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2015 Reconnaissance Report for Evans Creek Tributary 0107

2015 Reconnaissance Report for Evans Creek Tributary 0107


King County is working on an assessment to better understand the relationship between stormwater, hydrology, and natural conditions in the trib 0107 in the Greater Lake Washington Watershed.  In January 2015, trib 0107 was surveyed to collect data on general ecological conditions, channel shape and form, and to measure existing hydro-modifications (culverts, bridges, etc.). For context, the data collected in this assessment are compared with NOAA Fisheries’ PFC (Properly Functioning Conditions) for salmonid bearing streams (NMFS 1996).  For the purposes of this summary, PFC conditions are reported for width to depth ratios, pool frequency, riparian composition, and frequency of large woody debris.


Overall results from this survey show that trib 0107 does not meet the minimum requirements for PFC.  Transect data collected throughout trib 0107 show that a majority (75%) of the bankfull width to depth ratios actually meet the minimum for PFC.  However, data collected on substrate composition show that sand is the dominant substrate class in much of trib 0107 due to low gradient stream segments and a lack of large woody debris to encourage channel sinuosity and gravel recruitment.  Also with the extensive amount of sand throughout trib 0107, the average embeddedness (63%) of all transects was over the 20% that PFC considers properly functioning.  Riparian data also show that none of the reaches sampled met the minimum criteria (>80% forest) for properly functioning conditions (NMFS 1996) for riparian areas.  This overall lack of functioning riparian conditions have also resulted in a general lack of LWD recruitment to trib 0107.  Pools are important habitats for vertebrates and invertebrates alike.  Since pools are often formed by LWD, there were considerably fewer pools found throughout trib 0107 which did not meet PFC.  BIBI results for two separate sites collected since 2009 show that trib 0107 overall taxa results scored fair, with one good score in 2013 and one poor score in 2014.

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    2015 Reconnaissance Report for Evans Creek Tributary 0107 (3.11 MB)

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