Introduction
Building on a steep slope in Quebec presents a major challenge: managing stormwater runoff.
Without proper solutions, water can:
- Accumulate behind retaining walls,
- Increase hydrostatic pressure on the house,
- Cause slope erosion,
- Endanger upstream and downstream septic systems,
- Impact neighboring properties.
In Mont-Tremblant, the municipality requires a stormwater management plan for any construction on a sloped lot. This regulation helps protect homes, municipal infrastructure, and the environment.
Site Findings
In Mont-Tremblant, on a lot with more than 30% slope, the planned development includes:
- A residence with a basement and French drain,
- Two 1.5 m retaining walls,
- A septic tank upstream and a leaching field downstream,
- A municipal ditch at the bottom of the property.
This natural configuration concentrates runoff and increases the risk of infiltration and erosion without proper design.
Proposed Engineering Solutions
1️⃣ Interception trench
Captures and redirects slope water before it reaches walls or septic systems.
2️⃣ French drains
- Around the house foundations,
- At the base of retaining walls, to relieve water pressure and discharge by gravity toward the municipal ditch.
3️⃣ Roof water management
Gutters and downspouts connected to sealed pipes leading to a retention basin or vegetated swale.
4️⃣ Retention basin
Sized to local storm events, it retains and gradually infiltrates water before controlled release.
5️⃣ Complementary measures
- Vegetated swales with check-dams to reduce erosion,
- Culvert under the driveway to keep ditch flow,
- Tree and slope protection during construction.
Conclusion
With proper engineering, the project ensures:
✔️ Protection of the house and retaining walls,
✔️ Safety of septic systems,
✔️ Compliance with municipal requirements,
✔️ Long-term site durability in steep-slope conditions.
👷♂️ At Florcon, we design custom drainage and runoff management plans that comply with regulations and adapt to each site’s needs.
📞 Building on a sloped lot? Contact Florcon today for a safe and sustainable water management plan.
Runoff Management on a Steep Slope in Mont-Tremblant