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Science-policy interactions can both facilitate and hamper professional normative judgement, i.e. a value judgement about the desirability of a certain situation. Anthropogenic land subsidence, contributing to relative sea-level rise in the economically important Western peatland areas in the Netherlands is a case in point. The implementation of mitigation, adaptation and compensation measures is lagging, partly due to science-policy interaction problems potentially leading to conflicts between stakeholders, including agrarians, climate scientists and inhabitants. We find that professional normative judgement is enhanced when researchers and societal stakeholders reflect more critically on their role and engage in more inclusive science-policy interactions. [ABSTRACT FROM AUTHOR]

Land subsidence has to be controlled under global climate change and sea level rising for coastal megacities. Land subsidence caused by lowering groundwater level during underground excavation has become a dominant influence factor for land subsidence during urbanization and city renewal. How to manage the land subsidence induced by foundation pit dewatering (FPD) on an urban scale was urgent. Shanghai was selected as the research background. A subsidence and drawdown double control (SDDC) partition was established. The position of three times excavation depth (3H) horizontally away from the foundation boundary in the plane was defined as the boundary between dewatering subsidence and excavation settlement. Land subsidence of 3H (LS-3H) and groundwater drawdown on 3H (GD-3H) were defined as the evaluating and controlling indicators. An FPD conceptual model was summarized by the estimating and investigating of foundation pit information and numerical simulations were performed. A total of 6540 FPD scenarios were simulated for the LS-3H and GD-3H. Multi-factor regression analysis was conducted to obtain relations between the GD-3H and the shape, area, depth, and curtain depth of foundation pit on the basis of the numerical simulations. The regression models can be used to estimate the GD-3H and compared with the threshold specified by land subsidence prevention and control (LSPC) law, which can provide a reference for similar cases. [ABSTRACT FROM AUTHOR]

Scour holes are common features in deltaic rivers which can destabilise embankments through oversteepening of the river bed. Their development has been studied extensively from the hydraulic perspective, but another important control is the erodibility of the river bed which varies considerably due to thickening of heterogeneous deltaic substrate towards the coast. Therefore, we assessed the influence of delta-scale geological heterogeneity and local subsurface architecture on scour hole formation in addition to the hydrodynamic controls. We (1) created an inventory of 165 scour hole locations in the Rhine-Meuse delta, (2) assessed the hydrodynamic conditions at the locations, (3) extracted geometric characteristics and (4) determined the subsurface architecture from geological data. Central and lower delta branches have 0.6-0.7 scours per km while upper delta branches have less than 0.2. Downstream, 58% of scour holes were related to architectural elements, notably sand bodies from former Holocene channel belts and Early Holocene cohesive beds. These scours have steeper slopes due to higher proportions of cohesive sediments near the river bed. Furthermore, scours related to channel belt sand bodies are limited in downstream length and depth, up to maximum of approximately two times the water depth. From our results, we provide a delta-scale explanatory framework that relates the position of present-day river channels with respect to Pleistocene river deposits and Holocene fluvio-deltaic deposits to scour hole formation. Upstream rivers are incised in Pleistocene deposits showing less local variation in erodibility. The majority of scour holes here relate to engineering works. In central and lower delta branches, geologically inherited heterogeneity of the Holocene substrate at critical depths near the channel bottom adds to anthropogenic induced scours and results in high abundances. This demonstrates that downstream variation in subsurface architecture should be considered as a key control on scour locations and characteristics for management purposes. [ABSTRACT FROM AUTHOR]

In the unconstrained, low gradient setting of major delta plains, individual meander belts tend to function for relatively short periods of time due to repeated channel avulsion. Their short lifetime makes 'deltaic' channel belts suitable to study the products of steady meander evolution as the deposits and internal architectural elements preserved are often without complications of repeated bend cutoffs. This study investigated how sedimentary characteristics as preserved from subsequent stages of activity differ within the Stuivenberg channel belt. The Stuivenberg channel belt is a long‐studied example in the Holocene Rhine‐Meuse delta, The Netherlands, for which the meander evolution, i.e. geometry and dimensions through initiation, main activity and abandonment stages and durations of activity involved, was reconstructed. Mapping of the channel belt started from established coring based and LiDAR‐aided methods. Explorative approaches were used to assess active channel width at the onset of abandonment, and to reconstruct meander positions during earlier stages. The migration history of five consecutive meanders is revealed from convex and concave ridge‐and‐swale scrolls. Analysis identifies them to be the product of translation, expansion and rotation trajectories during a period of 800 years. Grain‐size composition throughout the sand body is interpreted given these positional contexts, with special attention to local coarsening of upper point bar facies in deltaic meander belts. The findings emphasize: (i) the need to separate abandonment stage from main activity stage when analysing three‐dimensional channel belt architectures; and (ii) the influence of meander evolution on lithological characteristics of initial stage versus mature stage parts of deltaic channel belt sands. [ABSTRACT FROM AUTHOR]

