Statewide Flood Resiliency Analysis

You need to be able to count on Iowa’s transportation system, no matter the weather conditions. Our core values of “customer focused’ and “people matter” are just a couple of the reasons we are taking a statewide look at how our roads might hold up in severe flooding.

Need for the Analysis

In 2021, our Resiliency Working Group began developing a Statewide Flood Resiliency Analysis that was eventually integrated into the State Long-Range Transportation Plan.

Identify & Assign

The group worked to develop a data-driven method to identify and assign a score to specific sections of interstates, U.S. and state highways that are most vulnerable to a 100-year flood event. That score allows Iowa’s decision-makers to prioritize construction projects geared to reinforce areas that may be more vulnerable to flood damage.

Analysis Structure

To come up with the score, the team looked at three broad components with seven individual factors for each component. The goal was to develop a composite score that would help us determine which roads were more vulnerable to flooding.

Robustness

This element of the scoring system analyzes the vulnerability of the highway network to a 100-year flood event based on the 100-year floodplain boundary, whether past flooding events have occurred, and roadway shoulder data to estimate how sensitive a specific location may be to flooding.

• 100-year flood exposure and bridge scour
  (45 percent)
• Evaluation of past flood events
  (15 percent)
• Roadway resistance
  (10 percent)

Redundancy

This element of the scoring system analyzes the availability of alternative routes that you could use in the event that a route becomes flooded or damaged by flooding.

• System availability (20 percent)

Criticality

This element of the scoring system identifies the roads that would have the most impact on the way the whole system works.

• Federal functional classification (4 percent)
• Annual average daily truck traffic (4 percent)
• Social vulnerability index (2 percent)

The data for each attribute were normalized on a 1 (worst) to 10 (best) scale and combined based on the weighting on a scale determined by the team. The maximum composite score is 100. Higher scores indicate roads that could be expected to hold up better in a 100-year flood event and lower scores indicate greater vulnerability to those events.

Results

The analysis helps identify roads where there is a greater risk of flood events and helps us determine where additional work could make the roads stronger related to flooding. The overall distribution of composite ratings ranged from 36.6 to 93.4, with an average of 82.4. Roads of most concern from a long-range planning standpoint, are those roads that had a composite score one or more standard deviations below the statewide average. There are 72 such roads which have a composite score of 75.1 or less.

View full size interactive map

Award Honors

In October of 2022, we won an award for our Statewide Flood Resiliency Analysis in the category of Transportation Planning from Iowa’s chapter of the American Planning Association. This award honors efforts to increase transportation choices for all Iowa travelers.