Well-Balanced Subcell Limiting for Discontinuous Galerkin Discretizations of the Shallow-Water Equations
Pith reviewed 2026-05-08 19:15 UTC · model grok-4.3
The pith
Reformulating the shallow water equations allows staggered fluxes that stay exactly balanced under node-wise DG limiting.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that a novel flux-differencing formulation for non-conservative systems constructs staggered DG fluxes whose non-conservative contributions vanish individually at equilibrium. This is achieved by introducing a reformulation of the shallow water equations in which the source term is proportional to the gradient of the total water height, allowing the design of fluxes that preserve equilibrium locally at the node level and thereby enable arbitrary nodal blending with low-order FV fluxes. The resulting DG/FV method is high-order accurate, robust, and exactly well-balanced under node-wise limiting, and the same construction applies to a broader class of nonlinear balance-law
What carries the argument
Staggered DG fluxes in local-times-jump form for non-conservative terms, built from the reformulation that makes the source term proportional to the gradient of total water height.
If this is right
- The hybrid method retains high-order accuracy under node-wise limiting.
- Steady states with variable bottom topography are preserved exactly at the discrete nodes.
- The scheme remains robust for dam-break flows, wet-dry fronts, and obstacle interactions.
- The construction extends to other nonlinear systems of balance laws.
Where Pith is reading between the lines
- Practical flood and coastal models could use fewer special equilibrium fixes.
- Similar staggered flux constructions may apply to other non-conservative hyperbolic systems such as those with gravity or chemistry source terms.
- The node-level exactness could simplify adaptive mesh refinement or parallel implementations.
Load-bearing premise
The reformulation of the shallow water equations in which the source term is proportional to the gradient of the total water height allows construction of staggered fluxes that preserve equilibrium locally at the node level.
What would settle it
A lake-at-rest test on non-flat topography in which the limited scheme produces non-zero velocities or height changes after many time steps.
Figures
read the original abstract
High-order discontinuous Galerkin (DG) methods equipped with subcell finite-volume (FV) limiters provide an efficient framework for the simulation of nonlinear hyperbolic balance laws featuring shocks and complex flow structures. However, for systems with non-conservative terms, the design of hybrid DG/FV schemes that simultaneously guarantee high-order accuracy, robustness, and well-balancedness remains challenging. In particular, for the shallow water equations with variable bottom topography, standard flux-differencing formulations combined with node-wise subcell limiting generally destroy the well-balanced property, even if both the underlying DG and FV methods are individually well-balanced. In this work, we propose a novel flux-differencing formulation for non-conservative systems that enables node-wise subcell limiting while preserving steady states exactly. The key idea is to construct staggered DG fluxes whose non-conservative contributions are in local-times-jump form and vanish individually at equilibrium. To achieve this, we introduce a reformulation of the shallow water equations in which the source term is proportional to the gradient of the total water height. This reformulation allows the design of staggered fluxes that preserve equilibrium locally at the node level, thereby enabling arbitrary nodal blending with low-order FV fluxes. The resulting DG/FV method is high-order accurate, robust, and exactly well-balanced under node-wise limiting. Numerical experiments, including two-dimensional dam-break configurations with wet/dry fronts and complex obstacle interactions, demonstrate the improved stability and accuracy of the proposed approach. Although this work focuses on the shallow water equations, the well-balanced hybrid DG/FV methods developed here are applicable to a broader class of nonlinear systems of balance laws.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes a reformulation of the shallow-water equations in which the source term is made proportional to the gradient of the total height H = h + b. This permits construction of staggered DG fluxes whose non-conservative contributions appear in local-times-jump form and therefore vanish nodewise at equilibrium states (constant H, u = 0). The resulting hybrid DG/FV scheme with arbitrary node-wise subcell limiting is shown to remain exactly well-balanced while retaining high-order accuracy and robustness. Numerical experiments on two-dimensional dam-break problems with wet/dry fronts and obstacle interactions are presented to illustrate the properties.
Significance. If the exact well-balanced property under arbitrary nodal blending holds, the work resolves a recognized difficulty in hybrid high-order schemes for balance laws: standard flux-differencing formulations lose equilibrium preservation once subcell limiting is introduced. The reformulation and staggered-flux construction supply a parameter-free mechanism that preserves the steady-state cancellation locally at each node, independent of the blending weights. This is a concrete advance for long-time simulations over variable topography and extends in principle to other non-conservative balance laws.
minor comments (4)
- Abstract: the phrase 'local-times-jump form' is used without a parenthetical reference to the equation or subsection where the form is defined; adding such a pointer would improve immediate readability for readers unfamiliar with the construction.
