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SLIM1D and SLIM2D

SLIM2D is used in shallow-water environments where wind and tides are sufficient to keep the water column rather well mixed. It solves the depth-averaged shallow water equations for the surface elevation and the horizontal velocity. When the horizontal flow is mainly unidirectional such as for a well-mixed river, the shallow water equations can be averaged over the section leading to the 1D section-averaged shallow-water equations. SLIM1D consists of linear river segments where variable river width and cross-section are taken into account. River segments can be joined to model a river network with accurate computation of bifurcation by the means of a Riemann solver.

1D-2D mesh of the Scheldt
2D-1D mesh of the Schledt river, estuary and its tributaries. SLIM2D is used in the estuary and coastal sea. Upstream of the estuary, the mesh becomes one-dimensional in the fresh tidal river network and ends at the limit of the tidal dominance. The arrows indicated the locations where freshwater discharges are imposed.

SLIM solves the model equations on an unstructured mesh with the Discontinuous Galerkin finite element method. This approach provides an optimal degree of flexibility both geometrically and functionally as it can accurately represent complex topographies and also model solutions with sharp gradients. Unlike more standard numerical methods, such as finite volumes, it introduces a minimal amount of numerical dissipation and thus preserves small-scale flow features such as recirculation eddies. The model equations can be forced by wind, tides, river discharges and large-scale currents from a global ocean model.

Currents as modelled with SLIM2D in the Great Barrier Reef. The use of an unstructured mesh with a 250m resolution and the Discontinuous Galerkin method allows us to simulate small-scale flow features such as recirculation eddies.

Most coastal areas are significantly influenced by tides. When approaching the coast, the tidal signal tends to amplify, especially in funnel-shaped embayments where the tidal range may reach considerable magnitudes. Combined with the fact that many estuaries and embayments also feature gradually sloping bathymetry, the total area submerged under water may vary significantly during the tidal cycle. To tackle this issues, SLIM2D is equipped with a wetting-drying algorithm that allows it to handle dry areas. The algorithm is based on an implicit time-stepping that combines computational efficiency with local mass conservation. The video below shows the water transport in the Columbia River estuary as modeled by SLIM2D. Dry tidal flats are clearly visible at low tide.

