NonBasicSpecificComments04

• Title: Comments 4
• Date: 10/23/2003
• SWSI - Doc Type: Comments

The magnitude and frequency of
high and low flows regulate numer-
ous ecological processes~ Frequent,.
moderately high flows effectively
transport sediment through the chan..
nel (Leopold et at 1964). This sedi-
ment movelJlent~ combined with the
force of moving waterJ exports or..
ganlc resourcesr such as detritus and
attached algae_ rejuvenating the bio-
logical communIty and allowing
many species with fast life cycles and
good colonizing ability to reestab..
Iish (Fisher 1983). Consequently ~ the
compositIon and relative abundance
of species that are present in a stream
or rIver often ~ef1ect the frequency
and intensity of high flows (Meffe
and Minckley 1981 t Schlosser 1985).
High flows provide further eca..
logical benefits.by maintaining eco-
system p~oductivlty and diversity~
For examplef high flows remove and
transport fine sediments that would
otherwise fill the interstitial spaces
in productive gravel habitats (Beschta
and Jackson 1979)..Floods import
woody debrIs into the channel (Keller
and Swanson 1979) 1 where it creates
n~Wf high-quality habitat (Figure 4;
Moore and Gregory. 1988, Wallace
and Benke 1 984) ~ By connecting the
channel to the floodpIaint high
overbank flows also maintain
broader productivity and diversity.
Floodplain wetlands p.rovide impor-
tant nursery ground.s for fish and
export organic matter .and organ-
isms back into the maIn channel a unk
et a1. 1989, Sparks 1995f Welcomme
1992), The scouring of floodplain
soils. rejuvenates habitat for plant
species that g~rminate only on bar...
ren, wetted surfaces that are free of
competition (Scott et a1. 1996) or
that require access to shallow water
tables (Stromberg et at 1997). Flood.
resistant, disturbance-adapted ripar-
ian communities are maintained by
flooding along rlver corridors, even
in river sections that have steep banks
and lack floodplains (Hupp and
Osterkamp 1 985)~.
Flows of low magnitude alsq pro..
vide ecological benefits~ Periods of
low flow may present recruItment
opportunities for riparian pl~nt spe-
cies in regions where floodplains are
frequently inundate~ (Wharton et
al. 1981). Streams that dry tempo-
rarily, generally in arid regionsJ have
aquatic (Williams and Hynes 1977)

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Figure 4. Geomorphic and 'ecological functions provJd"ed by different levels of flow ~
Water tables that sustain riparian vegetation and that delineate tn-channel baseflow
habitat are maintained by groundwater inflow and flood recharge (A). Floods of
varying sIze and timing are needed to maintain a diversity of riparian plant species
and aquatic habitat. Small floods occur frequently and transport fine sediments,
maintaining high benthic productivity and creating spawning habItat for fishes (B).
IntermedIate-size floods inundate Iow...lying floodplains and deposit entrained sedi-
ment, allowing for the establishment of pioneer species (C). These floods also import
accumulated organic materJa11nto the channel and help to ma.intain the characteristic
form of the active stream channel. Larger floods that recur on the order of. decades
inundate the aggraded floodplain terraces, where later successional species establish
(0). Rare, large floods can uproot mature riparian trees and deposit them in the channel,
creating high-quality habitat for many aquatic species (E).

a.t1d ripa~ian (Nilsen et at 1984) spe..
_cies witn special behavioral or physi-
ological adaptatiorls that suit them.
to these harsh conditions.
The duration of a specific flow
condition often det~tmines its eco-
logical significance. For example, dif.. .
fe:eenc.es in tolerance to prolonged
flooding in r~pai:ian plants (Chapman
et aI. I 982) and to prolonged low flow
in aquatic invertebrates (Williams and
Hynes 1977) (ind fishes (Closs and
Lake 1996) allow these species to
persist in locations from which they
might otherwise be displaced by
dominant~ but l~ss tolerant, species.
The timing, ar predictability, of
flow events is critical ecologically
because the life cycles of many
aquatic and riparian species are timed
to either avoid or exploit flows of
variable magnitudes. For example,
the natural timing of high or low
streamflows provides environmen-
tal cues for initiating life cycle tran-
sitions in fish, such as spawning
(Montgomery et at 1983, Nesler et
at 1988) 1 egg ha,tchil1:g (Nresje et aI.
1995), rearing (Seegrist and Gard
1978), movement onto the flood-
plain for feeding or reproduction
(Junk et al. 19891 Sparks 1995,
Welcomme 1992), or migratjon up-
stream or downstream (Trepanier et
al, 1996) . Natural seasonal varia-
tion in flow conditions can prevent

the successful establishment of non-
native species "Yith flow-dependent
spawning and egg incubation require..
ments; such as striped bass (MarDne
saxatilis; Turner and Chadwick
1972) and brown trout (Salmo trutta;
Moyle and Light 1 ~96 ~ Strange et al.
1992) ~
Seasonal access to floodplain wet-
lands is essential for the survival of
certain river fishes~ and such access
can directly link high wetland produc-
tivity with fish prod uction in the stream
channel (Copp ~9891 We1comme
1979). Studies of the effects on stream
fishes of both ,extensive .and limited
floodplain inundation (Finger and
Stewart 1987, Ross and Baker 1983)
indicate that some fishes are ada-pted
to exploiting floodplain habitats, and
these species decline in abundance
when floodplain use is restricted.
Models indicate that catch rates and
biomass of fish .are influenced by
botn maximum and minimum wet-
land area (Power et al. 19951
Welcomme and Hagborg 1977) ~ and
empirical work shows that the area
of floodplain water bodies during
nonflood periods influences the spe-
cies richness of those wetland habi-
tats (Halyk arid Balon 1983). The
timing of floodplain inundation is
important for some fish because mi-
gratory - and reproductive behaviors
must coincide with access to and avail..

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