Lower Middle Fork Willamette River Watershed Assessment
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Lower Middle Fork Willamette River Watershed Assessment August 2002 Prepared for: The Middle Fork Willamette Watershed Council Watershed Assessment Team • John Runyon, BioSystems: Project Management and Introduction • Tim Grubert, BioSystems: Sediment Sources • Jenny Allen, BioSystems: Document Preparation • Jim Reed, Consultant: GIS and map production • Val Rogers, Council Contractor: Hydrology, Riparian Habitat Conditions, and Water Quality • Kim Mattson, Ecosystems Northwest: Aquatic Habitat and Fish Populations, and Wetlands Lower Middle Fork Willamette Watershed Assessment Table of Contents 1.0 INTRODUCTION ...................................................................................................................... 1 1.1 THE WATERSHED ASSESSMENT AREA...............................................................................1 1.2 LANDFORMS AND GEOLOGY .............................................................................................2 1.3 LAND OWNERSHIP AND USES ...........................................................................................6 1.4 WATERSHED ASSESSMENT APPROACH .............................................................................9 1.5 ORGANIZATION OF THE DOCUMENT .................................................................................9 2.0 HYDROLOGY.......................................................................................................................... 10 2.1 INTRODUCTION ...............................................................................................................10 2.2 METHODS AND KEY QUESTIONS.....................................................................................10 2.3 RESULTS .........................................................................................................................10 2.4 RECOMMENDATIONS.......................................................................................................29 3.0 RIPARIAN HABITAT CONDITIONS .................................................................................. 31 3.1 INTRODUCTION ...............................................................................................................31 3.2 METHODS AND KEY QUESTIONS .....................................................................................31 3.3 RESULTS .........................................................................................................................36 3.4 RECOMMENDATIONS.......................................................................................................50 4.0 AQUATIC HABITAT AND FISH POPULATIONS ............................................................ 51 4.1 INTRODUCTION ...............................................................................................................51 4.2 METHODS AND KEY QUESTIONS.....................................................................................51 4.3 RESULTS .........................................................................................................................51 4.4 RECOMMENDATIONS.......................................................................................................71 5.0 WETLAND HABITAT CONDITIONS ................................................................................. 74 5.1 INTRODUCTION ...............................................................................................................74 5.2 METHODS AND KEY QUESTIONS .....................................................................................74 5.3 RESULTS .........................................................................................................................75 5.4 RECOMMENDATIONS.......................................................................................................84 6.0 WATER QUALITY.................................................................................................................. 86 6.1 INTRODUCTION ...............................................................................................................86 6.2 METHODS AND KEY QUESTIONS..............................................................................86 6.3 RESULTS .........................................................................................................................87 6.4 RECOMMENDATIONS.....................................................................................................119 7.0 SEDIMENT SOURCES ......................................................................................................... 121 7.1 INTRODUCTION .............................................................................................................121 7.2 METHODS AND KEY QUESTIONS ...................................................................................121 7.3 RESULTS .......................................................................................................................121 7.4 RECOMMENDATIONS.....................................................................................................136 8.0 REFERENCES ....................................................................................................................... 138 9.0 APPENDICES TO THE FISHERIES REPORT................................................................. 141 Page ii Lower Middle Fork Willamette Watershed Assessment 1.0 INTRODUCTION The purpose of this assessment is to characterize current watershed conditions in the Lower Middle Fork of the Willamette River and surrounding watersheds (Assessment Area). Information from the assessment is used to evaluate opportunities for improvements in watershed conditions, particularly the fish habitat and water quality. The assessment will aid the Middle Fork Willamette Watershed Council in identifying opportunites and priorities for watershed restoration projects. 1.1 THE WATERSHED ASSESSMENT AREA The watershed assessment focuses on the Lower Middle Fork Willamette River below Dexter Dam and the associated tributary watersheds of Hills, Little Fall, and Lost Creeks (Figure 1-1). The total assessment area encompasses 108,026 acres, a little over 12% of the entire 865,920 acre Middle Fork Willamette River Basin (Figure 1-2). For the the Assessment Area is divided into three watersheds: • The Lower Middle Fork Willamette Watershed. The watershed encompasses the river from the mouth of Lost Creek to the confluence with the Coast Fork, including Hills Creek, all other tributary streams and surrounding upland areas. For the riparian and fisheries portions of this report, the assessment area is extended at the base of Dexter Dam to include the channel and floodplain area along the river. • Little Fall Creek Watershed. The watershed includes the creek to its confluence with Fall Creek and all tributary streams and surrounding upland areas. • Lost Creek Watershed. The watershed includes the creek to its confluence with the Middle Fork of the Willamette River and all tributary streams and surrounding upland areas. The three watersheds in the Assessment Area are very similar in size, but they differ significantly in average elevation and precipitation (Table 1-1). The Lower Middle Fork Willamette watershed has both the lowest mean elevation and mean precipitation of the three, while the Little Fall Creek watershed has the highest values. Lost Creek and Little Fall Creek are similar to each other in terms of minimum and maximum elevations, but their mean values for elevation and precipitation are rather different. Table 1-1. General watershed characteristics of the three watersheds in the Assessment Area. Area Mean Minimum Maximum Mean Annual Watershed (Acres) Elevation (ft) Elevation (ft) Elevation (ft) Precipitation (in) Lower MFW 36,006 800 446 2710 49 Little Fall Creek 37,402 1989 616 4227 66 Lost Creek 34,618 1673 600 4243 55 Total 108,026 Page 1 Lower Middle Fork Willamette Watershed Assessment Figure 1-1. Watershed assessment area with the three watersheds: Lower Middle Fork of the Willamette, Little Fall Creek, and Lost Creek. 1.2 LANDFORMS AND GEOLOGY The Assessment Area is located primarily in the older, more deeply eroded Western Cascades portion of the Cascade Mountain physiographic province. This V-shaped region is bounded on the east by the younger, snow covered peaks of the High Cascades region of the province and on the west by the Willamette Valley. Page 2 Lower Middle Fork Willamette Watershed Assessment Figure 1-2. This map depicts all of the 5th-field watersheds comprising the Middle Fork Willamette River Basin (865,920 acres). The Assessment Area covers the lower three 5th- field waterheds -- Lower Middle Fork, Little Fall Creek, and Lost Creek – for a total of 108,026 acres, a little over 12% of the entire Basin. Page 3 Lower Middle Fork Willamette Watershed Assessment Geomorphic characteristics throughout much of the Assessment Area include the steep ridges, narrow valleys, and volcanic soils which typify the western slope of the Cascades. Figure 1-3 is a geologic map of the Assessment Area. Refer to table 1-2 for a description of the geologic map units. Past episodes of glaciation and active stream erosion have created a highly dissected landscape characterized by steep, high gradient stream reaches in the upper portions of the Assessment Area and low gradient stream reaches in the lower portions (Orr et al, 1992). Figure 1-3. Geology of the Assessment Area. Page 4 Lower Middle Fork Willamette Watershed Assessment Table 1-2. Description of Geologic Map Units (Walker