Structure Culvert¶

Overview¶

Structure Culvert BC defines a culvert (pipe/box opening) through the wall of a Structure BC body. There are two types:

Structure Culvert (i-direction): Culvert penetrating in the grid i-direction
Structure Culvert (j-direction): Culvert penetrating in the grid j-direction

flowchart LR
    U["upstream"] -->|"  flow direction  "| STR
    subgraph STR["Structure body"]
        C["culvert opening"]
    end
    STR -->|"  flow direction  "| D["downstream"]

Prerequisites¶

Structure BC is required

A Structure BC must already be set at the same location before adding a Structure Culvert BC.

The culvert edge (grid line) must be placed on the boundary face of a Structure BC cell. Placing the culvert edge outside a Structure BC cell causes a runtime error.

Structure Culvert (i-direction)¶

For culverts penetrating in the grid i-direction (typically the main-flow direction).

Setup Procedure¶

Step 1: Add a Boundary Condition Group¶

Right-click Boundary Condition Setting in the left panel and select Structure Culvert (i-direction) to add a new group. It will appear as New Structure Culvert (i-direction) in the left panel (see screenshot on the previous page).

Step 2: Select the Culvert Edge¶

Select the new group and use the edge selection tool to pick a single i-direction grid edge on the structure wall face. The selected edge is highlighted in pink/magenta.

Culvert edge selection: the pink edge is placed on the boundary face of the Structure body

In the screenshot above, the culvert edge (pink) is selected on the left boundary face of the Structure body (dark area). The blue areas on the right are other Structure BC groups.

Edge placement

The selected edge must be a boundary face of a Structure BC cell. Selecting an edge outside the Structure body triggers an error at runtime.

Step 3: Set Culvert Parameters¶

Parameter	Unit	Description
Vertical size of Culvert	m	Culvert height (vertical dimension)
Horizontal size of Culvert	m	Culvert width (horizontal dimension)
Invert elevation of Culvert	m	Absolute elevation of the culvert invert (bottom)

Culvert parameter dialog showing all three parameters and the BC list in the left panel

Example values shown: Vertical size = 0.05 m, Horizontal size = 0.2 m, Invert elevation = 0.11 m

Elevation relationships (top to bottom):

Elevation (high → low)	Meaning
Water surface	Computed water level
Structure Top Elevation	Structure crest (Structure is solid below this)
Invert elevation + Vertical size	Culvert top
↕ Vertical size	Height of culvert opening
Invert elevation	Culvert invert (bottom of opening)
eta	Riverbed elevation

Step 4: Verify the Constraint¶

To ensure solid material exists above the culvert:

Required condition

Structure Top Elevation  >  Invert elevation + Vertical size

Correct example:

Invert elevation = 0.100 m
Vertical size = 0.300 m → Culvert top = 0.400 m
Structure Top Elevation = 0.500 m ✓ (0.100 m of solid above culvert)

Incorrect example:

Invert elevation = 0.100 m
Vertical size = 0.300 m → Culvert top = 0.400 m
Structure Top Elevation = 0.350 m ✗ (culvert extends beyond structure crest)

Structure Culvert (j-direction)¶

For culverts penetrating in the grid j-direction. The setup procedure is identical to i-direction.

In Boundary Conditions, select Structure Culvert (j-direction) and select a j-direction grid edge on the structure wall face.

Common Errors and Solutions¶

Error 1: Culvert face not on a Structure face¶

ERROR: Structure Culvert (i-direction) face at( i  j ) group N
       is not on a Structure face. Calculation stopped.

Cause: The selected culvert edge is not on the boundary face of a Structure BC cell.

Solution:

In iRIC, check which cells have Structure BC assigned.
Re-open the Structure Culvert BC settings and reselect the edge so it lies on a Structure cell boundary.

How to verify

Zoom in on the grid in the iRIC pre-processing view. Confirm that the culvert edge lies on the inner boundary face of the Structure BC cells (shown as blue highlights).

Issue: No solid above the culvert¶

No error is raised, but the culvert opening extends to or above the structure crest — no solid material remains above the culvert.

Diagnosis: Check the 3D view. If no solid structure is visible above the culvert opening, the crest elevation is too low.

Solution: Increase Structure Top Elevation to satisfy:

Structure Top Elevation > Invert elevation + Vertical size

Checking Results in Post-Processing¶

After the simulation, verify the following in the 3D post-processing view:

Flow velocity vectors appear inside and downstream of the culvert opening
Solid Structure material is present above the culvert
Flow converges and passes through the culvert as expected

3D post-processing result showing two Structure bodies and multi-layer velocity vectors (Time: 299 sec)

The screenshot above shows the steady-state result (299 sec) of the ijStructure test case. The upstream Structure has a culvert configured; flow passes through the culvert at the lower layers (red arrows) while overflowing the crest at upper layers (cyan arrows). The downstream Structure has overflow only (no culvert).