The Hannibal Board of Public Works (HBPW) on Thursday morning investigated the cause of a storm sewer failure that occurred this week near the intersection of Bridge and North streets in downtown Hannibal.
"We are unsure of what exactly happened to cause it," said Mathew Munzlinger of the HBPW. "We are trying to pump it down to see whether the side is blown out, or the top is blown out, so we can have an idea of what we're up against."
The site of the storm sewer failure, the force of which damaged the paved surface above it, is a short distance from where river water has been seeping up through the pavement after going beneath the downtown flood levee. Munzlinger did not believe the seepage was a contributing factor to the storm sewer's failure.
"I think it is probably a result of the heavy rain we had the other night. It just overwhelmed the system," he said.
A case could be made that the flood was a contributing factor to the failure of the storm sewer. According to HBPW flood protocol a gate in the stormwater drainage system must be closed when the Mississippi River reaches 25 feet to prevent flood water from backing into the stormwater system. Runoff water could not flow into the river as it normally would have, because the gate was closed.
"The water coming down the hill against this pipe probably caused it to blow out a sidewall or blow out the roof," Munzlinger said.
Munzlinger estimated it will take months to complete repairs.