We conducted two multi-factor analyses of coho winter habitat for this assessment. The first was the Potential Coho Winter Habitat Analysis. As requested by the MidCoast Watersheds Council Tech Team, this analysis located stream reaches that were classified as "unconfined" (having flat areas near the stream), low-gradient (0 to 2 degrees, or 0 to 3.5% slope), and flowing through hydric soils. The Functioning Coho Winter Habitat Analysis used the results of the potential habitat analysis, and added in four 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 low gradient, "unconfined" as defined by DEM analysis, and flowing through hydric soils. By contrast, the Functioning Coho Winter Habitat analysis was a 6th field ranking.

There are many possible definitions of "functioning coho winter habitat." The MidCoast Watersheds Council requested we incorporate the following factors into this multi-factor analysis:

Factor	Effect of high value on ranking (+/-)
Length of potential habitat (unconfined* low-gradient streams flowing through hydric soils)	+
LWD frequency (pieces/100m)	+
Percent pools by area	+
Channel widths per pool	-
Length of side channel habitat	+

* see DEM analysis of stream confinement for details on definition of "unconfined"

We used the following data sources for the above factors:

Factor	Data source	Analysis link
Length of "unconfined" low-gradient streams flowing through hydric soils	Digital elevation model DEM)	derived_stream_confinement.htm der_stream_gradient.htm hydric_soils.htm
LWD frequency (pieces/100m)	AHI data	ahi_lwd100.htm
Percent pools by area	AHI data	ahi_percent_pools.htm
Channel widths per pool	AHI data	ahi_channelwidths.htm
Length of side channel habitat	AHI data	ahi_side_channel_length.htm

Six of the factors in the analysis consist of AHI data. AHI data came from three separate sources -- USFS Region 6 tabular data, ODFW GIS data, and Lincoln District AHI data. For those factors that were analyzed as numeric means or percentages (LWD, % pools, and channel widths per pool), there were protocol differences between the different data sources. Because of these differences, we needed to use a ranking method that would be independent of the specific values for each parameter. We used several steps to rank 6th fields for each numeric AHI factors:

1. Determine average value for 6th field from each data source separately.
2. Determine ranking for each 6th field from each data source separately.
3. Average the rankings from the three data sources to get single "average rank".

For length of side channel habitat, we summed the lengths from all data sources and ranked the 6th fields from top (rank 1, greatest length of gravel-dominated riffles) to bottom (shortest length) based on the total length. We used the same procedure for the DEM-derived length of unconfined, low-gradient streams flowing through hydric soils.

We combined all of the above factors into a single ranking for each 6th field (cohow_rk in aqhab_sum_final.zip). Values for the ranking ranged from 38 (best) to 506 (worst).

Only 6th fields with AHI data could be ranked in this analysis. Some 6th fields lacking AHI data may have good coho habitat functions. We recommend AHI surveys for areas not yet surveyed but offering good coho winter habitat potential, and we also recommend re-survey of areas surveyed several years ago to determine whether habitat has changed since the earlier survey. 

We followed the above ranking procedures because we felt they provided the best interpretation of the data. However, many different ranking systems are equally defensible for an analysis of this type. If they wish, MCWC members will be able to re-rank 6th fields using alternative systems by manipulating the aquatic habitats summary shapefile aqhab_sum_final.zip.

As requested by MCWC, we used absolute lengths for analysis of potential habitat and side channels. Proportional lengths, rather than absolute lengths, provide certain advantages in tracking change over time. A discussion of proportional lengths versus absolute lengths is found in "Interpreting the results of aquatic habitat analyses: Absolute lengths versus proportion of surveyed lengths"

The rankings can help prioritize 6th fields for actions designed to improve coho winter habitat, such as creation or restoration of off-channel habitat and placement of large woody debris. 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 coho winter 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 Coho Winter 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 | homepage