Going with the flow

A press release from the University of California-Santa Barbara: Millions of Americans live in flood-prone areas. In 2012 alone, the cost of direct flood damage hit nearly half a billion dollars. However, because the factors contributing to flood risk are not fully understood, river basin management — and even the calculation of flood insurance premiums — may be misguided.

A new study by UC Santa Barbara’s Michael Singer and colleagues presents a paradigm shift in flood hazard analysis that could change the way such risk is assessed in the future. The results are published in the journal Geophysical Research Letters.

Existing analyses attribute flood hazard to how often high water flows occur. They don’t, however, take into account the ability of river channels to accommodate them. The researchers present a novel method that compares the effects of channel capacity and stream flow on flood hazard frequency. They also document how flood hazard has changed over time in more than 400 streams across the United States.

“Our results demonstrate that changes in river channel boundaries directly impact flood hazard trends across the U.S.,” said Singer, an associate researcher at UCSB’s Earth Research Institute. “We show that in order to accurately calculate flood hazard and insurance premiums for river basins, channel capacity needs to be considered jointly with stream flow.”

...The findings revealed that important trends in channel morphology through time were three times more common than those related to water quantity, indicating that changes in the channel’s geometry tend to offset increases in water flow. “That raised alarm bells,” Singer said. “It suggests that a lot of areas that we might not have considered to have trends in flood risk actually do.”...

Red represents increases and blue decreases in flood hazard frequency. Deeper colors indicate sites with statistically significant trends. Image from the UC Santa Barbara website