Where does a Vancouver catch basin fit with permeable paving?

A catch basin is the overflow safety net for a permeable paver system — not the primary drainage mechanism, but an essential component when infiltration capacity is exceeded.

Permeable interlocking concrete pavement (PICP) is designed to handle rainfall by allowing water to pass through the open-graded aggregate joints and into a reservoir base layer of clean, gap-graded crushed stone beneath the pavers. Under normal Metro Vancouver rainfall conditions, this infiltration system manages the water without any surface runoff. But Metro Vancouver is not a normal rainfall environment — and that's where catch basins become critical.

How Permeable Paving Handles Water (And Where It Falls Short)

The open-graded aggregate base beneath a PICP system acts as a temporary underground reservoir. Water infiltrates through the joints, fills the void space in the base (typically 30-40% void ratio in a properly specified open-graded aggregate), and then slowly percolates into the subgrade soil or is directed to a perforated drain pipe that outlets to the municipal storm system or a dry well.

The design infiltration rate of a new PICP system is typically far higher than Metro Vancouver's average rainfall intensity. A well-built permeable base can absorb 100-300mm of rain per hour, while Vancouver's most intense storms rarely exceed 30-40mm per hour. In theory, the system should never be overwhelmed. In practice, three things can push water beyond the base's capacity: sustained multi-day rainfall events (common in Metro Vancouver from November through February, where cumulative totals can exceed 200mm over a week), sediment loading that reduces infiltration rates over time (the joints and base gradually clog with fine particles, reducing permeability), and high water table conditions (particularly relevant in Richmond, Delta, and low-lying parts of Surrey and Langley, where the subgrade may already be saturated and cannot accept additional infiltration).

Where the Catch Basin Fits In

In a properly engineered Metro Vancouver PICP installation, the catch basin serves as the overflow outlet — positioned at the lowest point of the paved surface or at the edge of the permeable zone. When the base reservoir fills to capacity (during extended winter storms or after years of reduced infiltration from sediment accumulation), water that cannot infiltrate fast enough rises to the surface. Without a catch basin, that water ponds on the surface or flows uncontrolled off the paved area. With a catch basin, it is captured and directed to the storm drain in a controlled way.

The catch basin in a PICP system is typically set with its grate slightly below the finished paver surface — usually 6-12mm lower than the surrounding pavers. This is the reverse of how catch basins are set in conventional impervious paving, where the grate is at or slightly below grade to collect all surface runoff. In a PICP system, you want water to infiltrate first and only reach the catch basin when the base is saturated. Setting the grate too high means it collects water before the permeable system can do its job; setting it too low creates a depression that collects sediment and debris and clogs the catch basin faster.

The catch basin connects to either the municipal storm sewer (requires a connection permit from your municipality's engineering department) or an on-site dry well or soakaway pit. In Richmond and Delta where the water table is high and municipal connections may be required, confirm the outlet requirements with the city's engineering department before design is finalised.

Maintenance Implications for Metro Vancouver

Catch basins in PICP systems need more frequent inspection than those in conventional paving because the permeable system is actively filtering sediment — and that sediment eventually reaches the catch basin. In Metro Vancouver's wet climate, inspect and clean the catch basin grate and sump at least twice per year — once in October before the rainy season and once in April after it ends. The PICP joints themselves should be vacuumed with a regenerative air sweeper every 2-3 years to restore infiltration capacity; this is a professional service, not a DIY task.

If you're planning a permeable driveway or patio in Metro Vancouver, the catch basin placement, outlet design, and connection to the storm system should be part of the initial design — not an afterthought. Vancouver Interlock can match you with experienced PICP installers from the Vancouver Construction Network who understand both the permeable system design and the municipal drainage connection requirements specific to your municipality. Browse the directory at vancouverconstructionnetwork.com/directory?trade=interlock or get matched for free through Vancouver Interlock.