When the heavy rains hit northeast Johnson County on Aug. 26, water spilled over the banks of area streams, trapping motorists and washing one car downstream to leave it pinned against a culvert.
The water also played havoc with an aging stormwater infrastructure. That was especially evident in Mission where a huge sinkhole opened behind houses at the end of 62nd Terrace. The water, channeled through corrugated metal storm pipes, lifted an entire section of the huge pipe out of the ground and carried it downstream.
At the heart of the problem, said Mission Public Works Director John Belger, is the aging system of metal pipes that rust out. When water rusts the pipe and then forms new channels through the soil, it washes dirt downstream creating the potential for a sinkhole in the gaps left behind.
The metal pipe has a lifespan of about 30 years, Belger said, and most of the stormwater pipe in Mission is older than that. Eventually, it will all need to be replaced.
The Aug. 26 sinkhole was not the first Mission has experienced. Even this summer the wet weather caused at least three other earlier failures. In 2013 a sinkhole developed in the parking lot near the Hobby Lobby store when metal pipe failed. Roeland Park also has experienced problems with failing corrugated metal pipes.
The metal piping was used years ago, Belger said, because it was light and cheap. Stormwater pipes put in today are either concrete or polyethylene with lifespans decades longer.
The other problem with the metal is that bands holding sections together rust and separate which allows water outside of the pipe. The continuous development since the stormwater infrastructure was put in place also means more water is being pushed through the system and some of the pipes are undersized.
At 62nd Terrace, water comes under Shawnee Mission Parkway moving north and then pops back up above ground a few yards after the spot of the sinkhole.
The stormwater pipes aren’t the only problem caused by stormwater. Mission is having engineering studies completed not only for repairs to the failed pipes, but also for a section along Rock Creek behind the Mission Bank parking lot.
Erosion on the bank has caused part of the lot to fail. Across the creek, the erosion has caused residential yards and fences to drop several feet.