Biodiversity Guide - The Intertwine

egional conservation strategybiodiversity guideAppendix I Watershedstable 9-1Watersheds in the Greater Portland-Vancouver Region, Organized by U.S. Geological Survey SubbasinSubbasin Watersheds Included in the Watershed AcresGreater Portland-Vancouver Regionwithin the RegionClackamas 1. Clackamas Subbasin (partial) 158,300Lewis 2. Lewis Subbasin (partial) 220,800Lower Columbia – Clatskanie 3. Lower Columbia-Clatskanie Subbasin (partial) 22,000Lower Columbia – Sandy 4. Lower Columbia-Sandy Subbasin (partial) 217,200Lower Willamette 5. Johnson Creek 60,1006. Salmon Creek-Frontal Columbia R 131,4007. Scappoose Creek-Frontal Columbia R 123,1008. Willamette R-Frontal Columbia R 78,700(includes Hayden Island – Columbia River)(Willamette R-Frontal Columbia)18,600(Hayden Island – Columbia River)Middle Willamette 9. Abernethy Cr-Willamette R 87,10010. Chehalem Creek-Willamette R 78,200Molalla-Pudding 11. Molalla-Pudding Subbasin (partial) 181,000Tualatin 12. Tualatin Subbasin 453,200Land coverClackamas Subbasin (partial)158,279 acres% of WatershedAgriculture 22%Regen. forest 3%Developed 8%Low Veg 7%Tree Cover 59%Water 1%Forest Patches* 55%JurisdictionsEstacada 2%Metro UGB** 9%Sandy 1%Rural 88%total 1,829,60010 feet, at the confluence with the WillametteRiver, to more than 7,200 feet, at Olallie Buttelocated along the southeast boundary of the subbasin.The subbasin totals 941 square miles, ofwhich about 250 are within the greater Portland-Vancouver region.Land cover in the entire Clackamas subbasin ispredominately (90 percent) forest and shrubland.Key Facts: The Clackamas subbasin within thegreater Portland-Vancouver region:Includes 59 percent tree cover, behind only theLewis and Lower Columbia-Sandy subbasins.Regionwide, the average percent tree cover is 49percent.n Contributes 8 percent of the total area but 11percent of the region’s forest patches (of which15 percent is publicly owned).n Has 4,228 acres within Federal EmergencyManagement Agency (FEMA) 100-year floodplains.n Includes about 1,500 acres of mappedwetlands.The majority is privately owned, although agenciesincluding the U.S. Bureau of Land Management,U.S. Forest Service, Oregon Parks andRecreation Department, and Metro own somesignificant natural areas in the region. Portions ofthe cities of Sandy, Gladstone, Oregon City, Estacada,Happy Valley, and Damascus are locatedwithin the Clackamas subbasin.A variety of habitat types can be found in theClackamas subbasin. The U.S. EnvironmentalProtection Agency (EPA) has developed the conceptof ecoregions. Three Level IV ecoregions arerepresented within the portion of the Clackamassubbasin that falls within the greater Portland-Vancouver region: prairie terraces, valley foothills,and Western Cascades lowlands and valleys.Prairie Terraces. This area, which is located alongthe Clackamas River downstream of River MillDam, consists primarily of the lower Clackamasmainstem and lower tributary areas. This areais nearly level, slightly depressional, or includesundulating fluvial terraces with sluggish, meanderingtributary streams. Historically, seasonalwetlands and ponds were common. Many streamsare now channelized (for example, portions ofGoose and Foster creeks), as is the mainstem ofthe Clackamas River.Valley Foothills. This area includes the headwaterportions of the lower Clackamas tributaries, Rockand Richardson creeks, and the lower portions ofClear, Deep, and Eagle creeks. The area is characterizedby rolling foothills with medium-gradientsinuous streams that are deeply incised in someareas. The areas of greatest relief often occur inthe lower to middle portions of these watersheds,where the largest streams have incised into theunderlying geology, 1 with the headwater areashaving relatively flat or rolling topography. A fewbuttes (such as the Boring lava domes) occur inthis area.Western Cascades Lowlands and Valleys. This areaincludes most of the mainstem Clackamas Riverand floodplain upstream of River Mill Dam; theupper extent of the Deep, Clear, and Eagle creeks;North Fork Eagle Creek; and the lower elevationportions of the middle and upper Clackamastributaries, i.e., Fish Creek, Roaring River, OakGrove Fork, Collawash River, and Hot SpringsFork. The area is characterized by low mountainridges, buttes, valleys, and medium-gradient riversand streams.Humans have occupied the Clackamas subbasinfor thousands of years. The original NativeAmerican inhabitants were bands from two majortribal groups, the Clackamas Chinook and theNorthern Molalla. Populations of both tribalgroups were decimated in the early 1800s by aseries of epidemics thought to have been broughtto the area by fur trappers. The ClackamasChinook primarily occupied the lower lying andnorthern parts of the subbasin, while the NorthernMolalla occupied the higher elevation andsouthern parts.Historically, the Clackamas Basin was about65 percent conifer forest and 27 percent prairieand savanna, with only about 3 percent oak. Mostof the oak and approximately 20,000 acres ofprairie and coniferous forest were converted toagriculture, while about 10,000 acres of coniferforest and the remainder of oak and prairie wereconverted to urban cover in portions of Clackamas,Boring, Estacada, Gladstone, and Sandy. A42 percent increase in the area covered by waterin the basin could be attributable to classificationerror, but it may also reflect the creation offlooded gravel pits near urbanized areas.The Clackamas supports a significant populationof winter steelhead, resident and anadromouscutthroat trout, and native lamprey.The subbasin also sustains one of the last two*Tree/regen. forest patches >30 acres.n Is only 9 percent publicly owned.1 The lower lying areas of the Clackamas subbasin were inundated during a series of floods—the “Missoula” or “Bretz” floods—**Cities in Portland area UGB.during the last ice age The floods deposited a relatively thick layer of loose boulders, rocks, and soil. As a result, for some Clackamastributaries, headwaters initiate on the buttes or in flatter areas and create deeper canyons close to the mouth of the stream.236 237