Land subsidence severely threatens most of the coastal plains around the world where high productive industrial and agricultural activities and urban centers are concentrated. Coastal subsidence damages infrastructures and exacerbates the effect of the sea‐level rise at regional scale. Although it is a well‐known process, there is still much more to be improved on the monitoring, mapping and modeling of ground movements, as well as the understanding of controlling mechanisms. The International Geoscience Programme recently approved an international project (IGCP 663) aiming to bring together worldwide researchers to share expertise on subsidence processes typically occurring in coastal areas and cities, including basic research, monitoring and observation, modelling and management. In this paper, we provide the research communities and potential stakeholders with the basic information to join the participating teams in developing this project. Specifically, major advances on coastal subsidence studies and information on well‐known and new case studies of land subsidence in China, Italy, The Netherlands, Indonesia, Vietnam and Thailand are highlighted and summarized. Meanwhile, the networking, dissemination, annual meeting and field trip are briefly introduced. [ABSTRACT FROM AUTHOR]

ABSTRACT Koster, K.; Cohen, K.M.; Stafleu, J., and Stouthamer, E., 2018. Using 14C-dated peat beds for reconstructing subsidence by compression in the Holland coastal plain of the Netherlands. Subsidence in the Holland coastal plain of the Netherlands was reconstructed from the vertical displacement of Holocene peat layers below their reference groundwater levels at the time of peat formation. This quantifies the part of subsidence that is due to compression processes and allows specification of the current state of peat compression in a map. 14C-dating of peat layers found intercalated in the Holocene sequence were used in the reconstruction. This dataset was combined with results from a recent coastal-deltaic plain wide three-dimensional (3D) interpolation of reference palaeo-groundwater levels, at which the intercalated peats are thought to have formed before they were buried, compressed, and vertically displaced. Empiric relations between reconstructed displacement and the thickness of overburden were determined and deployed in a national 3D geological subsurface model to establish a subsidence map with continuous cover of the coastal plain. The resulting maps show compressed peat layers under urbanized areas with 1 to 8 m of natural and anthropogenic overburden have subsided 1 to 5 m below the original level of formation. In the agricultural area of the coastal plain, where overburden is merely decimetres thick, consisting of fluvial flood- and sea-ingression deposits, peat generally experienced less than 1 m subsidence. The reference-level reconstruction method is deployable over large coastal plain areas to reconstruct subsidence caused by postdepositional vertical displacement of intercalated peat layers. It could therefore serve as an alternative approach for methods based on soil mechanics, which require input often not available for coastal plains on regional scales. [ABSTRACT FROM AUTHOR]

By redistributing water and sediment in delta plains, avulsions of river branches have major environmental impacts, notably in changing hydrological and peat-forming conditions in floodbasins. The central part of the Rhine-Meuse delta, with its extensive databases including detailed lithological data and high-resolution age control, offers a unique opportunity to study middle-Holocene avulsion impacts on floodbasin groundwater level and peat formation. Avulsion has caused local accelerations of rising groundwater tables to be superimposed on decelerating base-level rise. This is evident from comparing single-site groundwater rise for multiple floodbasins in the river-dominated part of the delta, with regionally averaged groundwater-rise reconstructions. Floodbasin type (lacustrine versus terrestrial wetland), size and openness, partly through effects on discharge dispersal, affect how strongly the floodbasin groundwater tables respond to avulsion-diverted discharge. Cross-sectional lithology repeatedly indicates a shift from high-organic wood peat to loworganic reed peat in the vicinity of the avulsed channel, resulting from changes in water-table regime and nutrient status. Avulsive impact on the floodbasin groundwater table was most pronounced during the transition from transgressive to high-stand stage (between ca. 6000 and 4000 years ago), owing to developing floodbasin compartmentalization (size reduction, confinement) resulting from repeated avulsion. By way of environmental impacts on groundwater tables and vegetation, avulsions thus affect the heterogeneity of floodbasin facies. [ABSTRACT FROM AUTHOR]

