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M i d d l e F o r k W i l l a m e t t eR i v er

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W i l l a m e t t e R i v e r

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S o u t h F o r k S p e n c e r C r e e k

A m a z o n C r e e k D i v e r s i o n C h a n n e l

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MountPisgah

ShortMountain

Sk innerButte

SpencerButte

VitusButte

BriggsHill

Oak Hill

SporesPoint

Mohaw kValley

CantrellHill

MoonMountain

Lorane Hwy

Lorane Hwy

Spencer Creek Rd

Bailey

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Bailey Hill Rd

River Rd

River Rd

Willame

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Clear Lake Rd

Willamette Hwy

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Gimpl Hill Rd

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Prairie Rd

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Shallow Landslide Susceptibility Map of Eugene and Springfield, Lane County, Oregon2018

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¬«58Lane County

Eugene South

Eugene North

Eugene West Springfield

West Springfield East

Coburg

Eugene Southwest

Lane County

Walterville

Goshen

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Study Area Com m unities Map

Wi l l a m e t t e

V a l l e y

C a s c a d eR a n g e

S p e n c e r B u t t e

M o u n t P i s g a h

W i l l a m e t t e

R i v e r R i v e r

M c K e n z i eFe r n Ri d g e

L a k e

Fa l l C r e e k L a k e

OREGON

Study Area Location Map

Source Data:Oregon Lidar Consortium, 2008-2009 and 2013-2015, 3-foot bare earth lidar digital elevation modelfor Coburg (44123-B1), Creswell (43123-H1), Crow (43123-H3), Eugene East (44123-A1), Eugene West(44123-A2), Fox Hollow (43123-H2), Jasper (43122-H8), Junction City (44123-B2), Springfield (44122-A8), Walterville (44122-A7).Water features are from the USGS National Hydrography Dataset (2015). Highways and signed routesare from the Oregon Department of Transportation (2013). Additional physical and cultural locationsare from the Geographic Names Information System (GNIS), U.S. Geological Survey (2013). Eugeneand Springfield community boundaries and building footprints are from Lane Council of Governments(2017).

Projection:Oregon Statewide Lambert Conformal Conic, Unit: International Feet.Horizontal Datum: NAD 1983 HARN. UTM Coordinates: Zone 10N, NAD83.Software:Esri® ArcMap® 10.6Cartography:Jon J. Franczyk

Lane County

Eugene South

Eugene NorthEugene

WestSpringfield

West Springfield East

Coburg

Eugene Southwest

Generaliz ed Surficial Engineering Geology Map

(See Study Area Com m unities Map for m ore detail)

OREG

ONDE

P AR TM

E NT O F G E O L O G Y A N D M I NE RALI NDUSTRIES

1937

STATE OF OREGONDEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES

BRAD AVY, STATE GEOLOGISTww w.OregonGeology.org

Elevation ChangeFeet above sea level

4984

272

16.5

TRUE

NOR

THMA

GNET

IC N

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APPROXIMATE MEANDECLINATION, 2014

0 5 102.5Miles

0 5 102.5Kilometers

1:290,000SCALE

16.5

TRUE

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ORTH

APPROXIMATE MEANDECLINATION, 2014

SCALE 1:34,000

0 1 2 3 40.5Miles

0 1 2 3 40.5Kilometers

T his shallow landslide susceptibility m ap identifies landslide-prone areas that are defined following theprotocol of Burns and others (2012).On the basis of several factors and past studies (described in detail by Burns and Madin [2009]), adepth of 15 ft (4.5 m ) is used to divide shallow from deep landslides. W e prepared this shallowsusceptibility m ap by com bining three factors: 1) calculated factor of safety (FOS), 2) landslideinventory data, and 3) buffers, as described below. W e calculated the FOS by using conservative valuessuch as having the water table at the ground surface. W e used landslide inventory data from thecorresponding inventory m ap (Plate 1). T he com binations of these factors com prise the relativesusceptibility haz ard zones: high, m oderate, and low, as shown by the Susceptibility Hazard Z oneMatrix below. T he landslide susceptibility data are display ed on top of a base m ap that consists of thelidar-derived digital elevation m odel.

EXPLANATION

Each landslide susceptibility haz ard zone shown on this m ap has been developed according to anum ber of specific factors. T he classification schem e was developed by the Oregon Departm ent ofGeology and Mineral Industries (Burns and others, 2012). T he sy m bology used to display these haz ardzones is explained below.Shallow Landslide Susceptibility Zones: T his m ap uses color to show the relative degree of hazard.Each zone is a com bination of several factors (see Hazard Z one Matrix, below).

