Public invited to learn about Boise River flood risk at June 19 meeting

Published June 15, 2012

Public invited to learn about Boise River flood risk at June 19 meeting

BOISE, Idaho – Although the Boise River is no longer at flood stage, the risk of flooding remains. Future year flows could be significantly higher, causing property damage and putting lives at risk. To help the public better understand flood risk in the Boise area, the U.S. Army Corps of Engineers (Corps) and other Idaho Silver Jackets agencies will host a public meeting in Garden City on Tuesday, June 19, to provide information and present a new Web-based tool to help the community visualize that risk.

The information meeting will be held 6 to 8 p.m. in the Garden City Council Chambers located at 6015 Glenwood Avenue. The meeting facilities are physically accessible to people with disabilities. Presentations will be provided on the following topics:

  • the significant flood risk for those living in the lower Boise River floodplain
  • the information the Corps and Bureau of Reclamation use when making decisions about releases from the Boise River dams and reservoirs (Lucky Peak, Arrowrock, and Anderson Ranch)
  • an overview of 2012 reservoir flood operations
  • Boise River flood inundation maps, a flood-risk tool the public can access on the Internet that shows the extent and depth of flood water for 15 flows ranging from 4,900 cubic feet per second (c.f.s.) to 34,800 c.f.s. (7,000 c.f.s. is flood stage)
  • a Federal Emergency Management Agency (FEMA) study being conducted to revise Boise River flood insurance rate maps

The Idaho Silver Jackets team represented by the Corps, National Weather Service (NWS), and FEMA will be available to answer questions and discuss concerns. The Idaho Silver Jackets Team is an interagency team that is actively working to facilitate communication, and develop and share information to increase flood-risk awareness in the community. Other participating agencies include Idaho Bureau of Homeland Security, Idaho Department of Environmental Quality, Idaho Department of Water Resources, Natural Resources Conservation Service and U.S. Geological Survey.

The new flood inundation maps, which integrate as graphic-data layers with river maps on the NWS’ Advanced Hydrologic Prediction Service website, depict a section of the Boise River running through Ada County. Site users can select various levels of flow volume to see where the water will flow and what will likely be inundated in their community when the river crests beyond its banks. The Boise River Inundation Mapping Study produced the maps under the Corps’ Planning Assistance to States program in partnership with the Ada City-County Emergency Management, the City of Boise and Garden City. Boise is the first western U.S. city to get the maps, which are available in 68 other locations. The flood inundation maps and associated water depths can be viewed on the Web at

“Public safety is the Corps’ highest priority, and the Boise River is the highest flood-risk priority in the Walla Walla District,” said Lt. Col. David Caldwell, commander of the Corps’ Walla Walla District. “We’ve appreciated the opportunity to partner with other agencies and local governments to provide technical information that will help the community and its leaders better understand and prepare for flood risk. The inundation maps recently assisted with the Boise River flood response, and they’ll continue to serve us well.”

For more information about the June 19 public meeting, contact the Idaho Silver Jackets Coordinator Ellen Berggren at the Corps’ Boise Office at 208-345-2065.


The Boise River runs through the middle of the Boise metropolitan area, which is home to about 532,000 people and is the most populous metropolitan area in Idaho. Many homes and businesses are located within the 100-year-flood inundation area (a flow volume of 16,600 c.f.s. or 13.3 feet in depth as measured at the U.S. Geological Survey gauging station at the Glenwood Bridge). The Boise River reservoir system provides only about a 35-year level of flood-risk management benefit (7,000 c.f.s. or 10.2 feet in depth at the gauge).

The Corps of Engineers and the Bureau of Reclamation operate three dams on the Boise River upstream of the City of Boise as a system to manage flood risk and irrigation storage needs -- Lucky Peak Dam and Lake (Corps), Arrowrock Dam (Reclamation) and Anderson Ranch Dam (Reclamation).

During the past several decades, effective water management of the three-dam system during less-than 100-year-level inflows has resulted in a false sense of security in many Boise River flood plain communities. However, without improved flood-risk management facilities downstream of these dams, the Boise metropolitan area remains extremely vulnerable to flooding, particularly during the spring thaw season.

The lower Boise River Valley will eventually experience an 100-year or greater flood event which exceeds the reservoir system’s capacity, and those excess flows will be passed through the metropolitan area, putting lives and property at risk. Even if no people were harmed during such an event, homes, property and businesses in the flood zone valued at more than $2 billion are at risk.

The Corps continues to work closely with the Bureau of Reclamation and Boise-area emergency managers, both individually and collaboratively with multiple agencies’ representatives in the Silver Jackets forum, to raise public awareness of the very real risk of flooding in the lower Boise River Valley.

Public Affairs Office

Release no. 12-59