Biodiversity Guide - The Intertwine

egional conservation strategybiodiversity guideAppendix I Watersheds170 years of changes that have shaped currentconditions. The river channel and floodplain,wetlands, lakes, shoreline and sand bars, islands,and bluffs and ridges at the confluence of the Willamettehave undergone substantial change. Thesefeatures result in a biologically diverse albeitgreatly simplified community in this now heavilyurbanized area. 5Historical Condition of the Willamette RiverThe 187-mile-long Willamette River is the 19thlargest river in the U.S. by volume and drainsnorth into the Columbia River, the fourth largestriver, at Columbia River Mile 105. 6 As with anywatershed reach, the lower Willamette Riverreflects the cumulative impacts of conditionsthroughout the drainage area above it, includingflood control dams on important tributaries,urbanization, and agriculture. However, the lowerWillamette River is also strongly influenced bygeologic conditions quite different from those inthe upper basin. As the river flows over WillametteFalls, it transitions from a wide river toa deep, naturally constrained river. The floodplainin this reach is very narrow, and some ofthe river’s deepest waters (100 feet or more) arefound here. As the river passes Elk Rock Island,the channel re-opens. Historically this area was adynamic delta full of braided channels, ephemeralstreams, sloughs, lakes, and wetlands consistentwith a large, active floodplain. 7 As it entered theColumbia, the Willamette River was nearly onehalfmile wide, with a large shoal on the east riverbank near Linnton.In 1850, this basin was composed of 31 percentconiferous forest, 24 percent burned forest,13 percent prairie and savanna, 3 percent oak,and substantial floodplain and riparian forest.Today, the basin is more than half urban, containingthe city of Portland and part of Gresham, and12 percent agriculture. Less than 1 percent of thebasin is oak or prairie/savanna. Urban developmentconsumed about 40,000 acres of coniferousand burned forest and about 6,000 acres ofprairie, while agriculture consumed about 5,000acres each of prairie and riparian forest. Waterfeatures, primarily on the floodplain of theColumbia and Willamette rivers, have been substantiallyreduced by filling or draining.The Willamette and Columbia rivers flowednaturally until the 1930s, with high winter flowsand peaks occurring in the late spring. Winterand spring floods were both frequent andimportant drivers of ecosystem function. Theyrecharged wetlands, activated side-channels,moved sediments and wood, delivered nutrients,and shaped the channel. The Columbia River frequentlybacked up into the Willamette and flowedthrough many sloughs and gulches, includingSullivan’s Gulch (now Interstate 84), the ColumbiaSlough, and Hawthorne Slough. Even thisfar inland from the ocean, the Willamette Riverexperiences daily tides as far up as WillametteFalls. This part of the river was dominated bybeaches and wetlands with most water depths at20 feet or less. The Columbia Slough and SauvieIsland floodplain wetland system spanned morethan 55,000 acres and connected to both theWillamette and Columbia rivers.Current Condition of the Willamette RiverThe Willamette River – Frontal Columbia subbasinis the most urbanized watershed with thegreater Portland-Vancouver region, with 98 percentof the region falling within the Metro UrbanGrowth Boundary. More than half of the landcover is mapped as developed. Portland (Oregon’slargest city) sits on the lowest 19 miles of the Willamette’sriverbank and 17.8 miles of the Columbia’s.Portland is a major city at the confluence oftwo large rivers, where river-dependant industrythrived for decades; the city still provides significantjobs and benefits to the local economy.Flooding and significant flow variation historicallymade it difficult for businesses and urbancenters to operate at theriver’s edge. Constructionof upstream damson both theWillamette and Columbiarivers radicallyaltered the hydrologyof the lower WillametteRiver, reducing winterand spring dischargeand increasing summerflow. The ecologicallyvaluable annual floodpulses of the past arelargely gone.These altered patternsenabled the development and urbanizationof the area as we know it today. To furtherfacilitate development, sea walls, levees, andriprap structures reinforced the riverfront. Theriver was dredged and cleared of snags and debristo accommodate larger ships. Bridges for cars andrailroads crisscrossed the river. As a result, 89percent of the historical off-channel habitat andfloodplain was destroyed and 79 percent of theshallow water habitat (approximately 780 acres)was lost through deepening. A series of leveesmanaged by drainage districts has completelydisconnected the Columbia River from the floodplainbetween the Willamette and Sandy rivers.The Willamette River’s water quality declinedsignificantly but has recently improved somewhatthrough expensive but effective efforts. The lower6 miles of the Willamette River are a designatedfederal Superfund site on the National PrioritiesList.numerous birds, amphibians, fish, and mammals.During high flows these lakes were importantsources of nutrients, sediment, wood deposition,and flow attenuation for the Willamette andColumbia rivers.Today, most of the lakes have been filled orgreatly reduced. The former Caruthers Lake nowsupports the South Waterfront and Johns Landingcommunities. Couch, Guilds, Doane, Ramsey,and Rivergate were filled to support industrialdevelopment. Only a remnant of Doane Lakeexists today, completely isolated from the WillametteRiver. The remaining lakes and wetlandsat Oaks Bottom and Smith and Bybee Lakes showevidence of historical landfill encroachment. Allare actively managed to maintain water levels forwildlife and invasive vegetation control. However,these bodies of water still support numerous speciesof mammals and waterfowl, including osprey,blue herons, ducks, beavers, otters, coyote, andnative fish.Between the lakes were extensive wetlands,side channels, and riparian forests. The massiveMissoula (i.e., Bretz) Floods between 10,000 and20,000 years ago left scours and deposits alongthe banks, resulting in ridges and terraces thatwere covered in firs, oaks, and grasslands, withthe Tualatin Hills to the west dominated by firs.Lakes and WetlandsSeveral lakes occupied the west side of the river,including Caruthers, Couch, Guilds, and Doane.On the east side were Oaks Bottom, HawthorneSlough, Rivergate, Ramsey, and Smith and BybeeLakes. These lakes were frequently connected to5 Most of the information in this chapter was derived from Draft River Channel Characterization – Habitat and Biological Communities(City of Portland Bureau of Environmental Services, 2003). More detailed evaluations are in the Willamette Watershedflows and provided important migration, nest-the Willamette through braided channels or highSubbasin Status reports at http://www.portlandonline.com/bes/index.cfm?c=30938&6ing, rearing, and refugia habitat to migrating fishUSGS, http://pubs.usgs.gov/of/1987/ofr87-242/7 1852 Government Survey Maps, available at: http://www.glorecords.blm.gov/and waterfowl, as well as permanent residence to286 287