ÀÖÓãºǫ́

Utrecht University’s research focus area Future Deltas has been awarded four new research proposals. The group of scientists involved will receive more than three million euros in research funding. Three projects are funded by  and one by .

Three out of four projects will take place in the Dutch Rhine-Meuse delta and the Wadden Sea; the fourth project taking place in Bangladesh, where the scientists will work together with local researchers. Future Deltas is active worldwide; the takes place in amongst others Vietnam, Mozambique, the United States and Indonesia.

Living polders: dynamic polder management for sustainable livelihoods, applied to Bangladesh
Urbanising Deltas of the World Programme

Managed deltas are social-ecological systems that provide flood- and food security. However, land subsidence and sea level rise render deltas vulnerable to flooding, the impact of which is exacerbated by population growth and urbanization. These stresses affect institutional requirements for delta systems. Polders can mitigate these threats by offering flood protection and increased food production. In Bangladesh, polders increased yields, but at the delta level, they affected rivers’ drainage capacity and siltation. At the polder level, they caused land subsidence, and waterlogging.

In response, in 1990, local people themselves breached dikes of the Dakatia beel polder, to re-allow tidal flows. This eroded silt from the tidal channels enabling drainage of waterlogged areas, and re-allowed sedimentation inside polders, raising soil surfaces and fertility. Ever since, Tidal River Management has been experimented with, however, its full potential has not yet been reached due to fundamental knowledge gaps regarding physical and institutional boundary conditions.

Rather than being an obstacle, sediments provide a high potential for a Building with Nature approach, which works with rather than against the forces of nature. This project builds on this notion and seeks to explore the potential of Living Polders that accrete along with rising water levels. The project offers comprehension of integrated, coevolving physical and institutional processes across delta- and polder scales. Subsequently, it provides pathways to optimization through a Decision Support System for dynamic polder management and associated business cases. Project outcomes are evaluated for application elsewhere, thus offering business opportunities for the Dutch water sector.

Floods of the past – Design for the future
STW – water 2015

Design standards for flood protection in deltas require magnitude estimates of extreme (millennial) floods. The Dutch Delta Programme considers a design discharge of 18,000 m3/s an appropriate upper value the Rhine River at the German-Dutch border. Absence of a sufficiently long observational record of river discharge introduces considerable uncertainty in estimates of magnitude-frequency relations, which can only partly be solved by using statistical methods. Numerous historic flood marks along the German Rhine and sedimentary data of the youngest 2000 years contain valuable information on past extreme floods. In this interdisciplinary project we combine sedimentary and written archives from the delta with state-of-the-art reconstructions and 2D modeling of past events to quantify magnitudes of large historic floods of the lower Rhine. The resulting method and computations allow evaluating the potential limits to design flood magnitudes and inundation cascades in the current situation in the Netherlands and adjacent Germany.

SEAWAD: SEdiment supply At the WAdden Sea ebb-tidal Delta - From system knowledge to mega-nourishments
STW – water 2015

The Dutch coastal zone is prone to flooding. The Netherlands has chosen to protect the coast by means of soft adaptive solutions such as (mega) nourishments with the aim of maintaining the coastline. At present the sediment volume in the Wadden Sea coastal zone is insufficient due to the export towards the tidal basins. This is exacerbated by the accelerated sea-level rise and subsidence and subsequently larger nourishment volumes are requiered in the near future. Mega-nourishments like the Sand Motor turned out to be efficient. However, the morphological and ecological impacts of such a large-scale intervention in a complex system as the ebb-tidal delta of the Wadden Sea are insufficiently known. This is all the more critical, as the anticipated mega-nourishments will be in the vicinity of the protected World Heritage area. Within SEAWAD, we develop the system knowledge and tools to predict the effects of mega-nourishments on morphology and ecology (benthos distribution).

Piping in practice – Predicting piping underneath river dikes using 3D subsurface heterogeneity and groundwater flow modeling
STW – water 2015

Piping is a process of seepage-induced transport of sand underneath river dikes that could occur when rivers flood and can make dikes fail. Prediction of piping risk at delta scale is difficult because it demands detailed knowledge on composition of the natural substrate below the dike, e.g. grain size distribution, sorting and layering and on the way seepage water flows through this; horizontally, diagonally, via preferential paths. This project aims to identify locations of increased piping-risk below river dikes of the Dutch delta. The methods involve improved mapping of substrate below dikes throughout the delta, measurement of hydraulic characteristics of the subsurface at field test locations, and full-3D hi-res numerical modeling of the piping process. This will result in faster and more cost-efficient identification of piping-risk locations and better-informed calculation of dike stability, needed to maintain safety standards along 100-kms of dike.

: focus area of Utrecht University