On this day: Boise River reached flood stage in 2017...and that was just the beginning

March 6, 2018:

BOISE, Idaho (KBOI) — After a warm and dry January, (and first part of February), it appeared winter was looking to skip over the Gem State. But, as we entered mid-February, Mother Nature flipped a switch,thus allowing a series of winter storm systems to swing through the Pacific Northwest. This pattern change provided a nice (and necessary) boost for our snowpack in southwest Idaho's mountains, and gave skiers and boarders some much-appreciated powder to play in.

Ideally, snowpack should continue to build in Idaho's mountains through early April. This year, we've been eyeing these numbers more carefully, as snowpack had been sitting below average in many areas (and well below average in some spots). But last year, in 2017, we were dealing with an entirely different problem related to snowpack, reservoir storage, and river levels along the Boise River.

On this day: March 6, 2017

Last January and February, Idaho's mountains were getting handed more than enough snow. So much snow, in fact, that it started creating concerns downstream in the Boise Basin reservoirs (Lucky Peak, Arrowrock and Anderson Ranch) and the Boise River. The problem? There was a significantly larger amount of water that would ultimately melt and flow out of the mountains into the reservoirs, and eventually through the river system.

Cue flooding concerns.

On March 6, 2017, the USGS streamgage at the Glenwood Bridge measured river flows at 7,000 cubic feet per second. That's also considered flood stage for the Boise River. The following day, on March 7, the National Weather Service reported the Glenwood Bridge streamgage rose to approximately 7,150 cfs, putting the river officially 'above' flood stage. March 6, 2017 was when we considered the Boise River to be at flood stage though, meaning flooding along the banks was both possible and imminent.

Above, you can see that water managers began increasing flows on the Boise River beginning in mid February. Early March though, was considered the tipping point, and from there...well, most of us remember what happened. Flows continued to increase on the Boise River through early June, before finally dropping below flood stage again on June 16, 2017.

During those few months, flooding along the Boise River's banks was constant, damaging homes, bridges, and many paths and walkways along the river's banks. The USGS reported the Boise River reached it's highest stream flow of the season on June 7, 2017, at 9,614 cfs. The fastest flow ever recorded on the Boise River at Glenwood? 9,840 cfs, back in June 13, 1983

2018: A (very) different story

Currently, the Boise River is flowing at just 263 cfs. No, I'm not missing a number there: 263 cfs (which is well below the average flow rate for this point in the season, as referenced in the graph above.

Forecasts show that the river level is expected to climb slightly and slowly over the coming days, but not so much to whereas you'd notice a difference. Moral of the story: the river level is still very low at this point in the season, as water managers are looking to hold on to some of the water in the reservoirs for now.

As for the rest of the season? There's still plenty of winter (and spring) coming our way. While this winter has looked a lot different compared to last winter so far, the National Weather Service warns there is always danger for flooding along the Boise River in the spring, especially in the event of a strong spring rain, or an unusual amount of leftover snow that melts at a different point in the season.

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