- Section 3 (flux construction): the equivalence between the reformulated system and the original shallow-water equations is asserted but the algebraic steps that recover the standard momentum source term are not written out; a short displayed identity would remove any doubt.
- Numerical experiments: the order-of-accuracy study for the hybrid scheme on a smooth, non-equilibrium test case is not reported; inclusion of at least one such table (e.g., L2 errors versus polynomial degree) would directly support the high-order claim.
- Figure 4 (wet/dry dam-break): the color scale and contour levels are not stated in the caption; explicit mention of the plotted quantity (e.g., water height or total H) and the range would aid interpretation.
Simulated Author's Rebuttal
We thank the referee for the positive assessment and recommendation of minor revision. The referee's summary correctly identifies the core contribution: a reformulation of the shallow-water equations that places the source term proportional to the gradient of total height H, enabling staggered DG fluxes whose non-conservative terms vanish nodewise at equilibrium and thereby permit arbitrary node-wise subcell limiting while preserving exact well-balancedness. We appreciate the recognition that this addresses a known difficulty in hybrid high-order schemes for balance laws.
Circularity Check
No significant circularity identified
full rationale
The derivation begins with an explicit reformulation of the shallow-water equations that makes the source term proportional to the gradient of total height H = h + b. This is used to construct staggered DG fluxes in local-times-jump form whose non-conservative contributions vanish nodewise at equilibrium (constant H, u = 0). The hybrid DG/FV update is then obtained by arbitrary nodal blending with a low-order well-balanced FV scheme; the equilibrium preservation follows directly from the local vanishing property and does not rely on any fitted parameter, self-referential definition, or load-bearing self-citation. The paper states that the reformulation is equivalent to the original SWE and demonstrates the property through explicit flux differencing and numerical tests. No step in the chain reduces by construction to its own inputs.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Reformulation of the shallow water equations makes the source term proportional to the gradient of total water height.
Forward citations
Cited by 1 Pith paper
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Reference graph
Works this paper leans on
-
[1]
Z. J. Wang, K. Fidkowski, R. Abgrall, F. Bassi, D. Caraeni, A. Cary, H. Deconinck, R. Hartmann, K. Hillewaert, H. T. Huynh, N. Kroll, G.May,P.-O.Persson,B.vanLeer,M.Visbal, High-orderCFDmethods:currentstatusandperspective, InternationalJournalforNumerical Methods in Fluids 72 (2013) 811–845
work page 2013
-
[2]
B. Cockburn, G. E. Karniadakis, C.-W. Shu, The Development of Discontinuous Galerkin Methods, Discontinuous Galerkin Methods 11 (2000) 3–50
work page 2000
-
[3]
F. Hindenlang, G. J. Gassner, C. Altmann, A. Beck, M. Staudenmaier, C. D. Munz, Explicit discontinuous Galerkin methods for unsteady problems, Computers and Fluids 61 (2012) 86–93
work page 2012
-
[4]
H.Ranocha,M.Schlottke-Lakemper,J.Chan,A.M.Rueda-Ramírez,A.R.Winters,F.Hindenlang,G.J.Gassner, Efficientimplementationof modernentropystableandkineticenergypreservingdiscontinuousGalerkinmethodsforconservationlaws, arXivpreprintarXiv:2112.10517 (2021). Rueda-Ramírez et al.:Preprint submitted to ElsevierPage 19 of 25 Well-Balanced Subcell Limiting for DG Di...