SHALLOW LANDSLIDE SUSCEPTIBILITY CLASSIFICATION

Shallow Landslide Susceptibility Hazard Zone Matrix

T he m echanics of slope stability can be divided into two forces: driving forces and resisting forces.T hese forces are a function of the m aterial properties and the geom etry of the slope. T hese two forcesoppose each other, and slope stability can be thought of as their ratio.

A slope with a FOS > 1 is theoretically a stable slope because the shear strength is greater than theshear stress. A slope with a FOS < 1 is theoretically an unstable slope because the shear stress isgreater than the shear strength. A critically stable slope has a FOS = 1. Because of the inability to k nowall the conditions present within a slope, m ost geotechnical engineers and engineering geologistsrecom m end that slopes with a FOS < 1.5 be considered potentially unstable (T urner and Schuster,1996; Cornforth, 2005).W e calculated the FOS by using the infinite slope equation with conservative param eters. Saturatedconditions were used so that a “worst case” scenario could be evaluated. Because of lim itations relatedto a grid type analy sis, we rem oved isolated areas with sm all (less than 4 ft [1.2 m ] high) elevation

An inventory of all existing landslides in this area is shown on Plate 1. W e prepared this inventory m apby com piling all previously m apped landslides from published and unpublished geologic and landslidem apping, analy z ing lidar-based geom orphology, and review ing aerial photographs. W e also attributedeach landslide with classifications for activity, depth of failure, m ovem ent type, and confidence ofinterpretation. W e created the inventory by using the protocol developed by Burns and Madin (2009).W e extracted the shallow landslides from the inventory and used these to create this shallow landslidesusceptibility m ap.

Buffer for Factor of Safety Less Than 1.5: T his buffer was applied to all areas with a calculated FOSless than 1.5. T he buffer consists of a 2:1 horizontal to vertical distance (2H:1V). For exam ple, if them axim um depth for shallow landslides is 15 ft (4.5 m ), then the 2H:1V buffer would equal 30 ft (9 m ).

Buffer for Head Scarps: T his buffer was applied to all head scarps from the landslide inventory. T hebuffer consists of a 2:1 horizontal to vertical distance (2H:1V). T his buffer is different for each headscarp and is dependent on head scarp height. For exam ple, a head scarp height of 6 ft (2 m ) has a2H:1V buffer equal to 12 ft (4 m ).

Head ScarpHeight (V)

2H:1V Head ScarpBuffer (orange)

2H:1V Head Scarp Buffer

2 times V = 2H

Horizontal (H)Vertical(V)

2H:1V Factor of SafetyBuffer = 9 m (30 ft)

2H:1V Diagram

Block Diagram

Cross-Section (profile)

Cross-Section (profile)

Head ScarpHeight (V)

Maximum depthz = 4.5 (15 ft)

Lim itations include the following.1) Every effort has been m ade to ensure the accuracy of the GIS and tabular database, but it is notfeasible to com pletely verify all of the original input data.2) T he shallow landslide susceptibility m aps are based on three prim ary com ponents: a) calculatedfactor of safety, b) landslide inventory, and c) buffers. Factors that can affect the level of detail andaccuracy of the final susceptibility m ap include the following:

a) Factor of safety calculations are strongly influenced by the accuracy and resolution of theinput data for m aterial properties, depth to failure surface, depth to groundwater, and slopeangle. T he first three of these inputs are usually estim ates (m aterial properties) orconservative lim iting cases (depth to failure surface and groundwater), and local conditionsm ay vary substantially from the estim ated values used to m ak e these m aps.b) Lim itations of the landslide inventory are discussed by Burns and Madin (2009).c) Infinite slope factor of safety calculations are done on one grid cell at a tim e without regardto adjacent grids. T he results m ay underestim ate or overestim ate the level of stability for acertain area. W e developed buffers for areas with low factors of safety to counter the tendencyto underestim ate susceptibility. W e developed the focal relief m ethod to reduce the problemof overestim ation of susceptibility due to steep slopes with low relief. However,overestim ation and underestim ation of susceptible areas are still lik ely in som e isolated areas.

