We conducted two multi-factor analyses
of winter steelhead habitat for this assessment. The first
was the
Potential Winter
Steelhead Habitat Analysis. As requested by the MidCoast
Watersheds Council Tech Team, this analysis located stream
reaches that were classified as "
confined"
(lacking flat areas near the stream)and
medium-gradient
(1 to 5 degrees, or 1.75% to 8.75% slope). The
Functioning
Winter Steelhead Habitat Analysisused the results
of the potential habitat analysis, and added in two other
factors from AHI surveys as described below.
The
potential habitat analysis was a sub-6th field analysis
that provided data on specific stream reaches meeting
the criteria of medium gradient and "confined"
as defined by DEM analysis. By contrast, the Functioning
habitat analysis was a 6th field ranking.
| Factor |
Effect of high value on ranking (+/-) |
| Length
of potential habitat (confined,* med. gradient) |
+ |
| Length of riffle habitat |
+ |
| Length of riffle habitat with gravel-to-boulder
sized substrate dominant |
+ |
* see
DEM
analysis of stream confinement for details on definition
of "unconfined"
We used the following data sources for the above factors:
To
develop the 6th field ranking, we summed the length of "confined",
medium-gradient reaches for each 6th field, then ranked
the 6th fields for that total length. We also summed and
ranked total length of riffles, and length of riffles with
gravel-to-boulder-sized substrate dominant. We then combined
all three factors to form a final ranking for each
6th
field. All factors were weighted equally. A high value
for each factor increased the ranking. All of the analysis
variables are found in the aquatic habitats summary
shapefile.
The
rankings can help prioritize 6th fields for actions designed
to improve winter steelhead habitat. The rankings should
not be used alone for this purpose, but should be used
in conjunction with other data, particularly field verification
of suitable conditions.
Before
using the rankings, we recommend careful review of the
detailed methods for each individual analysis that entered
into the multi-factor analysis. All datasets have their
limitations and proper uses, and many of these are discussed
in the methods sections for the individual analyses.
The
data collected in AHI surveys can change considerably
over the course of a single year. Therefore, any future
analyses of winter steelhead habitat should use the most
recent AHI survey data. We recommend surveying new reaches
that appear to offer high potential habitat value, as
well as re-surveying critical reaches for which survey
data are more than a couple of years old.
Since AHI data
from USFS and Lincoln District sources was not georeferenced,
it was not possible to develop a site-specific, reach-by-reach
analysis of functioning habitat that incorporated all
of the available AHI data. However, it would be possible
to locate some specific reaches that meet all of the Functioning
Winter Steelhead Habitat criteria, by using the Aquatic
Habitat Inventory data that originated from the ODFW GIS.
This analysis would be a logical next step for the Basin
Planning Teams. For such a site-specific analysis, it
will be particularly important to consider the age of
the AHI data (survey date). Ground-truthing or re-survey
of critical reaches is recommended, particularly if the
AHI data in question are several years old.
Scale
is a consideration in site-specific analyses such as the
one described above. The ODFW data are entered on a 1:100k
streams layer, while the DEM analysis is conducted at
the 1:24k scale that is considered appropriate for watershed
assessment at the 5th field level. This scale difference
will need to be considered when conducted any site-specific
analysis that uses both DEM and ODFW GIS data.
Please address questions or comments
to:
Dr. Ralph Garono
Principal Investigator
Earth Design Consultants, Inc.
rgarono@earthdesign.com
Laura Brophy
Principal Investigator
Green Point Consulting
brophyl@peak.org |
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