Hydrology Table
The Hydrology Table configures design flows and basin parameters for every structure in the network.
Opening the Hydrology Table
Open the Hydrology Table from Tables menu > Hydrology.... A description of the active hydrology mode is shown at the top of the dialog.
Storm Selector
When more than one storm event is configured, a Storm dropdown at the top of the table lets you pick which storm's flow is shown/edited (Peak Flows Only mode) or which storm's IDF data drives the displayed computed flow (rational modes). The single peak-flow column's header updates to show which storm it currently represents (e.g. "Design Q (cfs)" or "Check Q (cfs)").
Peak Flows Only Mode
When the project is set to Peak Flows Only hydrology mode, the Hydrology Table displays a simple grid for direct flow entry.
| Column | Description |
|---|---|
| Structure | Node name (read-only) |
| Design Q / Check Q (cfs) | A single peak-flow column, editable. Its header switches between "Design Q (cfs)" and "Check Q (cfs)" based on the Storm selector above — it is not two separate columns. |
Enter peak flows directly into each row. A bulk-apply row is shown at the top in this mode: enter a value in "Bulk apply Q (cfs) to selected" and click Apply to set every selected row at once.
Manual Mode
In Manual mode, the peak-flow column and basin-assignment column are hidden. Instead, Area (ac), Weighted C, and Tc (min) become directly editable per node, and I (in/hr) and Q (cfs) are computed and shown read-only from the project's IDF data.
HydraLink / Parcels Modes
In HydraLink and Parcels modes, the table shows an Assigned Basins column (a checklist dropdown of external basins contributing to that node) in place of the peak-flow column. Area (ac), Weighted C, and Tc (min) are shown but are read-only here — they're the sums/weighted values computed from the assigned basins, not directly editable. I (in/hr) and Q (cfs) are also read-only.
| Column | Description |
|---|---|
| Structure | Node name (read-only) |
| Assigned Basins | Multi-select checklist for basin assignment (HydraLink/Parcels modes only) |
| Area (ac) | Drainage area in acres. Editable in Manual mode; read-only (basin sum) in HydraLink/Parcels modes. |
| Weighted C | Runoff coefficient. Editable in Manual mode; read-only (basin-weighted) in HydraLink/Parcels modes. |
| Tc (min) | Time of concentration. Editable in Manual mode; read-only (basin max) in HydraLink/Parcels modes. |
| I (in/hr) | Rainfall intensity looked up from the project's IDF data at this node's Tc (read-only, all rational modes) |
| Q (cfs) | Computed rational-method flow, Q = C×I×A (read-only, all rational modes) |
Basin Assignment
In HydraLink and Parcels modes, the Assigned Basins column shows which external basins contribute to each node. Basin assignment follows these rules:
- Multiple basins to one inlet: When multiple basins are assigned to a single inlet, HydraStorm computes a weighted runoff coefficient (C), takes the maximum time of concentration (Tc), and sums the drainage areas.
- One basin per inlet constraint: A single basin cannot be assigned to multiple inlets. If you try to assign a basin that is already assigned elsewhere, HydraStorm will warn you and require you to remove the existing assignment first.