely dominant over tidal dispersion during spring and neap tides in the wet season, to the extent that Salt transport upstream was effectively reduced, resulting in the estuary remaining in a relatively fresh state. In contrast, K increased gradually seaward (K ∼ 0.74) and landward (K ∼ 0.74) from the Salt Plug area (K ∼ 0.65) during the dry season, similar to an inverse and positive estuary, respectively. As a result, density-driven inverse gravitational circulation between the Salt Plug and the sea facilitates inverse estuarine circulation. On the other hand, positive estuarine circulation between the Salt Plug and the river arose due to density-driven positive gravitational circulation during the dry season, causing the upstream intrusion of high-salinity bottom water. Our results explicitly show that K varies spatially and depends on the river discharge. This result provides a better understanding of the distribution of hydrographic properties.
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Spatiotemporal Variation of Van der Burgh's coefficient in a Salt Plug estuary
2017Co-Authors: Dinesh Chandra Shaha, Yang-ki Cho, Bong Guk Kim, Md. Rafi Afruz Sony, Sampa Rani Kundu, Md. Faruqul IslamAbstract:Abstract. Saltwater intrusion in estuaries is expected to become a more serious issue around the world due to climate change. Van der Burgh's coefficient, K, is a good proxy for describing the relative contribution of the tide-driven and gravitational components of Salt transport in estuaries. However, debate continues over the use of K value for an estuary where K should be constant or spatially varying or a time-independent factor for different river discharge conditions. In addition, whether K functions in an inverse salinity gradient area of a Salt Plug estuary has not been examined thus far. In this study, we determined K during spring and neap tides in the dry (<30 m−3 s−1) and wet (>750 m−3 s−1) seasons in a Salt Plug estuary with an exponentially varying width and depth to examine the relative contributions of tidal versus density-driven Salt transport mechanisms. High-resolution salinity data were used to determine K. Gravitational circulation (K~0.8) was entirely dominant over tidal dispersion during spring and neap tides in the wet season such that Salt transport upstream was effectively reduced, resulting in the estuary remaining in a relatively fresh state. In contrast, during the dry season, K increases gradually seaward and landward (K~0.74) from the Salt Plug area (K~0.65), similar to an inverse and positive estuary, respectively. As a result, density-induced inverse gravitational circulation between the Salt Plug and the sea facilitates inverse estuarine circulation. On the other hand, positive estuarine circulation between the Salt Plug and the river area arose due to density-induced positive gravitational circulation induced by the tide during the dry season, causing the intrusion of high-salinity bottom water upstream. Our results explicitly show that K varies spatially and depends on the river discharge. This result provides a better understanding of the distribution of hydrographic properties as well as the distributions of pollutants, nutrients and biota within large estuaries.
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Salt Plug formation caused by decreased river discharge in a multi channel estuary
Scientific Reports, 2016Co-Authors: Dinesh Chandra ShahaAbstract:Freshwater input to estuaries may be greatly altered by the river barrages required to meet human needs for drinking water and irrigation and prevent Salt water intrusion. Prior studies have examined the Salt Plugs associated with evaporation and Salt outwelling from tidal Salt flats in single-channel estuaries. In this work, we discovered a new type of Salt Plug formation in the multi-channel Pasur River Estuary (PRE) caused by decreasing river discharges resulting from an upstream barrage. The formation of a Salt Plug in response to changes in river discharge was investigated using a conductivity-temperature-depth (CTD) recorder during spring and neap tides in the dry and wet seasons in 2014. An exportation of saline water from the Shibsa River Estuary (SRE) to the PRE through the Chunkhuri Channel occurred during the dry season, and a Salt Plug was created and persisted from December to June near Chalna in the PRE. A discharge-induced, relatively high water level in the PRE during the wet season exerted hydrostatic pressure towards the SRE from the PRE and thereby prevented the intrusion of Salt water from the SRE to the PRE.
O. Franz - One of the best experts on this subject based on the ideXlab platform.
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Developing, modeling and in-situ-testing a long-term wellbore seal in the framework of the CO2 -EGR research project CLEAN in the natural gas field Altmark
Energy Procedia, 2011Co-Authors: M.z. Hou, Lars Wundram, Meinhardt Schmidt, R. Meyer, Steffen Schmitz, H. Wendel, H.j. Kretzschmar, O. FranzAbstract:Abstract In this paper we present a new concept developed to improve the abandonment procedure of wellbores in depleted hydrocarbon fields, amongst others in Enhanced Gas Recovery (EGR) operations. The sealing concept is designed for the long-term containment of CO 2 and considers the creep ability of deep Permian Zechstein Salt formations in about 3,000 m depth. It is designed to amend the current standard abandonment procedure and consists of (a) an expansive gel filling in the reservoir formation, (b) a sealing element with cement extending to the impermeable caprock and (c) a Salt Plug as the major long-term sealing component, compatible in its composition and property to the surrounding caprock (halite). The focus of the project work described here is to develop and to model the last-mentioned long-term Salt sealing element. Numerical results show that the creep ability of the mentioned Salt formations can close a formerly reamed well section and hence recover the geological Salt barrier with or even without using a crushed Salt backfill. A field test is conducted in the North German Altmark Rotliegend gas field (Sachsen Anhalt) in order to study the technical feasibility for recovering the initial caprock integrity, to verify numerical models and to proof the sealing capability and therefore the sealing concept.
Michel Allenbach - One of the best experts on this subject based on the ideXlab platform.
