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.

Deltas and coastal plains worldwide developed under the influence of relative sea level rise (RSLR) during the Holocene. In the Netherlands, Holocene RSLR results from both regional sea level rise and regional subsidence patterns, mainly caused by glacial isostatic adjustment (GIA: Scandinavian forebulge collapse) and longer-term North Sea Basin tectono-sedimentary subsidence. Past coastal and inland water levels are preserved in geological indicators marking the gradual drowning of an area, for example, basal peats. Such geological water level indicators have been used in the Netherlands for varying types of research. However, uniform overviews of these data exist only for smaller local subsets, rather than for the entire Netherlands. In this paper, we present a dataset of 712 Holocene water level indicators from the Dutch coastal plain that are relevant for studying RSLR and regional subsidence, compiled in HOLSEA workbook format (https://doi.org/10.5281/zenodo.11098446, De Wit and Cohen, 2024). This format was expanded to allow for the registration of basal-peat-type geological indicators, the documentation of Dutch-setting-specific parameters and their accompanying uncertainties, the assessment of the indicative meaning, and the appropriate correction of the raw vertical positions of the indicators. Overall, our new, internally consistent, expanded documentation provided for the water level indicators encourages users to choose the information relevant to their research and report RSLR uncertainties transparently. With respect to the indicators, 59 % were collected in 1950–2000, mainly in academic studies and survey mapping campaigns; 37 % were collected in 2000–2020 in academic studies and archaeological surveying projects; and 4 % were collected in this study, with the latter mainly being collected in previously undersampled central and northern regions of the Netherlands. Prominent regional differences exist in the vertical position and abundance of the indicators. Older indicators in our dataset are primarily located in the deeper seaward area of the Netherlands. These indicators correspond well with previous transgression reconstructions partly based on the same data. The younger, landward set of indicators in the Rhine–Meuse delta inland and Flevoland regions corresponds to the transgression phase reaching further inland, from 8000 cal BP onwards. Northern indicators of Middle Holocene age (8–5 ka cal BP) generally lie 2–3 m lower than those in the south. This difference is less for younger data, showing spatial and temporal variation in RSLR throughout the Netherlands.

Coastal wetlands have historically been portrayed as too marginal for early crop cultivation during the Mesolithic–Neolithic transition due to their dynamic hydrology, low elevation, and poor drainage. However, growing evidence suggests that these environments played a crucial role in the spread of agriculture. We examined buried and submerged channel–levee systems beneath present‐day Lake IJssel (the Netherlands) to investigate the spatial and temporal extent to which wetland levees provided suitable grounds for cultivation as rivers functioned while the sea level rose. The study area lies along the lower reaches of the paleo‐Vecht River, one of two local rivers crossing the Swifterbant‐type area, with key sites located 10–20 km inland. Integrating sedimentary geology, archaeological soil micromorphology, and radiocarbon dating of research cores, we identify buried soil horizons indicating periods of reduced sedimentation and relatively stable, dry conditions conducive to human activity. Micromorphology reveals charred plant material, ceramic fragments, and disturbed soil aggregates comparable to tilled fields at Swifterbant settlements. Radiocarbon dating places these features between ca. 4500 and 4200 BC , coinciding with upstream occupation. These findings add to growing evidence of widespread, sustained land use in these wetland environments and highlight the value of micromorphology in detecting subtle traces of human activity in landscape‐scale studies.

Deltas and coastal plains worldwide developed under the influence of relative sea level rise (RSLR) during the Holocene. In the Netherlands, Holocene RSLR results from both regional sea-level rise and regional subsidence patterns, mainly caused by glacial isostatic adjustment (GIA: Scandinavian forebulge collapse) and longer-term North Sea Basin tectono-sedimentary subsidence. Past coastal and inland water levels are preserved in geological indicators marking the gradual drowning of an area, for example basal peats. Such geological water-level indicators have been used in the Netherlands for varying types of research. However, uniform overviews of these data exist only for smaller local subsets and not for the entire Netherlands. In this paper we present a data set of 712 Holocene water-level indicators from the Dutch coastal plain that are relevant for studying RSLR and regional subsidence, compiled in HOLSEA workbook format. This format was expanded to allow for registering basal-peat type geological indicators, documenting Dutch-setting specific parameters and accompanying uncertainties, to assess indicative meaning, and to appropriately correct the raw vertical positions of the indicators. Overall, our new, internally consistent, expanded documentation provided for the water-level indicators encourages users to choose the information relevant for their research and report RSLR uncertainties transparently. From the indicators, 59 % was collected in 1950–2000, mainly in academic studies and survey mapping campaigns; 37 % was collected in 2000–2020 in academic studies and archaeological surveying projects, 4 % was newly collected (this study), the latter mainly in previously under sampled central and northern Netherlands regions. Prominent regional differences exist in the vertical position and abundance of the indicators. Older indicators in our data set are mostly located in the deeper seaward area of the Netherlands. These indicators correspond well with previous transgression reconstructions, that are partly based on the same data. The younger, landwards set of indicators in the Rhine-Meuse central and Flevoland regions corresponds with the transgression phase reaching further inland, from 8000 cal. BP onwards. Northern indicators of Middle Holocene age (8–5 ka cal. BP), in general lie 2–3 meters lower compared to those in the south. For younger data this difference is less, showing spatial and temporal variation in RSLR throughout the Netherlands.

