Search

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.

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.

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