Flood Control

Boise Foothills

The City of Boise operates and maintains a series of flood control structures on each of the four main foothills gulches (Stuart Gulch, Crane Gulch, Hulls Gulch and Cottonwood Creek). Most of these structures were either installed or upgraded following a major wildfire in the fall of 1996. While these facilities provide vastly improved flood protection, these will not completely protect property in an extreme flooding event.

Street Flooding

Streets can flood during heavy rainfall events due to clogged storm drains. Storm drain maintenance is the responsibility of the Ada County Highway District (ACHD). Please contact ACHD at (208) 387-6100 to report street flooding problems.

Boise River

The Bureau of Reclamation and the U.S. Corps of Engineers manage three upstream dams on the Boise River drainage. The dams provide irrigation water storage and flood control. The need for water storage and space reserves for flood control is a balancing exercise based upon snow pack levels, historic runoff records of snow pack, and reservoir level conditions.

Attempts are made to keep flows below 6500 cubic feet per second (cfs) in the spring. However, this flow rate is generally exceeded about once every five years. For the Boise River, 7000 cfs is considered to be at the lower level flood stage; 16600 cfs is considered a 100-year flood event.

Floodplain Management

The Planning and Development Services Department is responsible for floodplain development regulations. The City of Boise has a Floodplain Ordinance for the Boise River and foothills gulches. The ordinance applies to properties located in a floodplain. Federal Emergency Management Agency (FEMA) insurance rate mapping applies to development within identified floodplains and areas of shallow flooding.