3003 W CASINO RD BOEING AIRPORT RD ACCESS 2016-01-01 MF Import

� ' Blvd, is a 600-foot reach that has been channelized adjacent to a new stormwater detention pond. The stream pazses through a short (SO foot) 48-inch round culvert and enters an � area with natural stream characteristics. This reach extends Cor about 1 mile and provides excellent potential habitat for coho salmon and cutthroat trout. Woody debris is abundant through out the reach ar 1 adjacent vegetation overhangs much of the channel. The average � gradient is about 3%, h �wever, the channel has characteristia of a lower gradient (1%) stream due to the abundance of woody debris which controls much of the drop in elevation. The only concerns in this reach, from the perspective of fish habitat, is that er�sion is � occurring at several points wherc the stream is eroding the bank adjacent to the ciry of F.verett's sewer line right of way. 1 Access by anadromous fish to the reach described above is precluded by the culvert at Mukilteo Boulevard, which is located 1200 feet upstream of tidewater. This culvert is a 48-inch box culvert that is approximately 250 feet long with a gradient of about 3%. 7he culvert dischargcs below the road as a 4-[oot falls that has a minimal plunge-pool. 'Ihe lack � ot a plunge-pool,the height of the falls, and the sheet tlow that occurs in the culvert renders this strucwre a total Ulockage to migration by anadromous fish. Immediately downstream of the road and the culvert, the creek washes against a steep clay bank on the left shore � causing erosion. Below this point the stream flows about 1200 feet through a canyon to Possession Sound. The average gradient through the canyon is about 10%a; however much of the drop is controlled by woody debris that crcates small falls and cascades. Several of � these hydraulic controls tould pose ditficulties for upstream migration salmonids,but all urr. considered passable under certain flow conditions. � Tlu Creek enters Possession Sound through twin 75-foot 48-inch concrete culverts with about 3% gradient. The downstream end of the culverts are located at an elevation , of about +13 feet (Mean Lowcr L.ow Water). The elevation of the culvert and thc high 1 velocities that occur in the pipe present a tide-dependent barrier to migration by anadromous �sh. An extreme high tide would be necessary to allow enough back:looding to render the culvert passable. A review of the projected high tides for the period when 1 fish would be attempting access during the fall of 1989 (October 1•December 31), yielded a conclusion that backflooding sufficient to allow passage would not occur during the period. It is concluded that the cul�^rt constitutes a total blockage to migration by salmoniJs. � Previous workers have electro6shed tlie lower reaches (downstream of Mukilteo Boulevard), and teported catches of cutthroat trout (Aaker, pers comm). further, no , catches have been reported from above the boulevarJ (Brown and Caldwcll, 1982). These results are consistent with the conclusion that Mukilteo Boulevard is a barrier to migration. � Water quality is a concern in the drainage, previous workers have documented incidents of poor water qualiry, and have subsequently concluded the potential for use of this stream by fish is poor (Brown and Calclwell 1982). Dramatic stcps are being taken in � the drainage to control stormwater, and reduce pollutant loadings to the stream. Further, based on comparisons of limited past data and current data, water qualiry appears to be improving in the systom. , Overall, Powder Mill Gulch Creek provides an excellent opportuniry for mitigation; however, water qualiry may rcduce the effecciveness of mitigacion in the uppermost reaches � of the Creek where pollutants concentrations are highest. The presence oi cutthroat trout - 23 - �