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

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

(2) the volume of sediment stored in Paonia Reservoir versus the volume of fine sediment
introduced to the North Fork Gunnison by other sediment sources downstream from the
reservoir. We know that the North Fork Gunnison River is predominantly braided, and
that the reservoir stores fine sediment. What remains uncertain is whether this fine
sediment trapping and storage has any substantial effect on downstream channel
planform and stability. For example, the river might still be braided but less laterally
mobile if Paonia Reservoir were not present, because the fine sediment stored in the
reservoir would instead be incorporated into downstream river banks, helping to increase
the erosional resistance of these banks.

III What should we do next?
Recommendations for future work along the North Fork Gunnison River include
both additional research, and management actions.
Additional research: We recommend that NFRIA establish a monitoring program that
would facilitate calculation of effective discharge. Effective discharge may be defined as
the flow level that alters the cross-sectional geometry of a river by mobilizing sediment
stored on the streambed or eroding the channel banks. A monitoring program to
determine effective discharge requires establishing several surveyed and bench-marked
cross sections along the river. These cross sections are periodically re-surveyed as flow
levels change, in order to determine the flow levels that correspond to channel change.
The flow level associated with channel change will not be a single number. Different
cross sections are likely to respond to different flows, because of variability in erosional
resistance. For example, a cross section with banks formed of cobbles overlain by finer
sediments, and stabilized by cottonwoods or other riverside vegetation, will require
greater flow to initiate channel change than a cross section with loose gravel or cobble
banks.
Management actions: We recommend that NFRIA promote actions that will enhance the
stability of the streambed and banks along the North Fork Gunnison River. Of most
importance are removing instream gravel mines and minimizing in-channel disturbances
from bulldozers or backhoes, as well as allowing natural riverside vegetation to grow.
Instream gravel mines and other disturbances weaken the naturally occurring layer of

6