Beyond Heavy Cranes: Re-engineering Seawalls for Isolated Coastlines

Coastal protection in archipelagic Asia fails on logistics long before it fails on funding

Between 2019 and 2023, 97% of humanitarian aid went to emergency response, reconstruction, relief and rehabilitation. Less than 3% went to prevention and preparedness. Across total development aid over the same period, as little as 2 dollars in every 100 was allocated primarily to disaster risk reduction. Those are UNDRR's figures, and they describe a system that pays for consequences.

The usual explanation is political. Prevention is invisible; response is televised. That explanation is true and incomplete. In countries repeatedly exposed to serious marine hazards, and particularly in archipelagic ones, there is a second reason, and it is a construction reason.

The plant problem

Permanent coastal works assume a supply chain. Quarried armour stone and the barges to move it. Floating cranes. Piling rigs. A marine contractor willing to mobilise, and a quay that can take the vessel.

In a capital city, that is procurement. On an island of a few thousand people, several hours by boat from the nearest port, with no landing that a barge can use, it is not procurement. It is a physical impossibility at any budget that settlement will ever see. Southeast Asia contains thousands of such places, and they sit precisely where storm tracks come ashore.

So those communities get what they can carry. Sandbags, then geotextile sand containers, then gabions. Each product is honest about what it is. The coastal engineering literature classifies sand-filled geotextile containers as temporary, interim embankment protection. Gabion revetments are generally understood to provide short-term protection, on the order of 5 to 10 years. They are the right answer for the first week and a reasonable answer for the first season. Nobody who specifies them believes they are the answer to the next thirty years.

The permanent structure is supposed to follow. Usually it does not, or it arrives so late that the interim works have already failed twice and been replaced twice.

What the delay looks like where the money exists

Quincy, Massachusetts was awarded just over 2 million dollars by FEMA to strengthen seawalls damaged in the March 2018 storms. The award was announced two years after the damage. In England, 135 metres of collapsed seawall at Stokes Bay took four months and 1.2 million pounds to rebuild. After Typhoon Haiyan, Philippine planners identified contradictory procurement and land acquisition policy, and administrative delay, as central obstacles to reconstruction; recovery was measured in years.

Those are the well-resourced cases, with roads, contractors and functioning institutions. They set the realistic ceiling, not the floor.

Hong Kong, and the shoreline on either side of it

Hong Kong is the instructive counter-example. After Typhoons Hato in 2017 and Mangkhut in 2018, the Civil Engineering and Development Department commissioned AECOM to carry out a feasibility study of coastal hazards under climate change and extreme weather and to formulate improvement measures. Works followed. UNDRR's own account records that there was generally no flooding inside the Tai O protection zone during Mangkhut, while depths outside it reached 0.7 m or more, and that the fishing villages at Lei Yue Mun were protected with rock-armoured bunds and gabion walls. Hong Kong's economic losses from both storms were lower than those of neighbouring Guangdong and Macau.

Two features of that record deserve more attention than they usually get.

The first is what it took: a global consultancy, a government engineering department, a multi-year study programme and the marine contracting capacity of one of the densest construction markets on earth. That combination is not available to most coastlines exposed to the same storms.

Second, even within that programme, the small waterfront villages received gabion walls. The 5 to 10 year answer. Not because the engineering was careless, but because a small, access-constrained fishing settlement is a hard site for conventional permanent marine works anywhere, including in Hong Kong.

What changes if the heavy marine plant requirement is removed

We develop a modular marine construction system in which standard HDPE pipes act as permanent formwork, reinforcement is GFRP only, and the assembled frame is filled in place with structural marine concrete.

What matters for this discussion is what actually has to arrive on site.

The heaviest empty component weighs about 25 kg. Pipes are cut to length before delivery; fittings travel palletised. Assembly uses socket and butt fusion welding of polyethylene pipe, an existing global trade skill, and no proprietary tools are required. A minimum slope cover section weighs about 605 kg dry, and a section pre-assembled up to about 13 m long weighs about 6 t dry. The light, empty formwork is transported and positioned, then filled in place, so a light crawler crane, a lorry crane or a small barge is sufficient, and no high-capacity floating crane is needed. The finished, filled section carries the mass required for stability.

Our current working estimate for dry assembly is 35 to 60 person-hours for a 20 m section, depending on configuration. That is a company estimate rather than a measured production rate, and we present it as such.

What this is not

Filling takes one to three days, and the concrete then has to gain strength before the structure is a structure. Concrete is the load-bearing part of every configuration we build. No version of this system works empty, filled with rubble, or rushed.

The mix specification is demanding: near self-compacting consistency with slump flow typically 550 to 650 mm, minimum class C35/45 for marine exposure, water-cement ratio not exceeding 0.45, with standard 28-day cube testing retained from each pour. The reference terraced configuration consumes roughly 72 m³ of structural concrete and about 1,305 t of graded granular fill per 100 m of shoreline.

That should be read as a constraint, not a footnote. It means ready-mix supply or site batching, a pump, and aggregate haulage. It means you don't deploy this inside a warning window. If a storm makes landfall in 36 hours, use sandbags; we are not competing for that job, and we will not pretend otherwise.

We're competing for the job after it. A permanent structure on a site where a permanent structure was previously undeliverable.

Why permanent is worth more every year

Sea level in the Philippine Sea rose 5 to 7 mm per year between 1993 and 2015, compared with a global rate of 2.8 to 3.6 mm. Design crest levels set today will be revised, and revised again.

A modular system answers that differently from a monolithic one. In our terraced configuration, each added row raises the crest by 1.25 m on the existing fittings, without demolishing the earlier works. The first investment stays in the ground and carries the next increment. For a ministry planning under an adaptation pathway rather than a single design horizon, that is a financial property, not a marketing one.

Where we are

We are candid about status. Hydraulic and structural validation is in progress with university partners through physical and numerical modelling. We do not publish a transmission coefficient, because it has not been measured. We do not state a service life, because it has not been verified. Performance figures are company estimates until a monitored pilot says otherwise.

What we do claim is narrower and, we think, more useful. Permanent coastal protection is missing from thousands of exposed coastlines not only because nobody funded it. It is that nobody could get the equipment there. That is a solvable problem, and solving it moves money from the 97 per cent to the 3 per cent.

We would welcome conversations with national disaster and coastal agencies, development banks and coastal engineering consultants working on access-constrained sites in the region.