Water Quality Improvement Project
Tucannon Watershed Area:
The Tucannon/Pataha watershed is located in southeastern Washington State in
Garfield and Columbia counties. The Tucannon River drains a watershed area of
approximately 318 square miles. It flows into the Snake River 4 miles upstream
of Lyons Ferry state Park. Pataha Creek enters the Tucannon River about 11 miles
above the Tucannon’s confluence with the Snake River. The Pataha drains a
watershed of 185 square miles.
The Tucannon basin ranges from 540 feet (165 meters) above sea level at the
confluence of the Tucannon and the Snake River, to 6,400 feet (1,950 meters) above sea
level in the Blue Mountains. The climate is semi-arid. Average annual
precipitation ranges from 5-10 inches in the lowlands of the Snake River up to
45 inches in the Blue Mountains.
Historically the lower elevation areas were covered with canyon grasslands
and shrub-steppe vegetation. Much of this land has now been converted to
livestock and crop (mainly non-irrigated crops such as wheat) production.
Coniferous forests still dominate the higher elevations of the Blue Mountains.
Much of this area is under state or federal ownership. Land use in the watershed
is primarily rural with few urban areas. The city of Pomeroy is the most
populated area in the watershed, with a population in the year 2000 of 1,517.
Water quality issues
Water quality standards are designed to protect the beneficial uses of our
streams and lakes. Beneficial uses can include drinking water, irrigation,
fishing, habitat and recreation (swimming, wading, and boating). When a water
body does not meet Washington State water
quality standards it is placed on the state’s
Section 303(d) list of impaired water
The primary water quality concerns in the Tucannon River and Pataha Creek are
temperature, fecal coliform and pH. Both waterbodies were placed on the 303(d)
list for exceeding state water quality standards for these parameters. The Tucannon
River was also listed for turbidity. To learn more about these parameters please visit
Importance of the Different Impairments page.
Once placed on the 303(d) list, a water quality improvement project (also
known as a Total Maximum Daily Load, or TMDL) is normally completed. Visit the
TMDL web site for more information on
TMDLs. Information about Ecology’s 303(d) listings is available by visiting the
Water Quality Assessment web site.
Why this matters
Water temperature influences what types of organisms can live in a
water body. Cooler water can hold more dissolved oxygen that fish and
other aquatic life need to breathe. Warmer water holds less dissolved
oxygen. Threatened and endangered salmon need cold, clean water to
One way to cool water temperature is to shade the water body by adding or
retaining streamside vegetation.
What is being done
Temperature problems in the Tucannon and Pataha creeks are being addressed
through a streamlined Total Maximum Daily Load (TMDL) approach.
The streamlined approach is simpler and faster than the conventional TMDL
method. It works by:
- Using as much existing local data and data collection resources as
- Avoiding complicated computer modeling when feasible.
- Writing TMDL reports that are as short and clear as possible.
- Writing reports that are more management-focused.
- Getting water quality improvements on the ground as soon as possible,
supporting existing efforts.
This particular TMDL project was selected for an innovative approach because:
- The water quality problems are mainly from non-point sources. This makes
it easier to determine what the problems are and how to fix them.
- The Snake River watershed, where the Tucannon/Pataha watershed is
relatively small. Small watersheds tend to have less complicated water
quality problems, and so are easier to fix.
- Some data needed to do a TMDL in this watershed already exists. This
reduces the amount of sampling work Ecology needs to do.
- Local governments and citizens are already implementing some actions to
address water temperatures, so the creeks are already on the fast track to
The streamlined TMDL process is being piloted in the Tucannon/Pataha
watershed by addressing temperature first. We chose temperature because of all the parameters
that are identified as problems in the watershed, temperature is perhaps
the best fit for this type of process. Once this TMDL is complete the intention
is to apply the lessons learned to address the remaining parameters using
similar streamlined TMDL procedures.
Status of the project
Ecology’s staff developed a technical analysis of the
temperature problem in the watershed. They refined the report, assisted by the WRIA 35 watershed
planning unit, which agreed to serve as the advisory group for the TMDL. They
completed a draft report showing the results and recommending remedial
The draft report was reviewed by the public during a comment period ending
May 21, 2010. Ecology addressed comments received and
submitted the final version of the TMDL-implementation plan (water quality
improvement report, or WQIR) to EPA for approval on July 14, 2010. EPA approved
the WQIR on September 27, 2010.
There are a number of possible factors that could cause a water-body’s
temperature to rise, altered hydrologic function and lack of riparian shade
being perhaps the most significant. Of these, riparian shade is the easiest
problem to address, and is therefore usually the focus of implementation work.
The streamlined TMDL approach, piloted in the Tucannon/Pataha watershed, uses a
shade deficit method to calculate a shade target for the Tucannon and Pataha
Rivers and their tributaries. Simply put, this approach uses GIS and
high-resolution aerial photographs in conjunction with a computer model to
determine a shade target by calculating the system potential shade and
subtracting existing shade. Shade information will be combined with hydrologic
data to prioritize reaches for restoration. The person managing implementation
is responsible for applying the shade estimates to determine what kind of
riparian restoration is required for a particular reach they’re working in.
This technical work replies heavily on previous field data collected by
various organizations in the watershed. Ecology did not collect any new field
data for this project. The exception is the temperature data collected at the
only two point source discharges – the Pomeroy wastewater treatment plant and
the Tucannon fish hatchery. These data are included in the shade work used to
develop a TMDL that addresses all temperature problems across the entire
Tucannon River and Pataha Creek Temperature TMDL -
Water Quality Improvement Report and Implementation Plan (Ecology publication)
WRIA 35: Watershed Planning (Asotin County)
http://www.asotinpud.org/watershedplanning/index.html (not available online)
Snake River Salmon Recovery Board
Transforming Watersheds: Middle Tucannon River - Columbia County
(Ecology Water Quality story)
Pomeroy Wastewater Treatment Plant: Effluent Dissolved Oxygen Solution
(Ecology Water Quality story)
WRIA 35: Middle Snake Watershed Information (Water website)
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