Bluff Hazard Zones, Tillamook County, DOGAMI, 2001

Citation:

Citation Information:

Originator: Oregon Department of Geology and Mineral Industries
Publication Date: 2001
Title: Bluff Hazard Zones, Tillamook County, DOGAMI, 2001
Edition: Preliminary
Geospatial Data Presentation Form: vector digital data
Series Information:

Series Name: Open File Report
Issue Identification: O-01-03

Publication Information:

Publication Place: Portland, Oregon
Publisher: Oregon Department of Geology and Mineral Industries

Other Citation Details: A text report accompanies the vector digital data
Online Linkage: http://www.oregongeology.com
Larger Work Citation:

Citation Information:

Originator: Oregon Department of Geology and Mineral Industries
Publication Date: 20011231
Title: Evaluation of coastal erosion hazard zones along dune and bluff backed shorelines in Tillamook County, Oregon: Cascade Head to Cape Falcon
Other Citation Details:
Other Digital map data files associated with this Open-file Report include: Historical shorelines - 1927, 1953, 1955, 1986, 1994, 1997, 1998; Dune hazard data - Neskowin cell beach data, Netarts cell beach data, Rockaway cell beach data, Sand Lake cell beach data; Erosion data - Spot erosion rates; Hazard zones - Active hazard zone, Bluff hazard zones, high dune hazard zone, low dune hazard zone, moderate dune hazard zone; Landslides - Tillamook coastal landslides; Misc. geology -Basalt, Slide block widths Tillamook.
Online Linkage: http://www.oregongeology.com

Description:

Abstract:
Polygon data capturing coastal erosion hazard zones for bluffs of Tillamook County coast. Three complementary erosion hazard scenarios were mapped for bluffs utilizing bluff erosion rates, potential for block failures, and empirically derived angles of repose for the bluff materials.The three zones define HIGH, MODERATE, and LOW risk scenarios for expansion of the active hazard zone by bluff top retreat. Similar to the dune-backed shorelines, the three hazard zones depict decreasing levels of risk that they will become active in the future, but an increase in the magnitude of erosion. This data set is one portion of a larger study of the entire Tillamook County Coastline. For full details on study results and methods please consult DOGAMI Open-file Report O-01-03, and associated digital files.
Purpose:
To assess existing and potential coastal erosion hazards along the Tillamook County shoreline, extending from Cascade Head in the south to Cape Falcon in the north. Further, to assist County planners in effective decisionmaking adjacent to the shoreline.
Supplemental Information:
Hazard zones on bluff-backed shorelines were mapped based on an understanding of several geological parameters including bluff erosion rates, potential for block failures, and empirically determined angles of repose for the bluff materials. Predicting whether a particular part of a bluff will erode away over the life of a proposed development depends on understanding the influence of several parameters. These include:
· Bluff slope;
· Bluff height;
· Bluff material properties;
· Groundwater level and resulting pore pressures;
· Surface water runoff;
· Wave climate;
· How much material is present at the toe of the bluff (e.g. slide debris, dune sand, logs, etc.) that can both buttress and protect the bluff from wave erosion;
· Whether any buttressing material is moving seaward (active slide blocks), and;
· Vegetative cover.

In a very real sense, each bluff must be judged based on the local geology, likely future climate (rainfall and storms), and its current state of instability in the erosion cycle. Owing to limitations of this regional county investigation, we are only be able to take into account parameters such as the bluff slope, height, material properties (rock or soil composition), and the historical response of broad classes of bluff to coastal erosion. As a result, detailed, site-specific investigations are necessary to provide projections of the erosion hazard for a particular development on coastal bluffs.

Time Period of Content:

Time Period Information:

Single Date/Time:

Calendar Date: 2001
Time of Day: Unknown

Currentness Reference: 20010625

Status:

Progress: Complete
Maintenance and Update Frequency: None planned

Spatial Domain:

Bounding Coordinates:

West Bounding Coordinate: -124.060154
East Bounding Coordinate: -123.890947
North Bounding Coordinate: 45.76826
South Bounding Coordinate: 45.047306

Keywords:

Theme:

Theme Keyword Thesaurus: NA
Theme Keyword: Beach Morphology
Theme Keyword: Coastal Erosion
Theme Keyword: Geology
Theme Keyword: Hazard
Theme Keyword: Bluff

Place:

Place Keyword Thesaurus: NA
Place Keyword: Tillamook County
Place Keyword: Oregon Coast

