DOGAMI OPEN-FILE REPORT SERIES
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PUBLICATION
PREVIEW
Open-File Report O-21-15, Flood depth and channel migration zone
maps, Benton, Marion, Morrow, And Washington Counties, Oregon
by Christina A. Appleby, Matt C. Williams, Lowell H. Anthony, and
Ian P. Madin; 72 p. report, 225 p. appendix, four Esri® geodatabase with
internal metadata, external metadata in .xml format, nineteen spreadsheets
What's in this report?
This
report describes the methods and results of flood depth and channel migration
zone mapping for Benton, Marion, Morrow, and Washington Counties, Oregon. This
information can help communities plan and prepare for natural disasters.
Presentations
DOGAMI staff recorded
virtual presentations for each of the counties that describes the work from this
publication and the accompanying landslide, coseismic liquefaction
susceptibility, and coseismic soil amplification class maps in Open-File Report
O-21-14 (Hairston-Porter, R.
and others, 2021). These presentations are available at the following links:
Washington County Presentation
Report downloads:
·
Report (72. p, 4.93 MB file)
·
Appendix (225. p, 483 MB file)
·
GIS data bundle: 4
geodatabases with metadata (4.35 GB, zip file)
·
Spreadsheet bundle: 19 spreadsheets (906 MB,
zip file)
·
Complete publication bundle:
report, appendix, geodatabases, metadata, and spreadsheets (4.83 MB, zip file)
·
Benton County bundle:
report, appendix, geodatabase, metadata, and spreadsheets (2.6 GB, zip file)
·
Marion County bundle:
report, appendix, geodatabase, metadata, and spreadsheets (1.87 GB, zip file)
·
Morrow County bundle:
report, appendix, geodatabase, metadata, and spreadsheets (104 MB, zip file)
·
Washington County bundle:
report, appendix, geodatabase, metadata, and spreadsheets (269 MB, zip file)
EXECUTIVE SUMMARY
This study provides Oregon communities with new information
about the natural hazards from floods and channel migration. During 2018 to
2021, the Oregon Department of Geology and Mineral Industries (DOGAMI) produced
flood depth maps for rivers in Benton, Marion, and Morrow Counties and based on
Federal Emergency Management Agency (FEMA) flood insurance studies. Also
developed are channel migration zone maps for major rivers within Benton,
Marion, Morrow, and Washington Counties. These maps are the first of their kind
published for these study areas.
We produced flood depth maps for the 10-, 50-, 100- and 500-year
flood zones using the adopted FIS maps for each individual stream within the
study area most current data (as of December 2020). The maps were created by
interpolating each flood model’s cross section elevation data into a continuous
water surface elevation (WSEL) surface, and then subtracting the corresponding
lidar-based ground surface digital elevation model (DEM). Although this
approach is simple, great care was needed to prepare the data for this process in order to create accurate and detailed representations of
the modeled flood depths.
Channel migration zone (CMZ) maps define the area within which a
given stream is likely to move laterally during the next 30- and 100-years. In
this study, we mapped CMZs along a total of 464 river miles, across 20 rivers
in four counties. The components that comprise these CMZ maps are the active
channel, historical migration area, 30-year and 100-year erosion hazard area,
avulsion hazard area, and flagged stream banks. The method we used was
primarily based on the interpretation of historical aerial photographs,
high-resolution lidar topography, geologic and flood inundation maps.
These maps were designed to be used in risk assessments to
identify people, places, buildings, and infrastructure most vulnerable to
floods and channel migration at a neighborhood-scale. The maps in this study do
not replace a site analysis by a land surveyor, geologist, or engineer. The
hazard maps and risk assessment results can be used by local and state
emergency managers, planners, community leaders, residents, and other
stakeholders to make informed decisions about flood hazards including their
mitigation, land use, and environmental management. These hazard maps will
provide a timely and valuable resource for the county and community planning
efforts including when developing Natural Hazard Mitigation Plan (NHMP)
updates.
GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.7 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml
formatted files.
Each dataset listed below has an associated, standalone .xml
file containing metadata in the Federal Geographic Data Committee Content Standard
for Digital Geospatial Metadata format.
Flood GIS data
|
Dataset name |
Description |
|
Depth_10yr |
This raster dataset depicts the 10-year flood depth (in feet)
based on the effective FEMA Flood Insurance Studies. |
|
Depth_50yr |
This raster dataset depicts the 50-year flood depth (in feet)
based on the effective FEMA Flood Insurance Studies. |
|
Depth_100yr |
This raster dataset depicts the 100-year flood depth (in feet)
based on the effective FEMA Flood Insurance Studies. |
|
Depth_500yr |
This raster dataset depicts the 500-year flood depth (in feet)
based on the effective FEMA Flood Insurance Studies. |
CMZ GIS Data
|
Dataset type |
Description |
|
Channel Migration Zone (CMZ) |
This polygon represents the area within which a channel is
likely to move laterally during the next 100-years. |
|
Active Channel (AC) |
This polygon represents the area within the floodplain that
regularly conveys water including the exposed, unvegetated sediment deposits
both within and adjacent to the river. |
|
Historical Migration Area (HMA) |
This polygon represents the channel has occupied in the
historical photographic record, including the active channel. |
|
30-Year Erosion Hazard Area (EHA) |
This polygon represents the areas at risk from lateral
migration and channel widening over across 30-years based on historical
erosion rates. |
|
100-Year Erosion Hazard Area (EHA) |
This polygon represents the areas at risk from lateral
migration and channel widening over across 100-years based on historical
erosion rates. |
|
Avulsion Hazard Area (AHA) |
This polygon represents the areas at greatest risk of rapid
channel diversion and occupation. |
|
Flag |
This polyline represents the channel banks which have been
identified for further geotechnical inspection due to signs of recent
migration or location directly adjacent to landslide deposits |
|
Study Area |
This polygon represents the study area extent. |
SPREADSHEETS
The spreadsheets provide a summary of the channel description
and notes for all rivers within this study by river segment. These descriptions
include physical channel characteristics (e.g., river segment length, slope,
sinuosity, etc.), geomorphic and geologic conditions, erosion rates, and
observed avulsions, and more.
APPENDIX
The appendix
PDFs contain maps showing the channel migration zones for all rivers within
this study for Benton, Marion, Morrow, and Washington Counties. The figure below
shows an example of the style of these maps. Each map shows the channel
migration zone, active channel, historical migration area, 30- and 100-year
erosion hazard area, avulsion hazard area, and flagged stream banks.
