Bouma, T.J.

Gourgue, O.

Schwarz, C.

Temmerman, S.

van Belzen, J.

van de Koppel, J.

Open Marine Archive

40 
Oral presentation Post-doc level 
A new bio-geomorphic model approach accounting for subgrid-scale 
heterogeneity of biogenic structures  
Gourgue Olivier1, van Belzen Jim1,2, Schwarz Christian3, Bouma Tjeerd2, van de Koppel Johan2 and 
Temmerman Stijn1 
1  Universiteit Antwerpen, Onderzoeksgroep Ecosysteembeheer (UA-ECOBE), Universiteitsplein 
1, 2610 Wilrijk, Belgium 
E-mail: ogourgue@gmail.com  
2  Koninklijk Nederlands Instituut voor Onderzoek der Zee: Estuarine and Delta Systems (NIOZ-
EDS), Korringaweg 7, Postbus 140, 4400 AC Yerseke, The Netherlands 
3  Department of Physical Geography, Faculty of Geosciences, Utrecht University, P.O. Box 80115, 
3508 TC Utrecht, The Netherlands 
 
In hydrodynamic and morphodynamic models, the effect of biogenic structures (such as 
vegetation, mussel beds or oyster reefs) on flow and sediment transport is generally expressed 
through the hydraulic roughness. The accuracy of bio-geomorphic model predictions depends 
on their ability to represent the spatial complexity of these biogenic structures, which is largely 
limited by computational power. This requires practical model choices, such as limiting the 
spatial resolution (that is, the model grid size), usually assuming a uniform spatial distribution 
at the subgrid scale. In this communication, we show that this uniformity assumption leads to 
considerable overestimation of the flow resistance if the subgrid distribution of biogenic 
structures is spatially correlated (that is, presenting clustered patterns). We also introduce a 
novel model approach that solves this multiscale issue by redefining the hydraulic roughness to 
account for this subgrid heterogeneity. 
 
Our approach builds on the similarity between the Chézy formula in fluid dynamics and Ohm's 
law in electricity. Taking the analogy further, we recalculate the coarse-scale hydraulic 
roughness just as the total resistance of an electronic circuit that combines resistors 
(equivalent to subgrid-scale biogenic structures in our analogy) connected in series (along-flow) 
and in parallel (across-flow). Although very simple, our approach improves considerably the 
flow routing in hydrodynamic models that operate at coarser scales than the scale at which 
biogenic structures are defined. As a result, fine-scale biogenic heterogeneity can now be 
accounted for at a reasonable computational cost, increasing the accuracy of large-scale bio-
geomorphic model predictions. 
 
In this communication, we illustrate the effectiveness of our subgrid approach by considering 
the flow deviation around expanding patches of tidal marsh vegetation. This process is a crucial 
mechanism for the initiation and development of channel networks in tidal marshes, which then 
facilitate the delivery of sediments to the vegetated platforms, hence building up elevation and 
increasing resilience to sea level rise. With our new subgrid approach, accounting for all these 
feedback mechanisms between tidal hydrodynamics, sediment transport and salt marsh 
vegetation dynamics is now possible, even when considering large-scale systems. 
 
Our new subgrid method has also potential for further applications in large-scale modeling of 
river flood plains, estuaries and other coastal shallow waters. For instance, it would provide 
improved model predictions quantifying the impact of large-scale coastal wetlands (tidal 
marshes and mangrove forests) on the landward propagation of storm surges, giving deeper 
insights in essential ecosystem services provided by biogenic structures. 
 
Keywords: Modeling; Flow; Vegetation; Bio-geomorphic; Multi-scale 
  


A new bio-geomorphic model approach accounting for subgrid-scale heterogeneity of biogenic structures

http://www.vliz.be/imisdocs/publications/325000.pdf

A new bio-geomorphic model approach accounting for subgrid-scale heterogeneity of biogenic structures

Abstract

Similar works

Full text

Available Versions

Open Marine Archive