WALLA WALLA, Wash. – An U.S. Army Corps of Engineers hydraulic engineer from the Walla Walla District’s Boise Outreach Office headed downstream on the south shore of Boise River yesterday to provide technical assistance to Ada City-County Emergency Management (ACCEM) officials who discovered seepage and sink holes developing in a gravel pit located near Eagle Island.
Brandon Hobbs, who was born in Idaho Falls and worked for a Boise engineering firm before joining the Corps in 2010, met with ACCEM and Flood Control District Number 10 staff there to help plan a way to stop river water from seeping into the gravel pit and potentially creating serious erosion issues along the river in that area.
Repairs are in progress using a clay mixture to block the seepage, according to a May 3 ACCEM news release. Corps and local emergency management officials diligently monitor the shoreline as river flows continue to run above flood stage.
Gravel extraction and residential ponds near the river are susceptible to pit capture. Pit capture occurs when an active river channel erodes a strip of land separating the river from a pit. This causes the river to migrate into the pit and convert the off-channel pit into a part of the river. Pit capture can create severe stream channel erosion, degrade water quality, and result in loss of riparian and aquatic habitat.
Record high temperatures in the Treasure Valley causing major snow melt, followed by heavy rainfall on April 26 caused significantly high inflows into the Boise River system. Peak inflows reached 25,000 cubic feet per second. Current inflows are about 8,700 c.f.s.
The Corps’ Walla Walla District activated its Emergency Operations Center (EOC) on April 30 to better synchronize communications with other federal, state and local entities and be ready to respond to any requests for assistance due to flooding from Boise River communities. Corps EOC meetings include emergency management officials from the Idaho Bureau of Homeland Security, Ada and Canyon counties, incorporated cities and local flood control districts. Bureau of Reclamation officials, local water managers, Idaho Silver Jackets members, levee managers and elected officials also participate in the EOC meetings to address flooding and water-management issues on the Boise River and other areas of potential flooding within the Corps Walla Walla District area of operations. As of Thursday, May 3, no other rivers in the district are at or above bankfull, except for the Boise River. Ada County declared a disaster due to the Boise River flooding situation on May 3.
The Corps and the Bureau of Reclamation operate three dams on the Boise River as a system to manage flood control and irrigation storage needs -- Lucky Peak Dam and Lake (Corps), Arrowrock Dam (Reclamation) and Anderson Ranch Dam (Reclamation).
Water discharged from Lucky Peak was increased to about 8,000 c.f.s. at the Glenwood Bridge gauging station on May 2 in order to maintain flood storage for future snow melt and possible additional spring storms. Water managers anticipate flows will remain at this level for 10-14 days. Additional increases may be necessary, depending upon the amount of rainfall and snowmelt runoff entering the reservoir system. Water managers anticipate that a full supply of irrigation water will be available this season.
Hydromet records indicate that inflows during April were the second highest recorded since 1952. The last time flows at the Glenwood gauge reached 8,000 c.f.s. was in 1998 due to careful management of the system.
The Corps’ EOC stands ready to assist states and municipalities with flood-management support, if requested, said Jeff Stidham, Walla Walla District emergency management specialist. That assistance could include technical expertise, supplies and materials, equipment or contracts for emergency flood-fighting work.
“We're watching rivers and streams throughout the district and staying in touch with local emergency officials, so we can quickly respond to any requests for assistance,” said Stidham. “Our top priority is public safety, so we’re encouraging folks in flood-prone areas to stay tuned to information and advisories provided by the National Weather Service or their local emergency-service agencies and be ready to take action according to local flood response plans.”
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