Access Constraints: None
Use Constraints: This regional investigation is not intended for use as a site-specific analysis tool. It can be used to identify areas in need of more detailed site-specific geotechnical studies.
Point of Contact:

Contact Information:

Contact Person Primary:

Contact Person: Jonathan C. Allan
Contact Organization: Oregon Department of Geology and Mineral Industries

Contact Position: Coastal geomorphologist
Contact Address:

Address Type: mailing and physical address
Address: 313 SW 2nd, Suite D
City: Newport
State or Province: Oregon
Postal Code: 97365

Contact Voice Telephone: 541 574-6642
Contact Facsimile Telephone: 541 265-5241

Data Set Credit:
This investigation was supported by a professional services agreement with Tillamook County and from resources of the State of Oregon Department of Geology and Mineral Industries (DOGAMI). County funds were derived from the Project Impact program of the Federal Emergency Management Agency. The project was greatly facilitated by the Netarts Littoral Cell Management Planning Project supported by the Oregon Department of Land Conservation and Development, Oregon Parks and Recreation Division, and Tillamook County. We are especially grateful to John Beaulieu (Director of DOGAMI), Dennis Olmstead (Deputy State Geologist), Zhenming Wang (acting Earthquake Program Director for DOGAMI), Paul Komar (Oregon State University), John Marra (Department of Land Conservation and Development), Richard Rinne (Hart Crowser, Inc), and Doug Gless (H.G. Schlicker & Associates, Inc), for their insightful comments on this report. Thanks must also be extended to Randy Dana, Department of Land Conservation and Development, for his help in collating the NOS T-sheets, Chris Chickadel, Oregon State University, for helping out with the ARGUS photographic data, and James Good, Oregon State University, who offered helpful advice early on in the project. We are also extremely grateful to Stuart Albright of Hart Crowser, Inc. for sending invaluable geotechnical data from The Capes project. Eileen Hemphill-Halley of the US Geological Survey and University of Oregon kindly provided data analyses of diatoms present in Quaternary deposits of The Capes landslide.
Native Data Set Environment: Microsoft Windows Vista Version 6.1 (Build 7601) Service Pack 1; ESRI ArcCatalog 9.3.1.4000

Positional Accuracy:

Horizontal Positional Accuracy:

Horizontal Positional Accuracy Report:
Owing to limitations of available base maps, none of the mapped bluff hazard zones are located closer than plus or minus ~33 feet horizontal and ~20 feet vertical (40 foot elevation contours).

Vertical Positional Accuracy:

Vertical Positional Accuracy Report: Elevations in this data set are relative to the North American Vertical Datum of 1988 (NAVD’ 88)

Lineage:

Source Information:

Source Citation:

Citation Information:

Title: Preliminary report for Tillamook County shoreline

Source Scale Denominator: 12000
Type of Source Media: CD-ROM
Source Time Period of Content:

Time Period Information:

Range of Dates/Times:

Beginning Date: 1999
Beginning Time: Unknown
Ending Date: 2001
Ending Time: Unknown

Source Citation Abbreviation: DOGAMI OFR O-01-03
Source Contribution: Original DOGAMI files were in MapInfo format, and in UTM Zone 10N NAD27 projection.

Process Step:

Process Description:
For the entire project, the process steps included the following: 1. Work with local advisory groups to guide the investigation. 2. Obtain appropriate historical aerial photography. 3. Search the literature for hazard data. 4. Map existing open coastal shoreline landslides, classifying them as prehistoric, potentially active, or active. 6. Collect shoreline topographic profiles and other data necessary to estimate the width of a zone of shoreline variability on dune-backed open coastal shorelines. 7. In collaboration with County and technical advisers, establish a methodology for mapping erosion hazard areas. 8. Map the erosion hazard areas. 9. Digitize all line data. 10. Transmit all digital data to County. 11. Provide follow-up advice on use of the maps in policy development.
Process Date: 1999

Process Step:

Process Description:
Detailed explanations of how each of the hazard zones were established for specific geological situations encountered in Tillamook County are given in Appendix A. The north-south extent of shoreline segments mapped with specific methods is given in the geographic information database that accompanies this report. Hazard zones are drawn in transitions between segments utilizing professional judgment. Professional judgment is really the basis for drawing any geological hazard zone, but the procedure described below has been uniformly applied to make the hazard zones reasonably reproducible by multiple workers.
1. Determine bluff composition, structure, and extent of all landslides, including ancient (prehistoric) slides.

