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

.

the month of September for the Colorado River near the
staleline in C0)nrado.

Habitat Time Series

From time series and duration analyses, the water man-
agement community can determine the likelihood of given
flow events occurring under various proposed regulation
schemes. It therefore behooves the fishery manager to trans-
late fishery habitat events into similar kinds of analyses. To
do this for each river segment. one must first assemble flow-
habitat functions such as those shown in Fig. 3 and 7, which
represent the output from an instream water temperature
macrohabitat model and the microhabitat model PHABSIM,
respectively. With the hydrologic time series and the flow
habitat functions, the dynamics of the physical habitat can
be described for a specific river reach over time, while
simultaneously illustrating various water management
effects.
Ageneralized equation for the habitat versus streamflow
function,ean be written as follows:
(4) HA, = /;<Q,)L
where HA, is the quantity of usable physical habitat. Q is
the streamflow. and fi(Q) is the functional relation illus-
trated by Fig. 7. The subscript i refers to the specific fish
species or life stage under investigation and L is the length
of stream determined from a macro model (Fig. 3) to be
represented by fi(Q) at time t.
From a time series of flows for a specific river segment
(Q,), the amount of usable physical habitat at time (t) can
be calculated. The result of a unit length transformation of
the fi(Q) function from Fig. 7 is illustrated in Fig. 8 for
adult rainbow trout. The hydrologic time series for this river
is also plotted in Fig. 8 for comparison. These time traces
illustrate several important concepts that appear to be true
for many fish species in many different types of streams:
(1) the physical habitat time series is less variable than the
streamflow time series; (2) high flow events may be as
detrimental to fish as low flows; and (3) during some time
periods, a moderate reduction in streamflow can result in
a large reduction in physical habitat (e.g.. compare August
1973 with August 1972) and other time periods when the
converse is true (compare June 1971 with December 1973).
Average monthly flow data were used to generate the hab-
itat time series in Fig. 8. If daily flows were used and the

9 45
::- - PHYSICAL HABITAT
,
E --- STREAMFLOW
.. en
~ ....
~ 6 30 :Il
m
< I , >
~ I \ :::
iii ~ I , , , I
, I I , 'Tl
< ,~. : , , , , I roo
:I: I , , I , 0
,,, I I I '" , ::E
-' : \1 , , ,I I
< , " I " , 15 3'
U I I , , I { ,
I ,
0, ' I I I I , !"
I 1,\ : I \ , I
> I I , ..
:I: ~' V I I I I
I
Q. , I \ -
\ \
'I I \
0 0
1971 1972 1973 1974

WATER YEAR

FIG, 7. Mean monthly streamflow and physical habitat for adult
rainbow trout during 1971 through 1974 in the North Fork Sno-
qualmie River, Washington.

22

~J

e,;
E
-

<
w
[[
e( 4.5
l-
e(
t:
m
e(
J:
g 1.5
o
~

6

- - - ~>- -
- .-
I- -
- r--
-- - --
-- - c-
-

3

o

1965

1970

1975

1980

WATER YEAR

FIG, 8. Annual limiting microhabitat for adult rainbow trout in the
North Fork Snoqualmie River, Washington.

habitat results averaged to arrive at the average monthly
habitat values, the monthly values would not be the same.
The habitat values for one water year, based on daily and
monthly data, are compared in Table 2. The differences are
not large for the North Fork Snoqualmie River; however.
they still illustrate how important it is to use the same trans-
formation procedure when comparing water management
options such as those for pre- and post-project conditions.
The choice between monthly or daily streamflow hydrologi-
cal series depends on the objective of the analysis, available
data, and funds. For example, daily values could be used
for a gaged site where the water resources system is being
simulated by using daily flows. In contrast, monthly stream-
flows would be used for a location with few existing stream-
flow measurements and where the streamflow record must
be synthesized by regression with nearby sites.
Chronological time sequences are important for fishery
studies because habitat analyses for all life stages are not
applicable for every month of the year. For instance, rain-
bow trout spawning may occur from April to June. Spawn-

TABLE 2. Comparison of the results of different microhabitat gen-
eration procedures for adult brown trout (Salmo trulla) in the
North Fork Snoqualmie River, Washington, October 1972 to Sep-
tember 1973.

Month

Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.

Daily
streamflows

Monthly
streamflows

(Square metres per linear metre of stream)

4.85
5.86
5.52
6.41
5.80
6.62
6,74
6.53
6.53
4.79
2.26
3.48

5.34
6.89
5.52
6.34
6.16
6.98
7.08
6.50
6.59
5.19
2.26
4.79