Map plate for DOGAMI Open-File Report O-13-08, Landslide ... - Landslide Hazard and Risk...Title:...
1
by William J. Burns, Katherine A. Mickelson, Cullen B. Jones, Sean G. Pickner, and Kaleena L. B. Hughes Oregon Department of Geology and Mineral Industries, Portland, Oregon Rachel Sleeter U.S. Geological Survey, Menlo Park, California The project described in this publication was supported in part by Intergovernmental Agreement IGS 11-21-2011 from Clackamas County, Oregon OPEN-FILE REPORT O-13-08 Landslide Hazard and Risk Study of Northwestern Clackamas County, Oregon HIGH: High susceptibility to deep landslides. Deposits mapped as historical and/or active are outlined in black. MODERATE: Moderate susceptibility to deep landslides. LOW: Low susceptibility to deep landslides. DEEP-LANDSLIDE SUSCEPTIBILITY CLASSIFICATION This map depicts susceptibility to deep landslides in this area. For the purpose of this map, deep landslides are defined as those with a depth to the failure plane of greater than 15 ft (4.5 m) (Burns and Madin, 2009). This susceptibility map was prepared by combining four factors: 1) landslide inventory data taken from the corresponding inventory map, 2) head scarp buffers, 3) moderate zone buffer, and 4) geologic factors (susceptible geologic units and contacts, slope angles, and preferred direction of movement). The combinations of these factors comprise the relative susceptibility hazard zones: high, moderate, and low as shown in the Hazard Zone Matrix below. The deep-landslide susceptibility data are displayed on top of a base map that consists of an aerial photograph (orthorectified) overlain on the lidar-derived digital elevation model. For additional detail on how this map was developed see Burns (2008). Each landslide susceptibility hazard zone shown on this map has been developed according to a classification scheme using a number of specific factors. The classification scheme was developed by the Oregon Department of Geology and Mineral Industries; see accompanying text report. The symbology used to display these hazard zones is explained below. Deep-Landslide Susceptibility Zones: This map uses color to show the relative degree of hazard. Each zone is a combination of several factors (see Hazard Zone Matrix, below). EXPLANATION High Moderate Low i nc l uded — — i nc l uded — — — Lands l i des , Hea dSca r p- F l a nks , Bu f er s Final Hazard Zone Contributing Factors Mi ni m a lGeo l ogi c Fact o r s Geo l ogi c Fact o r s , H i ghZoneBu f er — i nc l uded * * See exp l a na t i on o f co r r es pond i ng cont r i bu t i ng f act o r s b el ow. Deep-Landslide Susceptibility Hazard Zone Matrix Landslide Inventory: This map is an inventory of existing deep-landslide deposits and head scarps in this area. This inventory map was prepared by compiling all previously mapped landslides from published and unpublished geologic and landslide mapping, lidar-based geomorphic analysis, and review of aerial photographs. Each landslide was also attributed with classifications for activity, depth of failure, movement type, and confidence of interpretation using the protocol developed by Burns and Madin (2009). This map uses color to show different landslide features as explained below. EXPLANATION Lands l i de Head Sca r ps Deep- Lands l i de Dep os i t s 3 2 1 Head Scarp Buffers: Buffers were applied to all head scarps from the landslide inventory. In most cases the first buffer results in a minimum buffer distance and the second buffer (described below) results in the maximum buffer distance. In all cases the greater of the two was used. The first buffer (orange on diagram) consists of a 2:1 horizontal to vertical distance (2H:1V). This buffer is different for each head scarp and is dependent on head scarp height. For example, a head scarp height of 6.5 ft (2 m) has a 2H:1V buffer