Exact answer known1D2D · mixedCandidate

Flooded yard draining into a pipe

Does the flood drain down to the right level, and all of it out of the pipe?

Test A12-011
Chen (2007)
Version 1.0.0

Right answer: Exact, from conservation · Chen (2007)
Results: 4 models · closest 5.8 % off · see them ↓
Must: leave the yard at the gully's lip (within 1 cm)

Sketch, not to scale.

What happens

A walled yard holds 30 cm of water that drains through a gully, raised 5 cm above the floor, into a pipe too small to take it all at once. The water above the gully's lip must leave through the pipe; the 5 cm below it must stay.

Why it matters

How quickly and how completely floodwater drains back into sewers decides how long streets stay flooded.

A good model must

leave the yard at the gully's lip (within 1 cm)
send 225 m³ out of the pipe (within 2 %)
end with the water accounted for (0.5 %)

Exact answer and models

Water balance over time

Water stored on the surface and in the pipes, minus what came in, plus what went out: zero for a model that neither makes nor loses water. Shaded: the pass limit at the end of the run, ±1.4 m³ (0.5 %).

Point at the chart to read every model's value; click a name to hide or show it.

Water discharged at the outfall

By the end, exactly 225 m³ must have left through the pipe.

Point at the chart to read every model's value; click a name to hide or show it.

How models did

In rank order: by each model's percent difference from the right answer, the largest over the test's accuracy checks (lower is better; results within 10 % of each other share a rank). Mass error, timing and NSE are shown beside it, not folded in. Each model runs the same inputs. Compare them in the results viewer →

Rank	Model	Difference	Largest difference in	Mass error	Run time
1	SWMM + ANUGA coupled 1D/2D	5.8 %	Final level	<0.01 %	45.0 s
2	HEC-RAS 7.0 pipe networks · 1D/2D	16 %	Final level	1.4 %	17.8 s
3	OpenSWMM 6 coupled 1D/2D	24 %	Final level	0.55 %	3.5 s
4	OpenSWMM 6 coupled 1D/2D · cross mesh	27 %	Final level	0.31 %	8.1 s

SWMM + ANUGA

EPA SWMM 5.2.4 pipes coupled to an ANUGA 4.0.1 surface by the suite's own explicit coupler (1 s weir/orifice exchange at the manholes): a worked example of a 1D/2D model, not a product

#1 5.8 % off

Run time, finest grid: 45.0 s · AMD EPYC 9V74 80-Core Processor, 2 cores, 15.6 GB, Linux 6.17.0-1022-azure (GitHub Actions (github-hosted, ubuntu24))

Settings: suite coupler: explicit 1 s weir/orifice exchange (Chen et al. 2007), levelling-limited

Final level

• 2.9 mm off

5.8 % of the 5 cm crest depth

Water discharged

• 1.2 % off

Water balance

· 0.0049 % off

conservation, reported beside the score

While the pipe runs full, SWMM's reported pipe and manhole volumes exceed its own balance by up to 3.1 m³ (1.2 %), which disappears as the pipe empties: its end-of-run continuity error is 0.000 %.

Scored with method 3.0 · Score card: SWMM–ANUGA coupled (SWMM 5.2.4 + ANUGA 4.0.1)

Run it yourself

SWMM–ANUGA coupled (SWMM 5.2.4 + ANUGA 4.0.1) · runs on Linux · produced by scripts/run_coupled_cases.py in open-solvers.yml.

git clone https://github.com/scott-jeffers/benchmark1d2d && cd benchmark1d2d
git checkout 71dc10fc07a9
conda create -n anuga -c conda-forge anuga=4.0.1 python=3.12 pip scipy
conda activate anuga
python -m pip install -e ".[dev]" swmm-toolkit==0.17.0
python scripts/run_coupled_cases.py A12-011

The model files the suite wrote for this run (.zip, 0.77 KB): the exact inputs the solver read (one folder per grid, where the test has several), with their SHA-256.

The suite's own coupler moves the water; its code is the script.

The test itself (inputs, exact answer, checks): A12-011.zip. Check the score card with benchmark1d2d verify-card: its signature by the suite's public development key shows the card has not changed since it was written, not who wrote it.

HEC-RAS 7.0

HEC-RAS 7.0.1 with its own storm-drain pipe networks: nodes, conduits and top inlets joined to a 2D SWE-ELM surface, HEC-RAS's defaults; the network is written into the geometry file headless and HEC-RAS's compute builds its cells. HEC-RAS 7.0.1 leaves the pipe solver's settings out of what it hands its engine for these headless plans, so the suite adds HEC-RAS's defaults and runs the engine again (the run time includes both passes)

#2 16 % off

Run time, finest grid: 17.8 s · AMD EPYC 7763 64-Core Processor, 2 cores, 16 GB, Windows 2025Server (GitHub Actions (github-hosted, win25-vs2026))

Settings: hecras pipe network written into the geometry HDF (nodes, conduits, top inlets), 2D SWE-ELM surface, defaults

Final level

• 8.1 mm off

16 % of the 5 cm crest depth

Water discharged

• 1.6 % off

Water balance

· 1.4 % off

conservation, reported beside the score

The yard drains to 58 mm, 8 mm above the 5 cm gully crest, and 221.3 of the 225 m³ leaves by the outfall (1.6 % short). The balance gains 3.7 m³ (1.4 %); HEC-RAS's own report shows 0.88 %.

