Environmental Engineering Reference
In-Depth Information
Environmental Flows describes the quantity, quality and timing of water lows required to sustain
freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these
ecosystems.
Rather than identifying a single, low-low criterion, environmental lows consider all aspects
of the low hydrograph as they impact aquatic health. For example, the National Research Council
(NRC 2005) identiied four critical components of a low hydrograph (Figure 4.29; Hersh and
Maidment 2006):
•
Subsistence low is the minimum streamlow needed during critical drought periods to
maintain tolerable water quality conditions and to provide minimal aquatic habitat space
for the survival of aquatic organisms.
•
Base low is the “normal” low conditions found in a river in between storms, and base
lows provide adequate habitats for the support of diverse, native aquatic communities and
maintain groundwater levels to support riparian vegetation.
•
High-low pulses are short-duration, high lows within the stream channel that occur dur-
ing or immediately following a storm event; they lush ine sediment deposits and waste
products, restore normal water quality following prolonged low lows, and provide longitu-
dinal connectivity for species movement along the river.
•
Overbank low is an infrequent, high-low event that breaches riverbanks. Overbank lows
can drastically restructure the channel and loodplain, recharge groundwater tables, deliver
nutrients to riparian vegetation, and connect the channel with loodplain habitats that pro-
vide additional food for aquatic organisms.
The Brisbane Declaration presented summary indings at the 10th International River Symposium
and International Environmental Flows Conference, held in Brisbane, Australia, in September 2007.
The declaration also developed a global action agenda that included:
•
Estimate environmental low needs everywhere immediately.
•
Integrate environmental low management into every aspect of land and water management.
•
Establish institutional frameworks.
700
Overbank flow
600
500
400
High flow pulses
300
Base flow
Subsistence
flow
200
100
0
Oct.
Dec.
Feb.
Apr.
Jun.
Aug.
Oct.
FIGURE 4.29
Streamlow hydrograph for the Guadalupe River at Victoria, Texas (USGS Gage No.
08176500) for water year 2000 with low components identiied. (From NRC, The science of instream lows:
A review of the Texas instream low program, Committee on Review of Methods for Establishing Instream
Flows for Texas Rivers, National Research Council, The National Academies Press, Washington, DC, 2005.)
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