SCHUSTER SLOPE LANDSCAPE MANAGEMENT PLAN January 15, 2015 1
WHY DO WE NEED A LANDSCAPE MANAGEMENT PLAN? 2
PROCESS FOR DEVELOPING THE SCHUSTER SLOPE LANDSCAPE MANAGEMENT PLAN 3
NORTH DOWNTOWN SUB AREA PLAN SLOPE DESIGN STANDARDS Adopted by City Council, October 2014 4
PUBLIC OUTREACH July 16, 2014 Public Open House August / September Online Survey 5
USING BEST SCIENCE 6
A MANAGEMENT PLAN THAT ADDRESSES MANY INTERESTS 7
INTRODUCTION Presentation Outline Geologic setting Why we need a Landscape Management Plan A landscape approach to slope stability Balancing the objectives a plan to address many interests and site constraints Landscape Management Plan the details How can vegetation management accommodate views? Management Plan Implementation 8
GEOLOGIC SETTING 9
SLOPE STABILITY Definitions Slope morphology Geologic setting Slope processes GEOLOGIC SETTING 10
DEFINITIONS SLOPE TERMS Toe of slope Slope face Slope crest (top of slope) Upland area GEOLOGIC SETTING 11
DEFINITIONS SLOPE GRADIENT GEOLOGIC SETTING 12
DEFINITIONS ANGLE OF REPOSE The maximum slope at which loose soil will remain in place without sliding. 67% Slope 1:1.5 ft GEOLOGIC SETTING 13
PRO GLACIAL SLOPE Advancing continental ice sheet scoured our Commencement Bay Characteristic steep-side U shaped valley GEOLOGIC SETTING 14
POST GLACIAL SLOPE Retreating glaciers left behind over steepened slopes Slopes unstable Massing wasting process of erosion/sloughing, landsliding, etc. altering slope Slopes continuing to retreat in attempt to reach equilibrium conditions GEOLOGIC SETTING 15
PROJECT AREA GEOLOGY Glacial till/ice contact deposits Olympia beds Pre-Vashon glacial sediments Troost, K.G. In review. Geologic Map of the Tacoma North 7.5-Minute Quadrangle, Washington. U.S. Geological Survey Miscellaneous Field Investigation. Scale 1:24,000. GEOLOGIC SETTING 16
HISTORIC SLOPE INSTABILITY Two mapped landslides along Stadium Way LiDAR images show history of slope instability along entire slope GEOLOGIC SETTING 17
Mapped Landslides GEOLOGIC SETTING 18
Garfield Gulch Old RR ROW GEOLOGIC SETTING 19
Old Slide Scarps GEOLOGIC SETTING 20
Stadium HS Old Landslide GEOLOGIC SETTING 21
Old Landslide GEOLOGIC SETTING 22
SLOPE PROCESSES Mass wasting processes (rooting plants, borrowing animals and insects, freeze-thaw, and mechanical weathering) create a zone of weak, loose soil on slope face Thickness dependent on type of soil On steep slopes, zone of weak soil subjected to downslope movement as a result of gravity Slow downslope movement referred to as soil creep This weak layer of soil can also be subject to shallow debris flows or skin slides Debris flows remove the weak soil layer exposing the underlying parent soil Mass wasting begins and the process starts anew GEOLOGIC SETTING 23
SOIL CREEP Soil moving downslope due to gravity GEOLOGIC SETTING 24
EFFECTS OF SOIL CREEP GEOLOGIC SETTING 25
DEBRIS FLOWS/LANDSLIDING GEOLOGIC SETTING 26
SLOPE PROCESSES Lower slope dominated by skin slides Upper slope dominated by soil creep, but potential for debris flows if slope not properly managed. GEOLOGIC SETTING 27
WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 28
MANAGEMENT ELEMENTS Slope Stability Stormwater Benefit Forest Health Public Safety Views WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 29
SLOPES Slope stability Soil binding root systems Site constraints Over half project area >60% slopes Shallow failures Difficult plant establishment WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 30
SLOPES WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 31
STORMWATER BENEFIT Reduce surface impact/flow Evergreen, multilayered vegetation Site constraints Deciduous trees Sparse understory Erosion WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 32
FOREST HEALTH Restore native vegetation Target ecosystem Site constraints Invasives Lack of diversity Lack of rejuvenation Tree disease WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 33
PUBLIC SAFETY Create safe environment Vegetation management Site constraints Irregular users Hazard trees Slope stability WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 34
VIEWS Opportunity to provide views Pruning and species selection Site constraints Mismanagement Lack of species diversity Invasives WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 35
LANDSCAPE MANAGEMENT PLAN THE DETAILS 36
LANDSCAPE MANAGEMENT PLAN LANDSCAPE MANAGEMENT PLAN DETAILS 37
SLOPES Engineering solutions Erosion control Additional requirements may apply based on slope conditions LANDSCAPE MANAGEMENT PLAN DETAILS 38
STORMWATER BENEFIT 2 out of every 3 trees evergreen Layered understory Dense root network LANDSCAPE MANAGEMENT PLAN DETAILS 39
FOREST HEALTH Invasive removal Plant diversity Natives, >90% LANDSCAPE MANAGEMENT PLAN DETAILS 40
PUBLIC SAFETY Crime Prevention Through Environmental Design Natural surveillance Natural access control Tree assessments LANDSCAPE MANAGEMENT PLAN DETAILS 41
VIEWS Phased approach Establish layered understory and canopy Pruning and maintenance Select tree removal LANDSCAPE MANAGEMENT PLAN DETAILS 42
VIEWS LANDSCAPE MANAGEMENT PLAN DETAILS 43
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VIEWS LANDSCAPE MANAGEMENT PLAN DETAILS 50
CONCLUSIONS Geologic settings Why we need a Landscape Management Plan Landscape Management Plan Details Slope Stability Stormwater Benefit Forest Health Public Safety Views 51
MANAGEMENT PLAN IMPLEMENTATION 52