Crevasse splays are common geomorphological features in alluvial and deltaic floodplains. Although crevasse splays can develop into full avulsions, thereby transforming large areas of floodbasins, little is known about their sedimentary and geomorphological development at the decadal scale and their avulsion potential. We used aerial photography and lithological cross-sections to reconstruct crevasse-splay formation in the largely unmanaged floodplain of the Saskatchewan River in the Cumberland Marshes (Saskatchewan, Canada). Based on surface geomorphology and subsurface deposits, various stages of crevasse-splay development were described which were linked to both external forcing and internal morphodynamics. Initial splay deposition, following a levee breach during a large flood, occurred as a broad but relatively thin sandy sheet in a down-basin direction in the receiving backswamp area. In a next phase, these primary crevasse-splay deposits blocked local down-basin flow, thereby forcing the crevasse-splay channel in a direction perpendicular to the parent channel and original floodbasin gradient. This created an asymmetrical splay sequence composition, which differs in appearance from more commonly observed dendritic crevasse splays. It is concluded that sedimentation patterns in the splay have been influenced by inherited effects of previously formed deposits. Feedbacks of the original floodbasin gradient and earlier stages of splay formation are suggested as prominent mechanisms in creating the current morphology, orientation, and architecture of its deposits. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The quantitative significance of coarse-grained deposits in the overbank realm, such as crevasse-splay deposits, has not been studied at the delta scale or at the Holocene timescale. Such knowledge would be beneficial for understanding and explaining sediment distribution in delta plains. This study addresses delta-scale distribution of sand-containing basin fills and their sand-body proportion variability, based on eight valleywide cross sections in the Holocene Rhine- Meuse delta in the Netherlands. We found that sand-containing basin fills form 7.1% of the fluviodeltaic wedge, of which splay deposits are most frequently observed midway between the delta apex and the coast. Organic-clastic lake fills and bay-head delta deposits, in contrast, are limited to the distal delta plain. Over four successive periods (between 9000 and 800 cal yr BP), the largest proportions of splay deposits remain at 50-150 km downstream of the upstream-shifting delta apex. We show that intermediate floodbasin widths (between 3.1 and 3.6 km in the Holocene Rhine-Meuse delta) yield the highest proportions of splay deposits. High rates of base-level rise and wide floodplains both facilitate the creation of accommodation, which in turn provides conditions for peat-forming wetlands in which organic-clastic lake fills can develop. The results show that sand bodies form 26%-30% of sand-containing basin fills. This proportion is shown to be controlled by, among other variables, channel planform and superelevation of the trunk channel and substrate composition. We conclude that potentially large volumes of nonchannel sand bodies exist in distal delta plains. They constitute up to 39% of the reservoir volume in the distal Rhine-Meuse delta and yield relatively high connectedness ratios. [ABSTRACT FROM AUTHOR]

The article presents a research report conducted on the Land Subsidence with its monitoring, impact and mechanism in the coastal cities. It states that land subsidence is a geohazard which is consisted in the lower ground surface. The geohazard is a geological state which takes place because of natural and humaninduced processes occurring in the deep subsoil.

The Mekong delta, like many deltas around the world, is subsiding at a relatively high rate, predominately due to natural compaction and groundwater overexploitation. Land subsidence influences many urbanized areas in the delta. Loading, differences in infrastructural foundation depths, land-use history, and subsurface heterogeneity cause a high spatial variability in subsidence rates. While overall subsidence of a city increases its exposure to flooding and reduces the ability to drain excess surface water, differential subsidence results in damage to buildings and above-ground and underground infrastructure. However, the exact contribution of different processes driving differential subsidence within cities in the Mekong delta has not been quantified yet. In this study we aim to identify and quantify drivers of processes causing differential subsidence within three major cities in the Vietnamese Mekong delta: Can Tho, Ca Mau and Long Xuyen. Satellite-based PS-InSAR (Persistent Scatterer Interferometric Synthetic Aperture Radar) vertical velocity datasets were used to identify structures that moved at vertical velocities different from their surroundings. The selected buildings were surveyed in the field to measure vertical offsets between their foundation and the surface level of their surroundings. Additionally, building specific information, such as construction year and piling depth, were collected to investigate the effect of piling depth and time since construction on differential vertical subsidence. Analysis of the PS-InSAR-based velocities from the individual buildings revealed that most buildings in this survey showed less vertical movement compared to their surroundings. Most of these buildings have a piled foundation, which seems to give them more stability. The difference in subsidence rate can be up to 30 mm/year, revealing the contribution of shallow compaction processes above the piled foundation level (up to 20 m depth). This way, piling depths can be used to quantify depth-dependent subsidence. Other local factors such as previous land use, loading of structures without a piled foundation and variation in piling depth, i.e., which subsurface layer the structures are founded on, are proposed as important factors determining urban differential subsidence. PS-InSAR data, in combination with field observations and site-specific information (e.g., piling depths, land use, loading), provides an excellent opportunity to study urban differential subsidence and quantify depth-dependent subsidence rates. Knowing the magnitude of differential subsidence in urban areas helps to differentiate between local and delta wide subsidence patterns in InSAR-based velocity data and to further improve estimates of future subsidence. [ABSTRACT FROM AUTHOR]