equal to 13 ft (4 m). The second buffer (red on diagram) is different for each head scarp and is dependent on the average of the horizontal distance between internal scarps. For example, an average horizontal distance of 150 ft (50 m) has a 2H:1V buffer equal to 300 ft (100 m). Moderate Susceptibility Zone: This map displays the scores of the relative geologic susceptibility zone factors, a moderate zone buffer applied around the high susceptibility zone, and the mapped deep-landslide deposits in this area. A moderate zone buffer was applied around the high-susceptibility zone of each landslide deposit. This buffer is different for each landslide deposit and is dependent on head scarp height. Each geologic zone factor was given a score of 0, 1, or 2. Thus, if all factors have the highest score at some particular location, the final factor score is 8. A minimal combined factor score threshold between 3 and 5 along with educated judgment was used to delineate the boundary between the low and moderate zones. The geologic zone factors are: EXPLANATION Deep- Lands l i de Dep os i t s Moder at e Zone Bu fer Geo l ogi c Sus c ep t i bi l i t y Zone Fa ct o r s Sco r e 1 ( l ow) 2 3 4 5 6 7 8 ( hi gh) 1) Susceptible geologic units 2) Susceptible geologic contacts 3) Susceptible slope angles for each engineering geology unit polygon 4) Susceptible direction of movement for each engineering geology unit polygon The geologic susceptibility zone factors and the moderate zone buffer data sets along with professional judgment were used to create the boundary between the moderate and low deep-landslide susceptibility zones. U. S . Geo l ogi cal Su r v ey 7 . 5 - mi nu t e quad r a ngl e maps ar e d i v i ded i nt o quar t er quad r a ngl es . Ea ch quar t er quad r a ngl e ha s t wo pl at e num ber s ; t he f i r s t pl at e num ber i nd i cat es t he s ha l l ow- l ands l i de sus c ep t i bi l i t y map, a nd t he s econd pl at e num ber i nd i cat es t he co r r es pond i ng deep- l ands l i de s us c ep t i bi l i t y map. P l at es 1 a nd 2 ( no t s hown her e) ar e ov er v i ew maps f o r t hi s p ubl i cat i on. Cartography by William J. Burns and Katherine A. Mickelson, Oregon Department of Geology and Mineral Industries. This map also benefited from internal review and comments by Ian Madin, DOGAMI Chief Scientist. IMPORTANT NOTICE This product is for informational purposes and may not have been prepared for or be suitable for legal, engineering, or surveying purposes. Users of this information should review or consult the primary data and information sources to ascertain the usability of the information. This publication cannot substitute for site-specific investigations by qualified practitioners. Site-specific data may give results that differ from the results shown in the publication. See the accompanying text report for more details on the limitations of the methods and data used to prepare this publication. REFERENCES Burns, W.J., 2008, Regional landslide hazard maps of the southwest quarter of the Beaverton quadrangle, West Bull Mountain Planning Area, Washington County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-08-09, 17 p., scale 1:8,000. Burns, W.J., and Madin, I.P., 2009, Protocol for inventory mapping of landslide deposits from light detection and ranging (lidar) imagery: Oregon Department of Geology and Mineral Industries Special Paper 42, 30 p. Highland, L., compiler, 2004, Landslide types and processes: U.S. Geological Survey Fact Sheet 2004-3072 (ver. 1.1), 4 p. 3) The susceptibility maps are based on the topographic and landslide inventory data available as of the date of publication. Future new landslides may render this map locally inaccurate. 