`fort.14` cheat sheet · Dominik Mattioli

Quick reference for ADCIRC's fort.14 mesh format. The authoritative parsing contract for ADMESH lives at specs/002-size-field-defaults/contracts/fort14-paired-edge.md. The official ADCIRC docs are at https://adcirc.org/home/documentation/users-manual-v53/input-file-descriptions/adcirc-grid-and-boundary-information-file-fort-14/.

For the conceptual primer (what these BC categories mean), see Concepts §5.

Layout

AGRID                              ! mesh title
NE  NN                             ! n_elements  n_nodes
JN  X(JN) Y(JN) DP(JN)             ! NN node records: id  x  y  depth
JE  NHY  NM(1) NM(2) NM(3)         ! NE element records: id  3  n0 n1 n2 (1-based)
NOPE                               ! number of open-ocean boundary segments
NETA                               ! total number of open-ocean boundary nodes
... open-ocean records ...
NBOU                               ! number of land/normal-flow boundary segments
NVEL                               ! total number of land boundary nodes
... land records (vary by IBTYPE) ...

ADMESH's reader is in admesh/fort14.py. Indices in the file are 1-based; ADMESH stores them 0-based internally (subtracts 1 on read, adds 1 on write — see Concepts §7).

IBTYPE codes (land boundary section)

IBTYPE	Meaning	Per-node fields	ADMESH support
0	mainland (no normal flow)	`node_id`	✅
1	island (no normal flow, closed loop)	`node_id`	✅
2	external barrier with prescribed flux	`node_id`	✅ (read-through)
3	outer barrier (weir, paired-edge)	`node_id BARLANHT BARLANCFSP`	✅ spec-002
4	internal barrier (weir, paired)	`node1 node2 BARINHT BARINCFSB BARINCFSP`	✅ spec-002
10	mainland (with rad-stress)	`node_id`	✅ (read-through)
11	island (with rad-stress)	`node_id`	✅ (read-through)
12	external barrier (with rad-stress)	`node_id`	✅ (read-through)
13	outer barrier with rad-stress (paired)	as IBTYPE 3	✅ spec-002
20	culvert (paired)	as IBTYPE 4	⚠️ partial
24	internal barrier + culvert (paired)	`node1 node2 BARINHT BARINCFSB BARINCFSP PIPEHT PIPECOEF PIPEDIAM`	✅ spec-002

The bolded entries are paired-edge records — each line ties two nodes together as the two sides of a hydraulic structure (weir, levee, culvert). spec-002 added explicit support for these in the reader / writer round-trip; see issue #10 for the release-gate context.

What a paired-edge record looks like

For an internal barrier (IBTYPE 4 or 24), the BC file groups two parallel rows of boundary nodes — one row per side of the structure — and each line of the record lists both node IDs:

flow direction →                                         flow direction →
   north of barrier  ←─────────────────────────────────  ●        ←──┐
                                                         ▲           │ N
                                                         │           │ O
                                              ┌──────────┘           │ D
                                              │                      │ E
   ▼ vertical                                 │                       │
       barrier  ████  ████  ████  ████  ████  ████  ████  ████        │
       height                                   │                     │
                                              ┌─┘                     │
                                              │                       │
                                                         ▼            │
   south of barrier  ←─────────────────────────────────  ●        ←──┘

   IBTYPE 4 record (one paired edge per line):
     node1   node2   BARINHT   BARINCFSB   BARINCFSP
       12      18      4.5       1.05         0.45
       13      19      4.5       1.05         0.45
       14      20      4.5       1.05         0.45
                                                ⤷  same hydraulic
                                                   structure, three
                                                   paired edges

A reader that splits per-node (assuming one node ID per line) silently drops half the pairing and corrupts the BC structure. ADMESH parses paired-edge records column-aware via Mesh.boundary_segments[*].barrier_data.

Round-tripping in ADMESH

import admesh

mesh = admesh.read_fort14("input.14")
mesh.to_fort14("output.14")

# Idempotent: round-tripping a Mesh through fort.14 is exact.
assert mesh.equals(admesh.read_fort14("output.14"))

Reference fixtures

Fixture	Tier	Location	Use
`tests/fixtures/fort14/synthetic/*`	0	this repo	unit tests, every PR
`wetting_and_drying_test.14`	1	ADMESH-Domains registry	small ADCIRC sample
`wnat_test.14`	2	ADMESH-Domains registry	Western North Atlantic (0.1.0 release gate)

Tier-1 and Tier-2 fixtures have moved to the ADMESH-Domains sibling registry — pull them via the admesh-domains package rather than vendoring locally.

Common gotchas

1-based vs 0-based: file is 1-based; in-memory ADMESH Mesh is 0-based. Don't mix them.
NHY is always 3 in v52 grid format (triangles only). Quad meshes use a different file format and are not in scope for v1.
Paired-edge records list TWO node ids per line (IBTYPE 4, 13, 24). A reader that assumes one-id-per-line silently drops half the pairing.
BARLANHT depths are negative-down to match ADCIRC's depth convention (positive = below datum).
Inline = comments are sometimes present on segment header lines. ADMESH's parser tolerates them (added in spec-002 to handle wetting_and_drying_test.14).