Geomorphology and endangered fish habitats of the upper Colorado River: 2. Linking sediment transport to habitat maintenance

Abstract

Abstract. Alluvial reaches of the Colorado River near Grand Junction, Colorado, provide important habitat for the endangered Colorado squawfish. This paper examines recent changes in the geomorphology of the Colorado River and addresses the question of what can be done to improve existing fish habitats. Observations of channel change during periods of above-average runoff from 1993 through 1995 indicate minor scour and fill of the main channel, but more significant scour and enlargement of side-channel and backwater habitats and flushing of fine sediment from the bed. Modeled relations between discharge and dimensionless shear stress ** indicate that the threshold of bed load transport (** = 0.03) occurs at about half the bank-full discharge; these flows are exceeded about 26 days per year on average. The bank-full discharge produces an average ** of 0.047 and is exceeded about 8 days per year. The width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of --•1.5 times greater than the critical shear stress. The effective discharge is slightly less than the bank-full discharge, and approximately 80% of the total sediment load is carried by the highest 10% of all discharges. In this paper we develop criteria for flows that will maintain or improve habitats used by Colorado squawfish. Given the wide range in habitat characteristics, we believe that the processes of habitat formation and maintenance in the upper Colorado River are best studied using a broad-based geomorphic approach. Accordingly, we formulated three objectives for this study.

Mixed stream channel morphologies: implications for fish community diversity

“…The observed patterns of diversity are probably the result of habitat patches created by variations in flow and other physical characteristics in reaches of mixed morphologies. Pool-riffle reaches and reaches of mixed morphologies exhibited important differences in their morphological and hydraulic characteristics, and a number of these variables have been identified as important in determining the quality of fish habitat, including: water depth; current velocity; flow variability; substrate type and size; cover; roughness elements; confinement; and large woody debris (Poff and Allan, 1995;Dunham and Vinyard, 1997;Leftwich et al, 1997;Montgomery and Buffington, 1997;Pitlick and Van Steeter, 1998;Flebbe, 1999;Inoue and Nunokawa, 2002). Pool-riffle channel types are associated with shallow, faster moving water alternating with deeper, slower moving pools.…”

An empirical‐stochastic, event‐based program for simulating inflow from a tributary network: Framework and application to the Sacramento River basin, California

“…It is noteworthy that predam peaks of flow within the leveed channel at Verona are lower than postdam ones, and this matter is discussed below. Otherwise, predam and postdam simulated flood peaks bound the historical data and illustrate the potential range of variability, especially for flows of intermediate frequencies that transport most sediment [Singer and Dunne, 2001] and drive important ecological processes [Mahoney and Rood, 1998;Milhous, 1998;Pitlick and Van Steeter, 1998;Johnson, 2000]. HYDROCARLO simulations generally bracket historical flood peaks at Verona for other exceedence probabilities.…”

The role of topographic variability in river channel classification

“…As a result of these strong foundations, channel classification has come to the forefront of river science and management as a central feature of methods for understanding, protecting, and restoring rivers in North America (Buffington and Montgomery, 2013;Kondolf, 1995;Rosgen, 1994), Europe (e.g., González del Tánago and García de Jalón, 2004;Orr et al, 2008), Australia (Brierley and Fryirs, 2005), and South Africa (Rowntree and Wadeson, 1998). Channel classification is of critical importance today for river management, because anthropogenic changes to flow regimes (Magilligan and Nislow, 2005;Molles et al, 1998), sediment regimes (Graf, 1980;Pitlick and Van Steeter, 1998;Wohl et al, 2015), and the physical structure of rivers (Price et al, 2012) have led to widespread degradation of river ecosystems worldwide (Arthington, 2012;Dynesius and Nilsson, 1994).…”