Van Duzen River Watershed Analysis Cumulative Watershed Effects Final Report July 15, 2002 Arcata, CA Cumulative Watershed Effects TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................................i LIST OF TABLES........................................................................................................................iv LIST OF FIGURES .......................................................................................................................v LIST OF MAPS...........................................................................................................................vii 1.0 INTRODUCTION...............................................................................................................1 1.1 Purpose 1 1.2 Approach and Process...................................................................................................3 2.0 WATERSHED OVERVIEW...............................................................................................5 2.1 Watershed Overview......................................................................................................5 2.2 Ownership and Land Use...............................................................................................6 2.3 Basin History ..................................................................................................................7 2.4 Geology and Soils ..........................................................................................................8 2.4.1 Geologic Units, Stratigraphy, and Structure of the Van Duzen Watershed...........9 2.4.2 Structure..............................................................................................................13 2.4.3 Seismic Setting....................................................................................................14 2.5 Soils 16 2.6 Fish Species and Distribution.......................................................................................19 2.6.1 Fish......................................................................................................................19 2.6.2 Steelhead Trout...................................................................................................19 2.6.3 Chinook Salmon ..................................................................................................20 2.6.4 Coho Salmon.......................................................................................................20 2.6.5 Cutthroat Trout ....................................................................................................21 2.7 Amphibians and Reptiles Species and Distribution......................................................21 2.7.1 Southern Torrent Salamander (Rhyacotriton variegatus)....................................21 2.7.2 Tailed Frog (Ascaphus truei) ...............................................................................22 2.7.3 Northern Red-legged Frog (Rana aurora aurora)................................................23 2.7.4 Foothill Yellow-legged Frog (Rana boylii)............................................................24 2.7.5 Northwestern Pond Turtle (Clemmys marmorata marmorata) ............................24 2.8 Climate and Hydrology.................................................................................................25 2.8.1 Climate ................................................................................................................25 2.9 Hydrology .....................................................................................................................30 2.10 Flood History ................................................................................................................33 2.10.1 Flood History from Historic Gage Records..........................................................33 2.10.2 Summary of Flood History...................................................................................36 2.10.3 Peak Flow Generating Processes .......................................................................37 2.11 Vegetation ....................................................................................................................38 2.11.1 Historic Vegetation ..............................................................................................38 Final Report Page i Van Duzen River Watershed Analysis Cumulative Watershed Effects 2.11.2 Current Vegetation ..............................................................................................40 2.11.3 The Role of Fire...................................................................................................40 3.0 SCOPING OF ISSUES ...................................................................................................42 4.0 MODULE FINDINGS ......................................................................................................45 4.1 Sediment Sources........................................................................................................46 4.1.1 Mass Wasting......................................................................................................46 4.1.2 Surface Erosion...................................................................................................51 4.1.3 Sediment Budget.................................................................................................52 4.2 Stream Processes........................................................................................................60 4.2.1 Hydrologic Change..............................................................................................60 4.2.2 Stream Channel ..................................................................................................63 4.2.3 Riparian Condition...............................................................................................64 4.3 Biological Resources....................................................................................................66 4.3.1 Fisheries Habitat .................................................................................................66 4.3.2 Amphibian and Reptile Habitat............................................................................66 5.0 SUB-BASIN KEY FINDINGS..........................................................................................68 5.1 Sediment Sources........................................................................................................68 5.2 Riparian Function and Fog Effect.................................................................................72 5.3 Cummings Creek..........................................................................................................73 5.3.1 Estimated Sediment Inputs .................................................................................73 5.3.2 Analysis of Potential Channel Response.............................................................74 5.3.3 Potential Resource Vulnerabilities.......................................................................75 5.4 Grizzly Creek................................................................................................................77 5.4.1 Estimated Sediment Inputs .................................................................................77 5.4.2 Analysis of Potential Channel Response.............................................................78 5.4.3 Potential Resource Vulnerabilities.......................................................................80 5.5 Hely Creek ...................................................................................................................81 5.5.1 Estimated Sediment Inputs .................................................................................81 5.5.2 Analysis of Potential Channel Response.............................................................82 5.5.3 Potential Resource Vulnerabilities.......................................................................83 5.6 Hydesville Creek ..........................................................................................................84 5.6.1 Estimated Sediment Inputs .................................................................................84 5.6.2 Analysis of Potential Channel Response.............................................................86 5.6.3 Potential Resource Vulnerabilities.......................................................................86 5.7 Root Creek ...................................................................................................................87 5.7.1 Estimated Sediment Inputs .................................................................................87 5.7.2 Analysis of Potential Channel Response.............................................................88 5.7.3 Potential Resource Vulnerabilities.......................................................................89 5.8 Stevens Creek..............................................................................................................91 5.8.1 Estimated Sediment Inputs .................................................................................91 5.8.2 Analysis of Potential Channel Response.............................................................92 Final Report Page ii Van Duzen River Watershed Analysis Cumulative Watershed Effects 5.8.3 Potential Resource Vulnerabilities.......................................................................93