A catch basin is the grated drain in a driveway, a parking area, a courtyard or a low point in a yard. It collects surface water and sends it into the storm system, and it has a sump below the grate designed to trap sediment before it reaches the pipe.
It is simple, it is cheap to maintain, and it is almost universally neglected until it overflows.
Why they stop working
Leaves. The obvious one, and the seasonal one. A grate covered in wet leaves is a sealed surface — water arrives and has nowhere to go.
A full sump. The chamber below the grate fills with silt, grit and debris. When it is full, sediment starts passing into the outlet pipe, which is exactly what the sump existed to prevent. Clearing that sump is the entire maintenance requirement and it is rarely done.
Blocked outlet pipe, downstream of the basin, where sediment that passed the full sump has settled.
Roots, entering the pipe or the basin structure.
A damaged structure — a cracked basin, a collapsed section, a grate that has broken.
The timing that matters
Late summer to early autumn. Before the rain, not during it.
The reasoning is straightforward. The heavy leaf fall and the heavy rain arrive close together, and a basin that is already sediment-filled in September has no capacity when it is needed. Clearing it beforehand means it starts the wet season with its full sump available.
There is a second, more practical reason. Once the rain starts, everyone whose basin has overflowed calls at once, and the work has to be done in the conditions that caused the problem.
What to check yourself
Lift the grate — most lift with a bar or a hook — and look in. If the sump is full to the outlet pipe, it needs clearing. If you can see the bottom, it is fine.
Clear leaves and debris off the grate through the autumn, particularly after a windy day. This takes a minute and it is the single most effective thing you can do.
Watch how water behaves in heavy rain. Water that pools around a basin instead of disappearing into it is telling you something now, while you still have time to act.
For commercial and strata properties
This is a liability question as much as a maintenance one. A parking area that floods is a hazard, and one that floods repeatedly and predictably is a hazard someone knew about.
Larger properties usually have multiple basins, and they do not fill at the same rate — the ones under trees fill fastest, the ones at low points collect most sediment. Knowing which are the problem basins is worth more than treating them all identically.
An annual scheduled clean before the wet season, with the problem basins checked more often, is the arrangement that works. It is inexpensive per basin and it is planned rather than emergency work.
Where they connect
Catch basins discharge into the storm system, which is separate from the sanitary sewer. What goes into a storm drain generally reaches watercourses with limited treatment, which is why municipalities are particular about what is allowed into them.
Practically, this means a blocked catch basin cannot be cleared by pushing the problem downstream, and it means anything spilled near one matters.
The economics
Clearing a catch basin is among the least expensive work in this trade. Dealing with a flooded parking area, water finding its way into a building at a low point, or a collapsed basin structure is not.
The gap between those two numbers is the argument for putting it in the calendar rather than waiting for the call.
Vancouver, Burnaby, Richmond, Coquitlam, Port Coquitlam, New Westminster. 604-865-7979.
Related: Storm drains and catch basins · Perimeter drainage installation and replacement · Sump pumps