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Water Biogeochemistry of a Mangrove-Dominated Estuary Under a Semi-Arid Climate (New Caledonia)
Estuaries and Coasts, 2017Co-Authors: Audrey Leopold, Cyril Marchand, Jonathan Deborde, Michel AllenbachAbstract:Mangrove water biogeochemistry has been frequently studied under tropical climates, but less is known regarding mangroves in semi-arid climates. In this study, we examine the carbon and nutrient biogeochemistry in a mangrove tidal creek and in the main branch of a semi-arid estuary in New Caledonia. Porewater seepage represents a source of nutrients (DON, NH_4 ^+, and DIP), carbon (DOC and CO_2), and alkalinity for the water column, but seawater dilution of the mangrove inputs is observed. Spatial and tidal variations in CO_2 fluxes along the tidal creek suggest that porewater seepage is a driver of CO_2 emission into the atmosphere. Large seasonal and spatial differences in the biogeochemical functioning of the main channel are observed and are mainly related to the seasonal rainfall pattern. During the rainy season, the watershed influences the entire estuary, which exhibits a typical positive circulation. During the dry season, the estuary turns into a Salt-Plug region with positive and negative circulations in the upper and lower reaches, respectively. In this case, the upper and lower reaches seem to function independently, and the biogeochemical functioning of their water column is not controlled by the same processes. Surprisingly, pCO_2@27 °C values tend to be higher during the dry season, as do the total alkalinity (TAlk) values, while the pH values exhibit an opposite trend. Moreover, the TAlk values are higher in the lower reaches during the wet season and in the upper reaches during the dry season. These results indicate high in situ biogeochemical reactions and high porewater influence during the dry season, likely because of a low flushing rate and high water residence time after Salt Plug establishment. Although our results suggest that Salt Plugs may significantly affect the water column’s biogeochemistry and may promote CO_2 emissions of mangrove-derived carbon, further investigations, especially mass balance studies, are required to quantify their role in the biogeochemical functioning of such estuarine systems.
M. Faruqul Islam - One of the best experts on this subject based on the ideXlab platform.
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Spatiotemporal variation of Van der Burgh's coefficient in a Salt Plug estuary
Hydrology and Earth System Sciences, 2017Co-Authors: Dinesh Chandra Shaha, Yang-ki Cho, Bong Guk Kim, Sampa Rani Kundu, M. Rafi Afruz Sony, M. Faruqul IslamAbstract:Abstract. Salt water intrusion in estuaries is expected to become a serious global issue due to climate change. Van der Burgh's coefficient, K, is a good proxy for describing the relative contribution of tide-driven and gravitational (discharge-driven and density-driven) components of Salt transport in estuaries. However, debate continues over the use of the K value for an estuary where K should be a constant, spatially varying, or time-independent factor for different river discharge conditions. In this study, we determined K during spring and neap tides in the dry ( 750 m−3 s−1) seasons in a Salt Plug estuary with an exponentially varying width and depth, to examine the relative contributions of tidal versus density-driven Salt transport mechanisms. High-resolution salinity data were used to determine K. Discharge-driven gravitational circulation (K ∼ 0.8) was entirely dominant over tidal dispersion during spring and neap tides in the wet season, to the extent that Salt transport upstream was effectively reduced, resulting in the estuary remaining in a relatively fresh state. In contrast, K increased gradually seaward (K ∼ 0.74) and landward (K ∼ 0.74) from the Salt Plug area (K ∼ 0.65) during the dry season, similar to an inverse and positive estuary, respectively. As a result, density-driven inverse gravitational circulation between the Salt Plug and the sea facilitates inverse estuarine circulation. On the other hand, positive estuarine circulation between the Salt Plug and the river arose due to density-driven positive gravitational circulation during the dry season, causing the upstream intrusion of high-salinity bottom water. Our results explicitly show that K varies spatially and depends on the river discharge. This result provides a better understanding of the distribution of hydrographic properties.
M.z. Hou - One of the best experts on this subject based on the ideXlab platform.
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Developing, modeling and in-situ-testing a long-term wellbore seal in the framework of the CO2 -EGR research project CLEAN in the natural gas field Altmark
Energy Procedia, 2011Co-Authors: M.z. Hou, Lars Wundram, Meinhardt Schmidt, R. Meyer, Steffen Schmitz, H. Wendel, H.j. Kretzschmar, O. FranzAbstract:Abstract In this paper we present a new concept developed to improve the abandonment procedure of wellbores in depleted hydrocarbon fields, amongst others in Enhanced Gas Recovery (EGR) operations. The sealing concept is designed for the long-term containment of CO 2 and considers the creep ability of deep Permian Zechstein Salt formations in about 3,000 m depth. It is designed to amend the current standard abandonment procedure and consists of (a) an expansive gel filling in the reservoir formation, (b) a sealing element with cement extending to the impermeable caprock and (c) a Salt Plug as the major long-term sealing component, compatible in its composition and property to the surrounding caprock (halite). The focus of the project work described here is to develop and to model the last-mentioned long-term Salt sealing element. Numerical results show that the creep ability of the mentioned Salt formations can close a formerly reamed well section and hence recover the geological Salt barrier with or even without using a crushed Salt backfill. A field test is conducted in the North German Altmark Rotliegend gas field (Sachsen Anhalt) in order to study the technical feasibility for recovering the initial caprock integrity, to verify numerical models and to proof the sealing capability and therefore the sealing concept.
