Evaluating Risk and Resilience in Stormwater Systems

The practice of risk and resilience assessment has been around for years for the evaluation of dams, levees, and bridges, because if one were to fail, the effects would be catastrophic. Now, we are seeing risk and resiliency evaluations being applied more broadly to stormwater systems. It is being used to prioritize stormwater improvements and help cities make infrastructure investment decisions. We interviewed Maeve VanLandingham, a stormwater project engineer, on the topic.

Why have risk and resilience assessments become more prevalent?
Due to the increasing cost associated with infrastructure replacement and the ever expanding need to address aging infrastructure, we are seeing a heightened interest in performing risk assessments for stormwater infrastructure to help prioritize improvements and maximize the impact of infrastructure investments. Another reality is that there are more stormwater system failures due to increases in storm intensity and duration caused by climate change. A risk assessment focused on the likelihood of a system failure occurring and the consequence if a failure does occur can help target the most at risk project locations.

To do a risk assessment, we look at a whole host of elements, including the type and number of features that would be impacted by a failure, the frequency of impact, the severity of the impact, and the displacement associated with a failure. Based on these and other elements, project risk can be assessed, and projects can be objectively compared to one another.

Resiliency in the stormwater world involves the ability of a feature or system to function through a wide range of climate conditions. A resilient stormwater system could include everything from the type of materials used for construction to how that system integrates into the natural environment. Assessing and improving the resiliency of a stormwater system can reduce long term operational costs and provide a better opportunity for that system to adapt to future climate changes.

Why should cities, counties, or federal entities make risk and resilience assessments?
Looking at the risk and resilience of a stormwater system offers a number of benefits. The first being financial. Using this approach to assess and prioritize helps cities invest resources where they are most needed. It also provides opportunity to implement solutions better able to withstand future climate related changes and that are more compatible with the natural environment.

How are risk assessments being used?
One example involves the assessment of stormwater pipes, using evaluation and assessment tools to determine which pipe segments can remain or be rehabilitated and which need to be replaced. This straightforward assessment looks at the risk of a pipe segment failure and what measures would be necessary to mitigate that risk for an acceptable length of time. This approach to risk assessment of pipes is a budget-friendly method that has a real cost savings advantage.

What is the process like for implementing a risk and resilience assessment?
We recommend starting with a simple assessment. Consider potential risks to a stormwater system. Then, evaluate the likelihood and consequence of that risk event occurring. Next, brainstorm what steps could be taken to reduce that risk. If you’re looking for a more complex approach, there are software programs that aid in evaluating various alternatives and take into account life cycle costs and associated risk reduction.