The Dallas County Secondary Roads Department will start Friday on a two-week project to replace the bridge crossing the Swan Lake Branch on 170th Street west of County Road P58 south of Perry.
The 1.28 mile stretch of 170th Street will be closed to through traffic from about 7 a.m. Friday, Sept. 27 to about 4:30 p.m. Friday, Oct. 11.
The bridge crossing the Swan Lake Branch on 180th Street, one mile to the south of the 170th Street bridge, is also slated for replacement this fall.
The Dallas County Board of Supervisors approved five right-of-way purchase agreements in April with Dallas County landowners, paying $3,166 for 1.05 acres’ worth of permanent easements needed for planned bridge replacements on 170th and 180th streets.
The two bridges cross the Swan Lake Branch, a tributary of the North Raccoon River. The Swan Lake Branch Watershed Plan was published in February 2018. The watershed comprises 15,775 acres south of Perry. Row crops occupy 89 percent of the watershed, with a resulting 400,000 pounds of nitrogen and 2,200 pounds of phosphorus entering the Raccoon River yearly, according to the watershed plan.
The reduction goals of the Iowa Nutrient Reduction Strategy calls for a nitrogen reduction target of 41 percent and a 29 percent reduction in phosphorus.
At present the Swan Lake Branch has very little in the way of conservation practices in place to prevent soil loss and reduce nutrients entering the waterway. Recommended conservation practices, including 6,000 acres planted in cover crops and 7,000 treated by wetlands, will cost about $2 million to implement and $335,000 annually to maintain.
