Steady Flow File Parsing Reference

Reference for HEC-RAS steady flow file (.f##) structure and the RasSteady authoring API.

Overview

Steady flow files define the constant profile inputs used by 1D steady plans:

• Profile names, such as Q10, Q50, and Q100
• Flow values at each flow-change station
• Profile-specific upstream and downstream boundary conditions
• Optional DSS import metadata used by the HEC-RAS steady flow editor

Use RasPlan.get_flow_path("01") or ras.flow_df to discover existing files, then use RasSteady to read, create, update, and write the .f## content.

File Location

Text Only

{project_folder}/{project_name}.f{number}

Example: C:\Projects\Muncie\Muncie.f01

File Structure

Header

Text Only

Flow Title=Multi-Profile Analysis
Program Version=6.60
Number of Profiles= 3
Profile Names=Q10,Q50,Q100

Number of Profiles= must match the number of names in Profile Names= and the number of flow values in every flow-change block.

Flow Change Blocks

HEC-RAS stores each flow-change location as a River Rch & RM= line followed by one fixed-width row or block of flow values:

Text Only

River Rch & RM=Main River,Upper Reach,5000
    2000    5000   10000
River Rch & RM=Main River,Upper Reach,2500
    2200    5500   11000

Each numeric block has one value per profile, in profile order.

Boundary Blocks

Boundary conditions are written per reach and per profile:

Text Only

Boundary for River Rch & Prof#=Main River,Upper Reach, 1
Up Type= 2
Dn Type= 3
Dn Slope=   0.001
Boundary for River Rch & Prof#=Main River,Upper Reach, 2
Up Type= 1
Up Known WS=   101.5
Dn Type= 1
Dn Known WS=   98.25

RasSteady exposes the HEC-RAS type codes as constants:

Constant	Code	Meaning
RasSteady.NO_BOUNDARY	0	No boundary on that side
RasSteady.KNOWN_WS	1	Known water surface
RasSteady.CRITICAL_DEPTH	2	Critical depth
RasSteady.NORMAL_DEPTH	3	Normal depth using friction slope
RasSteady.RATING_CURVE	4	Rating curve

Rating curves are written as a counted block of flow-water-surface pairs, which matches the HEC-RAS .f## file order:

Text Only

Dn Type= 4
Dn Rating Curve # Pts= 3
      40      80     120      85     300      90

API Usage

Read and Round Trip

Python

from ras_commander import RasPlan, RasSteady

flow_path = RasPlan.get_flow_path("01")
flow_data = RasSteady.read_flow_file(flow_path)

print(flow_data["profile_names"])
print(flow_data["flow_changes"][0]["flows"])

RasSteady.write_flow_file("Working.f02", flow_data)

Create a New Steady Flow File

This pattern replaces notebook cells that previously required opening the HEC-RAS steady flow editor by hand.

Python

from ras_commander import RasPlan, RasSteady

new_flow_path = project_folder / f"{project_name}.f02"

RasSteady.create_flow_file(
    new_flow_path,
    flow_title="Calibration Profiles",
    profile_names=["Base", "High"],
    flow_changes=[
        {
            "river": "Main River",
            "reach": "Upper Reach",
            "station": "5000",
            "flows": [1000, 2500],
        },
        {
            "river": "Main River",
            "reach": "Upper Reach",
            "station": "2500",
            "flows": [1250, 2750],
        },
    ],
    boundaries=[
        RasSteady.boundary(
            "Main River",
            "Upper Reach",
            upstream=RasSteady.critical_depth(),
            downstream=RasSteady.normal_depth([0.001, 0.002]),
        ),
    ],
)

# Apply the authored steady flow file to a plan after registering it in the
# project file or cloning an existing flow entry through RasPlan.
RasPlan.set_steady("02", "02")

Known Water Surface and Rating Curve

Compact boundary definitions can provide one value per profile. RasSteady expands them into profile-specific HEC-RAS boundary blocks when writing.

Python

boundaries = [
    RasSteady.boundary(
        "Main River",
        "Upper Reach",
        downstream=RasSteady.known_water_surface([98.5, 100.0, 101.2]),
    ),
    RasSteady.boundary(
        "Tributary",
        "Lower Reach",
        downstream=RasSteady.rating_curve(
            [
                {"flow": 100.0, "stage": 95.0},
                {"flow": 500.0, "stage": 100.0},
                {"flow": 1200.0, "stage": 105.0},
            ]
        ),
    ),
]

Validation Rules

RasSteady.validate_flow_file_data() runs before every write and raises a ValueError when:

• The profile name count does not match Number of Profiles=
• Any flow-change block has a flow count that differs from the profile count
• A compact known-water-surface or normal-depth boundary list has the wrong number of profile-specific values
• A profile-specific boundary references a profile outside 1..N
• A rating curve is empty or does not form stage-flow pairs

Fixed-Width Numeric Blocks

HEC-RAS uses 8-character fixed-width numeric columns for flow and rating curve values. RasSteady parses by column position and writes right-aligned values:

Text Only

Columns:  0-7      8-15     16-23
Values:   value1   value2   value3
Example:  "    2000    5000   10000"

Avoid parsing these rows with whitespace-only splitting in reusable code.

See Also

• HEC-RAS File Formats
• Unsteady File Parsing
• Steady Flow Analysis