Culverts beneath roadways are out of sight and out of mind until there’s something wrong with them. Then comes the work, as in two major projects this summer in the Covington and Maple Valley areas.

The bulk of the seasonal maintenance work for King County road crews involves repairing or replacing up to 100 culverts under roadways. The culverts range in size from 12 inches in diameter to 20 feet wide. Some allow small streams and tributaries – and fish – to pass beneath roads, while others are part of drainage systems. If a culvert begins to deteriorate or leak, it can cause the roadway to buckle, crack or collapse. A failing culvert can also erode the road’s shoulders.

The potential for any or all of that trouble had county roads replacing a culvert this week beneath Kent-Black Diamond Road, south of Covington. It’s one of the bigger such projects of the summer, officials said.

The old concrete pipe, buried deep, is full of tree roots, and the constricted flow of water has caused the culvert to start collapsing. The busy road above is a key arterial for southeast King County, officials said, so the county wants to replace the culvert before it endangers the roadway – a much worse alternative than the daily closures this week from 7 a.m. to 4 p.m. to allow the work. Traffic was detoured via State Route 18 and Auburn-Black Diamond Road.

Other large culvert projects this summer include one on Kanaskat-Kangley Road near Maple Valley.

Since most of the bigger projects are located in or near fish habitat, the work must be done within a three to four-month “fish window” to avoid disrupting spawning seasons, officials said. It varies by species, so some of the culvert work has already begun while other projects won’t start until August.

“Due to aging infrastructure, it is critical that we take care of our current system” in order to “not lose parts” of it, said Linda Dougherty, road services director for the county. “Our first priority is always to make sure our roads and bridges are safe and fully functional.”

Among county-owned bridges – some large, such as a new Tolt Bridge west of Carnation, others short – work planned for this summer includes replacing three or four short-span bridges in the lower Snoqualmie Valley. Construction is expected to start in late July or August and proceed through mid-October.

Meanwhile, the annual repaving – overlay, as it’s called – of county roads began this week in the Maple Valley and Hobart areas. Work in unincorporated areas north of Interstate 90 will begin in a few weeks.

King County maintains more than 1,800 miles of roadway. The asphalt surfaces wear out from the effects of traffic, age and weather. Overlaying roads restores their surfaces and protects the roadbeds from erosion, which officials said extends the life of roads and is less expensive than rebuilding them.

Overlay projects are grouped together by location to minimize costs and make crews more efficient, according to officials.