4) The lidar-based digital elevation model does not distinguish elevation changes that may be due to the construction of structures like retaining walls. Because it would require extensive GIS and field work to locate all of these existing structures and remove them or adjust the material properties in the model, such features have been included as a conservative approach and therefore must be examined on a site-specific basis. 5) Some landslides in the inventory may have been mitigated, thereby reducing their level of susceptibility. Because it is not feasible to collect detailed site-specific information on every landslide, potential mitigation has been ignored. a. Limitations of the landslide inventory, which are discussed by Burns and Madin (2009). b. Calculation of head scarp buffers is limited based on the head scarp height (first buffer) and an average of the horizontal widths of previous or downslope blocks (second buffer). It is assumed that most large deep landslides have the potential to fail retrogressively upslope; however, this is not always the case. c. The additional factors used to delineate the moderate susceptibility zone include susceptible geologic units, susceptible geologic contacts, susceptible slope angles for each engineering geology unit polygon, and susceptible direction of movement for each engineering geology unit polygon. These factors are combined and a final score is produced, but the delineation of the final moderate zone is based on visual overlap of these four factors; therefore, the accuracy and resolution of the output data can be overestimated or underestimated. LIMITATIONS The deep-landslide susceptibility map was developed following an established protocol (Burns, 2008) that incorporates several types of data. Several limitations are worth noting and underscore that any regional hazard map can be useful for regional applications but should not be used as an alternative to site-specific studies in critical areas. Limitations include the following. 1) Every effort has been made to ensure the accuracy of the GIS and tabular database, but it is not feasible to completely verify all of the original input data. 2) As discussed in the Explanation section, the protocol to develop deep-landslide susceptibility maps is based on four factors: 1) landslide inventory data taken from the corresponding inventory map, 2) head scarp buffers, 3) moderate zone buffer, and 4) geologic factors (susceptible geologic units and contacts, slope angles, and preferred direction of movement). All of these parameters can affect the level of detail and accuracy of the final susceptibility map. Because the maps are based on a combination of factors, all of which Beaver Creek Leland Rd. Spangler Rd. Carus Rd. Cahill Creek New Era Rd. HWY 213 Parrott Creek EFL 122 °33 ' 45 " W 122 °33 ' 45 " W 122 °37 ' 30 " W 122 °37 ' 30 " W 45 °18 ' 45 " N 45 °18 ' 45 " N 45 °15 ' 0 " N 45 °15 ' 0 " N 530 000 530 000 532 000 532 000 534 000 534 000 501 2000 501 2000 501 4000 501 4000 501 6000 501 6000 Deep-Landslide Susceptibility Map of the Southwest Quarter of the Oregon City Quadrangle, Clackamas County, Oregon SCALE 1:8,000 2013 0.25 0 0.25 0.5 0.75 1 0.125 Kilometers 0.25 0 0.25 0.5 0.75 1 0.125 Miles 1,300 0 1,300 2,600 3,900 5,200 650 Feet STATE OF OREGON DEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES www.OregonGeology.org W. Lawrence Givens, Governing Board Chair Vicki S. MCConnell, Director and State Geologist Andre V. Pollock, Assistant Director, Geologic Survey and Services Rachel L. Smith, Project Operations Manager Ian P. Madin, Chief Scientist O R E G O N D E P A R T M E N T O F G E O L O G Y A N D M I N E R A L I N D U S T R I E S 1 9 3 7 Base map for plates in this publication: Lidar data from DOGAMI Lidar Data Quadrangle LDQ-2009-45122C3-Estacada, LDQ-2009-45122C4-Redland, LDQ-2009-45122C5-Oregon City, LDQ-2009-45122C6-Canby, LDQ-2009-45122C7-Sherwood, LDQ-2009-45122D3-Sandy, LDQ-2009-45122D4-Damascus, LDQ-2009-45122D5-Gladstone, LDQ-2009-45122D6-Lake Oswego. Digital elevation model (DEM) consists of a 3-foot-square elevation grid that was converted into a hillshade image with sun angle at 315 degrees at a 60-degree angle from horizontal. The DEM was multiplied by 5 (vertical exaggeration) to enhance slope areas. 