Ask anyone who works on drains around here when they are busiest and you will get the same answer: the first sustained wet stretch after the dry season, then steadily through to March. It is not a coincidence and it is not just that more people are indoors. Rain changes the physics of what is happening in the ground around your pipes.
Saturated Ground Is the Whole Story
Bothell gets a large share of its annual rainfall spread across a long grey stretch rather than in dramatic bursts. That pattern matters more than the total. Short heavy storms hit dry ground that can absorb them. Months of steady drizzle produce something different: soil that never gets a chance to drain, and a water table that sits high from autumn into spring.
Once the ground around a buried pipe is saturated, three things start happening at once.
1. Infiltration Loads the Sewer Before You Use It
Groundwater under pressure finds every crack, offset joint, and failed seal in a side sewer and gets in. The trade calls it infiltration, and on an old clay or Orangeburg lateral it can amount to a genuinely significant flow. Your line is running part full before anyone in the house has flushed anything.
That is why a pipe that handled a summer barbecue for twenty people gives up during an ordinary Tuesday in December. The capacity available to you has quietly shrunk.
2. Surface Drainage Stops Absorbing
Yard drains, downspout lines, and catch basins are sized on the assumption that some water infiltrates into the soil. When the soil is already full, all of it has to go through the pipe. If those pipes are packed with the Douglas fir needles and big-leaf maple litter that came down in October, water pools instead: across the lawn, against the foundation, into the crawlspace.
A striking share of our winter "my drain is backing up" calls turn out not to involve the sewer at all. It is surface water with nowhere to go.
3. Wet Ground Moves
Saturated soil is heavier and less stable. On the slopes off Norway Hill and Westhill that produces differential settlement, which pulls joints apart and opens offsets. On the flat alluvial ground near the Sammamish River it produces bellies, sections of pipe that sag and hold standing water permanently. Both defects start small and both get worse every wet season.
Why It Feels Sudden
Because the failure is, even though the deterioration was not. A line with root intrusion at one joint, a slight belly, and winter infiltration can run acceptably for years. Each factor takes a little capacity. Then one evening the household load lands on top of all three at once and the margin is gone.
Homeowners usually describe this as "it was completely fine and then it just stopped." From the pipe's point of view it had been getting worse for a decade.
The September Checklist
Almost everything that goes wrong in December is cheaper to address in September, when nobody is in an emergency and the ground is workable.
- Clear the gutters, then the underground lines they feed. Clean gutters that drain into a packed underground pipe just move the blockage out of sight.
- Check yard drains and catch basins. Lift the grates. If you see standing water or packed needles, they need jetting before the rain arrives.
- Camera the sewer if it has backed up before. A line that failed last winter will fail again this one unless something changed. Better to find out why in dry weather.
- Test the sump pump. Pour a bucket in and confirm it kicks on and discharges. October is a bad month to discover a seized pump.
- Watch where roof water lands. Downspouts discharging next to the foundation are a crawlspace problem waiting for a wet week.
Warning Signs During the Season
If any of these show up between October and March, do not wait it out:
- Gurgling from a tub or floor drain when a toilet is flushed
- Fixtures getting slower over days rather than stopping suddenly
- A drain that only misbehaves after heavy rain, which points hard at infiltration
- Damp or standing water in the crawlspace
- Sewer smell in the yard along the line run
A drain that is fine in dry weather and troublesome after rain is telling you something specific and useful: groundwater is getting in somewhere. That is a pipe defect, and it will not resolve itself.
What We Do in the Wet Months
Mostly, we clear lines at inconvenient hours. The work we would rather be doing is the September version: a jetting pass on the surface drainage, a camera run on any sewer with a history, and a straight conversation about whether the line needs a repair or just an interval.
If it has already gone wrong, we answer 24 hours and we are based here, so the response is a local drive. If it has not gone wrong yet and you have been meaning to deal with it, this is the part of the year to call.
