BASIN File

What are BASIN files and how to open them

Are you having problems opening a BASIN file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BASIN files.

What is a BASIN file?

A .BASIN file is a HEC-HMS Basin Model Settings file.

HEC-HMS Basin Model Settings files store configuration data for a basin model used in the HEC-HMS hydrologic simulation software from the U.S. Army Corps of Engineers. They define how a watershed is physically represented in terms of its subbasins, reaches, junctions, reservoirs, and related losses, transforms, baseflow, routing, default methods, look & feel, and unit system. These settings shape how the watershed network behaves during simulations by determining method defaults, naming, units, display options, connectivity, and special options like drawing icons or showing flow direction.

These files are produced and used by HEC-HMS when a basin model is created or edited. Basin model settings are saved into files with the BASIN extension, and these can be imported into other HEC-HMS projects via File → Import → Basin Model. On import, dependent data such as time-series or grid discretization files may also be brought in. Internally, the basin model settings control defaults (loss, transform, baseflow, routing), files (background map, grid-cell/discretization definitions), unit system conversions, and various options for how network behavior is computed and displayed.

Internally, the file starts with a signature "Basin: " at offset zero (ASCII), and contains many keyword strings that indicate configuration options. Some of the strings present include COMPUTE LOCAL FLOW AT JUNCTIONS, BASIN SCHEMATIC PROPERTIES, PERCENT IMPERVIOUS AREA, DEVELOPED POWER BLOCK, ENABLE FLOW RATIO, UNIT SYSTEM, DRAW GRIDLINES, LOSSRATE, BASEFLOW, SUBBASIN, TRANSFORM, VERSION, LAST MODIFIED DATE, CANVAS X/Y among others.

How to open BASIN files

Important: Different programs may use files with the BASIN file extension for different purposes, so unless you are sure which format your BASIN file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 23, 2026

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