Subsidence is a land use problem in the western and northern Netherlands, especially where both shallow soft soil subsidence and deeper subsidence components, including glacio-isostatic adjustment (GIA), add up. The aim of this study is to improve the estimation of the GIA component within the total subsidence signal across the Netherlands during the Holocene, using coastal plain paleo-water level markers. Throughout the Holocene, the GIA induced subsidence in the Netherlands has been spatially and temporally variant, as shown by previous studies that used GIA modelling and geological relative sea-level rise reconstructions. From the latter work, many field data points are available based on radiocarbon dated coastal basal peats of different age and vertical position. These reveal Holocene relative sea-level rise to have been strongest in the Wadden Sea in the Northern Netherlands. This matches post-glacial GIA subsidence (forebulge collapse) as modelled for the Southern North Sea, being located in the near-field of Scandinavian and British former ice masses.In this study, geological data analysis of RSL and other paleo-water level data available from the Dutch coastal plain for the Holocene period is considered in addition. The analysis takes the form of designing and executing a 3D interpolation (kriging with a trend: KT), where paleo-water level Z(x,y,age) is predicted and the field-data points are the observations (Age, X, Y and Z as knowns). We use a spatio-temporal 3D grid that covers the Dutch coastal plain, and reproduces and unifies earlier constructed sea level curves and high-resolution sampled individual sites (e.g. Rotterdam). The function describing the trend part of the interpolation separates linear and non-linear components of relative water level rise, i.e.: long-term background subsidence and shorter-term GIA subsidence signal and postglacial water level rise. The kriging part then processes remaining subregional patterns. The combined reconstruction thus yields a spatially continuous parameterization of regional trends that (i) allows to separate subsidence from water level rise terms, and (ii) is produced independently of GIA modelling to enable cross-comparison. Results are presented for the coastal plain of the Netherlands ([SW] Zeeland – Rotterdam – Holland – Wadden Sea – Groningen [NE]). The percentage of the total coastal-prism accommodation space that appears due to subsidence, from the south to the north of the study area increases by 20%. Holocene-averaged subsidence rates from the first analysis ranged from ca. 0.1 m/kyr (Zeeland) to 0.4 m/kyr (Groningen), which is 5-10 times larger than present-day GPS/GNSS-measured rates.The research presented in this abstract is part of the project Living on soft soils: subsidence and society (grantnr.: NWA.1160.18.259). 

The evolution of the Holocene coastal plain in the Netherlands is strongly influenced by global sea-level rise and regional subsidence patterns. Added up these components are known as relative sea-level rise (RSLR), and explain the coastal plain build-up and accommodation space. Due to RSLR, geological indicators of gradual-drowning formed, such as basal peat layers. These indicators have been sampled and dated from different depths and locations across the coastal plain and are used to document rising coastal sea levels and inland groundwater levels. Databasing and spatial-temporal analysis of the large set of indicators (N=~720) serves to assess local and regional variabilities in RSLR.Collection of geological water level indicators in the Netherlands started as early as the 1950ies. It was carried out for various purposes: RSLR reconstruction, geological mapping of the coastal-deltaic plain, wetland paleoenvironmental reconstructions. Full formal overview of this data did not exist, as past reviews and data compilations (N=50-300) were subregion restricted and usage specific. Regional differences within the Netherlands, e.g. greater RSLR in the north than in the SW, are also long noticed, and mostly attributed to differential subsidence as caused by glacial isostatic adjustment (GIA: Scandinavian forebulge collapse, at non-linear rate) and longer-term North Sea Basin tectono-sedimentary subsidence (at a linear rate).Here, we present a uniform database of Holocene coastal plain water level indicators for the Netherlands, using the HOLSEA workbook format. By compiling a database of geological water level indicators, with an explicit and consistent standardized treatment of dealing with vertical uncertainties, age uncertainties, and indicative meaning of each indicator (e.g. does it resemble former inland groundwater level, or former sea-level), we enable more accurate break down of differential subsidence and its source components.Database compilation included documentation of all vertical corrections applied, such as for water depth, (paleo-)tides, long-term background land motion and for compaction, as well as the propagation of uncertainties associated with these corrections. The ~720 indicators are further categorized into sea level index points (SLIPs), sea-level upper limiting data (ULD) and sea-level lower limiting data (LLD). ULD data is further categorized to separate tidally, river gradient and local-hydrology influenced indicators. Vertically corrected relative sea-level positions and relative groundwater-level positions are reported separately.Spatial-temporal analysis of the Holocene water level data allowed for an interpolated reconstruction of Holocene RSLR, resulting in map-output that has continuous coverage of the Dutch coastal plain. Furthermore, this data-driven RSLR reconstruction is used to further disentangle components of RSLR: the Holocene water level rise part versus the two main land subsidence parts, independently from global sea-level analysis, basin-geological subsidence reconstructions and geophysical GIA-modelling output. We compare our reconstructed sea level plains to the RSLR output of glacio-isostatic adjustment modelling, which incorporate ice sheet deglaciation history and Earth-rheological models. This enhances our ability to quantify the contributions of GIA and basin subsidence to past and ongoing RSLR and subsidence in the Netherlands.