2005 orthophoto imagery is from Oregon Geospatial Enterprise Office and is draped over the hillshade image with transparency. Projection: North American Datum 1983, UTM zone 10 North. Software: Esri ArcMap 10, Adobe Illustrator CS2. Source File: Project\Clackamas Landslide\ClackamasStudy.mxd 39, 40 41, 42 47, 48 49, 50 55, 56 57, 58 63, 64 65, 66 71, 72 73, 74 35, 36 37, 38 43, 44 45, 46 51, 52 53, 54 59, 60 61, 62 67, 68 69, 70 7, 8 9, 10 15, 16 17, 18 23, 24 25, 26 31, 32 33, 34 3, 4 5, 6 11, 12 13, 14 19, 20 21, 22 27, 28 29, 30 CANBY SANDY REDLAND ESTACADA DAM ASCU S SHERW O O D GLADSTO NE O REGO N CI TY LAKE O SW EGO Damascus Lake Oswego West Linn Wilsonville Canby Happy Valley Milwaukie Sandy Oregon City Estacada Gladstone § ¨ ¦ 5 § ¨ ¦ 405 £ ¤ 26 £ ¤ 26 Ä Æ 99E Ä Æ 224 Ä Æ 211 Ä Æ 213 Ä Æ 551 Ä Æ 224 Ä Æ 551 Ä Æ 224 Ä Æ 224 PLATE INDEX AND LOCATION MAP For copies of this publication contact: Nature of the Northwest Information Center 800 NE Oregon Street, #28, Ste. 965 Portland, Oregon 97232 telephone (971) 673-2331 http://www.naturenw.org Landslide Inventory 1 Head Scarp Buffers Geologic Factors and Buffers 2 3 Head Sca r p ( HS) Ho r i zont al D i s t a nc e ( HS- I S1 ) IS1-IS2 HS-IS1 Ho r i zont al D i s t a nc e ( I S1 - I S2 ) ? ? Head Sca r p Hei ght ( V) Mi ni mum Head Sca r p Bu f er ( o r a nge) Hea d Sca r p Hei ght ( V) Mi ni mum Head Sca r p Bu f er 2H: 1V Deep- Seat ed Head Sca r p Set back = ? Av er a ge Ho r i zont al D i s t a nc e o f HS- I S1 , I S1 - I S2 , et c. Po t ent i al Fu t u r e Fai l u r e P l a ne I nt er na l Sca r p ( I S) B l ock D i a gr am ( af t er H i ghl a nd , 2004 ) Cr os - Sect i on ( Pr o f i l e) Head Sca r p Bu f er B l ock D i a gr am ( af t er H i ghl a nd , 2004 ) Cr os - Sect i on ( Pr o f i l e) OREGON PLATE 56
Transcript of Map plate for DOGAMI Open-File Report O-13-08, Landslide ... - Landslide Hazard and Risk...Title:...
by William J. Burns, Katherine A. Mickelson, Cullen B. Jones,Sean G. Pickner, and Kaleena L. B. Hughes
Oregon Department of Geology and Mineral Industries, Portland, OregonRachel Sleeter
U.S. Geological Survey, Menlo Park, CaliforniaThe project described in this publication was supported in part by
Intergovernmental Agreement IGS 11-21-2011 from Clackamas County, Oregon
OPEN-FILE REPORT O-13-08Landslide Hazard and Risk Study of
Northwestern Clackamas County, Oregon
HIGH: High susceptibility to deep landslides. Deposits mapped as historical and/or active are outlined in black.
MODERATE: Moderate susceptibility to deep landslides.
LOW: Low susceptibility to deep landslides.
DEEP-LANDSLIDE SUSCEPTIBILITY CLASSIFICATION
This map depicts susceptibility to deep landslides in this area. For the purpose of this map, deep landslides are defined as those witha depth to the failure plane of greater than 15 ft (4.5 m) (Burns and Madin, 2009).
This susceptibility map was prepared by combining four factors: 1) landslide inventory data taken from the corresponding inventorymap, 2) head scarp buffers, 3) moderate zone buffer, and 4) geologic factors (susceptible geologic units and contacts, slope angles, andpreferred direction of movement). The combinations of these factors comprise the relative susceptibility hazard zones: high, moderate,and low as shown in the Hazard Zone Matrix below. The deep-landslide susceptibility data are displayed on top of a base map thatconsists of an aerial photograph (orthorectified) overlain on the lidar-derived digital elevation model. For additional detail on howthis map was developed see Burns (2008).
