A SUPPLEMENTAL ASSESSMENT OF THE MOHAWK WATERSHED Prepared by: Charles W. Huntington Clearwater BioStudies, Inc. 23252 S. Central Point Road Canby, Oregon 97013 Prepared for: Mohawk Watershed Partnership Marcola, Oregon November 2000 TABLE OF CONTENTS TABLE OF CONTENTS...............................................................................................................i EXECUTIVE SUMMARY ........................................................................................................... iii ACKNOWLEDGEMENTS ...........................................................................................................v 1. INTRODUCTION...................................................................................................................1 2. STUDY AREA .......................................................................................................................2 3. METHODS ............................................................................................................................9 3.1. STREAMFLOWS AND WATER USE ..............................................................................9 3.1.1. Streamflows.....................................................................................................................9 3.1.2. Water Use .....................................................................................................................11 3.2. STREAM CHANNELS ...................................................................................................11 3.2.1. Channel Changes..........................................................................................................11 3.2.2. Responsive Stream Reaches ........................................................................................12 3.3. RIPARIAN AREAS, WETLANDS AND FLOOD-PRONE LANDS...................................12 3.3.1. Riparian Conditions .......................................................................................................12 3.3.1.a. Changes in the spatial extent of bottomland forest ......................................................12 3.3.1.b. Fragments of bottomland forest that could be high priorities for protection ..................14 3.3.1.c. Assessment of lowland riparian forest widths and streamside conditions ....................14 3.3.1.d. Landuse patterns near streams...................................................................................16 3.3.2. Riparian Protection Rules..............................................................................................16 3.3.3. Wetlands and Flood-Prone Areas..................................................................................16 3.4. SUBWATERSHED SENSITIVITY AND FOREST STANDS...........................................17 3.5. ELEVATED SEDIMENT YIELDS...................................................................................18 3.6. FISH HABITAT ..............................................................................................................18 3.6.1. Benchmark Analysis......................................................................................................20 3.6.2. Comparison to 1938 River Survey.................................................................................23 3.7. UNNATURAL BARRIERS TO FISH MIGRATION .........................................................23 3.8. WATER QUALITY .........................................................................................................23 3.9. FISH..............................................................................................................................23 4. RESULTS ...........................................................................................................................24 4.1. STREAMFLOWS AND WATER USE ............................................................................24 4.1.1. Streamflows...................................................................................................................24 4.1.2. Water Use .....................................................................................................................26 4.2. STREAM CHANNELS ...................................................................................................28 4.2.1. Channel Changes..........................................................................................................28 4.2.2. Responsive Stream Reaches ........................................................................................32 4.3. RIPARIAN AREAS, WETLANDS AND FLOOD-PRONE LANDS...................................32 4.3.1. Riparian Conditions .......................................................................................................32 4.3.1.a. Changes in the spatial extent of bottomland forest ......................................................35 4.3.1.b. Fragments of bottomland forest that could be high priorities for protection ..................37 4.3.1.c. Assessment of lowland riparian forest widths and streamside conditions ....................37 4.3.1.d. Landuse patterns near streams...................................................................................41 Supplemental Assessment of the Mohawk Watershed - i - Clearwater BioStudies, Inc. 4.3.2. Riparian Protection Rules..............................................................................................44 4.3.3. Wetlands and Flood-Prone Areas..................................................................................46 4.4. SUBWATERSHED SENSITIVITY AND FOREST STANDS...........................................49 4.4.1. Steep Slopes and Ancient, Deep-Seated Landslides.....................................................49 4.4.2. Rain-on-Snow Zones.....................................................................................................49 4.4.3. Forest Stands................................................................................................................51 4.4.4. Relationship Between Forest Stands and Subwatershed Sensitivity..............................51 4.5. ELEVATED SEDIMENT YIELDS...................................................................................51 4.6. FISH HABITAT ..............................................................................................................55 4.6.1. Benchmark Analysis......................................................................................................56 4.6.2. Comparison to 1938 River Survey.................................................................................66 4.7. UNNATURAL BARRIERS TO FISH MIGRATION .........................................................69 4.8. WATER QUALITY .........................................................................................................70 4.9. FISH..............................................................................................................................75 4.9.1. Native Species ..............................................................................................................75 4.9.2. Non-native Species .......................................................................................................75 4.9.3. Focal Species................................................................................................................79 4.9.3.a. Coastal Cutthroat Trout ...............................................................................................80 4.9.3.b. Spring Chinook Salmon...............................................................................................84 4.9.3.c. Limiting Factors for Cutthroat Trout .............................................................................88 4.9.3.d. Limiting Factors for Spring Chinook.............................................................................89 5. FRAMEWORK FOR WATERSHED IMPROVEMENT .........................................................91 5.1. ECOLOGICAL OBJECTIVES ........................................................................................92 5.2. ACTIONS CONSISTENT WITH ECOLOGICAL OBJECTIVES......................................93 5.2.1. Forest Lands.................................................................................................................94 5.2.2. Agricultural/Grazing Lands............................................................................................95 5.2.3. Rural-Residential Areas.................................................................................................96 5.3. WHERE TO FOCUS EARLY EFFORTS BY THE PARTNERSHIP................................98 6. LITERATURE CITED ........................................................................................................102 APPENDIX A STREAM SURVEY PROTOCOLS AND RESULTANT HABITAT DATA FOR THE MOHAWK WATERSHED APPENDIX B SUMMARIES OF ANALYSES OF STREAM SURVEY DATA COLLECTED OR COMPILED FOR THE MOHAWK WATERSHED PARTNERSHIP APPENDIX C WATER TEMPERATURE DATA FOR STREAMS IN THE MOHAWK WATERSHED APPENDIX D INFORMATION ON THE HISTORIC DISTRIBUTION OF SPRING CHINOOK IN LOW ELEVATION WILLAMETTE BASIN WATERSHEDS APPENDIX E PRIORITIZATION OF SUBWATERSHEDS FOR POTENTIAL CONSERVATION EMPHASIS Supplemental Assessment of the Mohawk Watershed - ii - Clearwater BioStudies, Inc. EXECUTIVE SUMMARY The following report summarizes information prepared for the Mohawk Watershed Partnership to help in the development of a conservation program for the Mohawk watershed, Oregon. It was