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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.

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 c

The Mekong Delta is under threat from natural and anthropogenic disruptions. With no action taken, the coastal parts of the delta could almost disappear by the end of this century due to relative sea level rise (RSLR). This study explores the potential of sedimentation-enhancing-strategies (SES), which could potentially save the Mekong Delta from drowning. By focusing on integrated mangrove shrimp systems, this study aims to quantify sediment accumulation and assess their effectiveness to function as SES and counter RSLR. Fieldwork conducted in Tra Vinh and Ca Mau provinces, Vietnam, involves monitoring eight mangrove shrimp systems over time to analyse sediment accumulation, composition, and deposition. Laboratory tests on accumulated sediments further delve into the sediment composition. The findings of this study contribute to a deeper understanding of sediment accumulation, dynamics, and composition within these systems. Moreover, the study estimates integrated mangrove-shrimp systems’ potential as SES for the entire Mekong Delta. Results indicate a high likelihood that these systems can effectively mitigate RSLR, observing pristine uncompacted sedimentation rates of 1.95 cm/30 days in Tra Vinh and 1.16 cm/30 days in Ca Mau. This could imply sedimentation accretion rates of about 24 and 14 cm/year in integrated mangrove shrimp systems in Tra Vinh and Ca Mau, respectively. Potentially, the current integrated mangrove shrimp areas could accumulate up to 30 million m3 of sediment annually.

The awareness on the importance that land subsidence plays on coastal processes at the regional scale is increased over the last two decades, and it clearly appears that land subsidence can contribute primarily to the relative sea level rise affecting coastal zones. Jakarta is one of the cities mostly affected by the combination of sea-level rise and land subsidence. In this paper, the activities carried out in Jakarta under the umbrella of the IGCP Project 663 were presented, and the possible measures and best practices mitigating land subsidence for the research associates and potential stakeholders were provided, with which can serve as inspiration for authorities and communities facing land subsidence. Meanwhile, major achievements of IGCP 663 in Jakarta were summarized and introduced, including dissemination session, scientific session and field trips. Specifically, major advances on coastal subsidence studies regarding the effect of relative sea level rise, subsidence mapping, monitoring and simulation, as well as the support of policy making are highlighted and summarized.

River deltas commonly have a heterogeneous substratum of alternating peat, clay and sand deposits. This has important consequences for the river bed development and in particular for scour hole formation. When the substratum consists of an erosion resistant top layer, erosion is retarded. Upon breaking through a resistant top layer and reaching an underlying layer with higher erodibilty, deep scour holes may form within a short amount of time. The unpredictability and fast development of these scour holes makes them difficult to manage, particularly where the stability of dikes and infrastructure is at stake. In this paper we determine how subsurface lithology controls the bed elevation in net incising river branches, particularly focusing on scour hole initiation, growth rate, and direction. For this, the Rhine-Meuse Estuary forms an ideal study site, as over 100 scour holes have been identified in this area, and over 40 years of bed level data and thousands of core descriptions are available. It is shown that the subsurface lithology plays a crucial role in the emergence, shape, and evolution of scour holes. Although most scour holes follow the characteristic exponential development of fast initial growth and slower final growth, strong temporal variations are observed, with sudden growth rates of several meters per year in depth and tens of meters in extent. In addition, we relate the characteristic build-up of the subsurface lithology to specific geometric characteristics of scour holes, like large elongated expanding scour holes or confined scour holes with steep slopes. As river deltas commonly have a heterogeneous substratum and often face channel bed erosion, the observations likely apply to many delta rivers. These findings call for thorough knowledge of the subsurface lithology, as without it, scour hole development is hard to predict and can lead to sudden failures of nearby infrastructure and flood defence works., Coastal Engineering, Education and Student Affairs, Rivers, Ports, Waterways and Dredging Engineering

In the Netherlands land subsidence is a continuously ongoing process. Consequently, an increasing number of people and economic assets are exposed to subsidence, damage costs are soaring, and flood risk and greenhouse gas emissions are increasing. In some areas tipping points have already been reached, where current land-use can no longer be maintained without considerable costs, underlining the urgency to take action. Together with a consortium consisting of universities, research institutes, governmental agencies, public and private partners we have developed a national, multidisciplinary research programme aiming to develop an integrative approach to achieve feasible, legitimate and sustainable solutions for managing the negative societal effects of land subsidence, connecting fundamental research on subsidence processes to socio-economic impact of subsidence and to governance and legal framework design. The program is designed to co-create insights that help to effectively mitigate and adapt to subsidence within the Netherlands by making major improvements in measuring and modeling the processes and consequences of subsidence, identifying, developing and critically evaluating control measures and designing governance and legal approaches that facilitate their implementation. Hereto we will develop (a) new satellite-based technology to measure, attribute and monitor subsidence, (b) solid understanding of the interacting multiple processes contributing to total subsidence, (c) sophisticated physical and economic numerical models to predict human-induced subsidence rates and impacts, and (d) implementation strategies that go beyond technical measures, to strengthen governance and financing capacities as well as legal frameworks. This fully integrated approach deals with all impacts of land subsidence on society and the economy., Pre-conference publication of a 2020 congress, postponed due to COVID-19, Mathematical Geodesy and Positioning

