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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through much of the past few hundred years. Channel characteristics such as discharge,
gradient, and sediment supply have been compared for meandering and braided rivers
around the world. When the numbers for the North Fork Gunnison are plotted on such a
comparative graph, the North Fork Gunnison consistently falls well within the domain of
braided rivers.
Aerial photographs also indicate, however, that the channel pattern of the North
Fork Gunnison River fluctuates through time, apparently primarily in response to
fluctuations in precipitation and discharge. During wet periods with high flows, such as
the 1980s-1990s, the North Fork Gunnison is likely to have a broad, rapidly shifting,
highly braided pattern. During drier periods with low flows, such as the 1930s, the river
is likely to have a nalTOWer channel with single-thread flow.
The presence of a braided channel pattern along the North Fork Gunnison does
not mean that human impacts have not altered the river. Human actions including
irrigation withdrawals and returns, clearing of riverside vegetation, and in-channel gravel
mining, may exacerbate or countera~t naturally-driven channel change associated with
wetter and drier periods. The net effect of the three human activities mentioned above is
to decrease bank stability along the North Fork Gunnison, and increase the degree of
braiding and bank erosion along the river. Where human activities such as gravel mining
trigger downcutting of the channel, the direction and rate of channel change may be
substantially altered: The water table along downcut, incised reaches of the channel may
be too low, relative to the height of the channel banks, for riparian vegetation to persist.
In the absence of this vegetation, unstable banks may require a much longer time to
become stable once more.

2) Although Paonia Reservoir traps much of the fine sediment that would otherwise
continue to move downstream, there are abundant sources of both coarse and fine
sediment downstream from the reservoir.

II What are our uncertainties?
Uncertainties that remain following our study are (1) the effect on the downstream
channel of dredging fine sediment from Paonia Reservoir and returning it to the channel,

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