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Altered streamflow and sediment entrainment in the Gunnison Gorge

Journal of the American Water Resources Association

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Abstract

The Gunnison River in the Gunnison Gorge is a canyon river where upstream dams regulate mainstem discharge but do not affect debris-flow sediment supply from tributaries entering below the reservoirs. Regulation since 1966 has altered flood frequency, streambed mobility, and fluvial geomorphology creating potential resource-management issues. The duration of moderate streamflows between 32.3 and 85.0 m3/s has increased threefold since 1966. This, along with flood-peak attenuation, has facilitated fine-sediment deposition and vegetation encroachment on stream banks. The Shields equation and on-site channel geometry and bed-material measurements were used to assess changes in sediment entrainment in four alluvial reaches. Sand and fine gravel are transported through riffle/pool reaches at most discharges, but the cobbles and boulders composing the streambed in many reaches now are infrequently entrained. Periodic debris flows add coarse sediment to rapids and can increase pool elevation and the streambed area affected by backwater and fine-sediment accumulation. Debris-flow supplied boulders accumulate on fans and in rapids and constrict the channel until reworked by larger floods. The response to streamflow-regime changes in the Gunnison Gorge could serve as an analog for alluvial reaches in other regulated canyon rivers.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Altered streamflow and sediment entrainment in the Gunnison Gorge
Series title:
Journal of the American Water Resources Association
Volume
33
Issue:
5
Year Published:
1997
Language:
English
Publisher:
American Water Resources Assoc
Publisher location:
Herndon, VA, United States
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
1041
Last page:
1054
Number of Pages:
14