To learn more…

Scherpereel, C., Alosairi, Y., Lambrechts, J., & Hanert, E. (2025). Hydrodynamic impacts of bridge construction and land reclamation on water residence time and flushing processes in Kuwait Bay. Marine Pollution Bulletin, 214, 117716. https://doi.org/10.1016/j.marpolbul.2025.117716
Hirsh, H. K., Oliver, T. A., Dobbelaere, T., Palacio-Castro, A. M., Barkley, H. C., Webb, A. E., Hanert, E., & Enochs, I. C. (2025). Statistical Prediction of In Situ Coral Reef Carbonate Dynamics Using Endmember Chemistry, Hydrodynamic Models, And Benthic Composition. Aquatic Geochemistry, 31(1), 4. https://doi.org/10.1007/s10498-025-09438-x
Dobbelaere, T., Holstein, D. M., Gramer, L. J., McEachron, L., & Hanert, E. (2024). Investigating the link between the Port of Miami dredging and the onset of the stony coral tissue loss disease epidemics. Marine Pollution Bulletin, 207, 116886. https://doi.org/10.1016/j.marpolbul.2024.116886
Dobbelaere, T., Dekens, A., Saint‐Amand, A., Alaerts, L., Holstein, D. M., & Hanert, E. (2024). Hurricanes enhance coral connectivity but also superspread coral diseases. Global Change Biology, 30(6), e17382. https://doi.org/10.1111/gcb.17382
Faryuni, I. D., Saint-Amand, A., Dobbelaere, T., Umar, W., Jompa, J., Moore, A. M., & Hanert, E. (2024). Assessing coral reef conservation planning in Wakatobi National Park (Indonesia) from larval connectivity networks. Coral Reefs, 43(1), 19–33. https://doi.org/10.1007/s00338-023-02443-y
Lecart, M., Dobbelaere, T., Alaerts, L., Randresihaja, N. R., Mohammed, A. V., Vethamony, P., & Hanert, E. (2024). Land reclamation and its consequences: A 40-year analysis of water residence time in Doha Bay, Qatar. PLOS ONE, 19(1), e0296715. https://doi.org/10.1371/journal.pone.0296715
Saint-Amand, A., Lambrechts, J., & Hanert, E. (2023). Biophysical models resolution affects coral connectivity estimates. Scientific Reports, 13(1), 9414. https://doi.org/10.1038/s41598-023-36158-5
Purkis, S. J., Oehlert, A. M., Dobbelaere, T., Hanert, E., & Harris, P. (Mitch). (2023). Always a White Christmas in the Bahamas: temperature and hydrodynamics localize winter mud production on Great Bahama Bank. Journal of Sedimentary Research, 93(3), 145–160. https://doi.org/10.2110/jsr.2022.066
King, S., Saint-Amand, A., Walker, B. K., Hanert, E., & Figueiredo, J. (2023). Larval dispersal patterns and connectivity of Acropora on Florida’s Coral Reef and its implications for restoration. Frontiers in Marine Science, 9, 1038463. https://doi.org/10.3389/fmars.2022.1038463
Sampurno, J., Ardianto, R., & Hanert, E. (2023). Integrated machine learning and GIS-based bathtub models to assess the future flood risk in the Kapuas River Delta, Indonesia. Journal of Hydroinformatics, 25(1), 113–125. https://doi.org/10.2166/hydro.2022.106
Saint-Amand, A., Lambrechts, J., Thomas, C. J., & Hanert, E. (2023). How fine is fine enough? Effect of mesh resolution on hydrodynamic simulations in coral reef environments. Ocean Modelling, 186, 102254. https://doi.org/10.1016/j.ocemod.2023.102254
Verhofstede, A., Dobbelaere, T., Harlay, J., & Hanert, E. (2023). Seychelles Plateau’s oil spill vulnerability. Marine Pollution Bulletin, 196, 115652. https://doi.org/10.1016/j.marpolbul.2023.115652
Patterson, R. G., Wolanski, E., Groom, R., Critchell, K., Playford, L., Grubert, M., Kennett, R., Tait, H., Udyawer, V., Lambrechts, J., & Campbell, H. A. (2023). Improving certainty in marine ecosystems: A biophysical modelling approach in the remote, data-limited Gulf of Carpentaria. Estuarine, Coastal and Shelf Science, 283, 108254. https://doi.org/10.1016/j.ecss.2023.108254
Hanert, E., Mohammed, A. V., Veerasingam, S., Dobbelaere, T., Vallaeys, V., & Vethamony, P. (2023). A multiscale ocean modelling system for the central Arabian/Persian Gulf: From regional to structure scale circulation patterns. Estuarine, Coastal and Shelf Science, 282, 108230. https://doi.org/10.1016/j.ecss.2023.108230
Sampurno, J., Vallaeys, V., Ardianto, R., & Hanert, E. (2022). Integrated hydrodynamic and machine learning models for compound flooding prediction in a data-scarce estuarine delta. Nonlinear Processes in Geophysics, 29(3), 301–315. https://doi.org/10.5194/npg-29-301-2022
Sampurno, J., Vallaeys, V., Ardianto, R., & Hanert, E. (2022). Modeling interactions between tides, storm surges, and river discharges in the Kapuas River delta. Biogeosciences, 19(10), 2741–2757. https://doi.org/10.5194/bg-19-2741-2022
Sampurno, J., Vallaeys, V., Ardianto, R., & Hanert, E. (2022). Modeling interactions between tides, storm surges, and river discharges in the Kapuas River delta. Biogeosciences, 19(10), 2741–2757. https://doi.org/10.5194/bg-19-2741-2022
