Riprap work bolsters Davison County's bridges in 2020
Half of costs covered by James River district
Water under the bridge? It is flowing better under nine key bridges in Davison County after work done in 2020.
Davison County Highway Department workers helped install nearly $45,000 in 1,895 tons of riprap rock under bridge structures to help preserve the integrity of the bridges’ and their backwalls.
The county received some help in paying that riprap cost earlier in December. The James River Water Development District approved a request from Highway Superintendent Rusty Weinberg for $22,350, or half of the project costs.
The riprap was installed, Weinberg said, on nine bridges following bridge inspections done in 2020 by Brookings-based Civil Design civil engineering. Adding the riprap would protect the quality of the bridges, help mitigate sediment getting into creeks by reducing water erosion and protecting against possible future flooding.
Backwalls are the vertical walls at the ends of bridges that extend up from abutments and support the bridge approaches and expansion joints. The county’s backwalls, many of them made of wood and timber, were damaged by erosion and flooding events and can cause scour, which is the removal of sediment from around bridge abutments and piers. Scour is a common cause of bridge failure, which makes addressing it important.
All nine bridges are located in the southern half of the county in Lisbon, Rome, Tobin and Union townships. Six of them happen to be within a 10-mile radius of Ethan.
“We were able to get them repaired and mitigated and get those addressed before winter arrived,” Weinberg said.
Riprap is the large, loose stones that is placed along a shoreline or waterway that will defend against scour and water erosion.
Weinberg calculated that the projects included more than 400 hours of work. The most expensive was 265th Street between 405th and 406th Avenues, which had 599 tons of riprap and more than 57 hours of work, with a project cost of $10,050.
As it related to the 2019 flooding, Weinberg explained to the JRWDD board that the work was not eligible for Federal Emergency Management Administration money because the bridges themselves were not damaged at the time of the flooding, and the issues were only visible after the water levels in the area had receded and bridge inspections were completed. The county typically has its bridges inspected every two years.
Chris Brozik, of Civil Design, appeared before the Davison County Commission on Dec. 8 to give the county board an update on the status of bridges in the county. When asked to give the county a letter grade for its current status, he said the county was above average before grading it as a B-minus.
“Which is good from an infrastructure standpoint. It’s good to do this work right away and it was dry and perfect weather to do it,” Brozik said.