Big floods often change how a community approaches emergency preparedness and response. After a devastating flood in 1978, the City of Rochester embarked on a massive flood control effort, building structures such as channels and reservoirs.
“All these are great, but the city still has residual risks,” said Barr Engineering’s Joe Waln, speaking to attendees of the Minnesota Chapter of the American Public Works Association’s fall 2019 conference. “They want to know, ‘If it floods, what will it look like?’”
Fortunately, there are publicly available tools that can answer this question for Rochester and other cities. Waln identified three ways communities can use these tools to better understand and plan for flood risks.
1. Check flood forecasts
The National Weather Service has gauges that measure flood levels of rivers and streams all over the country. Some provide short-term flood forecasts in the form of a line graph that depicts the flood stage (in feet) over a several-day period, for both the actual stage and the multi-day forecast.
2. Use inundation maps
The National Weather Service and US Geological Survey maintain a range of flooding-related data, including inundation map libraries.
Inundation maps make it easier to interpret what stream gauge levels like “stage 18” or “stage 22” mean for a given community, including if it could cause flooding. Users can even determine which flood-stage level would cause a specific area to flood.
Rochester, for example, developed a way to integrate inundation maps and other datasets into its GIS system. This makes the data more accessible and helps city officials understand and act on flood forecasts.
“They can quickly bring these maps up and print them for emergency responders,” said Waln, who worked with the city to integrate the data into a tool. “It improves response time.”
3. Identify action triggers
Once a community understands what a flood of a certain magnitude looks like, Waln recommends identifying the flood stages that would trigger closing a road, evacuating residents, or deploying emergency responders. He stressed inundation maps and other tools are key to this step: “Have the information available so you can say, ‘When this happens, this is what we’re going to do about it.’”
—Michelle Hoedeman, LTAP freelancer