The dam at Lake Oroville, a reservoir near Oroville, California, can hold back up to 3.5 million acre-feet of water, but federal regulations require 20 percent be set aside in a spillway for flood control.

Most years, that strategy works pretty well.

But not this year. When the main spillway broke, causing the water level to creep dangerously high, officials decided to use an untested emergency spillway on Feb. 11. The reservoir was at 901 feet that day, the highest recorded level since 1985.

The near failure of that spillway led to the evacuation of more than 180,000 people downstream. In the days before the evacuation, hourly outflow sensors recorded the dramatic drop in the release of water while main spillway damage was assessed. By midday Feb. 7, water releases were slowed to a trickle. From then, officials struggled to increase outflow without further damaging the spillway.

Some say it’s time to rethink how Oroville and other large dams are managed.

“Flood management is in tension with other services because a mostly empty reservoir … is the best hedge against floods,” Jeffrey Mount, a senior fellow at the Public Policy Institute of California wrote in a recent blog post.

Federal regulations require that 20 percent of Oroville Dam’s capacity be reserved for flood control purposes. Officials began releasing more water from the dam on Jan. 12, when water levels started to reach the flood control limit.

“By design, Oroville was relatively full when the latest floods arrived, reflecting its top priority (water supply) and compounding flood risk,” Mount wrote.

When the main spillway was damaged on Feb. 7, officials couldn’t properly respond to the heavy inflows. The remaining 20 percent of the dam filled quickly.

Chris Orrock, a spokesman for the Department of Water Resources, which operates the Oroville Dam, said this month’s crisis was triggered by the crippled spillway, not tension between flood control and water supply.

“You get criticized if you send too much water down the system and it gets washed out to sea,” Orrock said. “And you get criticized if you keep too much water in the reservoir. We do what’s best for the overall state water project while still meeting the needs of flood control for the reservoir.”