Scored with method 3.0 · Score card: HEC-RAS 7.0.1 pipe networks 1D/2D

Run it yourself

HEC-RAS 7.0.1 pipe networks 1D/2D · runs on Windows · produced by scripts/run_hecras_pipes.py in hecras.yml.

git clone https://github.com/scott-jeffers/benchmark1d2d && cd benchmark1d2d
git checkout 71dc10fc07a9
# Windows: HEC-RAS 7.0.1 from HEC (HEC-RAS_701_Setup.exe, SHA-256 1FE76297…3CEE73), silent install /S /v/qn
python -m pip install -e ".[dev]" "ras-commander==0.106.1" h5py psutil pywin32 pillow pythonnet tifffile
python scripts/run_hecras_pipes.py A12-011 --accept-hec-terms

The model files the suite wrote for this run (.zip, 116 KB): the exact inputs the solver read (one folder per grid, where the test has several), with their SHA-256.

The pipe network (nodes, conduits, top inlets) is written into the geometry HDF; HEC-RAS's preprocessor builds its cells.

OpenSWMM 6

OpenSWMM Engine v6 (pre-release) with its own 1D/2D coupling: a local-inertial 2D surface with each manhole tied to a mesh vertex, run with its defaults; the surface is the case's grid with each square cut into two triangles

#3 24 % off

Run time, finest grid: 3.5 s · INTEL(R) XEON(R) PLATINUM 8573C, 2 cores, 15.6 GB, Linux 6.17.0-1022-azure (GitHub Actions (github-hosted, ubuntu24))

Settings: OpenSWMM's own 1D/2D coupling, defaults; vertex-coupled manholes; two triangles per grid square

Final level

• 1.2 cm off

24 % of the 5 cm crest depth

Water discharged

• 4.1 % off

Water balance

· 0.55 % off

conservation, reported beside the score

The yard drains 12 mm below the 5 cm gully crest, so 4 % too much leaves by the outfall. OpenSWMM's exchange is meant to close at the crest, and a still pond 1 cm below it does not drain, but here it kept draining at 0.035–0.045 m³/s for about ten minutes while both the surface and the manhole head were below the crest. The 1.5 m³ missing from the balance is the network's own continuity error (0.62 % in its report).

Scored with method 3.0 · Score card: OpenSWMM Engine v6 1D/2D (two triangles per grid square) 6.0.0a4.dev1

Run it yourself

OpenSWMM Engine v6 1D/2D (two triangles per grid square) 6.0.0a4.dev1 · runs on Linux · produced by scripts/run_openswmm_coupled.py in open-solvers.yml.

git clone https://github.com/scott-jeffers/benchmark1d2d && cd benchmark1d2d
git checkout 71dc10fc07a9
python -m pip install -e ".[dev]" swmm-toolkit==0.17.0
python -m venv .venv-openswmm
.venv-openswmm/bin/python -m pip install "openswmm==6.0.0a4.dev1" numpy
python scripts/run_openswmm_coupled.py --openswmm-python .venv-openswmm/bin/python --mesh diagonal A12-011

The model files the suite wrote for this run (.zip, 12 KB): the exact inputs the solver read (one folder per grid, where the test has several), with their SHA-256.

OpenSWMM 6

The same OpenSWMM 6 1D/2D model on a finer-cut mesh: each grid square cut into four triangles by both diagonals (the mesh the suite's ANUGA surface uses)

#4 27 % off

Run time, finest grid: 8.1 s · INTEL(R) XEON(R) PLATINUM 8573C, 2 cores, 15.6 GB, Linux 6.17.0-1022-azure (GitHub Actions (github-hosted, ubuntu24))

Settings: OpenSWMM's own 1D/2D coupling, defaults; vertex-coupled manholes; four triangles per grid square

Final level

• 1.4 cm off

27 % of the 5 cm crest depth

Water discharged

• 5.1 % off

Water balance

· 0.31 % off

conservation, reported beside the score

As on the two-triangle mesh: the yard drains 14 mm below the crest and 5 % too much leaves by the outfall; the exchange keeps running below the crest while the yard drains. The balance closes (0.31 % short, the network's own continuity error).

Scored with method 3.0 · Score card: OpenSWMM Engine v6 1D/2D (four triangles per grid square) 6.0.0a4.dev1

Run it yourself

OpenSWMM Engine v6 1D/2D (four triangles per grid square) 6.0.0a4.dev1 · runs on Linux · produced by scripts/run_openswmm_coupled.py in open-solvers.yml.

git clone https://github.com/scott-jeffers/benchmark1d2d && cd benchmark1d2d
git checkout 71dc10fc07a9
python -m pip install -e ".[dev]" swmm-toolkit==0.17.0
python -m venv .venv-openswmm
.venv-openswmm/bin/python -m pip install "openswmm==6.0.0a4.dev1" numpy
python scripts/run_openswmm_coupled.py --openswmm-python .venv-openswmm/bin/python --mesh cross A12-011

The model files the suite wrote for this run (.zip, 22 KB): the exact inputs the solver read (one folder per grid, where the test has several), with their SHA-256.