-
[5]
T. C. Fisher, M. H. Carpenter, High-order entropy stable finite difference schemes for nonlinear conservation laws: Finite domains, Journal of Computational Physics 252 (2013) 518–557
work page 2013
-
[6]
M. H. Carpenter, T. C. Fisher, E. J. Nielsen, S. H. Frankel, Entropy stable spectral collocation schemes for the Navier-Stokes Equations: Discontinuous interfaces, SIAM Journal on Scientific Computing 36 (2014) B835–B867
work page 2014
-
[7]
G. J. Gassner, A Skew-Symmetric Discontinuous Galerkin Spectral Element Discretization and Its Relation to SBP-SAT Finite Difference Methods, SIAM Journal on Scientific Computing 35 (2013) A1233–A1253
work page 2013
-
[8]
G. J. Gassner, A. R. Winters, D. A. Kopriva, Split form nodal discontinuous Galerkin schemes with summation-by-parts property for the compressible Euler equations, Journal of Computational Physics 327 (2016) 39–66
work page 2016
-
[9]
M. Bohm, A. R. Winters, G. J. Gassner, D. Derigs, F. Hindenlang, J. Saur, An entropy stable nodal discontinuous Galerkin method for the resistive MHD equations. Part I: Theory and numerical verification, Journal of Computational Physics 1 (2018) 1–35
work page 2018
-
[10]
N.Wintermeyer,A.R.Winters,G.J.Gassner,D.A.Kopriva, AnentropystablenodaldiscontinuousGalerkinmethodforthetwodimensional shallow water equations on unstructured curvilinear meshes with discontinuous bathymetry, Journal of Computational Physics 340 (2017) 200–242
work page 2017
-
[11]
A.M.Rueda-Ramírez,F.J.Hindenlang,J.Chan,G.J.Gassner, Entropy-stableGausscollocationmethodsforidealmagneto-hydrodynamics, Journal of Computational Physics 475 (2023) 111851
work page 2023
-
[12]
A. M. Rueda-Ramírez, A. Sikstel, G. J. Gassner, An entropy-stable discontinuous Galerkin discretization of the ideal multi-ion magnetohy- drodynamics system, Journal of Computational Physics 523 (2025) 113655
work page 2025
-
[13]
F.Coquel,C.Marmignon,P.Rai,F.Renac,Anentropystablehigh-orderdiscontinuousGalerkinspectralelementmethodfortheBaer-Nunziato two-phase flow model, Journal of Computational Physics 431 (2021) 110135
work page 2021
-
[14]
M. Waruszewski, J. E. Kozdon, L. C. Wilcox, T. H. Gibson, F. X. Giraldo, Entropy stable discontinuous Galerkin methods for balance laws in non-conservative form: Applications to the Euler equations with gravity, Journal of Computational Physics 468 (2022) 111507
work page 2022
-
[15]
S. Hennemann, A. M. Rueda-Ramírez, F. J. Hindenlang, G. J. Gassner, A provably entropy stable subcell shock capturing approach for high order split form DG for the compressible Euler equations, Journal of Computational Physics (2020) 109935
work page 2020
-
[16]
Part II: Subcell finite volume shock capturing, volume 444, 2021
A.M.Rueda-Ramírez,S.Hennemann,F.J.Hindenlang,A.R.Winters,G.J.Gassner,AnentropystablenodaldiscontinuousGalerkinmethod for the resistive MHD equations. Part II: Subcell finite volume shock capturing, volume 444, 2021
work page 2021
-
[17]
A.M.Rueda-Ramírez,W.Pazner,G.J.Gassner, SubcelllimitingstrategiesfordiscontinuousGalerkinspectralelementmethods, Computers & Fluids 247 (2022) 105627
work page 2022
- [18]
-
[19]
A. Mateo-Gabín, A. M. Rueda-Ramírez, E. Valero, G. Rubio, A flux-differencing formulation with Gauss nodes, Journal of Computational Physics 489 (2023) 112298
work page 2023
-
[20]
D. Kuzmin, Monolithic convex limiting for continuous finite element discretizations of hyperbolic conservation laws, Computer Methods in Applied Mechanics and Engineering 361 (2020) 112804
work page 2020
-
[21]
J.-L. Guermond, B. Popov, I. Tomas, Invariant domain preserving discretization-independent schemes and convex limiting for hyperbolic systems, Computer Methods in Applied Mechanics and Engineering 347 (2019) 143–175
work page 2019
-
[22]
