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TUKWILA COMPREHENSIVE PLAN <br />The Natural Environment <br />Tukwilaenco mpat 9 square miles and much of thegity lies <br />within an extensive valley centered on the LowerGreen/Duwamish River, <br />watershed. The valley_is virtual' flat and almost entirely built out except <br />for the newly annexed:Tukwila South area which is slated for <br />deyelopment over the next JO to 15 years. The upland areas of the City <br />have rollino topoaraphiAnd_numerous areas wit sleep and_potentially, <br />table slo es. Many of the steep hillsides are forested_with second or <br />third growth trees and understories with a mix of native and invasive <br />vegetation. These areas tooether with the City:s numerous water resources <br />provide important fish and wildlife habitat that coexist with the built <br />environment. The following, is a summary of conditions in the constituent <br />elements of Tukwila's environment - more detail is found in the <br />Back .round Re ort. <br />Wetlands and Watercourses <br />As urban develo ment has occurred, natural draina. e corridors have been <br />altered orplaced in culvertsnd wetlands have been filled. Remnant <br />wetlands remain in some of the City'sparks, on undeveloped slopes <br />{formed by springs and roundwater seeps), in freeway interchanges,. and <br />in other areas of the City. The City has purchased Tukwila Pond and <br />Macadam wetland forpreservation. Tukwila Pond serves as both a <br />yvetland and tem_porary_storinwater storage pond forsommercial_ <br />development on its north side. Macadam wetland collects mostly naturally, <br />generated surface water from the steep slopes located on its east side. <br />(photo of Tukwila pond) <br />Stream alterations have affected wildlife and fish habitat. There are few <br />remaining open channels in the four main streams in Tukwila (Johnson <br />Creek Gilliam Creek Southgate Creek and Riverton Creek), which have, <br />been channelized, relocated and piped for much of their length. <br />Construction of urban streets and highway sy_stems and driveways required <br />watercourses to be laced in culverts, which have blocked or made fish <br />passage difficult. All the streams discharge into the Green/Duwamish <br />River. <br />Run-off coupled with steep in the upper reaches, of Gilliam, <br />South. ate and Riverton Creeks has caused scourin and erosion in the <br />stream channels resultint in dee ened ravines with steep_banks <br />instability, bank erosion and downstream sedimentation. The lower <br />reaches of Tukwila's streams are_generally lacking in_pools and_woody_ <br />debris which are important for good fish habitat. Thus the open reaches <br />of Tukwila's streams are generally in deteriorated conditions with <br />generally poor riparian habitat and narrow buffers. In fact, many <br />4 <br />December 2013 <br />