Stormwater Management

This week, we’ve passed inspection on our stormwater management system. This is a District requirement, targeting new builds and homes adding significant surface area in roof and hardscape.

When rainwater hits these impervious surfaces, run-off is generated, often more than the site can tolerate, which can overwhelm the District’s central stormwater infrastructure. It is the owner’s responsibility to design a system to absorb this additional run-off through a stormwater management plan (SWMP).

Initially the SWMP was waived for our project (we are adding very little floorspace ~150sqft total) but subsequently triggered by the new build designation. A geotech conducted a dispersion test last spring to find out how much water the earth can absorb on our property. Turns out we have super low natural site permeability - the test pit only drained 2” in 24 hours.

Enter the ‘brentwood box’, a subsurface storage module that collects and permeates runoff into the surrounding native soil before feeding to District drainage. The aim with this system is to reduce the stormwater flow rate off the site from 8.8 L/s currently to <0.68L/s.

A large hole (6.4x2.4m) was dug and leveled in our front yard, lined with geotextile fabric, and 48 Ecoblock modules double stacked (205L capacity each) for a total storage of 9,800 litres (!) The system is fed by two 0.9m diameter sumps, one for roof water discharge and one for perimeter drain discharge.

Backfill and top cover to follow and, at long last, we should be done with the drainage scope for our project ✅ Phew. Looking forward to having a level front yard again!

#netzero #netzerohome #stormwater #stormwatermanagement #drainage #greenbuilding #sustainability Example product images via Graf