Hydrology Modes

HydraStorm supports four mutually exclusive project-wide hydrology modes. The active mode is set in Project Settings > Hydrology and applies to every structure in the network. Each mode controls how peak design flows are determined at each node.

Peak Flows Only (Default)

The simplest mode. You enter peak design flows directly at each structure node, with no rational method computation and no basin data required. This is ideal when flows have already been computed externally, provided by a drainage report, or pulled from another modeling tool.

Enter flows in the Hydrology Table or the Q field in the Property Panel.

HydraLink

Import basin parameters (drainage area, runoff coefficient C, time of concentration Tc) and computed flows from a HydraLink project file (.hyd or .hlresults). HydraStorm matches HydraLink basins and junctions to pipe network structures by name, then by spatial proximity when names do not match.

This mode supports live file watching: when the linked HydraLink file changes on disk, HydraStorm prompts you to reload the updated data. See the HydraLink Integration page for full details on the matching pipeline and setup workflow.

Parcels

Read drainage area directly from Civil 3D Parcel geometry. The runoff coefficient (C) and time of concentration (Tc) are read from parcel User-Defined Properties (UDPs) or entered manually. Areas are automatically converted from square feet (Civil 3D native units) to acres.

Basin-to-node assignment is managed through the Hydrology Table. Multiple parcels can contribute to a single inlet, and the assignment manager enforces a one-inlet-per-basin rule to prevent double-counting.

Manual

Full rational method computation with user-entered area, C, and Tc per node. This is functionally identical to Parcels mode but without reading geometry from Civil 3D parcels. All parameters are entered directly in the Hydrology Table.

Manual mode is well suited for quick parametric studies, preliminary design, or situations where parcel geometry is not yet available in the drawing.

Mode Conversion

Any hydrology mode can be converted to Manual at any time. When you convert, HydraStorm copies all current parameter values into the Manual fields and breaks the link to the original data source (HydraLink file, parcel geometry, etc.).

Re-linking to a source mode is allowed. HydraStorm will display a confirmation dialog before overwriting your manually edited values.

This workflow is useful when you want to start from HydraLink data or parcel geometry but then need to tweak individual values for specific nodes without affecting the source data.

Mode Comparison

Feature	Peak Flows Only	HydraLink	Parcels	Manual
Rational method	No	Yes	Yes	Yes
IDF data required	No	Optional	Yes	Yes
Data source	User entry	.hyd / .hlresults	C3D Parcels	User entry
Tc accumulation	N/A	Yes	Yes	Yes
Live file watch	No	Yes	No	No
Convertible to Manual	Yes	Yes	Yes	N/A