GUI

Hydra’s desktop application lets you load, run, and explore simulations without using the command line. It is the front end to every available Hydra engine: water distribution models can be created and edited here; drainage models start from an imported SWMM model and are then edited, run and explored.

Download and Install

Download the installer for your platform from the releases page.

macOS: “Hydra is damaged and can’t be opened”

Hydra GUI macOS releases are notarised. If Gatekeeper still shows this warning after dragging Hydra to Applications, run this once in Terminal:

xattr -cr /Applications/Hydra.app

Then open the app normally.

Basic Workflow

Hydra organises work into projects. Each project holds a network model and one or more scenarios: independent parameter sets you can run and compare.

1. Create a project. On the Projects screen, click New Project. The wizard asks for the engine first, then project details, then a review. Choosing the engine up front is deliberate: .inp belongs to both EPANET and SWMM, so the file extension cannot decide the modelling domain on your behalf. With Water Distribution chosen, either import an existing EPANET .inp file or start from a blank network. Urban Drainage has no blank-network option: choose it and import a SWMM .inp. That is a limit on starting from nothing, not on editing: a drainage model is edited like any other once it is open. Hydra cannot represent a network with no elements at all, so a blank project opens onto a smallest-valid starter model, and only water distribution has one.
2. Configure and run. Press ⌘R (macOS) or Ctrl+R (Windows/Linux), or click the Simulate button in the scenario strip at the bottom of the screen. Select which scenarios to run and confirm.
3. Explore results. After the simulation completes, the network map updates with colour-coded results. Click any node or link to inspect its time-series values (pressure, head, flow, velocity, water age, etc.). Use the timeline scrubber to step through reporting periods.

Press ⌘K (macOS) or Ctrl+K (Windows/Linux) at any time to open the command palette, which lists every action (running simulations, switching views, imports and exports), filtered as you type by substring match. Type # in the palette to find any node or link by ID and zoom to it.

Keyboard Shortcuts

Beyond ⌘R (simulate), ⌘K (command palette), and ⌘Z / ⇧⌘Z (undo/redo), the app has shortcuts for navigation and the canvas. Press ? at any time to open the in-app cheatsheet, or see the full Keyboard Shortcuts reference. Common ones (⌘ on macOS, Ctrl elsewhere):

On the canvas, single-key tools select elements and add or measure geometry (select, edit, add node, add link, measure), and annotations can be placed on the map.

Editing the Network

The Editor tab holds one table per kind of element, listed down a rail on the left. Both engines are edited here and the screen is the same for each: the rail, the columns, the units and which values may be changed all come from the engine itself, so a water distribution model and a drainage model are edited the same way rather than through two editors that drift apart.

• Change a value by typing in its cell. There is no save step: an edit is part of the model when it lands, and the file on disk is written straight away.
• Add an element with the Add button above the table. The dialog offers only the kinds that engine can create and asks for exactly what that kind needs; a kind that cannot be created yet is absent, with the reason given.
• Rename or delete an element from the actions at the end of its row. A deletion says what else went with it, and one that something still points at is refused by name rather than left half-done.
• Undo and redo with ⌘Z / ⇧⌘Z (Ctrl+Z / Ctrl+Shift+Z), or from the history control in the top bar, which lists what each step will undo.

Some elements hold more than a row of values, and those appear beneath the table when the element is selected:

• Contents: a curve’s points, a pattern’s multipliers, a transect’s survey points.
• Records: a junction’s demand categories, a control measure’s layers, a snow pack’s surfaces, a unit hydrograph’s monthly responses.

On the canvas, links are drawn as polylines and their intermediate vertices are preserved; dragging a node moves the link’s endpoint while the vertices stay fixed.

The Issues panel collects network validation findings (structural problems detected before a run) and warnings produced by the last simulation run, with links to the affected elements.

If a model’s coordinates use a projected coordinate system, the CRS picker on the canvas can scan the network’s coordinates and suggest matching coordinate reference systems so the network lines up with the basemap. You can also define and save custom CRS entries.

Scenarios and Comparison

Scenarios let you keep independent parameter sets side by side within one project. Each is run on its own and its results are read on its own; there is no side-by-side overlay of one scenario against another.

The Results tab includes a system summary (key metric chips), result histograms, pipe criticality, pump energy, audit panels, and tank level charts.

Reports

The Report tab builds a document from the run. A report is an ordered list of sections, each one a block the engine publishes (a balance, a summary table, a chart), so the sections on offer are the ones that engine can actually produce for the model you have open.

Add sections from the palette. A block that cannot be produced for this scenario is shown with the reason instead of being hidden, so a section missing from your report is missing for a stated cause rather than silently. Sections can be reordered, and one that accepts options exposes them beside it.

The arrangement is saved with the project as a template, so the same report can be regenerated after the next run without rebuilding it.

Export from the tab in any of four formats:

Units

Choose between SI (metric) and US customary display units in Settings. This affects how values are shown and entered throughout the app; files and exports (INP, CSV, GeoJSON) always remain in the model’s native units. Settings also offers a light / dark / system theme.

Performance on Large Networks

Hydra GUI is tuned to stay responsive on larger models.

• Opening a project navigates immediately while network data finishes loading.
• Network Inspector node/link lists use virtualized rendering to avoid large DOM slowdowns.
• Basemap switching keeps network overlays attached so features remain visible while the style reloads.

Exporting and Output Files

Hydra saves simulation results inside the project folder on disk. To open the folder for a scenario, go to the Scenarios panel and click the Open in Finder icon next to the scenario name; it reveals the folder in your platform’s file manager (Finder, Explorer, or the Linux equivalent). The folder contains results.out: binary output in the format of the model’s own engine, EPANET-compatible for a water distribution model and SWMM-compatible for a drainage one, readable by post-processing tools built for either.

Other formats are available from the command palette (⌘K / Ctrl+K):

• Export INP… saves the current network as a model input file, in the format of the project’s own engine
• Export results as CSV… saves node and link result time series as CSV files (shown once results exist)
• Export results to GeoJSON saves nodes/links with attributes, including result values when available

For a plain-text .rpt report, run the exported .inp through the CLI.

Supported Networks

Any EPANET .inp file from any 2.x release works directly, with no conversion needed. See INP Format Support for the full coverage list. SWMM .inp files open the same way, into a drainage project.

Troubleshooting

See the Troubleshooting page for common issues including the macOS Gatekeeper error and Windows Defender prompts.