Water-law file (IOTA)
Declaration or authorisation under the French water law
Works affecting water and aquatic environments fall under the French water law (IOTA nomenclature), requiring a declaration or an authorisation depending on thresholds (e.g.
Water-law file (IOTA)
Works affecting water and aquatic environments fall under the French water law (IOTA nomenclature), requiring a declaration or an authorisation depending on thresholds (e.g. intercepted surface). ARKENOR prepares the file, including the characterisation of impacts on water and wetlands.
Trigger
Thresholds, not judgement.
French water law works from a schedule of activities and thresholds. Exceeding a threshold, surface drained, wetland area affected, watercourse crossed, volume abstracted, triggers either a declaration or a full authorisation, with very different timetables. The determination is objective, which is useful: it can be made early, from the design, without waiting for an opinion.
The most frequent trigger on building projects is not the watercourse but the drained surface. A large impermeable area changes runoff, and the file addresses both quantity and quality of what leaves the site.
Content
Stormwater is a design subject, not a compliance annex.
The file sets out how runoff is managed: retention, infiltration, treatment before discharge. Designing it late means retrofitting basins and structures into a layout that has no room for them, which is why stormwater strategy belongs with the masterplan.
Where wetlands are affected, the file carries a compensation component whose ratios are demanding, and it is examined alongside the impact assessment.
Regime
Declaration and authorisation are not the same procedure.
Below the authorisation threshold, a declaration is filed and the works may proceed after a waiting period unless the authority objects. Above it, an authorisation is required, with examination, public participation and a considerably longer timetable. The gap between the two regimes is measured in months, and the threshold is often crossed by a small increase in drained surface.
Knowing which side of the threshold a scheme falls on, and whether a modest design change keeps it on the lighter side, is one of the cheapest interventions available at feasibility stage.
Going further
Related pages.
The Water Act file connects to these procedures.
- Wetland delineation — the most demanding trigger
- Environmental impact assessment — examined alongside
- Offsetting measures — for wetland loss
- Natura 2000 incidence assessment — where effects travel through water
- Natural component (VNEI) — aquatic habitats and species
- Working with land developers — stormwater as a masterplan input
- XXL logistics — large impermeable surfaces
- Ecological expertise — the full set of procedures
- Working with land developers — where the threshold decision is made
- XXL logistics — large surfaces, frequent authorisation regime
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