8105

• UCREFRP Catalog Number: 8105
• Author: Haines, G. B., D. W. Beyers and T. Modde.
• Title: Estimation of Winter Survival, Movement and Dispersal of Young Colorado Squawfish in the Green River, Utah.
• USFW Year: 1998.
• USFW - Doc Type: Recovery Program Project 36,
• Copyright Material: YES

SUBADULT HUMPBACK CHUB IN THE COLORADO RIVER

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Historically, the Colorado River was a highly turbid, highly fluctuating system. Temperature varied
seasonally from near freezing to almost 300C. Flows could range annually from approximately 60 m3 s - I
during winter months to over 3000 m3 s - I (US Department of Interior, Bureau of Reclamation, 1995).
The dam has altered the hydrology of the river by eliminating large annual flood events, maintaining
artificially high base flows, trapping sediment and altering physio-chemical conditions (Stanford and
Ward, 1991). Water discharged from the dam is approximately 7-11oC and warms an average of 10 every
50 km downstream in the summer (Valdez and Ryel, 1995).
From the period of dam closing in 1962-1991, discharge fluctuated within a range of 60-850 m3 s - I
with unrestricted ramping rates. To reduce these fluctuations, the USBR implemented interim flows in
August 1991. This operating regime requires a minimum of 225 m3 s -I and a maximum of 550 m3 s - 1.
Up ramping (rate of discharge increase) does not exceed 70 m3 s -1 h -1, and down-ramping (rate of
discharge decrease) does not exceed 45 m3 s - I h - 1 (US Department of Interior, Bureau of Reclamation,
1995).
Within the Grand Canyon, the study area begins at the confluence of the Colorado River with the LCR
(RM 61.4), a calcium carbonate-enriched, spring-fed tributary to the Colorado River in Grand Canyon
(Figure I). The LCR flows clear except during heavy, upland rainstorms when it floods and becomes
sediment laden. With a base flow of 5.5 m3 s - I and a lO-year recurrence interval flood of 425 m3 s - 1,
the LCR is the largest tributary entering the Colorado River in Grand Canyon.

Geomorphology

Grand Canyon is the result of concurrent uplifting of the Colorado Plateau and down cutting of the
Colorado River through more than 1500 m of sedimentary and metamorphic rock (Beus and Morales,
1990). The river through Grand Canyon drops over 500 m in 450 km (279 miles) as a series of long, flat
stretches interrupted by steep drops. Half of the drop in elevation is in rapids, which constitute only 9%
of the total distance. Most of the rapids are formed by debris fans at the mouths of ephemeral tributaries
that deposit poorly sorted debris ranging in size from huge boulders to sand. These debris fans occur
where local fractures or faults transect the canyon at the river (Dolan and Howard, 1978). Debris flows
and tributaries deposit enough sediment to constrict the river, forming rapids. Associated with rapids are
large downstream zones of recirculation known as eddy complexes (Schmidt and Graf, 1990).
Channel slope and morphology in Grand Canyon change along the river corridor with shifts in local
geology and tributary influence (Leopold, 1969; Kieffer, 1990). More resistant lithology creates a narrow,

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Study Area

Figure 1. Map of the Colorado River through Grand Canyon

~ 1998 John Wiley & Sons, Ltd.

Rel(ul. Rivers: Res. Ml(mt. 14: 267-284 (1998)