5900 36TH AVE W SEPA 015 - 034 - SOUNDVIEW BUSINESS CAMPUS - VERITAS Land Use Decision Documents 2025-04-22

Channel Conditions and Dynamics Parameters to access channel conditions include width to depth ratio, streambank condition, and floodplain connectivity. Width to Depth Ratio The banks of Edgewater Creek are incised in certain areas. This, in combination with high flow rates recorded during winter months, indicates that the stream channel becomes deep, but that width of the stream does not extend outwardly by a significant margin. Therefore, given the relative narrowness of the channel, Edgewater Creek is presumed to have a low width to depth ratio. Based on these conditions Edgewater Creek is considered to be properly functioning for this element. The proposed project will not alter the width to depth ratio for Edgewater Creek or downstream systems. The proposed project will maintain the current width to depth ratio of the stream within the action area. Streambank Condition The stream bank along Edgewater Creek is incised in multiple areas and landwasting slides along the forested slope occur throughout the area. Slope stability is considered at risk for Edgewater Creek. This project will not occur along the steep slopes or banks associated with Edgewater Creek and, therefore, will maintain the baseline condition for this parameter. Floodplain Connectivity Although Edgewater Creek may be somewhat channelized in some areas, the wetlands abutting the steam throughout the lower reaches north of W. Mukilteo Blvd appear to be connected during high flow events. Based on these conditions, the Edgewater Creek action area is properly functioning for this element. This project will not change the existing floodplain connectivity and, as a result, will maintain the baseline condition for this parameter. Change in Peak/Base Flows Peak flow rates calculated for Edgewater creek are drastically higher than the base flow rates throughout the year. The 2-year storm event is over 7 to 25 times higher than that of the base flow depending on the reach, with differences becoming generally more extreme closer to the outfall. For these reasons, this metric is considered not properly functioning in the Edgewater Creek action area. This project will not change peak or base flows and, as a result, will maintain the baseline condition for this parameter. Drainage Network There has been an increase to the drainage network primarily due to impervious surfaces associated with residential and commercial development in the basin. Based on this, the baseline indicator is at risk in the Edgewater Creek basin. Biological Evaluation 16 WRI #14109 Soundview Business Campus Revision #2: October 2, 2015