W. Pazner, Sparse Invariant Domain Preserving Discontinuous Galerkin Methods With Subcell Convex Limiting, arXiv (2020)
work page 2020
-
[23]
Y.Lin,J.Chan, HighorderentropystablediscontinuousGalerkinspectralelementmethodsthroughsubcelllimiting, JournalofComputational Physics 498 (2024) 112677
work page 2024
-
[24]
H. Ranocha, Shallow water equations: Split-form, entropy stable, well-balanced, and positivity preserving numerical methods, GEM- International Journal on Geomathematics 8 (2017) 85–133
work page 2017
-
[25]
A. R. Winters, P. Ersing, H. Ranocha, M. Schlottke-Lakemper, TrixiShallowWater.jl: Shallow water simulations with Trixi.jl,https: //github.com/trixi-framework/TrixiShallowWater.jl, 2025
work page 2025
-
[26]
P.Ersing,S.Goldberg,A.R.Winters, Entropystablehydrostaticreconstructionschemesforshallowwatersystems, JournalofComputational Physics (2025) 113802
work page 2025
-
[27]
U. S. Fjordholm, S. Mishra, E. Tadmor, Well-balanced and energy stable schemes for the shallow water equations with discontinuous topography, Journal of Computational Physics 230 (2011) 5587–5609
work page 2011
-
[28]
A. M. Rueda-Ramírez, G. J. Gassner, A flux-differencing formula for split-form summation by parts discretizations of non-conservative systems: Applications to subcell limiting for magneto-hydrodynamics, Journal of Computational Physics 496 (2024) 112607
work page 2024
- [29]
-
[30]
H. Ranocha, M. Schlottke-Lakemper, A. R. Winters, E. Faulhaber, J. Chan, G. J. Gassner, Adaptive numerical simulations with Trixi.jl: A case study of Julia for scientific computing, Proceedings of the JuliaCon Conferences 1 (2022) 77
work page 2022
-
[31]
M. Schlottke-Lakemper, A. R. Winters, H. Ranocha, G. J. Gassner, A purely hyperbolic discontinuous Galerkin approach for self-gravitating gas dynamics, Journal of Computational Physics 442 (2021) 110467
work page 2021
-
[32]
M. Schlottke-Lakemper, G. J. Gassner, H. Ranocha, A. R. Winters, J. Chan, A. Rueda-Ramírez, Trixi.jl: Adaptive high-order numerical simulations of hyperbolic PDEs in Julia,https://github.com/trixi-framework/Trixi.jl, 2025
work page 2025
-
[33]
K.G.Powell,P.L.Roe,T.J.Linde,T.I.Gombosi,D.L.DeZeeuw, ASolution-AdaptiveUpwindSchemeforIdealMagnetohydrodynamics, Journal of Computational Physics 154 (1999) 284–309
work page 1999
- [34]
-
[35]
D. Derigs, A. R. Winters, G. J. Gassner, S. Walch, A novel averaging technique for discrete entropy-stable dissipation operators for ideal MHD, Journal of Computational Physics 330 (2017) 624–632. Rueda-Ramírez et al.:Preprint submitted to ElsevierPage 20 of 25 Well-Balanced Subcell Limiting for DG Discretization of the SWE
work page 2017
-
[36]
M. R. Baer, J. W. Nunziato, A two-phase mixture theory for the deflagration-to-detonation transition (DDT) in reactive granular materials, International journal of multiphase flow 12 (1986) 861–889
work page 1986
-
[37]
P. Chandrashekar, M. Zenk, Well-balanced nodal discontinuous Galerkin method for Euler equations with gravity, Journal of Scientific Computing 71 (2017) 1062–1093
work page 2017
-
[38]
W. Chen, Y. Yu, X. Wang, Reducing the computational requirements of the differential quadrature method, Numerical Methods for Partial Differential Equations: An International Journal 12 (1996) 565–577
work page 1996
-
[39]
T.C.Fisher,M.H.Carpenter,J.Nordström,N.K.Yamaleev,C.Swanson, Discretelyconservativefinite-differenceformulationsfornonlinear conservation laws in split form: Theory and boundary conditions, Journal of Computational Physics 234 (2013) 353–375
work page 2013
-
[40]
F. Renac, Entropy stable DGSEM for nonlinear hyperbolic systems in nonconservative form with application to two-phase flows, Journal of Computational Physics 382 (2019) 1–26
work page 2019
-
[41]
A. I. Vol’pert, The spaces BV and quasilinear equations, Mathematics of the USSR-Sbornik 2 (1967) 225
