FLOOD10354

• Document ID: pr1202
• County: Delta
• Community: Paonia, Hotchkiss
• Stream Name: North Fork Gunnison River
• Basin: Gunnison
• Sub-Basin: North Fork Gunnison
• Water Division: 4
• Title: North Fork Gunnison River Project Executive Summary
• Date: 12/1/2002
• Prepared By: Colorado State University
• Watershed Pro - Doc Type: Project Report

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Fork Gunnison has highly erodible sedimentary rocks and a dry climate; together, these
factors produce abundant, fairly fine-grained sediment. Climate determines the flow
regime of a river. A river dominated by snowmelt will behave very differently than a
river that also has flash floods caused by summer thunderstorms. The North Fork
Gunnison is dominated by snowmelt that produces a broad, fairly gradual peak flow,
rather than a flash flood. Topography determines the space available for a river to move
back and forth across a valley bottom. A narrow mountain valley is unlikely to have a
laterally mobile braided river, even ifthe river has an abundant sediment supply. The
wider the valley bottom, the more likely the river is to either meander broadly, or to braid,
depending on the sediment supply and flow levels.
Given the caveats discussed above, the results from the North Fork Gunnison
River imply that:
(1) Not all rivers in Colorado are naturally single-channel or meandering rivers. Channel
rehabilitation or restoration programs thus need to evaluate what the characteristics of a
particular river are likely to be in the absence of human impacts, before immediately
assuming that a braided river is braided only because of human actions.
(2) Rivers are not static systems in the absence of human impacts. Although human
impacts may dramatically alter the appearance and function of a river, rivers change over
periods of weeks to hundreds of years as a result of fluctuations in natural factors.
Climate-driven changes in the North Fork Gunnison River over a period of decades
during the 20th century provide an example of river variability that was not driven solely
by human impacts.
(3) Human activities can substantially impact rivers. Although the North Fork Gunnison
River is likely to have been braided and laterally unstable throughout the past few
hundred years, human activities such as instream gravel mining and clearing of riparian
vegetation can substantially exacerbate channel instability and thus reduce both water
quality and aquatic habitat.

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