Not run yet: TUFLOW, InfoWorks ICM, MIKE+, PCSWMM 2D, Flood Modeller

Run it and add yours →

Status of this test

Candidate. To become frozen it needs: two independent codes pass; maintainer review recorded.

Download inputs (.zip)Check your results in the browser Cite this test View on GitHub

Technical details for reviewers Checks, reference, inputs, sources

Checks and why each limit was chosen

Check	Difference measured as a percentage of	Latest	Why this check
final_level expected_state_error of h · in the score	of the 5 cm crest depth	–	Yard level within 1 cm of the crest after two hours: the last of the water over a crest drains slowly (as a weir it slows with the head to the 3/2), so a coupling with any reasonable exchange law is within a few millimetres.
discharged_volume expected_state_error of V · in the score	already a percentage	–	Outfall volume within 2 % of 225 m³: the water above the crest has gone through the pipe.
water_balance continuity_error of volume · conservation, beside the score	already a percentage	–	By the end of the run, the water stored on the surface and in the pipes has changed by exactly what came in minus what went out. A coupling that moves water between the two models must not make or lose any; each engine's own continuity error is allowed within this limit.
convergence not applicable	–	–	Scored on exact states that follow from conservation (exchanged and discharged volumes, settled levels): they do not depend on the grid.

Reference

Exact states that follow from the inputs by conservation and hydrostatics: exchanged and discharged volumes, settled levels and steady flows, plus the model's own volume balance.

Expected state	Value	Why it must hold
final_level h at P1,P2	0.05 m	Water drains until the yard level reaches the gully crest, 0.05 m above the flat floor; nothing below the crest can enter.
discharged_volume V at outflow	225 m3	Initial 270 m³ (900 m² × 0.3 m) less the 45 m³ held below the crest (900 m² × 0.05 m); the pipe drains freely, so it holds none at the end.

Promotion checklist

Only frozen tests have fixed inputs and answers. This list is computed from the manifest and the published score cards; the rules are in the method.

✓Data licence verifiedfor candidateanalytic-public
✓All inputs availablefor candidateall committed or fetched by SHA-256
✓Reference (truth) availablefor candidateexact states from conservation
✓Every tolerance justifiedfor candidateeach gating criterion has a rationale
✓A published run passesfor frozen1 passing score card(s)
✓Order of accuracy shownfor frozennot applicable: Scored on exact states that follow from conservation (exchanged and discharged volumes, settled levels): they do not depend on the grid.
✗Two independent codes passfor frozenpassing codes: SWMM–ANUGA coupled — needs a second, independently written solver or engine
✗Maintainer review recordedfor frozenno maintainer review recorded

Inputs

File	Role	Format	SHA-256	Get it
`inputs/coupling.json`	coupling	json	`a94ee75f36fa…`	Download

About this test

Physics

A walled 30 × 30 m yard with a flat floor holds 0.3 m of water (270 m³). A gully at its centre, whose crest stands 0.05 m above the floor, drains into manhole M1 and a 0.3 m, 100 m pipe falling 1 m to a free outfall.

Final level: the water above the crest drains; the 5 cm below it cannot. The yard settles at the crest level, 0.05 m.
Discharged volume: \(270 - 900 \times 0.05 = 225\) m³ leaves by the outfall (the pipe drains freely and holds nothing at the end).

At first the gully could take far more than the pipe carries, so the manhole surcharges and the inflow is set by the pipe; at the end the last centimetres drain slowly over the crest (a weir slows as the head to the 3/2), so after two hours the level is a few millimetres above the crest for any reasonable exchange law.

What it checks

Surface-to-network exchange limited by a surcharged pipe, the crest cut-off, and the coupled water balance.

Citation

Chen, A. S., Djordjević, S., Leandro, J., and Savić, D. A. (2007). The urban inundated area: a coupled 1D/2D model for the interaction between sewer and surface. Proc. NOVATECH 2007. Rubinato, M., et al. (2017). Experimental calibration and validation of sewer/surface flow exchange equations in steady and unsteady flow conditions. J. Hydrol., 552, 421–432.

Sources

Chen, A. S., Djordjević, S., Leandro, J., Savić, D. A. (2007). The urban inundated area: a coupled 1D/2D model for the interaction between sewer and surface. www.researchgate.net/publication/257306339
Rubinato, M., Martins, R., Kesserwani, G., Leandro, J., Djordjević, S., Shucksmith, J. (2017). Experimental calibration and validation of sewer/surface flow exchange equations in steady and unsteady flow conditions. doi:10.1016/j.jhydrol.2017.06.024

Test A12-011_flood_draining_into_pipe · version 1.0.0 · data licence analytic-public