Measures of the Health of Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 188

discharger of pollutants obtains a permit and meets all the applicable requirements speciied in the
regulations issued under Sections 301 and 304 of the act. These permits are enforceable in both
federal and state courts, with substantial penalties for noncompliance.
The standards, particularly the numeric standards, are used to determine allowable, or per-
mitted, loads to waterbodies (the wasteload allocation process) or to determine if a waterbody
is meeting water quality objectives. If waterbodies are not meeting standards, then states must
report this to Congress (in the National Water Quality Inventory Report to Congress or 305(b)
report).
Another provision in the CWA is for the case where, following the implementation of the best
available technology and efluent limitations (for point sources), water standards are not achieved.
Under these conditions, Section 303(d) requires that states report impaired waterbodies to Congress
and establish total maximum daily loads (TMDLs), which are required to meet the water quality
standards. The TMDL includes the cumulative impacts of all point sources and nonpoint sources,
and allows for a margin of safety. Section 303(d) was largely unenforced until the early 1990s when
lawsuits forced environmental agencies to implement its provisions. Today, as a result of including
nonpoint sources, water quality control and management have shifted from point source control to
watershed management.
While water quality standards set some maximum (or minimum in the case of dissolved oxygen)
standard, the goal is not to drive waterbodies to those standards. For example, a common mini-
mum daily average dissolved oxygen concentration criterion is 5 mg L -1 . However, the goal of the
CWA is not to permit waste loads so that all waterbodies are driven to that standard, as relected
in antidegradation policies (as described in the U.S. EPA's Water Quality Handbook , Chapter 4:
Antidegradation [40 CFR 131.12]).
7.3 MINIMUM FLOWS (OR HOW MUCH WATER
DOES A RIVER NEED, AND WHEN?)
Similarly to minimum concentrations, an analogous approach has often been taken for lows. Flows
are, of course, a critical component of any aquatic environment. The question is, how much low,
and when?
The irst and most common approach is the determination and regulation of minimum low cri-
teria, analogous to minimum water quality criteria. Minimum low criteria are assumed to represent
the minimum amount of water required to protect deined criteria that often address the needs of
aquatic biota (Annear and Conder 1984). Minimum lows also represent the maximum allowable
depletion of natural lows without impairing the ecological services of rivers (Silk et al. 2000).
The concept of a single minimum low was developed from western U.S. water law to reserve
an amount of water from future legal consumptive use appropriations, to provide an instream water
right for ish. For example, minimum instream lows were established to determine the maximum
allowable abstractions. The general paradigm of minimum lows was “how much water can we take
out of a river or stream” rather than “how much water do we need to leave” (Hirsch 2006).
The concept of minimum instream lows is still in common use today. For example, minimum
instream low requirements are commonly established for dam releases to protect tailwaters and
downstream segments, for both aquatic health and human uses. The minimum release require-
ments for dams involve a constant release of a small, speciied volume of water from below each
dam during nongeneration or nonlood releases in order to protect downstream uses. One example
is to protect downstream isheries below hydropower operations. Many of the peaking hydropower
reservoirs in the south, by releasing bottom waters from the reservoirs, have created cold-water
isheries below the dams. In addition to the cold-water releases, during nongeneration the only low
in downstream rivers is often due to seepage from the dam. The cold-water releases, while often
not cold enough to support the reproduction of cold-water ish, such as rainbow and brown trout,
are cold enough to support viable put-and-take trout isheries. However, the isheries are dependent