The Boise River is rising. But will it flood again this spring? Here’s what to expect

Take a walk along the Boise River, and you’ll notice that most of the rocky outcroppings that offer great lounging spots are submerged, and many of the stairways and ramps that lead down toward the river are being engulfed by strong currents.

It’s not a sight unfamiliar to Boise residents. As temperatures rise and mountain snow melts and rushes into the valleys, many of Idaho’s peaceful rivers quickly turn into a turbulent rush.

Minor flooding is often an issue along the Boise River in the spring. In April 2023, the City of Trees’ main water thoroughfare suffered minor flooding as water levels rose, causing closures along the Boise Greenbelt near the Parkcenter Bridge area.

But are there any concerns about flooding this spring?

Not right now, Grant Bell told the Idaho Statesman. Bell is a reservoir regulator with the U.S. Army Corps of Engineers, Walla Walla District , the organization responsible for controlling water flow along major rivers in southwest Idaho and redirecting water into reservoirs.

“So far this year, we’ve had generally below-average snowpack. The snowpack kind of peaked in April and started to melt quite quickly,” Bell told the Statesman in a phone interview. “So, the runoff volume we’re expecting from the snowpack is still a little bit below average for this year. April itself alone was a little bit above average.”

How much water is available?

The Boise basin’s snow water equivalent — the measurement used for the amount of water contained within a snowpack — is at 87% of its median level, according to the latest Idaho SNOTEL report on May 2 .

Because of the low snowpack runoff in April, local rivers didn’t have as much water as typical for early spring. This led the U.S. Army Corps to begin releasing water from its reservoirs into rivers, Bell said, to create extra room in the reservoirs for the remaining snow melt as we move later into spring and summer.

According to the Bureau of Reclamation, the Boise River system — which draws water from the Anderson Ranch, Arrowhead, and Lucky Peak reservoirs — was at 90% capacity as of Friday.

Bell said the three reservoirs can contain 949,000 acre-feet of water. They started the year with about 120,000 acre-feet more than usual, and the 10% still available equates to 94,900 acre-feet of open space for additional snow melt and rain.

What’s the risk of flooding in Boise this spring?

Between the lower-than-average snowpack and available space in local reservoirs, Bell said there’s little risk of significant flooding along the river this year.

Water flow is measured in cubic feet per second (cfs). A 4,000 cfs flow can potentially cause minor flooding in low-lying areas — the river flow was 5,800 cfs when the Boise Greenbelt was flooded last year .

The highest flow the Boise River has reached this year is 4,000 cfs, Bell said, but has decreased to 2,500 cfs as of early May.

“Our action stage is considered 6,500 cfs on the Boise River, and then our minor flood stage starts at 7,000 (cfs),” Bell said. “So we’re definitely moving water, but we’re keeping flows well below flood stage. That way, we have more room to react to changing conditions.”

One of those changing conditions is the deluge of rain that’ll pass through the Treasure Valley this weekend .

Over an inch of rain could fall on Boise and surrounding areas in the coming days, but in part due to the U.S. Army Corps’ decision to leave room for extra water — and the fact an inch of rain won’t have a significant impact — it’s unlikely flooding will occur along the Boise River in the near future.

“It’s been pretty dry,” Bell said. “Precipitation is starting to pick up a little bit now and is a little bit more active in the forecast, but based on the current weather and snowpack in the basin, we’re in a good spot.”