Each landslide susceptibility hazard zone shown on this map has been developed according to a classification scheme using a numberof specific factors. The classification scheme was developed by the Oregon Department of Geology and Mineral Industries; seeaccompanying text report. The symbology used to display these hazard zones is explained below.
Deep-Landslide Susceptibility Zones: This map uses color to show the relative degree of hazard. Each zone is a combination ofseveral factors (see Hazard Zone Matrix, below).
EXPLANATION
High Moderate Lowinc luded — —
inc luded— ——
La ndslides,Hea dSc a rp -Fla nks,Buffers
Final Hazard ZoneContributing Factors
M inim a lGeologic Fa c torsGeologic Fa c tors,High Zone Buffer
— inc luded
*
*See exp la na tion of c orresp onding c ontrib uting fa c tors b elow.
Deep-Landslide Susceptibility Hazard Zone Matrix
Landslide Inventory: This map is aninventory of existing deep-landslidedeposits and head scarps in this area.This inventory map was prepared bycompiling all previously mappedlandslides from published andunpublished geologic and landslidemapping, lidar-based geomorphicanalysis, and review of aerialphotographs. Each landslide was alsoattributed with classifications for activity,depth of failure, movement type, andconfidence of interpretation using theprotocol developed by Burns and Madin(2009). This map uses color to showdifferent landslide features as explainedbelow.
EXPLANATIONLa ndslide Hea d Sc a rp sDeep -La ndslide Dep osits
321
Head Scarp Buffers: Buffers wereapplied to all head scarps from thelandslide inventory. In most cases thefirst buffer results in a minimum bufferdistance and the second buffer (describedbelow) results in the maximum bufferdistance. In all cases the greater of thetwo was used.
The first buffer (orange on diagram)consists of a 2:1 horizontal to verticaldistance (2H:1V). This buffer is differentfor each head scarp and is dependent onhead scarp height. For example, a headscarp height of 6.5 ft (2 m) has a 2H:1Vbuffer equal to 13 ft (4 m).
The second buffer (red on diagram) isdifferent for each head scarp and isdependent on the average of thehorizontal distance between internalscarps. For example, an averagehorizontal distance of 150 ft (50 m) has a2H:1V buffer equal to 300 ft (100 m).
Moderate Susceptibility Zone: Thismap displays the scores of the relativegeologic susceptibility zone factors, amoderate zone buffer applied around thehigh susceptibility zone, and the mappeddeep-landslide deposits in this area.
A moderate zone buffer was appliedaround the high-susceptibility zone ofeach landslide deposit. This buffer isdifferent for each landslide deposit and isdependent on head scarp height.
Each geologic zone factor was given ascore of 0, 1, or 2. Thus, if all factors havethe highest score at some particularlocation, the final factor score is 8. Aminimal combined factor score thresholdbetween 3 and 5 along with educatedjudgment was used to delineate theboundary between the low and moderatezones. The geologic zone factors are:
EXPLANATIONDeep -La ndslide Dep ositsM odera te Zone Buffer
Geologic Susc ep tib ility Zone Fa c tors Sc ore1 (low)234
5678 (high)
1) Susceptible geologic units2) Susceptible geologic contacts3) Susceptible slope angles for eachengineering geology unit polygon4) Susceptible direction of movement foreach engineering geology unit polygon
The geologic susceptibility zone factorsand the moderate zone buffer data setsalong with professional judgment wereused to create the boundary between themoderate and low deep-landslidesusceptibility zones.
U .S. Geologic a l Survey 7.5-m inute q ua dra ngle m a p s a re divided into q ua rter q ua dra ngles. Ea c h q ua rter q ua dra ngle ha s two p la te num b ers; the first p la te num b er indic a tes the sha llow-la ndslide susc ep tib ility m a p , a nd the sec ond p la te num b er indic a tes the c orresp onding deep -la ndslide susc ep tib ility m a p . Pla tes 1 a nd 2 (not shown here) a re overview m a p s for this p ub lic a tion.
