More flooding is certain in LA's future. Researchers want new models to help prevent disaster

Researchers out of UC Irvine have said that nationally used flood modeling lacks specificity when it comes to measuring risks in urban areas like Los Angeles County.

They've created their own modeling system, PRIMo-Drain, that can better predict which properties are at risk when using accurate, granular data.

How the flood modeling system works

In a new report, UCI engineering professor Brett Sanders and his team compared widely used national flood risk assessment modeling in areas like Los Angeles County against their own PRIMo-Drain model. Long story short: Traditional models don’t usually include infrastructure like levees and dams, unresolved drainage and topographic data, which means their modeling is less specific when it comes to measuring risks for the spreading of floods in cities.

That data on storm drain infrastructures is collected mostly from GIS (geographic information system) shape files maintained by public agencies like the Los Angeles Department of Public Works. The UCI researchers also updated those databases with aerial image capture of the conditions of levees mapped in public records.

“Once we have this relatively detailed representation of the land surface, of the flood infrastructure, we look at different types of flooding,” Sanders said.

Those types of flooding include river floods, coastal floods, and flash floods from intense rainfall, like what Los Angeles saw the past two winters. Estimates show the frequency of extreme rainfall under a warmer atmosphere to likely be higher in seasons to come.

In recent years, large rainfall events in Southern California have been kept at bay by flood control infrastructure like those aforementioned levees and dams (the technical word for them is mainstem). But water is starting to reach above levee and dam walls more often. Places like Santa Barbara and San Diego experienced these flooding scenarios in the latest few rounds of atmospheric rivers.

This is why PRIMo-Drain researchers want to get as specific as possible in future models. If they could measure where water goes after escaping flood control walls and what areas get flooded, even more accurate models could be put to use for cities.

According to Sanders, part of this is why the developers of the model engage in “collaborative flood modeling” with the Los Angeles Regional Collaborative for Climate Action and Sustainability out of UCLA. The idea is to ask people where they see flooding, what they think drives flooding, and for suggestions on data sources that could help improve the model.

The model became publicly available in 2023. Since then, organizations like the City of Los Angeles and Southern California Edison have used PRIMo for planning and vulnerability measurement purposes.

Strategies to maintain flood risk

Right now Sanders and researchers on the PRIMo team are engaged in a two year study in Los Angeles in partnership with Los Angeles County and community groups to look at alternative strategies to manage this risk to communities and who they would benefit. (The same team also conducted a 2022 study that found L.A. County’s Black residents face disproportionately high flood risks.)

There are three strategies they’ve identified as potential solutions. The first is a tried and true method: make levees taller so that channels have more capacity and can prevent water from escaping the levee walls.

Another strategy involves widening channels to create more capacity, which would eliminate some of the concrete in channels and allow for vegetation to begin growing.

Sanders said the third strategy would be to “capture more storm water in the upper parts of the watershed…with more parks, more green space, and more infrastructure that would promote the infiltration of rainwater into the soil.” Ideally, this would reduce the amount of water that flows down these channels and in doing so reduce the risk facing these lowland cities.

In the meantime, the researchers will continue working on updating their models during future rain events. According to Sanders, it’s still “really hard to say [the researchers’] method is more accurate” since it hasn’t been exposed to enough severe flooding.