SCHUSTER SLOPE LANDSCAPE MANAGEMENT PLAN. January 15, 2015

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1 SCHUSTER SLOPE LANDSCAPE MANAGEMENT PLAN January 15,

2 WHY DO WE NEED A LANDSCAPE MANAGEMENT PLAN? 2

3 PROCESS FOR DEVELOPING THE SCHUSTER SLOPE LANDSCAPE MANAGEMENT PLAN 3

4 NORTH DOWNTOWN SUB AREA PLAN SLOPE DESIGN STANDARDS Adopted by City Council, October

5 PUBLIC OUTREACH July 16, 2014 Public Open House August / September Online Survey 5

6 USING BEST SCIENCE 6

7 A MANAGEMENT PLAN THAT ADDRESSES MANY INTERESTS 7

8 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

9 GEOLOGIC SETTING 9

10 SLOPE STABILITY Definitions Slope morphology Geologic setting Slope processes GEOLOGIC SETTING 10

11 DEFINITIONS SLOPE TERMS Toe of slope Slope face Slope crest (top of slope) Upland area GEOLOGIC SETTING 11

12 DEFINITIONS SLOPE GRADIENT GEOLOGIC SETTING 12

13 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

14 PRO GLACIAL SLOPE Advancing continental ice sheet scoured our Commencement Bay Characteristic steep-side U shaped valley GEOLOGIC SETTING 14

15 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

16 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

17 HISTORIC SLOPE INSTABILITY Two mapped landslides along Stadium Way LiDAR images show history of slope instability along entire slope GEOLOGIC SETTING 17

18 Mapped Landslides GEOLOGIC SETTING 18

19 Garfield Gulch Old RR ROW GEOLOGIC SETTING 19

20 Old Slide Scarps GEOLOGIC SETTING 20

21 Stadium HS Old Landslide GEOLOGIC SETTING 21

22 Old Landslide GEOLOGIC SETTING 22

23 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

24 SOIL CREEP Soil moving downslope due to gravity GEOLOGIC SETTING 24

25 EFFECTS OF SOIL CREEP GEOLOGIC SETTING 25

26 DEBRIS FLOWS/LANDSLIDING GEOLOGIC SETTING 26

27 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

28 WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 28

29 MANAGEMENT ELEMENTS Slope Stability Stormwater Benefit Forest Health Public Safety Views WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 29

30 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

31 SLOPES WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 31

32 STORMWATER BENEFIT Reduce surface impact/flow Evergreen, multilayered vegetation Site constraints Deciduous trees Sparse understory Erosion WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 32

33 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

34 PUBLIC SAFETY Create safe environment Vegetation management Site constraints Irregular users Hazard trees Slope stability WHY WE NEED A LANDSCAPE MANAGEMENT PLAN 34

35 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

36 LANDSCAPE MANAGEMENT PLAN THE DETAILS 36

37 LANDSCAPE MANAGEMENT PLAN LANDSCAPE MANAGEMENT PLAN DETAILS 37

38 SLOPES Engineering solutions Erosion control Additional requirements may apply based on slope conditions LANDSCAPE MANAGEMENT PLAN DETAILS 38

39 STORMWATER BENEFIT 2 out of every 3 trees evergreen Layered understory Dense root network LANDSCAPE MANAGEMENT PLAN DETAILS 39

40 FOREST HEALTH Invasive removal Plant diversity Natives, >90% LANDSCAPE MANAGEMENT PLAN DETAILS 40

41 PUBLIC SAFETY Crime Prevention Through Environmental Design Natural surveillance Natural access control Tree assessments LANDSCAPE MANAGEMENT PLAN DETAILS 41

42 VIEWS Phased approach Establish layered understory and canopy Pruning and maintenance Select tree removal LANDSCAPE MANAGEMENT PLAN DETAILS 42

43 VIEWS LANDSCAPE MANAGEMENT PLAN DETAILS 43

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50 VIEWS LANDSCAPE MANAGEMENT PLAN DETAILS 50

51 CONCLUSIONS Geologic settings Why we need a Landscape Management Plan Landscape Management Plan Details Slope Stability Stormwater Benefit Forest Health Public Safety Views 51

52 MANAGEMENT PLAN IMPLEMENTATION 52