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The cable that crosses a river: is its real position written down anywhere?

7 min read

A breakwater of large rock armour lined up along the shore of a body of water, overcast sky, black-and-white photograph
Under these rocks, if there is a marinized cable, lies its one true position — and it is not written on the stone.

A trunk route has to cross a river, a navigable canal or a stretch of shallow-water shoreline: the design specifies a cable built for that environment, different from a buried cable and from an intercontinental submarine cable with in-line amplifiers. Five years pass: a third party asks to dig near that point, or the cable fails during a flood. The question is simple — where does it actually run, today, and with what protection — and the answer, almost always, is not written down in one document.

Not a submarine cable: a marinized terrestrial cable

The technical name is marinized terrestrial cable, MTC, defined by three ITU-T Recommendations almost never cited in an Italian specification: L.28, L.29 and L.30, approved between 2002 and 2007 by Study Group 6 and renumbered L.430, L.431 and L.432 on 15 February 2016 with no change to the text and no republication — the official PDFs are still signed with the historical number. The definition, identical in all three: “A marinized terrestrial cable is an underwater optical fibre cable construction, based on a conventional multi-fibre terrestrial cable core protected to withstand the marine environment, designed for unrepeated applications, that is, without underwater line amplifiers, hence without the need to carry electrical power and tested for use in non-aggressive shallow waters, with a varying repair capability.” In practice: an ordinary multi-fibre terrestrial cable, reinforced to survive underwater, with no in-line amplifiers or power feed, built for non-aggressive shallow water — not the cable of a long-haul submarine system, which is defined in ITU-T Recommendation G.972.

Protection changes zone by zone

L.29 opens with an admission: “the actual route is quite different from that foreseen as the laying reference route, as designed according to the various surveys, and the related documents are not updated.” L.28 — External additional protection for marinized terrestrial cables — at least fixes the protection, band by band. On the shore, “generally defined between the Beach Joint and the 5 m water depth”: “The cable should be protected with cast iron shells and buried at least 2-3 m.” In shallow water, “generally defined between 5 m and 30-40 m water depth”; on soft bottom “The cable should be buried at least 1 m”; on hard bottom the fallback is cast-iron shells, or, where several cables converge on a rocky landing, a helically wound steel sleeve. At crossings with other services the rule is geometric: “the crossings between cables shall be performed as near to a right angle (90 degrees) as possible”, and it is “highly recommended that crossing angles minor of 45 degrees be avoided”.

Markers: identifying the cable without opening a report

L.30 — Markers on marinized terrestrial cables — standardises the tape that identifies the cable on sight. A distance marker “should be applied to the cable typically every one km with an accuracy within ±0.25%”; the factory joint marker is a blue band; approaching a joint pit or a branching unit, three warning markers signal the approach at decreasing distance — red at six kilometres, yellow at two, light green at one: “The 6-km warning marker is not required where the length of the cable/link is less than 10 km.” The standard itself allows for variation: “Alternative markers can be considered, which are equivalent to the above, noting the possible advantages of the proposed markers” — an operator can adopt its own colour legend, fully compliant, and write it down nowhere but memory.

The as-laid report and the maintenance/repair log

L.29 — As-laid report and maintenance/repair log for marinized terrestrial cable installation — answers the opening question, requiring two separate deliverables. The As-laid Report contains “detailed As-laid position list (both in geographical and plane coordinates with progressive Kilometer Posts along the route) with all the relevant points such as Turning Points, course alterations, joint positions and crossing points with other services (active and retired)”, plus a general layout map and a detailed landing-point map with burial depth and onshore structures. The Maintenance/Repair Log, updated after every intervention, records the operation number and date, the repair ship, the details of the joint replaced and — the entry that decides whether the two documents actually speak to each other — the “position of failure (longitude, latitude and water depth)”, in the same geodetic reference as the initial report. The Recommendation’s last line is the most practical: “The As-laid Report and the Maintenance/Repair Log should be required in the installation or repair supply contracts, as well as the delivery time” — if delivery is not written into the contract, it is not guaranteed.

Where the answer is written — and where it is not written in one place

  • The as-laid report: delivered once, at completion — KPs, turning points, joints.
  • The maintenance/repair log: updated only if, after every repair, someone writes it down — and only if it uses the same geodetic reference as the initial report, otherwise the two files do not add up.
  • The landing-point map: a document separate from the general as-laid report, with the real burial depth and the onshore structures.
  • The markers on the cable: legible only until covered in sediment, and only if the colour legend — standard or alternative — is written down beyond the memory of whoever chose it.
  • The national Hydrographic Institute, or the local Authority: should receive the update after laying and after every repair with a significant route change — whether it actually does, or in time, is another matter.
  • The supply contract, for installation or repair: the one place where the report, the log and the delivery times become a written obligation, if someone put them in.

Six places. The day someone has to tell a third party where the cable runs before it digs nearby, the answer comes from putting them together — not improvising at the nearest manhole.

What we do not know

Compliance with ITU-T Recommendations remains voluntary: L.30 says so explicitly — “Compliance with this Recommendation is voluntary” — while L.28 and L.29, both 2002 editions, do not yet carry this wording: it was introduced later. L.28 has two appendices — protection examples and a bibliography — but the text we read does not carry the wording other Recommendations use to declare an appendix not an integral part: it is not here, so we do not cite it. We make no claim about any specific Italian obligation on as-laid reports or logs for water crossings: that is a different matter from the fifteen-day notice above forty metres under Law 9/2026, which concerns who gives notice before working, not what is handed over at completion. We do not cite any paid IEC standard on marinized-cable armouring: we have not read one.

The two axes, applied to a water crossing

First axis: before the first shore manhole is opened, the specification states that the As-laid Report and the Maintenance/Repair Log, L.29 §3-4, are contractual deliverables with itemised content and a delivery time — not generic documentation on completion. At acceptance, what gets checked is the landing-point map against the declared burial depths, the marker legend in writing, and the register of crossings against L.28’s minimum angle: lines with a number, written where we check specifications, not a generic crossing executed to good practice.

Second axis: the as-laid report, the maintenance log, the landing-point map and the follow-up OTDR traces stop living in separate files and come together, with CSIDIA, into the same single network map — because knowing whether a crossing still holds is decided by comparing measurements tied to the same joint identifier, not by rebuilding the history from zero under a third party’s request. On that map an AI compares successive measurements and the crew decides whether and where to act — on-premises, on self-contained machines, or a dedicated cloud with a data centre in Italy, always under shared management. It applies to a consortium canal as much as to the as-built documentation of a whole route.

From the site survey, at no cost, we bring the list relevant to your crossing: as-laid report found or not, log updated after the last intervention or not, landing-point map with burial depth available or not, marker legend documented or not — including the blank boxes. Talk to a technician: better before a third party asks where the cable runs, not while it is already digging.

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