Environmental Engineering Reference
In-Depth Information
FLIR images
Video images
Mainstem =
33.0°c
Tributary = 24°C
30
25
23.0°c
(a)
Mainstem = 26.2°C
34.0°c
Tributary = 27.8°C
30
25
24.0°c
(b)
FIGURE 4.27 Examples of remote sensing of tributary mixing zones (TMZs). Typical FLIR output consists
of GPS-tagged digital images covering approximately 100 × 150 m with less than 1 m of spatial resolution
and ±0.5°C accuracy. (a) and (b) show cool and warm TMZ, respectively. Cool TMZs have been documented
as critical salmonid refugia habitat in disturbed systems. (From CORMIX image gallery, Available at http://
www.cormix.info/picgal/rivers.php, source of photographs Oregon DEQ.)
to estimate the impacts of diversions or to mitigate water withdrawals in western states. The most
commonly used low has been the 7Q10 low previously discussed.
While minimum lows are common lows for design and regulatory purposes (many states
specify minimum lows in their state statutes), there has long been a recognition that while mini-
mum low lows may allow aquatic communities to subsist, they are not adequate to sustain ish
communities and aquatic health (Baron et  al. 2002; Poff et  al. 2009; Richter et  al. 2006 and
others).
4.6.1 b aSe f Low and L ow -f Low I ndIceS
One method that has been commonly used to characterize lows, based solely on the low magni-
tude, is the “low low” or “minimum low.” Waddle (2001) indicated a typical description from when
the concept of “low low” was common:
Water is taken out of the stream for a variety of uses, such as irrigated agriculture, municipal and indus-
trial. Low low means that amount of water that must be left in the stream for the ish. With anything
less than the low low, the ish will die.
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