In the Netherlands land subsidence is a continuously ongoing process. Consequently, an increasing number of people and economic assets are exposed to subsidence, damage costs are soaring, and flood risk and greenhouse gas emissions are increasing. In some areas tipping points have already been reached, where current land-use can no longer be maintained without considerable costs, underlining the urgency to take action. Together with a consortium consisting of universities, research institutes, governmental agencies, public and private partners we have developed a national, multidisciplinary research programme aiming to develop an integrative approach to achieve feasible, legitimate and sustainable solutions for managing the negative societal effects of land subsidence, connecting fundamental research on subsidence processes to socio-economic impact of subsidence and to governance and legal framework design. The program is designed to co-create insights that help to effectively mitigate and adapt to subsidence within the Netherlands by making major improvements in measuring and modeling the processes and consequences of subsidence, identifying, developing and critically evaluating control measures and designing governance and legal approaches that facilitate their implementation. Hereto we will develop (a) new satellite-based technology to measure, attribute and monitor subsidence, (b) solid understanding of the interacting multiple processes contributing to total subsidence, (c) sophisticated physical and economic numerical models to predict humaninduced subsidence rates and impacts, and (d) implementation strategies that go beyond technical measures, to strengthen governance and financing capacities as well as legal frameworks. This fully integrated approach deals with all impacts of land subsidence on society and the economy.

Land subsidence is a worldwide geohazard consisting in the lowering of the ground surface due to natural and human-induced processes occurring in the shallow and deep subsoil. Over the last two decades, land subsidence has caused damages and widespread impacts to a variety of infrastructures in coastal cities (Ma et al., 2011; Liu et al., 2016; Minderhoud et al., 2018). Meanwhile, it is particularly alarming as it reduces the ground elevation with respect to the sea level. The IGCP 663 aims to jointly carry out international academic communication and cooperation, to further and promote the international understanding, advanced technical analysis and evaluation methods of land subsidence, and exchange experiences and research results worldwide, especially in coastal cities and regions. The joint researches of IGCP 663 carried out during 2018 have improved the understanding of the land subsidence in typical coastal areas and cities, and the main causes of land subsidence in global coastal cities were figured out through several case studies in China, Italy, the Netherlands and Indonesia: groundwater withdrawal for drinking water (e.g., Jakarta, Chaussard et al., 2013), groundwater lowering for construction (e.g., Shanghai, Wang et al., 2018), oxidation of peat and compaction of soft soils (e.g. the Netherlands, Sanneke et al., 2018), extraction of hydrocarbons (e.g., northern Netherlands, Koster et al., 2018) and natural consolidation of Holocene deposits (e.g., Venice, Da et al., 2018; Tosi et al., 2018). Shanghai was set as an example of how could deal with land subsidence by taking measures of constructing comprehensive monitoring network, taking artificial recharge, restricting groundwater pumping, and making politics and regulations, etc (Wang et al., 2014). Moreover, we investigated the spatial distribution characteristics, physical and mechanical properties of the reclaimed soil and its underlying natural sedimentary soil along the coast of Shanghai, in ord

Since the 1970’s the perspective on ideal coastal management has changed in the Netherlands. A shift occurred to more eco-system based management with a focus on the implementation of the so called soft measures. Tidal mudflat and salt marshes are known for their functioning towards enhanced flood protection. In this study research has been conducted on the role of the foreshore in the Scheldt estuary. The foreshore includes mudflats and salt marshes between dike and waterfront. Stability of these systems has mostly been studied for shallow subsurface processes and to a lesser extent for deep subsurface stability. In this master thesis the stability of foreshores in de Eastern Scheldt has been studied coupling both shallow and deep subsurface stability. Subsurface characteristics were studied for 3 locations with different energetic conditions. Characteristics such as lithology, disturbance layers and bulk density were used to assess the stability on 2 different scales; shallow subsurface (0-30 cm) and deeper subsurface (0-max. channel depth~15 m). Additionally, it was tested, whether foreshore stability could relate to an important failure mechanism of water defences shown within the Eastern Scheldt; the occurrence of so-called "flow slides". The stability in both the lateral and vertical stretch of tidal salt marshes and mudflats of all 3 locations in terms of erosion resistance was not to be related directly. The same holds for the probability of flow slides. Erosion resistance was influenced mainly by soil strengthening factors in the top-layer such as sediment density, moisture content and the presence of roots and shells. Based on this study, probability of flow slides is mainly influenced by the degree of consolidation of deeper lain sand layers and the total geometry of the channel to dike foreshore system. Within the scope of a better understanding of foreshore stability, more research is needed on the relation of soil characteristics with stability and ero

