Ordinance No. 20513 - Laserfiche WebLink

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The physical environment of the Willamette River was composed of three channel types: the primary channel with the most flow, side channels connected to the main channel forming islands, and blind channels connected at one end such as alcoves or sloughs In terms of area, 70 -80% of the islands and side channels have been lost in this reach, and 40% of the alcoves and 20% of the primary channel had been lost by 1995. This historically complex bankline created by multiple channels, alcoves and sloughs, increased the riparian area affected by the flood - pulse. The regular advance and retreat of water on the floodplain was the driving force that historically sustained biological productivity and diversity in the riparian zone. Bankline degradation due to artificial barriers such as riprap armoring has dramatically reduced the ability of the Willamette River to disperse water, soil and nutrients to the floodplain. Metro states this hydrologic fragmentation caused by disrupting lateral and downstream stream floodplain interactions, eliminates riparian vegetation, increases flood heights and water velocities, and reduces sinuosity, leading to increased bank and channel erosion and channel incision. Figure 4 depicts some of the necessary attributes of healthy river habitat. Current Ecological Conditions and Context One of the important ways to assess the current and potential ecological value of the EWEB site is to consider its context within the patchwork of formerly continuous riparian forest. To this end, we examined existing riparian vegetation on both the north and south sides of the Willamette River 4 Ibid. 5 Portland Metro. January 2002. Technical Report for Goal 5, Revised Draft. 0 Figure 4. Components of a healthy river system.