COMPOSITE IRR
Brochure 10 in IRR Series
December 22, 2003
- Land Use Committee
- Hugo
Neighborhood Association & Historical Society
- Member
of the CACNA Coalition
__________
Policy 3, Goal 11 Josephine County
Comprehensive Plan
Goal
11, Policy 3.B.(1) This Josephine County Comprehensive Plan (JCCP)1 policy
permits requests involving changes for lands from a resource designation (i.e., woodlot
resource) to a non-resource designation through the internal rate of return, or IRR
procedure.2 The Hugo Neighborhood Association has concerns with the
present application of the IRR system in the amendment process.3
“A lot or parcel is considered forest
land when the predominant (more than 50%) soil or soils on the parcel have an internal
rate of return of 3.5 or higher (if a single forest-rated soil is present), or composite
internal rate of return of 3.5 or higher (if multiple forest-rated soils are
present).”
Composite Internal Rate of
Return (CIRR)
How
do you apply the CIRR method?
1. Identify the soils on the applicable parcel (i.e.,
map symbol and soil name)2 & 4 or conduct you own soils
inventory.
2. Develop a simple soils grid to determine the
percent of each soil on the parcel.5
3. Use Soils Rating For Josephine County (IRR) for
each soil.2
3. Summarize information in table (see example
tables).
In
the Table 1 example, IRR ratings include, 46 percent of the soils less than 3.5, 2 percent
greater than 3.5, and 52 percent not rated. You
cannot calculate a CIRR without considering the forest productivity of all the soils. A non-rated soil creates a need to utilized JCCP
Policy 3.B.(2).
Example Table 1 - Site Soils Data
- Map Soil Name
IRR %of
- Symbol
Site
- 12D Brockman Cobbly Clay Loam
0.00
52%
- 79F Vannoy-Voorhies Complex
2.91
34%
- 21F Comutt-Dubakella Complex
2.78 12%
- 42C Holland Sandy Loam
3.83 02%
What
if a lot or parcel is composed of multiple forest rated soils and it is not obvious if the
internal rate of return is 3.5 or less for the parcel. In this case a CIRR needs to be
calculated (see example Table 2). For this
example soils 12D and 79F are assigned fictitious IRRs.
What is interesting about Table 2 is that 80 percent of the soils had an individual
IRR greater than 3.5, but the composite IRR at 3.51 was barely above 3.5.
Example Table 2 - CIRR
- Map IRR
%of Comp
- Symbol
Site Index
- 12D 2.00
X
11% = 22.00
- 79F 3.76
X
39% = 146.64
- 21F 2.78
X 09%
= 25.02
- 42C 3.83
X 41% = 157.03
-
Total 350.69
- Composite IRR Index 3.51
More Information
What
if we changed the percent of site slightly with less soils having an IRR above 3.5 (see
Example Table 3).
Example Table 3 - CIRR
- Map IRR
%of Comp
- Symbol
Site Index
- 12D 2.00
X
11% = 22.00
- 79F 3.76
X
39% = 146.64
- 21F 2.78
X 11%
= 30.58
- 42C 3.83
X 39% = 149.37
-
Total 338.59
- Composite IRR Index 3.49
Table 3
demonstrates that 78 percent of the soils had an individual IRR greater than 3.5, but the
composite IRR at 3.49 was just below 3.5.
More
Information. Would you like to learn more
about citizen involvement in land use planning? Contact
a member of the Land Use Committee of the Hugo Neighborhood.
Disclaimer. This brochure is as much about providing
information and provoking questions as it is about opinions concerning the adequacy of
findings of fact and land use decisions. It
does not provide recommendations to citizens and it is not legal advice. It does not take the place of a lawyer. If citizens use information contained in this
paper, its their personal responsibility to make sure that the facts and general
information contained in it are applicable to their situation. (Link)
1.
Josephine County. October 2000. The Comprehensive Plan For Josephine County. Grants
Pass, OR.
2. Lawrence F.
Brown. 1985. Using The Internal Rate Of
Return To Rate Forest Soils For Applications In Land Use Planning. Grants Pass, OR.;
Michael Snider. 1999. Locational Factors Affecting Woodlot Resource
Lands. Josephine County Planning Office. Grants Pass, OR.
3. Hugo
Neighborhood Association & Historical Society. 2003.
The IRR Series: Woodlot Resource To
Non-Resource Lands; Evaluation: Internal Rate of Return - IRR; Top IRR Rated
Agricultural Lands; Non-rated Soils Versus IRR System; Compliance With Goal 4 -
Forest Lands, Brown Report: IRR Zoning, and Amendments.
Grants Pass, OR.
4. United
States Department of Agriculture. Soil Conservation Service. December 1983. Soil Survey
of Josephine County, Oregon. (Presently the Natural Resources Conservation Service).
5. David
Summer’s land use application before the
Josephine County Rural Planning Commission August 25, 2003.
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