Cartography by William J. Burns and Katherine A. Mickelson, Oregon Department of Geology and Mineral Industries.
This map also benefited from internal review and comments by Ian Madin, DOGAMI Chief Scientist.
IMPORTANT NOTICE
This product is for informational purposes and may not have been preparedfor or be suitable for legal, engineering, or surveying purposes. Users ofthis information should review or consult the primary data andinformation sources to ascertain the usability of the information. Thispublication cannot substitute for site-specific investigations by qualifiedpractitioners. Site-specific data may give results that differ from theresults shown in the publication. See the accompanying text report formore details on the limitations of the methods and data used to preparethis publication.
REFERENCESBurns, W.J., 2008, Regional landslide hazard maps of the southwest quarter of the Beaverton quadrangle, West Bull MountainPlanning Area, Washington County, Oregon: Oregon Department of Geology and Mineral Industries Open-File Report O-08-09, 17 p.,scale 1:8,000.
Burns, W.J., and Madin, I.P., 2009, Protocol for inventory mapping of landslide deposits from light detection and ranging (lidar)imagery: Oregon Department of Geology and Mineral Industries Special Paper 42, 30 p.
Highland, L., compiler, 2004, Landslide types and processes: U.S. Geological Survey Fact Sheet 2004-3072 (ver. 1.1), 4 p.
3) The susceptibility maps are based on the topographic and landslide inventory data available as of the date of publication. Futurenew landslides may render this map locally inaccurate.
4) The lidar-based digital elevation model does not distinguish elevation changes that may be due to the construction of structureslike retaining walls. Because it would require extensive GIS and field work to locate all of these existing structures and remove themor adjust the material properties in the model, such features have been included as a conservative approach and therefore must beexamined on a site-specific basis.
5) Some landslides in the inventory may have been mitigated, thereby reducing their level of susceptibility. Because it is not feasibleto collect detailed site-specific information on every landslide, potential mitigation has been ignored.
a. Limitations of the landslide inventory, which are discussed by Burns and Madin (2009).
b. Calculation of head scarp buffers is limited based on the head scarp height (first buffer) and an average of the horizontalwidths of previous or downslope blocks (second buffer). It is assumed that most large deep landslides have the potential to failretrogressively upslope; however, this is not always the case.
c. The additional factors used to delineate the moderate susceptibility zone include susceptible geologic units, susceptiblegeologic contacts, susceptible slope angles for each engineering geology unit polygon, and susceptible direction of movement foreach engineering geology unit polygon. These factors are combined and a final score is produced, but the delineation of the finalmoderate zone is based on visual overlap of these four factors; therefore, the accuracy and resolution of the output data can beoverestimated or underestimated.
LIMITATIONSThe deep-landslide susceptibility map was developed following an established protocol (Burns, 2008) that incorporates several typesof data. Several limitations are worth noting and underscore that any regional hazard map can be useful for regional applications butshould not be used as an alternative to site-specific studies in critical areas. Limitations include the following.
1) Every effort has been made to ensure the accuracy of the GIS and tabular database, but it is not feasible to completely verify all ofthe original input data.
2) As discussed in the Explanation section, the protocol to develop deep-landslide susceptibility maps is based on four factors: 1)landslide inventory data taken from the corresponding inventory map, 2) head scarp buffers, 3) moderate zone buffer, and 4) geologicfactors (susceptible geologic units and contacts, slope angles, and preferred direction of movement). All of these parameters can affectthe level of detail and accuracy of the final susceptibility map. Because the maps are based on a combination of factors, all of which
Beaver Creek
Leland Rd.
Spangler Rd.
Carus Rd.
Cahill Creek
New Era Rd.
