High Spring Flows Benefit Plants, Wildlife and People

The U.S. Army Corp of Engineers and Bureau of Reclamation announced that the flows released from Lucky Peak Reservoir will increase to around 7,000 cfs at Glenwood Bridge by Tuesday, March 7th. The increase in flows is expected to submerge large portions of the greenbelt and other low-lying areas but will help lessen flood risk later in the season, especially if rapid snow melt occurs.

Over the past decade, flow releases exceeded 7,000 cfs at the Glenwood Bridge in 2008, 2011 and 2012, and exceeded 6,000 cfs in 2009, 2010 and 2016 (USGS 2017). However, it is unusual for regulated flows of this magnitude to be released this early in the year. Current channel capacity ranges between 3,500 cfs and 10,000 cfs depending on location and changing conditions.

While minor flooding is expected to occur, high flows are beneficial to plants, wildlife and people along the Boise River. High flows inundate wetland and riparian areas within the floodplain that are not accessed during regular flows allowing for nutrient exchange; filtration, retention and removal of pollutants; groundwater recharge and discharge; food chain support; habitat for many species of birds and wildlife; and increased recreational and aesthetic opportunities. High flows also deposit sediment and clear away open ground for new plants to propagate, particularly willow and black cottonwood that are keystone ecosystem species.

 

 

 

Giving the River Space

High flows only become a problem when flooding of infrastructure occurs – a result of channel confinement and removal of floodplains by development, agriculture, transportation infrastructure and flood control measures. Healthy, connected floodplains give the River more room as it rises and slow down flood velocities, thereby reducing flood risk. Therefore, the Boise River Enhancement Plan identifies protection of existing floodplains as a top priority.

The Plan also identifies strategies to re-connect and enhance floodplains, including:

  • Lowering or setting back existing levees and berms
  • Re-contouring the floodplain to allow wetland and riparian habitats to re-establish
  • Removing barriers to stranded side channels
  • Excavating side channels and off-channel areas, such as wetlands.

Protecting and enhancing floodplains allows the river the capacity to safely pass higher flows that benefit us all.

Literature Cited

USGS. 2017. USGS 13206000 Boise River at Glenwood Bridge near Boise, Idaho. U.S. Department of Interior, Geological Survey, National Water Information System. Accessed March 5, 2017 at https://nwis.waterdata.usgs.gov/nwis/uv?cb_00060=on&format=gif_stats&site_no=13206000&period=&begin_date=2008-01-01&end_date=2017-03-05