North Fork Lost Man Creek Fish Passage Project

REDW

Purpose and Need for Action The North Fork Lost Man Creek project site consists of one stream crossing that contains two adjacent parallel culverts (Figure 3). The combined volumes of the culverts are too small to accommodate a 100-year flow event. A 100-year discharge is estimated to be about 750 cubic feet per second (cfs); a twoyear discharge is estimated to be about 200 cfs. The existing culverts can safely accommodate about 115 cfs. At flows greater than 115 cfs, water backs up behind the road fill and begins to saturate the fill, increasing the likelihood of failure. Failure of the stream crossing would cause sediment to be delivered into Lost Man Creek and eventually into Prairie Creek, damaging fish habitat. The Lost Man Creek Trail would be unusable by either administrative vehicles or hikers and bicyclists if the stream crossing fails. In addition to being undersized, the two culverts have partially crushed inlets and the outlets are approximately two feet above the natural channel grade, which creates a barrier to upstream fish passage (Figures 4 and 5). The purpose of this project is to remove two damaged, undersized culverts at the stream crossing on North Fork Lost Man Creek and to replace the culverts with a bridge. This project is needed to improve access to spawning habitat for threatened fish species and to prevent additional damage to fish habitat from sediment associated with failure of these drainage structures. The bridge is needed to ensure the Lost Man Creek Trail continues to provide a safe and enjoyable experience for hikers and bicyclists and the road provides administrative access needed for watershed restoration and other resource management projects in Redwood National Park.

North Fork Lost Man Creek Fish Passage Project

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