work page 1967
-
[42]
A. M. Rueda-Ramírez, G. J. Gassner, A Subcell Finite Volume Positivity-Preserving Limiter for DGSEM Discretizations of the Euler Equations, in: WCCM-ECCOMAS2020, pp. 1–12
-
[43]
C.-W. Shu, S. Osher, Efficient implementation of essentially non-oscillatory shock-capturing schemes, Journal of computational physics 77 (1988) 439–471
work page 1988
-
[44]
C.Geuzaine,J.-F.Remacle, Gmsh:A3-Dfiniteelementmeshgeneratorwithbuilt-inpre-andpost-processingfacilities, Internationaljournal for numerical methods in engineering 79 (2009) 1309–1331
work page 2009
-
[45]
D. A. Kopriva, A. R. Winters, M. Schlottke-Lakemper, J. A. Schoonover, H. Ranocha, HOHQMesh: An all quadrilateral/hexahedral unstructured mesh generator for high order elements, Journal of Open Source Software 9 (2024) 7476
work page 2024
-
[46]
D. A. Kopriva, A. R. Winters, M. Schlottke-Lakemper, H. Ranocha, HOHQMesh.jl: A Julia frontend to the Fortran-based HOHQMesh mesh generator for high order elements,https://github.com/trixi-framework/HOHQMesh.jl, 2024
work page 2024
- [47]
-
[48]
S.Danisch,J.Krumbiegel, Makie.jl:Flexiblehigh-performancedatavisualizationforJulia, JournalofOpenSourceSoftware6(2021)3349
work page 2021
-
[49]
Well-balancedsubcelllimitingfordiscontinuous Galerkin discretizations of the shallow-water equations
A.M.Rueda-Ramírez,P.Ersing,A.R.Winters,G.J.Gassner,Reproducibilityrepositoryfor"Well-balancedsubcelllimitingfordiscontinuous Galerkin discretizations of the shallow-water equations",https://doi.org/10.5281/zenodo.19913123, 2026
-
[50]
S. T. Zalesak, Fully multidimensional flux-corrected transport algorithms for fluids, Journal of Computational Physics 31 (1979) 335–362
work page 1979
- [51]
- [52]
-
[53]
C.Lohmann,D.Kuzmin,J.N.Shadid,S.Mabuza, Flux-correctedtransportalgorithmsforcontinuousGalerkinmethodsbasedonhighorder Bernstein finite elements, Journal of Computational Physics 344 (2017) 151–186
work page 2017
-
[54]
P.-O.Persson,J.Peraire, Sub-CellShockCapturingforDiscontinuousGalerkinMethods, 44thAIAAAerospaceSciencesMeetingandExhibit (2006) 1–13
work page 2006
-
[55]
S. Soares-Frazão, Y. Zech, Experimental study of dam-break flow against an isolated obstacle, Journal of Hydraulic Research 45 (2007) 27–36
work page 2007
-
[56]
A. Chertock, S. Cui, A. Kurganov, T. Wu, Well-balanced positivity preserving central-upwind scheme for the shallow water system with friction terms, International Journal for numerical methods in fluids 78 (2015) 355–383
work page 2015
- [57]
-
[58]
B.M.Ginting, Central-upwindschemefor2Dturbulentshallowflowsusinghigh-resolutionmesheswithscalablewallfunctions, Computers & Fluids 179 (2019) 394–421
work page 2019
-
[59]
L.Cea,E.Bladé,Asimpleandefficientunstructuredfinitevolumeschemeforsolvingtheshallowwaterequationsinoverlandflowapplications, Water resources research 51 (2015) 5464–5486
work page 2015
-
[60]
J. Hou, Q. Liang, F. Simons, R. Hinkelmann, A 2D well-balanced shallow flow model for unstructured grids with novel slope source term treatment, Advances in Water Resources 52 (2013) 107–131
work page 2013
-
[61]
J. L. Ayog, G. Kesserwani, J. Shaw, M. K. Sharifian, D. Bau, Second-order discontinuous Galerkin flood model: Comparison with industry- standard finite volume models, Journal of Hydrology 594 (2021) 125924
work page 2021
- [62]
-
[63]
arXiv preprint arXiv:2508.21226 (2025)
B.Christner,J.Chan, Entropystablefinitedifferencemethodsviaentropycorrectionartificialviscosityandknapsacklimiting, arXivpreprint arXiv:2508.21226 (2025). Appendices We describe a generic 2D version of the node-wise subcell limiting scheme in Appendix A. Specific details regarding the 2D shallow water equations are provided in Appendix B. Finally, we desc...
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