Homeless advocates question Des Moines' bridge "riprap"

City crews recently installed a cement-rock mixture known as "matrix riprap" underneath two Des Moines bridges vandalized by fires.

Why it matters: Homeless advocates criticized the rough surfaces on social media this week, saying it deters people from sleeping or loitering under the bridges.

• But city leaders say bridge stabilization was the driving factor behind the projects.

How it works: The rocky material is placed along bridge foundations, and glued together — often with a cement-based grout.

• Riprap prevents people from removing bridge support materials and helps secure infrastructure during floods, according to research by Minnesota's Department of Transportation.

Flashback: Fires under the Martin Luther King Jr. Parkway and University Avenue bridges damaged their structural support systems in recent years and caused about $170,000 in damages.

What they're saying: The city determined the best solution to repair the damage was to embed the rocks in concrete, city engineer Steven Naber told us yesterday.

• Melissa O'Neil, CEO of Central Iowa Shelter & Services, told Jason in March that riprap is necessary to protect the infrastructure and public's safety.
• City leaders aren't out to make the lives of homeless people more miserable, she said after a public meeting where the bridge problems were discussed.

Of note: DSM is launching new homeless assistance programs, including a pop-up care village that we told you about in July.