---

name: parsing-basin-models description: | Parses HEC-HMS basin model files (.basin) to extract and modify subbasins, junctions, reaches, loss parameters, transform parameters, baseflow, and routing. Use when reading basin files, modifying hydrologic parameters, analyzing basin structure, or updating curve numbers, lag times, and routing coefficients. Handles clone workflows for QAQC. Trigger keywords: basin file, subbasin, junction, reach, loss method, curve number, transform, lag time, baseflow, routing, Muskingum, parse basin, get parameters.

Parsing Basin Models

Quick Start

Copyfrom hms_commander import HmsBasin

# Read basin components
subbasins = HmsBasin.get_subbasins("project.basin")
junctions = HmsBasin.get_junctions("project.basin")
reaches = HmsBasin.get_reaches("project.basin")

# Get/set parameters
loss_params = HmsBasin.get_loss_parameters("project.basin", "Subbasin1")
HmsBasin.set_loss_parameters("project.basin", "Subbasin1", curve_number=85)

Primary Sources

Code: hms_commander/HmsBasin.py - Complete API with docstrings

Examples: examples/03_project_dataframes.ipynb - Basin operations

Rules: .claude/rules/hec-hms/basin-files.md - Basin file patterns

File Format: tests/projects/.../02_Basin_File.md - HMS file structure

When to Use This Skill

• Extracting basin components for analysis
• Modifying loss method parameters (CN, deficit, constant rate)
• Updating transform parameters (lag time, time of concentration)
• Analyzing basin connectivity (downstream relationships)
• Cloning basins for QAQC comparison

Core Capabilities

1. Component Extraction

Returns DataFrames with basin elements:

• get_subbasins() - Area, downstream, loss/transform methods
• get_junctions() - Connectivity nodes
• get_reaches() - Channel routing elements

2. Parameter Operations

Get/set hydrologic parameters:

• Loss methods (Deficit & Constant, SCS CN, Green & Ampt, etc.)
• Transform methods (SCS UH, Clark UH, ModClark, etc.)
• Baseflow methods (Recession, Constant Monthly, etc.)
• Routing methods (Muskingum, Lag, ModPuls, etc.)

See: hms_commander/HmsBasin.py for complete method list

3. Clone Workflows

Non-destructive basin cloning:

• Preserves original basin
• Updates description with clone metadata
• Appears in HEC-HMS GUI
• Enables side-by-side QAQC comparison

See: .claude/rules/hec-hms/clone-workflows.md for CLB Engineering pattern

Common Workflows

Workflow 1: Extract All Components

Copysubbasins = HmsBasin.get_subbasins("project.basin")
print(f"Found {len(subbasins)} subbasins")
print(f"Total area: {subbasins['Area'].sum()} sq mi")

Workflow 2: Bulk Parameter Update

Copy# Update all curve numbers
subbasins = HmsBasin.get_subbasins("project.basin")
for name in subbasins.index:
    HmsBasin.set_loss_parameters("project.basin", name, curve_number=85)

Workflow 3: Clone for QAQC

Copyfrom hms_commander import init_hms_project, hms, HmsBasin

init_hms_project("project")
HmsBasin.clone_basin("Baseline", "Updated_Basin", hms_object=hms)
# Now modify Updated_Basin parameters for comparison

Reference Files

• reference/get_subbasins.md - DataFrame structure and usage
• reference/loss_methods.md - All loss method parameters
• reference/transform_methods.md - All transform method parameters
• examples/parameter_sweep.md - Bulk parameter updates

Related Skills

• cloning-hms-components - Complete clone workflow
• executing-hms-runs - Run after modifying parameters