Introduction and background
Transversal torrent control structures (TTCSs) — check dams, bed sills, consolidation and debris-retention works — have been built across Alpine mountain streams for more than a century to mitigate hydro-geomorphic risk. The need for systematic regional-scale assessment has grown with the increasing frequency of extreme precipitation events and the progressive ageing of infrastructure built decades ago. Research groups working in the Italian Alps proposed some multi-parameter indices that need up-to-date information on the TTCSs: the Potential Fragility Index (PFI) [1], tested on 3,556 structures in Friuli-Venezia Giulia Region (FVG) (Northeastern Italy); the Maintenance Priority Index (MPi) [2], derived from multi-temporal high-resolution topography and the FVG regional database; and the Sediment Continuity Ratio (SCR) [3], which quantifies the interaction of TTCSs with sediment cascades. These indices share a common data dependency: a complete, attribute-rich, geolocated inventory of structures, including intrinsic variables (year of construction, height, material, typology) and extrinsic context (channel reach classification, process domain, lithological setting).
Such inventories exist but are fragmented and not constantly updated. The FVG database published through IRDAT [4] is exemplary, open-licensed under IODL 2.0 and served via OGC WMS/WFS. Equivalent database across the Alpine arc (e.g., Italian regions, Austrian WLV, Swiss cantons, French RTM, Slovenian DRSV) vary widely in accessibility, completeness, and interoperability. No pan-Alpine, openly licensed, interoperable TTCS inventory currently exists. This work targets the OpenStreetMap (OSM) as a complementary interoperability layer that any regional inventory could conflate against.
The waterway=check_dam tagging proposal ([5], initiated 2021, still pending) offers a structurally rich classification of check-dam types and materials, but is semantically poor with respect to PFI/MPi/SCR variables and does not cover the full TTCS typological range (e.g., bed sills fall outside its scope). Prior OSM-science work on authoritative data integration ([6], [7]) and citizen-science inventories for natural hazards ([8]) provides methodological grounding, but the TTCS domain has not been addressed.

Aim
This work is organised around two connected questions. The first concerns the OSM schema: can the existing waterway=check_dam proposal (and a companion schema for grade-protection sills) be extended to carry the variables required by published hydro-geomorphic indices, compatibly with established tagging conventions? The second concerns OSM's empirical coverage: i) how complete, positionally accurate and attribute-rich is the existing TTCS representation when benchmarked against an authoritative regional database; ii) what does the gap suggest about the potential for a safety-aware, distributed contribution model using OSM as a shared layer between authoritative institutional sources and citizen field observation, transferable across the Alpine arc?

Methodology and early results
The schema crosswalk maps each input variable of the PFI, MPi and SCR indexes to existing or newly proposed OSM keys. Intrinsic variables largely align with existing conventions: typology (check_dam=*), material (material=*), height (height=*), construction year (start_date=*), operator (operator=*), and condition (condition=*). Extrinsic variables would require new sub-keys modelled as an authoritative overlay rather than community-observable attributes (e.g. check_dam:reach=*, check_dam:process_domain=*, check_dam:lithology=*), as they depend on geomorphological expertise and external authoritative datasets. The crosswalk also identifies the need for a companion sibling proposal, waterway=bed_sill, for grade-control sills, functionally distinct from check dams in function, geometry, and failure modes, framed as community contributions to the OSM tagging process, not as parallel schemas.
Building on this crosswalk, a conflation pilot (to the authors' knowledge, the first OSM-to-cadastre comparison for TTCSs) will compare the IRDAT FVG database with OSM coverage in a test catchment from the Chiarel et al. (2026) study area. The closest methodological precedent is the OSM conflation of the US National Inventory of Dams [9], which targeted large dams with no fragility attributes; this pilot extends the pattern to torrential structures and PFI/MPi attribute coverage.
A snapshot analysis of the OSM planet (2026-04-22, Geofabrik extract) quantifies the current gap. Italy carries only 17 waterway=check_dam features against 12,881 waterway=weir, a schema-adoption ratio of 0.11 %. Across European countries, the ratio reaches 0.56 %, driven almost entirely by Switzerland (652 features, 82 % of the European total). Changeset analysis reveals this concentration stems mainly from a single mapper working from national imagery (SwissImage / Swisstopo), not a coordinated process or import. Accordingly, none of the PFI/MPi input variables (start_date, condition, material, height) exceeds 1 % completeness Europe-wide: mass without quality.
A contributing factor is the status of the waterway=check_dam proposal itself: initiated in 2021, formally pending for five years. Without an approved tag, both iD and JOSM exclude it from default presets, leaving the schema invisible to most mappers who rely on preset-guided workflows and reinforcing the low-adoption condition that keeps the proposal stalled.

Discussion
The empirical results reveal a gap that is not merely quantitative but structural. The TTCS domain is intrinsically specialist: structures sit in remote, often hazardous catchments; relevant attributes require geomorphological expertise; and post-import verification — routine for urban features — demands physical access and domain knowledge that cannot be expected of the general OSM community. These characteristics explain why, even where authoritative database are openly licensed, the path to OSM import has not been activated: ODbL compatibility must be verified, a technically sound import process must be designed, and a community with sufficient competence must commit to maintaining the result.
The response to this structural gap should not be to lower expectations but to design for it explicitly. Methodologically, this work provides the first systematic alignment of an OSM tagging schema with a validated family of hydro-geomorphic risk indices for torrent control structures and proposes the first OSM-to-database conflation study in this domain; a future work on a companion waterway=bed_sill proposal would complete the typological coverage.
Practically, this work sketches an activation pathway whose feasibility remains to be verified. On the OSM side, this involves reopening the waterway=check_dam proposal and exploring whether preset-backed workflows could lower the participation barrier. On the institutional side, it requires early dialogue with agencies holding authoritative TTCS inventories (e.g., IRDAT FVG, WLV Austria, French BD-RTM) to assess ODbL-compatible release and structured import. Grounding this pathway in peer-reviewed, validated indices may help position OSM as a legitimate interoperability layer for hazard-domain applications, potentially enabling regional-scale PFI/MPi/SCR screening across the Alpine arc.
Several directions remain open: i) identifying which TTCSs can be safely documented is a prerequisite for any participatory contribution model and itself an open research problem requiring input from territorial authorities and domain experts; ii) how to structure long-term participation is equally unclear: the model would need to emerge from community dialogue, not be designed in advance; iii) extension to additional Alpine regions and monitoring of schema adoption are further directions this work can only point to.
All artefacts (e.g., crosswalk tables, conflation notebooks, analysis pipeline) will be released under open licences and based on open-source code to support reproducibility.