3) T his susceptibility m ap is based on the topographic and landslide inventory data available as of thedate of publication. Future new landslides m ay render this m ap locally inaccurate.4) T he lidar-based digital elevation m odel does not distinguish elevation changes that m ay be due tothe construction of structures lik e retaining walls. Because it would require extensive GIS and fieldwork to locate all existing structures and rem ove them or adjust the m aterial properties in the m odel,such features have been included as a conservative approach and m ust be exam ined on a site-specificbasis.5) Som e landslides in the inventory m ay have been m itigated, thereby reducing their level ofsusceptibility. Because it is not feasible to collect detailed site-specific inform ation on every landslide,

LIMITATIONS

Burns, W .J., and Madin, I.P., 2009, Protocol for inventory m apping of landslide deposits from lightdetection and ranging (lidar) im agery: Oregon Departm ent of Geology and Mineral Industries SpecialPaper 42, 30 p., geodatabase tem plate.Burns, W .J., Madin, I.P., and Mick elson, K.A., 2012, Protocol for shallow-landslide susceptibilitym apping: Oregon Departm ent of Geology and Mineral Industries Special Paper 45, 32 p.Cornforth, D.H., 2005, Landslides in practice: Investigation, analy sis, and rem edial/preventativeoptions in soils: Hobok en, N.J., John W iley and Sons, Inc., 596 p.Turner, A. K., and Schuster, R. L., eds., 1996, Landslides: investigation and m itigation: W ashington, D.C.,National Research Council, Transportation Research Board Special Report 247, 673 p.

REFERENCES

SHALLOW LANDSLIDE SUSCEPTIBILITY CLASSIFICATION

1:130,000SCALE16.5

TRUE

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APPROXIMATE MEANDECLINATION, 2014

0 2.5 51.25 Miles0 2.5 51.25 Kilometers

123°0'0"W

123°0'0"W

General Features

123°0'0"W

123°0'0"W

44°0'0"N

123°0'0"W

44°0'0"N

LOW:Low susceptibility to shallow

MODERATE:Moderate susceptibility to shallow landslides.HIGH:High susceptibility to shallow

Factor of Safety (FOS)1

Factor ofSafety

Resisting ForcesDriving Forces=

Landslide Inventory2

3 Buffers for Head Scarps and Factor of Safety Less Than 1.5

44°0'

0"N

44°0'0"N

44°0'0"N44°0'0"N

123°0'0"W

Contributing Factors Final Hazard Zone

Factor of Safety (FOS)Landslide Deposits and Head Scarps

Buffer

High Moderate Low< 1.25

2H:1V (head scarps) 2H:1V (FOS < 1.5)

1.25 - 1.50 > 1.50included

44°0'0

"N

123°0'0"W

44°0'0"N

123°0'0"W

16.5

TRUE

NOR

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APPROXIMATE MEANDECLINATION, 2014

0 5 102.5Miles

0 5 102.5Kilometers

1:122,000SCALE

IMS-60

By Nancy C. Calhoun, W illiam J. Burns, Jon J. Francz y k ,and Gustavo Monteverde

PLATE 2

Landslide Hazard and Risk Study ofEugene-Springfield and Lane County, Oregon

Funding for this project was partially provided by theFederal Em ergency Managem ent Agency (EMW -2015-CA-00106).

INTERPRETIVE MAP SERIES

Community Boundaries

Eugene NorthEugene West

Eugene SouthEugene South West

Coburg

Springfield EastSpringfield West

T his product is for inform ational purposes and m ay not have been prepared for or be suitable forlegal, engineering, or survey ing purposes. Users of this inform ation should review or consult theprim ary data and inform ation sources to ascertain the usability of the inform ation. T hispublication cannot substitute for site-specific investigations by qualified practitioners. Site-specificdata m ay give results that differ from the results shown in the publication. See the accom pany ingtext report for m ore details on the lim itations of the m ethods and data used to prepare thispublication.

NOTICE

T he eastern portion of Lane County contains the cities of Eugene, Springfield, and Coburg. Becauselandslides are one of the m ost widespread and dam aging natural haz ards in the state, it isim portant to m ap and assess the risk in the study area. T he purpose of this study is to assist thecities and county in understanding the landslide haz ard better and thus increase their ability toreduce future risk . T he study publication consists of a text report, three m ap plates, and GIS data.

ABOUT THIS PUBLICATION

123°14'57"W

43°57'

14"N

123°14'56"W

44°08'

56"N

123°14'56"W

44°08

'56"N

123°14'57"W

43°57

'14"N

Explanation of Symbols

River

Study AreaCity / County Boundary

Study ExtentHighway

River / LakeLane County(Outside Study Area) Lane County

(Within Study Area)

Explanation of SymbolsD

Stream

SummitRoad

Waterbody

Study Area

Buildings

The unit names listed below ingenerally increasing strength(weaker to stronger)

Landslides (deep) deposits

Recent alluvial deposits

Older alluvium

Residual soil on sedimentary rocks

Residual soil on volcaniclastic rocks

Residual soil on tuff

Residual soil on mafic rocks

Bedrock at surface

Man-made fill