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Bitterroot River Flooding

Plan-WVA Bitterroot River Flooding 512 x 219 Spring backwater flooding (typically mid-May through mid-June) by the Bitterroot River into connected floodplain sloughs and oxbows occurs regularly (that is, at a 5–10 year recurrence interval).

Flooding at 1st Bench in the WVAThe National Water Information System website operated by the US Geological Survey posts Bitterroot River water levels at Bell Crossing. When the measure there is at or above 12,800 cfs the parking lot at the Wildlife Viewing Area is flooded; a 10,900 cfs reading will flood the asphalt trail at the first concrete bench and prevent access to the education shelter. When high water is in place, barricades will be positioned in flooded areas to address safety issues and access. 

 

Flooding Barricade at WVA Parking LotThe river fluctuates in water volume depending on winter snowpack and spring precipitation. These fluctuations regularly flood braided river channels and may create new ones. Much of this flooding and migration is natural and can be beneficial. Runoff in the Bitterroot River is highest in spring, with about 55 percent of the river’s discharge occurring in May and June following snowmelt and local rainfall (McMurtrey et al. 1972 cited in CCP). Natural flows in the Bitterroot River decline from spring peaks throughout the summer and remain relatively stable through winter. Records of flow and flood frequency relationships for the Bitterroot River near Florence date back to 1950. For this period of record, the river exceeded 1,050 cubic feet per second (cfs) at a 50-percent recurrence interval, or a frequency of every other year. Bank full discharge at Florence is about 13,000 cfs. This high flooding discharge causes extensive flooding throughout higher floodplain areas but occurs very infrequently (that is, at a greater than 50-year recurrence interval). At flows greater than 10,000 cfs, some modest backwater flooding on the refuge occurs with a greater than 7-foot stage height. 
 

Last Updated: May 31, 2014
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