Natural Drainage Servitude for Dominant Land: Slope Calculation in Toulon

PROPERTY LAW — SERVITUDE

You bought a sloped plot in Toulon, and every storm turns your garden into a retention basin. Water from the neighboring plot, higher up, cascades straight into yours. You measured the height difference with a ruler and a spirit level: roughly 80 cm over 15 metres. That works out to a 5.3% slope. You assume this is normal — the law of the dominant estate. What nobody tells you: Art. 640 of the Civil Code sets precise limits, and in Toulon, with its clay-heavy soils, the critical threshold is often exceeded.

What You See — And What It’s Really Hiding

You see water flowing. Gullies cut into the soil, sometimes rubble spilling over the property line. You tell yourself: « It’s his land, he’s higher up, it’s his right. »

Frankly, that’s what I find in 8 out of 10 cases in Toulon. Owners simply endure it, believing the natural drainage servitude gives the dominant estate an absolute right. In reality, Art. 640 of the Civil Code specifies that this drainage must occur « naturally », without being aggravated by works. The neighbour had built a retaining wall and sealed off a large part of his plot with concrete. The result: the flow reaching the lower plot had tripled. This was no longer natural drainage — it was aggravated discharge. The real question isn’t « Is water flowing? » but « Is water flowing MORE, and FASTER, than before the works? »

Dominant land Your land Lower land Level +5.20 m NGF Level +4.40 m NGF Calculated slope: 5.0% Property boundary Your boundary Neighbour’s boundary Aggravated runoff

The Slope Calculation That Changes Everything

Slope is Δh/L × 100. Δh = height difference, L = horizontal distance. Simple? Yes, but you need the right values. In Toulon, the reference systems are NGF-IGN69 for elevations and RGF93/Lambert 93 for coordinates. Measured with a ruler, you get 80 cm over 15 m. With a Leica TS16 total station (±1 cm accuracy), I often find something different. Take a real case from the town centre: high point at 5.20 m NGF, low point at 4.40 m NGF, distance 16.00 m. Δh = 0.80 m. L = 16.00 m. Slope = (0.80 / 16.00) × 100 = 5.0%.

That figure alone tells you nothing. It must be compared to the land’s natural slope before the works. Eurocode 7 – §2.4.5.2 on geotechnical actions – considers that a slope change of more than 20% relative to the original slope can alter drainage patterns. If the natural slope was 4.0% and it becomes 5.0%, that’s a 25% increase. That’s significant. What this means in practice: the neighbour cannot, through his own works, increase the runoff speed toward your plot by more than 20%. In Toulon, with slopes commonly between 4% and 8%, this threshold is crossed quickly.

What Happens If You Do Nothing

Within 6 months, erosion worsens. Gullies turn into ravines. Topsoil washes away.

By year 2, the foundations of your fence or a garden shed can be undermined. It’s not uncommon in Toulon to see a house whose terrace slab has cracked because of water draining from the upper plot. The cost? Between €8,000 and €15,000 for underpinning repairs. By year 5, if the soil is clay-rich (common in the Var), wetting-drying cycles cause swelling and differential settlement. Cracks appear on walls. Secondary pathologies follow: rising damp, mould growth. Treatment becomes costly, often exceeding €25,000. And your insurer may well refuse cover, citing a lack of maintenance or a known construction defect.

Remedies and Guarantees: What You Can Demand

Your weapon is Art. 640 of the Civil Code, para. 1: « Lower estates are bound, in favour of higher ones, to receive the waters that flow from them naturally… ». The key word is « naturally ». If the drainage has been aggravated, you can demand restoration. The process: send a registered letter with acknowledgement of receipt to the neighbour, detailing the nuisance. If they don’t respond, instruct an expert (a planning/urbanism expert, for instance) to carry out a joint survey using a total station and calculate the potential flow rate. As a last resort, the Toulon judicial court has jurisdiction. Don’t wait. In Toulon, case processing times are long. Act at the first signs of trouble.

Frequently Asked Questions

What is the maximum slope allowed for natural drainage in Toulon?

There’s no absolute maximum slope, but Art. 640 of the Civil Code prohibits any aggravation of drainage. Eurocode 7 treats a slope increase of more than 20% relative to the natural slope as significant. In Toulon, with natural slopes between 4% and 8%, even a 1% increase can already be contentious.

How do I prove the neighbour has aggravated water drainage?

You need to compare the current slope with the natural slope before any works. A planning expert can measure it using a total station (±1 cm accuracy) and NGF-IGN69 reference data. If the slope has increased by more than 20%, or if the flow rate has multiplied (for example, tripled after surface sealing), aggravation is established.

What can I do if my neighbour has sealed their land with concrete and water floods my property?

You can require them to stop the aggravation — for example, by installing a retention basin or limiting surface sealing. If nothing changes, take the matter to the Toulon judicial court. Art. 640 of the Civil Code allows you to obtain damages and restoration of the original state. A bailiff’s report and an expert report are essential.

How much does an expert assessment of slope and drainage cost in Toulon?

An assessment by a planning expert costs between €800 and €1,500 depending on complexity (surveying, report, travel). For a simple total-station measurement, expect €500 to €800. It typically takes 1 to 2 weeks. It’s a worthwhile investment to build a solid case file.

Can I build a wall or fence to protect my land from surface runoff?

Yes, but be careful: you must not aggravate drainage onto other properties. A retaining wall should be designed so it doesn’t increase flow rate or velocity. In Toulon, given the clay soils, drainage also needs to be planned. Consult a building expert to comply with Art. 640 and avoid a dispute.

Frequently Asked Questions

My neighbour has sealed their land with concrete — what can I do if water floods my property?

If your neighbour’s works (retaining wall, concreting) increase the flow rate or speed of water reaching your plot, this is no longer natural drainage. Article 640 of the Civil Code prohibits aggravation of the servitude. Have the slope measured before and after the works by a planning expert. In Toulon, exceeding the natural slope by 20% is considered significant.

How much does an expert assessment for a water drainage servitude cost in Toulon?

An assessment including a topographic survey (total station) and report costs between €800 and €1,500 including VAT depending on complexity. It takes 1 to 2 weeks. This price includes the slope calculation, comparison with the natural state, and a preliminary legal analysis. It’s a worthwhile investment before mediation or legal proceedings.

How do I calculate my land’s slope to prove aggravation?

Measure the height difference (Δh) between the high point and the low point, and the horizontal distance (L). Slope = (Δh / L) × 100. For legally sound precision, use a planning expert with a total station (±1 cm accuracy). In Toulon, elevations reference NGF-IGN69. Compare with the natural slope before development: if the increase exceeds 20%, drainage has been aggravated.

What is the legal threshold for aggravation of a water drainage servitude?

Article 640 of the Civil Code requires natural drainage. Case law and Eurocode 7 consider an increase of more than 20% in slope or flow rate compared to the natural state to constitute aggravation. In Toulon, with slopes of 4 to 8%, this threshold is often crossed after surface sealing. An expert can demonstrate it.

What if my neighbour refuses to acknowledge the aggravation of drainage?

Start with a bailiff’s report after a storm. Next, have a topographic assessment carried out by a planning expert. If the neighbour refuses an amicable solution, send a formal notice by registered letter along with the assessment. As a last resort, take the matter to the Toulon judicial court. The process can take 6 to 12 months, but you can obtain damages and restoration of the original state.

📅 Updated on 22/08/2026 — By Cassini Expertise, independent building expert for the Alpes-Maritimes & Var. Free quote: 04 22 46 06 04.

📅 Mis à jour le 25/09/2026 — Cassini Expertise, expert bâtiment indépendant (06·83·13·40).