We obtained GIS coverages of Oregon's
1998 List of Water Quality Limited Waterbodies (the "303[d]
list"). The zipped coverages, obtained from the Oregon Department
of Environmental Quality
website,
included two ArcInfo export files, one for streams (s303_98.e00),
and one for lakes and reservoirs (l303_98.e00). The lakes
coverage included only two lakes in the study area (Devil's
Lake, listed for chlorophyll a and pH, and Mercer Lake,
listed for algae and aquatic weeds). Since these were the
only two listed lakes, lakes were not incorporated into
the quantitative analysis. The 303(d) listed streams coverage
is based on the
1:100k
streams layer. The 303(d) coverage was intersected with
the
6th Field Watershed
layer, and total length of listed streams was calculated
for each 6th field. We then joined the table of total lengths
to the 6th field GIS layer and color coded 6th fields by
this length. The length shown includes streams listed for
all criteria. Most of the stream length (90%) was listed
for high temperatures; about 10% of the listed length was
impaired by habitat modification or sedimentation, while
about 5% was listed for fecal coliform contamination.
The 303(d) list is used as a first step
in locating water quality-impaired reaches, as described
in the OWEB Watershed Assessment Manual. However, the 303(d)
list does not include all streams that are impaired by high
temperatures, sedimentation, fecal coliform, or other factors.
Most of the 303(d) listed streams are mainstem rivers or
large tributaries. .
The methodology for the DEQ's 303(d)
list is described at the
DEQ
website.
Click to Enlarge
Avg: 6,396 m (303(d) streams per 6th Field)
Max: 19,035 m (303(d) streams per 6th Field)
Min: 0 m (303(d) streams per 6th Field)
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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