Local

What flooding can we expect as Boise River approaches 9,500 cfs? At 10,500? At 12,000?

Will the Boise River rise as temperatures warm this week?

Douglas Hardman, Ada County Emergency Management director, talks about expected inflows into the Boise River reservoir system as temperatures warm. (Wednesday, May 3, 2017)
Up Next
Douglas Hardman, Ada County Emergency Management director, talks about expected inflows into the Boise River reservoir system as temperatures warm. (Wednesday, May 3, 2017)

With federal water agencies planning to raise Boise River flows to 9,500 cubic feet per second next week, it’s worth pointing out a website that gives Valley residents a hint of what to expect — when flood waters might cover roads, for instance, or limit access to neighborhoods.

At 9,500 cfs, for example, you will see parts of Warm Springs Golf Course in water, and at 10,500 cfs ParkCenter Boulevard will be flooded at ParkCenter pond.

The National Weather Service’s Advanced Hydrologic Predictive Service prepares the report on what various levels mean for Boise Valley flooding. It also maintains a map that shows what areas are inundated at various river levels.

Here’s the flooding experts say you can expect at flows (and relative heights) measured at Glenwood Bridge in Garden City. One note: much of this is based on maps and modeling and is just a best guess at what we’re likely to see as we enter uncharted floodwaters.

16,000 cfs, or 13.3 feet

Major flooding will occur near the river in Boise, Garden City, Eagle, Star and Caldwell. Some residential areas in low-lying areas near the river will be flooded with water entering some houses. A flood of this magnitude has not occurred on the Boise River since 1943. Most of the area within the 100-year flood plain, including many city parks near the river, will be underwater. Debris piling up on bridge crossings will cause additional flood damage.

12,000 cfs, or 12.5 feet

Flooding will occur in low areas and parkland adjacent to the river in Boise, Garden City, Eagle, Star and Caldwell. Flooding of low-lying residential streets in areas adjacent to the river is likely, especially on portions of Eagle Island. Debris damming on bridges crossing the river will occur and may cause water to spill over the road surfaces leading up to the bridge. Park Center Boulevard in Southeast Boise will be flooded near the Park Center Pond.

10,500 cfs, or 12.0 feet

Flooding over Park Center Boulevard in southeast Boise near the Park Center Pond. Flooding near the river will occur in low areas of Boise, Garden City, Eagle, Star and Caldwell. Portions of Eagle Island will be submerged with flooding of residential property in low-lying areas near the river likely. The water should remain below the level of most residential structures, but access in and out of some neighborhoods may be limited by high water.

9,500 cfs, or 11.5 feet

Moderate flooding of low areas near the river in Boise, Garden City, Eagle, Star and Caldwell. Debris in the river will collect on bridges crossing the river. Water will cover portions of Warm Springs Golf Course and Municipal Park in East Boise. The water may affect some residential property near the river, but should stay below the level of most residential structures. The river will spill over its banks between 45th and 47th Street in Garden City into the warehouse district.

8,900 cfs, or 11.3 feet

Large sections of the Greenbelt will be submerged and severe bank erosion will occur. Flooding will occur in low areas close to the river in Boise, Garden City, Eagle and Caldwell, but the water should remain below the level of most residential areas. Water will seep into the Garden City warehouse district between 45th and 47th streets.

8,500 cfs, or 11.1 feet

Large sections of the Greenbelt will be submerged and severe bank erosion will occur. Flooding will occur in low areas close to the river in Boise, Garden City, Eagle and Caldwell, but the water should remain below the level of most residential areas. Water will begin seeping into the Garden City warehouse district between 45th and 47th streets.

8,200 cfs, or 10.9 feet

Large sections of the Greenbelt will be submerged and severe bank erosion will occur. Flooding will occur in low areas close to the river in Boise, Garden City, Eagle and Caldwell, but the water should remain below the level of most residential areas. Water will begin seeping into the Garden City warehouse district between 45th and 47th streets.

7,000 cfs, or 10.3 feet

Large sections of the greenbelt path adjacent to the river will be submerged. Erosion of river banks will also become a significant problem. Debris in the river including small trees and logs may begin piling up at bridge crossings. Minor flooding will be observed on sections of Eagle Island and in other low spots near the river. Minor flooding will spread downstream to low areas near the river in Star and Caldwell.

6,500, or 10.0 feet

Large sections of the Greenbelt path adjacent to the river will be submerged. Minor flooding may affect portions of Eagle Island.

4,000, or 8.4 feet

Water will begin seeping onto low spots on the Greenbelt path next to the river especially near bridge underpasses.

Bill Manny: 208-377-6406, @whmanny

Highest Boise River peaks

1. 9,840 cfs on June 13, 1983

2. 8,350 cfs on May 31, 1998

3. 8,310 cfs on May 5, 2012

4. 8,030 cfs on May 7, 1986

5. 7,630 cfs on June 29, 1982

6. 7,564 cfs on June 6, 1983

7. 7,440 cfs on April 30, 2006

8. 7,300 cfs on March 27, 1997

Recent year peak flows

April 11, 2016: 6,420 cfs

May 9, 2015: 1,770 cfs

March 31, 2014: 2,130 cfs

May 21, 2013: 1,520 cfs

May 5, 2012: 8,310 cfs

May 18, 2011: 7,230 cfs

June 11, 2010: 6,180 cfs

June 7, 2009: 6,320 cfs

National Weather Service, Advanced Hydrologic Predictive Service

Related stories from Idaho Statesman

  Comments