2. Map the bluff top or top edge of the active or potentially active landslide headwall. Exclude all mass movement hazard areas that are prehistoric (e.g. unit PHls) or potentially active but queried (e.g. Pals?). Everything seaward of this line is the active hazard zone.

3. Determine the projected bluff top (or projected landslide headwall position) at the slope of repose for the bluff material, making sure that each soil or rock unit in the bluff has the appropriate slope of repose (Table 5). On active or potentially active landslides, project the slope of repose from the toe of the headwall at its subsurface intersection with the
slide plane. Use local geotechnical data to find this intersection if available; if no data is available, use the procedure of Appendix D.

4. For Pleistocene or Holocene sand or soil bluffs, map the projected bluff top position for a slope of 2:1 from the current slope toe (factor of safety of 50 percent relative to a 1.5:1 slope).

5. Using Table 6, determine an estimated minimum expansion of the active hazard zone (or projected position at the slope of repose from Table 5, whichever is the most landward) by multiplying the mean erosion rate of the basal soil or rock unit by 60 years. This is the landward boundary of the high hazard zone.

6. Using Tables 6 and 7, determine the maximum expansion of the active hazard zone (or projected position at the slope of repose from Table 5, whichever is most landward) by multiplying the maximum erosion rate by 100 years. Add to this the maximum block failure width from Table 7. This represents the landward boundary of the low hazard zone for most bluffs.

7. For bluffs composed of Pleistocene or Holocene sand, move the low hazard zone boundary to the projected position of the previously mapped 2:1 slope, if the drawn boundary is not already landward of the 2:1 slope.

8. Draw the moderate hazard zone boundary at the mean position between the high and low hazard zone boundaries (i.e. sum the lateral distances of the high and low hazard zones and divide by 2).

9. Adjust the low and moderate hazard zone boundaries for any inland landslides that are intersected by the projected expansion of the active coastal erosion hazard zone. Use geologic judgment and endeavor to:

a. Encompass the parts of inland landslides that may be further destabilized by future coastal erosion.
b. Match the general risk levels implied by the hazard zone designations (i.e. inland prehistoric or queried potentially active landslides in the “low” zone; and active or potentially active landslides in the “high” or “moderate” zones).
c. Predict the probable future expansion of these inland landslides should coastal erosion reach them.

Process Contact:

Contact Information:

Contact Person Primary:

Contact Person: Jonathan C. Allan
Contact Organization: Oregon Department of Geology and Mineral Industries

Contact Position: Coastal geomorphologist
Contact Address:

Address Type: mailing and physical address
Address: 313 SW 2nd, Suite D
City: Newport
State or Province: Oregon
Postal Code: 97365

Contact Voice Telephone: 541 574-6642
Contact Facsimile Telephone: 541 265-5241

Process Step:

Process Description:
The original MapInfo Interchage Format files were exported from CD-ROM and converted to ESRI Shapefile format. The data was reprojected during this transformation in to the Oregon statewide Lambert projection.
Process Contact:

Contact Information:

Contact Person Primary:

Contact Person: Tanya C. Haddad
Contact Organization: Oregon Coastal Management Program

Contact Position: Coastal Atlas Coordinator
Contact Address:

Address Type: mailing and physical address
Address: 800 NE Oregon St, #1145
City: Portland
State or Province: OR
Postal Code: 97232
Country: USA

Contact Voice Telephone: 971-673-0962
Contact Facsimile Telephone: 971-673-0911
Contact Electronic Mail Address: tanya.haddad@state.or.us

Cloud Cover: 0

Direct Spatial Reference Method: Vector
Point and Vector Object Information:

SDTS Terms Description:

SDTS Point and Vector Object Type: G-polygon
Point and Vector Object Count: 79

Horizontal Coordinate System Definition:

Planar:

Map Projection:

Map Projection Name: Lambert Conformal Conic
Lambert Conformal Conic:

Standard Parallel: 43
Standard Parallel: 45.5
Longitude of Central Meridian: -120.5
Latitude of Projection Origin: 41.75
False Easting: 1312335.958
False Northing: 0

Planar Coordinate Information:

Planar Coordinate Encoding Method: Coordinate Pair
Coordinate Representation:

Abscissa Resolution: 0
Ordinate Resolution: 0

Planar Distance Units: international feet

Geodetic Model:

Horizontal Datum Name: North American Datum of 1983
Ellipsoid Name: Geodetic Reference System 80
Semi-major Axis: 6378137
Denominator of Flattening Ratio: 298.257

Detailed Description:

Entity Type:

Entity Type Label: tillamook_cnty_bluff_hazard_zones_DOGAMI_2001

Attribute:

Attribute Label: FID
Attribute Definition: Internal feature number.
Attribute Definition Source: ESRI
Attribute Domain Values:

Unrepresentable Domain: Sequential unique whole numbers that are automatically generated.

