2010/03/31 Council Agenda Packet

7 .,:!',, ,, ` _ Following the realignment of Bigelow Creek, stream •,.,1-- - baseflow and stormwater flows from the Bigelow sub- ,Ta `,� ., { : �.j,C:,� basin will no longer flow into the railroad ditch system and ,' -' '� „ discharge to the Snohomish River adjacent to the Landfill site. This change will decrease the total stream length on t ' `\ r 'j = the Riverfront Development site, but the restored tidal ' . r' system will provide a significantly higher level of habitat t -k function than does the current drainage system. ? a -, , %. ela 'S/3. z c : ,4,V To enhance pedestrian and bicycle traffic through the site, -"Sl;f i° .I r the Public Amenities Master Plan proposes a long, >' tiZ4. ► ' curving trestle bridge over the new Bigelow Creek stream 4 , - outfall, a signature feature of the Riverfront Development L' °''''s--•14-7-i projects public open space. Refer to the discussion under V `' , \� h '� 'Trails'which follows. 4 Included in the master plan is the construction of a Typical stream flow regional surface water quality improvement facility for the Bigelow Creek basin; most of the Bigelow Creek basin was developed prior to the advent of modern stormwater best management practices. The city has been awarded a planning grant by the Washington State Department of Ecology to design a water treatment facility for the Bigelow Creek basin. The area of the Riverfront Development site north of the WSDOT treatment ponds (which address runoff from Interstate 5) is being evaluated as a candidate site for a proposed constructed wetland. Work on the surface water quality improvement project may occur before, during, or after the Bigelow Creek restoration work proposed by the Public Amenities Master Plan. Both actions are being coordinated by the city, and both projects will be designed to be independently constructed and operated. West Ditch DrainagelNorth Wetland Complex Similar to Bigelow Creek, the West Ditch Creek sub-basin historically flowed eastward to the Snohomish River through a large forested riparian wetland system composed of the current North Wetland Complex, the West Wetland Complex, and the Simpson Pad. Surface flows from this sub- basin were diverted north through Wetland C after the construction of the Walton Mill on the present- day Simpson Pad. Flows from the West Ditch Creek drainage currently flow north, down the vacant railroad corridor and past Wetland C, because of a blocked culvert under the easternmost railroad track. The West Ditch Creek corridor south of the 41st Street secondary access bridge will be restored in conjunction with the wetland and habitat mitigation projects the BNSF Railway has proposed within its easements south of the new roadway. North of the access bridge and the 41St Street overcrossing, portions of the West Ditch Creek corridor will be restored as part of a mitigation project proposed by the private developer. Wetland and habitat mitigation will offset impacts from development and associated roadway improvements on the Ellipse Mill and Simpson Pad sites. Neither the mitigation proposed by Burlington Northern Santa Fe nor that by the private developer is part of the Public Amenities Master Plan, but these projects complement and are coordinated with the master plan effort to maximize the restoration potential of this corridor. Downstream from the private developer's mitigation area, the master plan proposes to re-establish the historic connection between baseflow in the West Ditch Creek sub-basin and the central Wetland C, and enhance the existing tidal channel that bisects this expansive wetland. The master plan proposes that the drainage through Wetland C be named"Walton Creek", after the lumber mill that once operated on this site. 18 RR/el-front Development Public Amenities Master Plan 55