Selecting Inputs¶
Each scenario references a specific set of inputs. The inputs themselves are project-level data: pointing a second scenario at the same terrain does not copy it, and changing which inputs a scenario references never modifies the underlying data.
The scenario settings pane splits these into Required and Optional.
Required inputs¶
A build refuses to start until these are set, and Hydrata names the one that is missing rather than failing part-way through:
- Terrain: the elevation surface, either uploaded or imported. See Elevation.
- Boundary: the domain boundary lines, which also carry the boundary condition types. See Boundaries.
- An inflow or a rainfall: at least one of the two. An Inflow is a line carrying a flow rate or a hydrograph; a Rainfall is a polygon carrying an intensity or a design storm. A scenario may reference one of each.
A name, a base mesh size greater than zero and a duration greater than zero are required too. Those are run settings rather than inputs.
Optional inputs¶
| Input | Effect if omitted |
|---|---|
| Friction | A single default Manning's n of 0.04 is applied across the whole domain |
| Structures | Buildings do not affect the flow; the terrain surface is used as-is |
| Mesh Regions | The base mesh size is used uniformly across the domain |
Where a friction polygon does cover the ground, its own Manning's n applies, and the form offers 0.035 as a starting value. You can also supply friction as a raster instead of polygons. See Friction Maps.
A scenario can also reference a catchment and a drainage network. Those are built in the Hydrology tab rather than in this pane.
Removing an input¶
Deleting an input from the Inputs rail is refused while any scenario still references it, and the refusal explains itself rather than failing silently. It names the blocking scenarios, up to five of them before it switches to a count of the rest, lists them underneath, and tells you the way out: detach the input from those scenarios first, then delete it.
An idle scenario blocks the delete just as a running one does. A scenario you have finished with is still a reference, so archive or delete the scenario before deleting the input it holds.
Deleting the scenario itself is a separate action, and it cannot be undone. Neither delete nor archive is allowed while a Run is in progress; cancel the Run first.
Comparing scenarios¶
You can create multiple scenarios within a project, each with different inputs or settings. This is useful for:
- Sensitivity analysis: vary one input at a time
- Design comparison: test existing against proposed conditions
- Climate scenarios: run different rainfall intensities
Duplicate is the fastest way to set one of these up, because it carries every input reference across and leaves you changing only the thing you are testing.
Once two scenarios have results, compare mode puts them side by side: turn it on, then pick the two scenarios to compare. Scenarios you are no longer comparing can be archived to get them out of the rail without losing them, and restored later. See Running Scenarios.