Attribute:

Attribute Label: Geog_Local
Attribute Definition: Text description of setting

Attribute:

Attribute Label: ID

Attribute:

Attribute Label: Label
Attribute Definition: Rish Zones
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: HIGH risk
Enumerated Domain Value Definition:
Portrays the zone of bluff retreat that would occur if only gradual erosion at a relatively low mean rate were to occur after the slope reaches and maintains its angle of repose. The time interval of erosion was assumed to be 60 years.
Enumerated Domain:

Enumerated Domain Value: MODERATE risk
Enumerated Domain Value Definition:
Portrays an average amount of bluff retreat that would occur from the combined processes of block failures, retreat to an angle of repose, and maximum erosion for ~60-100 years. The zone boundary is derived by placing it halfway between the high and low risk boundaries.
Enumerated Domain:

Enumerated Domain Value: LOW risk
Enumerated Domain Value Definition:
Illustrates a “worst case” for bluff retreat in ~60-100 years. The zone portrays the bluff retreat that would occur if a bluff suffered a maximum slope failure, then eroded back to its angle of repose and continued to gradually retreat for ~100 years. For bluffs composed of Holocene to Pleistocene dune sand the additional bluff top retreat from rapid response to short-term wave erosion events and potential subaerial erosion is achieved by adding a 100 percent safety factor to the erosion calculations, and making sure that the resulting bluff top retreat corresponds to at least a 50 percent factor safety for the angle of repose (i.e. a 2:1slope). This degree of retreat has a low probability and could easily take much longer than 100 years, but reflects the extreme uncertainty of predicting how a large sand bluff might respond to erosion events.
Attribute:

Attribute Label: Shape
Attribute Definition: Feature geometry.
Attribute Definition Source: ESRI
Attribute Domain Values:

Unrepresentable Domain: Coordinates defining the features.

Overview Description:

Entity and Attribute Overview: See accompanying Open-File Report text for a discussion and explanation of digital map data attributes.
Entity and Attribute Detail Citation: Oregon Department of Geology and Mineral Industries Open File Report O-01-03

Distributor:

Contact Information:

Contact Person Primary:

Contact Person: Donald Haines
Contact Organization: Nature of the Northwest Info Center

Contact Position: Manager
Contact Address:

Address Type: physical address
Address: 800 NE Oregon Street
City: Portland
State or Province: OR
Postal Code: 97232
Country: USA

Resource Description: Bluff Hazard Zones, Tillamook County, DOGAMI, 2001, from OFR O-01-03
Distribution Liability:
Although these data have been processed successfully on a computer system at the Oregon Department of Geology and Mineral Industries (DOGAMI), no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that these data are directly acquired from DOGAMI, and not indirectly through other sources which may have changed the data in some way. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. The Oregon Department of Geology and Mineral Industries shall not be held liable for improper or incorrect use of the data described and/or contained herein.
Standard Order Process:

Digital Form:

Digital Transfer Information:

Transfer Size: 0.271

Custom Order Process: For the original OFR files in MapInfo format please contact the Oregon Department of Geology and Mineral Industries
Available Time Period:

Time Period Information:

Single Date/Time:

Calendar Date: 1/1895
Time of Day: Unknown

Metadata Date: 2/22/2013
Metadata Review Date:
Metadata Future Review Date:
Metadata Contact:

Contact Information:

Contact Person Primary:

Contact Person: Tanya C. Haddad
Contact Organization: Oregon Coastal Management Program

Contact Position: Coastal Atlas Coordinator
Contact Address:

Address Type: mailing and physical address
Address: 800 NE Oregon St, #1145
City: Portland
State or Province: OR
Postal Code: 97232
Country: USA

Contact Voice Telephone: 971-673-0962
Contact Facsimile Telephone: 971-673-0911
Contact Electronic Mail Address: tanya.haddad@state.or.us

Metadata Standard Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata Standard Version: FGDC-STD-001-1998
Metadata Time Convention: local time