An increasing number of people lives in coastal zones with a subsurface consisting of heterogenic soft-soil sequences. Many of these sequences contain substantial amounts of peat. While population growth and urbanization continues in coastal zones, they are threatened by global sea-level rise and land subsidence. Peat compaction and oxidation, caused by loading and drainage, are important contributors to land subsidence, and hence relative sea-level rise, in peat-rich coastal zones. Especially built-up areas, having densely-spaced urban assets, are heavily impacted by land subsidence, in terms of livelihoods and damage-related costs. Yet, built-up areas have been largely avoided in peat compaction and oxidation field studies. Consequently, essential information on the relative contributions of both processes to total subsidence and underlying mechanisms, which is required for developing effective land use planning strategies, is lacking. Therefore, we quantified subsidence due to peat compaction and oxidation in built-up areas in the Rhine-Meuse delta, The Netherlands, using lithological borehole data and measurements of dry bulk density, organic matter, and CO2 respiration. We reconstructed subsidence over the last 1000 years of up to ~4 m, and recent subsidence rates of up to ~140 mm·yr−1 averaged over an 11-year time span. The amount and rate of subsidence due to peat compaction and oxidation is variable in time and space, depending on the Holocene sequence composition, overburden thickness, loading time, organic-matter content, and groundwater-table depth. In our study area, the potential for future subsidence due to peat compaction and oxidation is substantial, especially where the peat layer occurs at shallow depth and is relatively uncompacted. We expect this is the case for many peat-rich coastal zones worldwide. We propose to use subsurface-based spatial planning, using specific subsurface information mentioned above, to inform land

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.

The Early Middle Ages (ca. 300 - 1000 AD) was a period of severe pan-European economic and demographic change. During this period population declined and human influence on the landscape diminished throughout large parts of Europe (Cheyette 2008). Traditionally archaeologists and historians regard these Early-Medieval developments as the result of cultural processes. However, recent reconstructions show frequent climate fluctuations (Büntgen et al. 2011) and dramatic landscape changes in the Netherlands for this period (Vos & Van Heeringen 1997; Stouthamer et al. 2011). This suggests that economic and demographic changes might not be induced by cultural processes only, but also by climate and landscape dynamics (e.g. riverflooding, sea ingressions). To determine how and to what extent environmental changes contributed to the Early-Medieval economic and demographic changes, the ‘The Dark Ages in an interdisciplinary light’ project was initiated. As part of the project, this contribution shows the landscape dynamics of the Dutch coastal area during the Early Medieval period. In this geomorphological dynamic region, major sea ingressions occurred forming large tidal inlets. Occupation in this region mainly occurred in the supratidal environment, e.g. on dwelling mounds (Vos & Gerrets 2005) and was most likely influenced by these landscape dynamics. Development of the geomorphological elements of these tidal systems (channels, tidal flats and salt marshes) is extensively mapped in a GIS and coupled to a database storing information on age of the tidal system and its individual geomorphological elements. This generates a new integrated overview of the development of tidal systems for every possible time step. Palaeogeographical maps can be derived and the GIS provides the possibility to statistically analyse sea ingression dynamics in the Early Middle Ages and how this differs from other periods of sea level highstand (~last 3000 years). By comparing these maps w

The Holocene Rhine-Meuse delta developed during the past ~8000 yr under a first rapid and later decreasing sea level rise in a back-barrier area along the North Sea. After about 3500 yr BP, natural delta evolution became increasingly influenced by humans, with different types of imprints: increased discharge and sediment load associated with deforestation in the hinterland affecting channel geometry and deposition; artificial avulsion; large-scale peat excavation; reclamation and drainage of flood basins resulting in compaction and oxidation of peat; river embankment preventing delta-wide overbank deposition and finalizing avulsion; channelization, changing channel belt geometry and causing shifts in sediment deposition within the delta. After the onset of the industrial revolution, contaminants have been deposited along with the river sediment on the embanked floodplains and in the estuary. The extremely well-documented human-affected evolution of the delta provides a unique opportunity to demonstrate how the Anthropocene can manifest itself in such an environment. We give an overview of human-affected processes in the Rhine-Meuse delta and discuss their effect on fluvial architecture, morphology and sediment composition, and how these may remain preserved within the delta sedimentary record.