Saint-Amand, A., Grech, A., Choukroun, S., & Hanert, E. (2022). Quantifying the environmental impact of a major coal mine project on the adjacent Great Barrier Reef ecosystems. Marine Pollution Bulletin, 179, 113556. https://doi.org/j.marpolbul.2022.113656
Dobbelaere, T., Holstein, D. M., Muller, E. M., Gramer, L. J., McEachron, L., Williams, S. D., & Hanert, E. (2022). Connecting the Dots: Transmission of Stony Coral Tissue Loss Disease From the Marquesas to the Dry Tortugas. Frontiers in Marine Science, 9, 778938. https://doi.org/10.3389/fmars.2022.778938
Vincent, D., Lambrechts, J., Tyler, R. H., Karatekin, Ö., Dehant, V., & Deleersnijder, É. (2022). A numerical study of the liquid motion in Titan’s subsurface ocean. Icarus, 388, 115219. https://doi.org/10.1016/j.icarus.2022.115219
Lopez‐Gamundi, C., Dobbelaere, T., Hanert, E., Harris, P. M., Eberli, G., & Purkis, S. J. (2022). Simulating sedimentation on the Great Bahama Bank – Sources, sinks and storms. Sedimentology, 69(7), 2693–2714. https://doi.org/10.1111/sed.13020
Dobbelaere, T., Curcic, M., Le Hénaff, M., & Hanert, E. (2022). Impacts of Hurricane Irma (2017) on wave-induced ocean transport processes. Ocean Modelling, 171, 101947. https://doi.org/10.1016/j.ocemod.2022.101947
Wolanski, E., & Hopper, C. (2022). Dams and climate change accelerate channel avulsion and coastal erosion and threaten Ramsar-listed wetlands in the largest Great Barrier Reef watershed. Ecohydrology & Hydrobiology, S1642359322000015. https://doi.org/10.1016/j.ecohyd.2022.01.001
Figueiredo, J., Thomas, C. J., Deleersnijder, E., Lambrechts, J., Baird, A. H., Connolly, S. R., & Hanert, E. (2022). Global warming decreases connectivity among coral populations. Nature Climate Change, 12(1), 83–87. https://doi.org/10.1038/s41558-021-01248-7
Le, H.-A., Lambrechts, J., Deleersnijder, E., Soares-Frazao, S., Gratiot, N., Ortleb, S., & Deleersnijder, E. (2020). Numerical modelling of flow dynamics in the Tonle Sap by means of a discontinuous Galerkin finite-element model. In W. Uijttewaal, M. J. Franca, D. Valero, V. Chavarrias, C. Ylla Arbós, R. Schielen, & A. Crosato (Eds.), River Flow 2020 (1st ed., pp. 1148–1154). CRC Press. https://doi.org/10.1201/b22619-160
Frys, C., Saint-Amand, A., Le Hénaff, M., Figueiredo, J., Kuba, A., Walker, B., Lambrechts, J., Vallaeys, V., Vincent, D., & Hanert, E. (2020). Fine-Scale Coral Connectivity Pathways in the Florida Reef Tract: Implications for Conservation and Restoration. Frontiers in Marine Science, 7. https://doi.org/10.3389/fmars.2020.00312
Le, H.-A., Lambrechts, J., Ortleb, S., Gratiot, N., Deleersnijder, E., & Soares-Frazão, S. (2020). An implicit wetting–drying algorithm for the discontinuous Galerkin method: application to the Tonle Sap, Mekong River Basin. Environmental Fluid Mechanics. https://doi.org/10.1007/s10652-019-09732-7
Le, H.-A., Gratiot, N., Santini, W., Ribolzi, O., Tran, D., Meriaux, X., Deleersnijder, E., & Soares-Frazão, S. (2020). Suspended sediment properties in the Lower Mekong River, from fluvial to estuarine environments. Estuarine, Coastal and Shelf Science, 233, 106522. https://doi.org/10.1016/j.ecss.2019.106522
Dobbelaere, T., Muller, Erinn, Gramer, Lewis, Holstein, Daniel, & Hanert, E. (2020). Coupled Epidemio-Hydrodynamic Modeling to Understand the Spread of a Deadly Coral Disease in Florida. Frontiers in Marine Science, 7, 16. https://doi.org/10.3389/fmars.2020.591881
Vincent, D., Lambrechts, J., Karatekin, Ö., Van Hoolst, T., Tyler, R. H., Dehant, V., & Deleersnijder, E. (2019). Normal modes and resonance in Ontario Lacus: a hydrocarbon lake of Titan. Ocean Dynamics. https://doi.org/10.1007/s10236-019-01290-2
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Delandmeter, P., Lambrechts, J., Marmorino, G. O., Legat, V., Wolanski, E., Remacle, J.-F., Chen, W., & Deleersnijder, E. (2017). Submesoscale tidal eddies in the wake of coral islands and reefs: satellite data and numerical modelling. Ocean Dynamics, 67(7), 897–913. https://doi.org/10.1007/s10236-017-1066-z
Pham Van, C., de Brye, B., Deleersnijder, E., Hoitink, A. J. F., Sassi, M., Spinewine, B., Hidayat, H., & Soares-Frazão, S. (2016). Simulations of the flow in the Mahakam river–lake–delta system, Indonesia. Environmental Fluid Mechanics, 16(3), 603–633. https://doi.org/10.1007/s10652-016-9445-4
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Le Bars, Y., Vallaeys, V., Deleersnijder, É., Hanert, E., Carrere, L., & Channelière, C. (2016). Unstructured-mesh modeling of the Congo river-to-sea continuum. Ocean Dynamics, 66(4), 589–603. https://doi.org/10.1007/s10236-016-0939-x
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