Environmental Engineering Reference
In-Depth Information
1.0
0.8
0.6
0.4
0.2
0.0
Site-specific
microhabitat data
SI
Cross section B
Flow
Cross section A
01234
01
Velocity (ft. s -1 )
234
epth (ft.)
1.0
0.8
0.6
SI
0.4
V 1 V 2 V 3
D 1 D 2 D 3
C 1 C 2 C 3
A 1 A 2 A 3
Velocity
Depth
Cover
Area
Habitat
suitability
criteria
0.2
0.0
0.0
0.2
0.4
Cover
0.8 1.0
(a)
(b)
100,000
Seasonal relation
between discharge
and microhabitat
for each life stage
Weighted
usable
area
PHABSIM
0
0
Discharge
100
(c)
FIGURE 7.4 Overview of PHABSIM. (From USGS, Available at http://www.fort.usgs.gov/Products/
Software/iim/5phases.asp.)
of interest, or the target species. For example, a particular target species may have an optimal range
of stream velocities, and below or above that range, the species may not occur. The criteria are
typically scaled from one to unity. Based on the measured or predicted habitat indicators, a speciic
value is determined for each of the habitat suitability criteria, which when multiplied by the cross-
sectional area yields a wetted usable area for a speciic low condition. The wetted usable area can
be recomputed for another low condition, such as following a proposed low abstraction for irriga-
tion, and compared to the base condition to assess the change in habitat that would be expected.
That change can then be used as the basis for management or mitigation decisions. The methodol-
ogy and application of PHABSIM are discussed in Chapter 4 and in detail by Waddle (2001).
7.4.2 rVa
The RVA is based on the premise that the natural integrity and diversity of streams and rivers have
developed in response to natural variations in low, and the best way to maintain that integrity and
diversity is to maintain the natural low conditions (Armstrong et al. 2004). So, the method recom-
mends that lows be managed to maintain the natural
Flow magnitude
Return interval (or frequency)
Duration, timing
Rate of change
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