C-DRONE GUIDE · 23 JULY 2026
Coastal erosion monitoring by drone: photogrammetry, shoreline retreat, price
A coastal municipality that must rule on a building permit threatened by dune retreat, an inter-municipal body holding the GEMAPI mandate documenting the impact of a winter storm on its shoreline, or a consulting firm tasked with tracking the effectiveness of a coastal defence structure: in all three cases, the historic method — beach profiles surveyed on foot with differential GPS, supplemented every few years by an institutional airborne LiDAR flight — remains reliable over the long term but too rare to document the effect of a single storm. A drone closes that gap: in an outing of a few hours, it covers several kilometres of coastline at centimetre resolution, repeatable after every significant weather event. Here is how this technology measures shoreline retreat, what the Climate and Resilience law changes for the local authorities concerned, and what it costs in 2026.
Published on 23 July 2026, reviewed on 27 July 2026 — regulations in force as of July 2026.
Why monitor coastal erosion by drone
Monitoring the erosion of a beach or dune system traditionally relies on beach profiles: points aligned perpendicular to the shoreline, surveyed on foot with differential GPS at regular intervals, then compared from one survey to the next to estimate retreat or sand accumulation. This method stays precise but one-off — it only documents a handful of sections of the coast, not an entire stretch. On a larger scale, the French state supplements this monitoring with institutional airborne LiDAR campaigns, such as the national Litto3D programme: precise and exhaustive, but run several years apart, incompatible with tracking a single storm or a sand-recharge project.
A drone fills the gap between these two methods: in an outing of a few hours, it covers several kilometres of coastline at centimetre resolution, repeatable after every storm or on a monthly basis if the monitoring calls for it. A coastal municipality, an inter-municipal body holding the GEMAPI mandate (management of aquatic environments and flood prevention), or a consulting firm can thereby precisely document what a foot survey only partly sees and what an airborne LiDAR flight will not see again for years.
How a drone measures shoreline retreat
A typical mission combines an automated flight in parallel strips over the beach and dune system, at a height calculated to guarantee sufficient overlap between photos, with a scatter of ground control points (GCPs) positioned using differential GPS before the flight — these are what guarantee the precision and repeatability of the georeferencing from one survey to the next. Structure-from-motion (SfM) photogrammetric processing recomposes, from hundreds of overlapping photos, an orthophoto and a digital surface model (DSM) of the surveyed area. Repeated after each storm or at a regular interval, the same method makes it possible to difference two successive DSMs — a so-called DSM-of-difference calculation — to map areas of accretion and erosion, deduce a volume of sand lost or gained, and measure a retreat (or advance) of the dune toe in metres.
A study carried out on Truc Vert beach in Gironde, France, by Laporte-Fauret, Marieu, Castelle, Michalet, Bujan and Rosebery (2019, Journal of Marine Science and Engineering) tested this low-cost approach over 4 km of coastline and nearly a square kilometre of beach-dune system, comparing a consumer drone fitted with an action camera and a professional 20-megapixel model: the latter produced surface models with a vertical error of around 5 cm, more than sufficient to detect the effect of a storm on dune morphology (see the study on Google Scholar). Earlier research by Gonçalves and Henriques, published in 2015 in the ISPRS Journal of Photogrammetry and Remote Sensing, laid the methodological groundwork for this kind of drone-based coastal topographic monitoring, with ground resolutions better than 5 cm (see the study on Google Scholar). See also our guide to drone surveying and photogrammetry for more detail on this method applied to other use cases.
What the Climate and Resilience law changes for coastal municipalities
Since the Climate and Resilience law of 22 August 2021, municipalities exposed to shoreline retreat must map that risk over two time horizons — under 30 years and beyond 30 years — and incorporate that map into their local planning document. Ordinance no. 2022-489 of 6 April 2022 clarified the framework for this adaptation, opening up the possibility of a specific pre-emption right and a spatial-recomposition mechanism for threatened properties. The repeated topographic data produced by drone monitoring feeds directly into this mapping work: it substantiates the actual rate of retreat observed on the ground, supplements the historical series used by consulting firms, and tracks the effectiveness of a defence structure or a beach-recharge project from one survey to the next.
The flight itself most often falls under the open category, sub-category A2 or A3 depending on how busy the site is — a beach patrolled in high season does not call for the same precautions as a deserted dune system in winter. The difficulty does not always come from the airspace: a dune system classified as a national nature reserve, a Natura 2000 site, or land owned by the Conservatoire du littoral (the French coastal protection agency) often requires a separate access authorisation, particularly off marked paths or during the nesting season of protected birds — a logic comparable to what our guide to flying a drone in the mountains and in national parks covers. As with any professional mission, checking regulated zones on the Géoportail map, registering the operator on AlphaTango and professional third-party liability insurance remain essential, independent of the site access authorisation — see also our guide to flying a drone at the beach for the rules that apply to individual rather than professional use.
The price of drone coastal erosion monitoring in 2026
The price mainly depends on the length of coastline to cover, the desired monitoring frequency, and the density of ground control points needed for centimetre-level accuracy. Orders of magnitude observed in France in 2026:
| Service | Observed price (excl. VAT) |
|---|---|
| One-off survey after a storm, under 2 km of coastline | €900 to €1,800 |
| Full photogrammetric survey (orthophoto + georeferenced DSM), 2 to 5 km | €1,800 to €3,500 |
| Placing and surveying ground control points with differential GPS | +€400 to €900 per survey |
| Differential (DSM) comparison with a previous survey, volume calculation | +20 to 35% of the collection cost |
| Multi-year monitoring integrated into a local shoreline management strategy | quoted individually, depending on frequency |
That price should be weighed against a foot survey of beach profiles, cheaper per unit but limited to a few sections of coastline, or an institutional airborne LiDAR campaign, more accurate over a very long stretch but run only every few years: the drone occupies the middle ground where a local authority's operational monitoring actually happens, between two official campaigns or right after a storm that will not wait for the next scheduled flight.
Frequently asked questions about drone coastal erosion monitoring
Does the drone replace institutional airborne LiDAR (Litto3D)? No: it complements it over a shorter stretch of coastline and at a much higher frequency, useful between two official campaigns or right after a storm.
Can a drone fly over a coastal nature reserve or a Conservatoire du littoral site? It depends on the site manager: the airspace may be open even while site access remains subject to authorisation, particularly during the nesting season.
What accuracy can be expected from drone monitoring? Around a few centimetres in elevation, provided the ground control points are correctly placed and surveyed with differential GPS.
How often should a survey be repeated? After every significant storm for a one-off diagnosis, or once or twice a year for regular monitoring built into a local shoreline management strategy.
Put it into practice
- Drone surveying & photogrammetry: rates and cities covered from €800
- Drone security & surveillance: rates and cities covered from €600
- Surveying & photogrammetry in Vannes Bretagne
- Surveying & photogrammetry in Bastia Corse
- Surveying & photogrammetry in Saint-Malo Bretagne