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Mapping cold-water refuges on the East Fork Lewis River guides restoration and a $24M floodplain reconnection
Summary
A thermal assessment using airborne FLIR and ground surveys identified cold-water refuges in the East Fork Lewis River and produced a prioritized list of ~30 project concepts; a large Ridgefield Pits floodplain reconnection (~$24 million) is under construction and expected to improve hyporheic connectivity and reduce warm-water gravel-pit traps.
Keith (Lower Columbia Estuary Partnership) described a three-year thermal assessment for the East Fork Lewis River that combined helicopter-mounted thermal infrared (FLIR) mapping, ground validation and stakeholder prioritization to find small-scale cold-water refuges that juvenile salmon depend on during hot summers. The study ranked about 30 candidate project areas and moved several into design.
Keith walked through Site 15 (Upper Daybreak side channel) as an example: FLIR imagery showed a cooler side channel next to a warmer main-stem reach, suggesting hyporheic or groundwater inputs that create refuge; restoration concepts include enhancing hyporheic exchange, strategic large-wood placement, riparian planting and limited grading to improve groundwater connection.
He highlighted the Ridgefield Pits project, a large-scale floodplain reconnection that filled abandoned gravel pits, regraded floodplain surfaces, placed wood and re-established multi-channel habitat; the project aims to reduce warm-water ponds, raise groundwater connectivity and create more shadeable, smaller channels that are easier to cool and plant. Groundwater monitoring wells were installed for Ridgefield to evaluate project effects.
Why it matters: summer thermal stress is a key barrier to salmon survival in the Lower East Fork; targeted protection and enhancement of cold-water refuges can maintain rearing habitat and increase resilience to rising temperatures.
