Dam Tailwaters - Hydro-Environmental Analysis: Freshwater Environments - page 500

Section 303(d) of the Clean Water Act). To help resolve this and other issues, the U.S. Environmental
Protection Agency (U.S. EPA) assembled a federal advisory commission (FAC) to review and make
recommendations to the agency. In their report on the TMDL program (USEPA 1998), the FAC identi-
ied existing large dams as an “extremely dificult problem” since they create a physical structure or
physical modiication that would be impossible or virtually impossible to remove. The FAC's recom-
mendation was that the U.S. EPA require states to include waters impaired (not meeting water quality
standards) wholly or partially by the existence of dams, or their operations, on their 303(d) list (Part 1,
thereby requiring TMDL studies to quantify allowable loads to alleviate the impairment; Martin and
Kennedy 2000). The U.S. EPA instead chose to categorize the water quality impairments due to dam
releases as resulting from “pollution” rather than a pollutant, that is, solely resulting from hydromodi-
ication, and excluded the impact of dams for the portion of the list of impaired waters (Part 1) requir-
ing a TMDL. That is, the U.S. EPA stated that it “does not believe that TMDLs should be the solution
to problems substantially caused by hydromodiication” ( Federal Register , Vol. 64, No. 162). That
categorization has been challenged, and the courts to date have agreed that, essentially, regulation as
a point or a nonpoint source, requires the “addition” of a pollutant and that a dam does not result in
the “discharge of a pollutant” as deined by the Clean Water Act, so that, for example, a reduction in
oxygen due to a dam release does not constitute an “addition.”
However, there have been a number of TMDL studies by states on tailwater quality, such as
those related to low DO concentrations. In 2000, for example, the Georgia Environmental Protection
Division (GAEPD) issued a multibasin TMDL report for “Total maximum daily load (TMDL) devel-
opment for low dissolved oxygen below dams,” in which they listed eight tailwaters as being impaired
and argued that “since the impairment is caused by the low DO levels in the dams' release waters and
is not due to a speciic pollutant, the TMDL is equal to the dams' release waters meeting the appro-
priate DO criterion for the downstream waters' designated use.” Other more recent examples include:

• TMDLs for dissolved oxygen for White River below Bull Shoals Dam and North Fork River

below Norfork Dam (reaches 11010003-002U and 11010006-001); Arkansas Department
of Environmental Quality (prepared by FTN Associates, Ltd.)

• TMDL for Lake Taneycomo in Taney County, Missouri; Missouri Department of Natural

Resources (submitted November 15, 2010; approved December 30, 2010)

Other examples of water quality concerns for tailwaters were related to temperature and gas
supersaturation (TDG and gas bubble disease). Like oxygen, it could easily be argued that gas
supersaturation may not be considered due to the “addition” of a pollutant, but due to the physics
associated with water spilling, such as over a spillway. However, TMDLs have been completed,
which address TDG in the mainstream Columbia River from the Canadian border to its mouth at
the Paciic Ocean in addition to speciic locations (ODEQ and WADEQ 2002), such as below Lake
Pend Oreille, Idaho. In those cases, the allocation was based on a change in concentration (or tem-
perature “delta”) rather than a speciic loading.
It has been argued that regardless of whether the discharge from dams could be viewed as a
point or a nonpoint source, resulting in the “addition” of pollutants, the water quality below dams
is subject to meeting water quality standards and to a variety of regulatory controls. These controls
have and will continue to impact the design and operation of dams.

18.3.3 r eLeaSe f LowS
Dams by their design alter the low regime in the dam tailwaters. Changes may be pulses in lows,
such as due to hydropower facilities, or, in some cases, the near absence of release lows. That is,
in some cases, the releases from dams may be primarily limited to seepage through the dam rather
than intentional releases. That, of course, may have dramatic impacts on the chemical and biological
characteristics of the tailwaters.