6007

• UCREFRP Catalog Number: 6007
• Author: Carter, J. G., R. E. Valdez, R. J. Ryel and V. L. Lamarra
• Title: Fisheries Habitat Dynamics in the Upper Colorado River
• USFW Year: 1985
• USFW - Doc Type: Journal of Freshwater Ecology
• Copyright Material: YES

meander in order to obtain good representation of different habitat types.
This reach was judged to be representative of the upper Colorado River
between Rifle (river mile 241) and DeBeque (river mile 210), Colorado, based
upon overall stream morphology which reflected consistent gradient, bed
material and meander wavelength (Ruhe 1975). Although the endangered
Colorado squawfish is not found in this area and the candidate razorback
sucker occ-urs in low numbers, the reac h appears to be representati ve of
areas further downstream that support the endangered fishes (Valdez et al.
1982) .

Habitat Mappi ng

Detailed maps of the river and floodplain-were generated from photo-
interpretation of aerial photographs. Maps were developed at a hori zontal
scale of 1" = 200' with 2-foot contours.

River habitats were mapped on 3 March 1983 and weekly from 6 June to 2
September 1983 in the 2-mile study section of river. The habitats were
designated as one of the following 12 categories: backwater, eddy, pool,
isolated pool, embrynat, concavity, riffle, river, rapid, rubble flat,
shorel ine, and flooded woodlands (Archer et al. 1980; Wick et al. 1981).
Each habitat was located afield and sketched on a river map. Dimensions of
each habitat were visually estimated and measured from maps, while
extinction or significant changes in habitats between mapping days were
dated and noted on the appropriate map. Estimation of habitats areas from
maps was found reliable since the photo interpretative maps provided
sufficient shorel ine detail for sketching the habitats. A separate map was
developed for each sample period. Numbers'and-surface area of habitats were
mathematically correlated with discharge levels reported from USGS Station
09093700 near DeBeque, Colorado to assess habitat area available for various
flow levels in the study area.

RESULTS AND DISCUSSION

During the 6-month study period, from 3 March, 1983 to 2 September,
1983, flows in the Colorado River varied from 1,710 to 28,300 cfs. The
peak flow occurred on 26 June and the minimum on 3 March. Discharge values
for the period of weekly mapping (June - September) are shown in Figure 2.
The appearance, longevity and extinction of each habitat type was documented
by weekly mapping between 6 June and 2 September, as well as during the
original survey conducted on 3 March. Maps showing the distribution and
areal extent of habitats in the study reach at high flow, low flow and two
intermediate flows are shown in Figures 3, 4, 5, and 6. Total surface area
for each habitat was related to river discharge to illustrate gradual as
well as sudden changes in available habitat.

Of the twelve habitats examined, seven manifested changes in surface
area relative to flow: backwaters, flooded woodlands, rapids, riffles,
runs, eddies and rubble flats. Areal changes in the remaining five habitats
(embayments, concavities, pools, shorelines and isolated pools) did not
appear to be directly rel ated to river discharge. Those habitats that were
observed to exhibit predictable and regular changes with flow were
generally associated with physical features of the river that were inundated
when the river flowed beyond its normal channel banks (backwaters, flooded
woodlands and rubble flats) or were manifestations of river hydraulics at
the various flow stages; the area of rapids, runs and eddies increased with
di scharge whil e the area of ri ffl es decreased. Quanti ta ti ve rel ati onshi ps
describing the dynamics of habitat area as functions of river discharge for
the twelve habitat types are shown in Table 1.

251