HWY 213
Parrott Creek
ES-R+EFL
EFL
EFL 122°33'45"W
122°33'45"W
122°37'30"W
122°37'30"W
45°18'45"N45°18'45"N
45°15'0"N45°15'0"N
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530000
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532000
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534000
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Deep-Landslide Susceptibility Map of the Southwest Quarter of the Oregon City Quadrangle, Clackamas County, Oregon
SCALE 1:8,000
2013
0.25 0 0.25 0.5 0.75 10.125Kilometers
0.25 0 0.25 0.5 0.75 10.125Miles
1,300 0 1,300 2,600 3,900 5,200650Feet
STATE OF OREGONDEPARTMENT OF GEOLOGY AND MINERAL INDUSTRIES www.OregonGeology.orgW. Lawrence Givens, Governing Board ChairVicki S. MCConnell, Director and State GeologistAndre V. Pollock, Assistant Director, Geologic Survey and ServicesRachel L. Smith, Project Operations ManagerIan P. Madin, Chief Scientist
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
Base map for plates in this publication:
Lidar data from DOGAMI Lidar Data Quadrangle LDQ-2009-45122C3-Estacada,LDQ-2009-45122C4-Redland, LDQ-2009-45122C5-Oregon City, LDQ-2009-45122C6-Canby, LDQ-2009-45122C7-Sherwood, LDQ-2009-45122D3-Sandy, LDQ-2009-45122D4-Damascus, LDQ-2009-45122D5-Gladstone, LDQ-2009-45122D6-Lake Oswego.Digital elevation model (DEM) consists of a 3-foot-square elevation grid that was converted into a hillshade image with sun angle at 315 degrees at a 60-degree angle from horizontal.The DEM was multiplied by 5 (vertical exaggeration) to enhance slope areas.
2005 orthophoto imagery is from Oregon Geospatial Enterprise Office andis draped over the hillshade image with transparency.
Projection: North American Datum 1983, UTM zone 10 North.
Software: Esri ArcMap 10, Adobe Illustrator CS2.
Source File: Project\Clackamas Landslide\ClackamasStudy.mxd
39, 40 41, 42 47, 48 49, 50 55, 56 57, 58 63, 64 65, 66 71, 72 73, 74
35, 36 37, 38 43, 44 45, 46 51, 52 53, 54 59, 60 61, 62 67, 68 69, 70
7, 8 9, 10 15, 16 17, 18 23, 24 25, 26 31, 32 33, 34
3, 4 5, 6 11, 12 13, 14 19, 20 21, 22 27, 28 29, 30
CANBY
SANDY
REDLAND ESTACADA
DAM ASCU S
SHERW O O D
GLADSTO NE
O REGO N CITY
LAKE O SW EGODamascusLake Oswego
West Linn
Wilsonville
Canby
Happy ValleyMilwaukie
Sandy
Oregon City
Estacada
Gladstone
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§̈¦405
£¤26
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ÄÆ
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ÄÆ
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224
PLATE INDEX AND LOCATION MAP
For copies of this publication contact:Nature of the Northwest Information Center
800 NE Oregon Street, #28, Ste. 965Portland, Oregon 97232
telephone (971) 673-2331http://www.naturenw.org
Landslide Inventory1
Head Scarp Buffers
Geologic Factors and Buffers
2
3
Hea d Sc a rp (HS)
Horizonta lDista nc e(HS-IS1) IS1-IS2
HS-IS1
Horizonta lDista nc e(IS1-IS2)
?
?
Hea d Sc a rpHeight (V )
M inim um Hea d Sc a rpBuffer (ora nge)
Hea d Sc a rpHeight (V )
M inim um Hea dSc a rp Buffer 2H:1V
Deep -Sea tedHea d Sc a rp
Setb a c k=
?
Avera ge Horizonta lDista nc e of HS-IS1,
IS1-IS2, etc .
Potentia lFutureFa ilurePla ne
Interna l Sc a rp (IS)
Bloc k Dia gra m (a fter Highla nd, 2004)Cross-Sec tion (Profile)
Hea d Sc a rp Buffer
Bloc k Dia gra m (a fter Highla nd, 2004)Cross-Sec tion (Profile)
OREGO N
PLATE 56
