7371

• UCREFRP Catalog Number: 7371
• Author: Stalnaker, C. B., R. T. Milhous and K. D. Bovee.
• Title: Hydrology and Hydraulics Applied to Fishery Management in Large Rivers.
• USFW Year: 1989.
• USFW - Doc Type: D. P. Dodge, ed. September 14-21, 1986.
• Copyright Material: YES

in!.! habitat value~ are mcallin~lcss dUrIng the other lllollth~
be-cause the lilc st:lge IS not rresclll durin~ those months
Juvenile and lIdult habllat. how('\'Cr. IS needcd throughOlIl
the year for a resident fish sUl.:h as the rainbow trout. Com,e-
que~tly, hydrologic timc series of monthly or daily values
are needed for fishery studies. as opposed to the average
annual flow values often used by water managers.

Effective Spawning and Incubation

Much research has been conducted on the size of gravel
needed for spawning and the hydraulic conditions needed
for redd building. Criteria for describing adequate depth.
velocity, substrate, and percent fines in the interstitial
spaces are available for several riverine salmonid species
McMahon 1983; Baldrige and Amos 1981; Hickman and
Raleigh 1982; Raleigh et a!. 1983, 1984; Raleigh and Nel-
son 1985). Computer programs have been written to track
the hydraulics above specified micro areas on river beds
from the spawning through the incubation period (Milhous
1982a; Bovee 1985). From output ofthe PHABSIM micro-
habitat model. one can identify specific areas within a
stream reach suitable for spawning. Even though spawning
may have been successful in a given area of streambed, five
events may occur that render it useless: (l) dewatering for
2 wk or longer during incubation; (2) freezing of embryos
in shallow water; (3) scour - the resuspension of suitable
size spawning gravel and its removal from the site; (4) depo-
sition of fine materials within the interstitial spaces of the
redd during the incubation period; and (5) movement of the
redd gravels during the fry emergence period.
The effective spawning and incubation program simulates
the hydraulic conditions over each of the suitable spawning
areas for the several months of the incubation period and
identifies the amount of the spawning area that is still intact
at the computed time of hatching and emergence. Use ofthis
program requires information about near bottom velocities
that result in scour and deposition, and the depths at which
dewatering or freezing occurs. The quantity of suitable
microhabitat is determined by computing the surface areas
having suitable conditions for both spawning and incubation
for the period from spawning to hatching for each year in
the time series. This can be repeated with simulated flow
time series for a proposed water regulation scheme, and
comparisons made. A variation of this type of analysis is
possible when flow can be controlled by releases from a
reservoir throughout the spawning and incubation period.
Figure 9 shows a nomograph constructed for various incu-
bation flows at a specified set of spawning flows in the Ter-
ror River, Alaska. From such nomographs, the best
combination of spawning and incubation conditions can be
determined for the amount of water that is forecasted to be
available for management during a specific year.
Use of these engineering techniques, coupled with biolog-
ical criteria makes it possible to illustrate impacts of alterna-
tive water management schemes. This capability can also be
applied to real-time fishery management decisions. Water
managers typically forecast water supply 1 to 6 months in
the future and compare this with existing storage and the
projected water supply and demand. The fishery manager
can be effective, using the tools described here, and the
forecasting capabilities of the water management engineers,
to suggest that specific flows be maintained during the

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Spawning Flow (m3. 5 -1 )

FIG, 9. The relation between effective spawning habitat area for
pink salmon (Oncorhynchus gorbuscha) and spawning flow for
specified incubation flows in Terror River. Alaska. Numbers at the
end of each curve show incubation flow (from Milhous 1982a).

spawning season that are biologically compatible with the
anticipated water supply during the incubation and hatching
season. A common observation in rivers having uniform
gravel bottoms is that fairly high flows during the spawning
season result in the spawners building redds high up on the
stream cross-section near the margins of the stream. Subse-
quently, if water supply drops, it may become impossible
to maintain flows over these redds during the entire incuba-
tion period. If this could be forecasted, a better management
scheme would be to reduce the flow during the spawning
period, forcing the spawners lower into the channel where
it is more probable that flows can be maintained during the
incubation period. In other streams where spawning gravels
may be limiting and control is feasible, the flow necessary
to provide adequate conditions over the limited gravel bars
can easily be computed and specified.

Temperature Analysis

It is well known that the length of the incubation period
for salmonids is variable and is predominantly determined
by the temperature of the water during the incubation
period. The degree day accumulation (above a specified
threshold temperature) for hatching has been well estab-
lished for many salmonids (Piper et al. 1982). By using the
degree-day output from a macrotemperature simulation one
can derive the phenology of a species to determine the time
of spawning, duration of incubation. and emergence. A
hydrologic time series is used as input into the temperature
model to yield degree-day simulations for various flow reg-
ulation schemes. For a particular species, the incubation
period and hatching time is computed from the temperature

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