Estuaries shaped by biomorphodynamics, inherited landscape conditions and human interference

Project Information

ESTUARIES

Grant agreement ID: 647570

DOI

10.3030/647570

Project closed

EC signature date 16 July 2015

Start date 1 December 2015

End date 31 May 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 000 000,00

EU contribution

€ 2 000 000,00

Coordinated by

UNIVERSITEIT UTRECHT
Netherlands

Periodic Reporting for period 4 - ESTUARIES (Estuaries shaped by biomorphodynamics, inherited landscape conditions and human interference)

Reporting period: 2020-06-01 to 2021-05-31

Summary of the context and overall objectives of the project

ESTUARIES are shallow coastal water bodies with river inflow shaped by biomorphological processes, with patterns of channels and shoals, sand/mud flats, tidal marshes, vegetated banks and peat. Development was influenced by early Holocene landscape that drowned under sea-level rise, and by human interference.

Estuaries harbour highly productive natural habitats and are of pivotal economic importance for food production, access to harbours and urban safety. Accelerating sea-level rise, changing river discharge and interference threaten these functions, but we lack fundamental understanding and models to predict combined effects of biomorphological interactions, inherited landscape and changing drivers.

My aims are to develop models for large-scale planform shape and size of sandy estuaries and predict past and future, large-scale effects of biomorphological interactions and inherited conditions. Objectives are:
1. to characterise biomorphological patterns and dynamics on shoals, bars and channels
2. to identify critical eco-engineering species and formulate rules for their habitats and effects
3. to create predictive numerical models for large-scale effects of biomorphological interactions
4. to identify large-scale effects of eco-engineers in experimental analogue models of estuaries
5. to formulate testable geological hypotheses about underlying conceptual models in reconstructions
6. to systematically unravel effects of biomorphological interactions from imposed conditions

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

• We developed a topological analysis method for multi-temporal channel networks based on graph theory incorporating directional propagation of reversing tidal flow, sediment and disturbances. So far, the network structure appears sensitive to direction in the topological sense but further work on graph theory is necessary.
• We developed object-based image analysis (OBIA) ruleset to discriminate shape characteristics of patch-, tidal flat- and marsh patterns based on spectral properties in aerial photographs of systems in nature and in the Metronome images. Using these, we aim to characterise changes of object properties through time, distinguishing at least between channels, sand bars, mud flats and vegetated flat.
• We built code to apply the species and their effects to any given estuary for application to field data and our numerically modelled estuaries.
• We tested hypotheses of large-scale effects of biomorphological interactions for selected ecosystem engineers and compared these against control runs without vegetation. Furthermore we tested interactions with mud and conducted runs for tidal rivers and for tide-dominated estuaries at a timescale of centuries.
• We discovered several ‘weed’ species that pioneer different habitats in our laboratory analogue models when distributed by flow and by seeding. These work considerably better than the alfalfa used until now by the international community and we already observed interesting eco-engineering effects including enhanced mud sedimentation.
• We experimentally tested hypotheses of small- and large-scale effects of biomorphological interactions from runs with limited numbers of species compared to control runs, all run by protocols representing recruitment at a regular interval of a few years and excluding extreme events.
• We studied to what degree alternative reconstructions are possible for specific Holocene estuaries based on different conceptual models and unravelled unexplored connections with potentially applicable models from the morphodynamics community.
• We formulated hypotheses how specific aspects of estuary planforms are attributable to externally imposed constraints (and timing where relevant)
o confining effects of valley geometry on estuary dimensions and planform geometry, partly determined by human interference in peat that initiated ingressive estuaries
o Coastal sand supply, partly determined by substrate, has a large effect on the response of estuaries to early Holocene sealevel rise
o We identified significant effects of cohesive or resistant substrate underlying growing estuaries but have not yet found that estuarine margin stability is imposed by substrate except in bedrock cases.
o river water and sediment supply, accounting for avulsion, strongly determines estuarine development as evidenced by contrasting cases in the Holocene coastal plain.
• We systematically modelled idealised estuaries (presently without biomorphodynamic interactions) to isolate effects of idealised boundary conditions including coastal and fluvial influxes from inherited morphologies varying between narrow antecedent valley(s) to wide coastal plain. We focus on coastal influx because this is the most challenging for long-term morphodynamic modelling, and the upstream aspects are being developed in WP3.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Significant achievement 1: Large-scale effects of macro-benthic animals on estuarine morphology and mud distribution (Brückner et al 2021), which is the first model of its kind. Deltares will likely help translate and disseminate this code much more broadly.
Significant achievement 2: Spectacular self-forming landscapes with live plants in the laboratory (Metronome experiments, Weisscher et al submitted), which advances this technology in several ways and opens up more advances in analogue modelling.
Significant achievement 3: Long-term modelling of wave-dominated coastal systems (Boechat Albernaz et al 2019 and in prep), the code for which has now been implemented in the standard version of the Delft3D open source software package (Deltares)
Significant achievement 4: The quantitative, objective and automated network identification tool has proven powerful for comparison of systems in the world, in models and in experiments, and to demonstrate effects of controlled variables and human interference (van Dijk et al 2021). Likewise, the quantitative, objective and automated ecotope mapping tool (Kleinhans et al. close to submission) has proven powerful in producing big data of large areas that would otherwise remain unmapped. This tool is now the standard for the Dutch government (Rijkswaterstaat) and applied for the first time to the Wadden Sea, an extremely large and worldwide unique wetland system.
Significant achievement 5: Engage the public, teach the teachers: A multi-audience communication and impact strategy has proven successful in mainstreaming the Metronome experiments and the idea of raising land by natural processes to adapt to future sea level rise, both in the media and in primary and secondary education. My annual www.uu.nl/bruningslecture (recorded lectures and movies of our own work online) draws about 100 attendants from other universities, governmental institutes and engineering/consultant companies, mainly from the Netherlands but also from Belgium, Germany, England, France, Italy, Denmark and China. The resulting visibility led to interviews in national newspapers, the most important news website and national television, as well as international press in UK, USA, Germany, Italy and Sweden. In turn, this led to my involvement in the national Delta committee which investigates and debates strategies for climate adaptation.

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