276-8 Monitoring Channel Mobility and Complexity in the Dolores River below McPhee Dam, Southwest Colorado

Session: Natural and Urban Channel Responses to Disturbance, Management, and Restoration

Presenting Author:

Authors:

Abstract:

Riparian corridors through drylands provide critical habitat, the quality of which can be degraded due to operations of dams and diversions. In those affected rivers, water managers should be equipped with quality information about how different flows influence critical ecosystem components downstream. However, it can be difficult to monitor more remote streams in and out of flood and drought. Here, we present the results of a multi-year field monitoring campaign paired with using newer high temporal-resolution satellite platforms (i.e. Planetscope) to monitor changes to a managed dryland river. We further develop discharge-based channel complexity ‘rating curves’ to assist water managers.

The Dolores River below McPhee dam flows through a series of remote canyons and open valleys on its way to meet the Colorado River near Moab, UT. It flows in a range of ~5-40 cfs unless reservoir levels upstream requires a larger release – which can reach up to 4000 cfs. During those rare releases, there is a desire to help the river meet the needs of numerous stakeholders, but high among them is optimizing habitat for both native and managed fisheries. Salient issues are channel narrowing, sedimentation of spawning surfaces, and loss of diverse in-channel habitat for juvenile fish.

We paired an on-the-ground monitoring campaign (including repeat profiles and UAV surveys) with satellite observations of releases in 2019 and 2023 to document side channel length and floodplain connectivity (inundation %) at a range of discharges across six segments through varying geomorphic settings.

Results show only minimal channel planform changes in response to floods, but below a major sediment source (Disappointment Creek), fine sediment builds up between releases and is flushed during them. Complexity analysis shows that there are critical thresholds in some segments of the river, beyond which side channels are opened up to inundation and connectivity jumps. In tighter canyon segments, discharge seems to have little effect on channel complexity. Within the most common discharge range (~5-40 cfs) inundation is similar, but when the river spends prolonged periods of time below 5 cfs, inundation drops off precipitously.

Although there is substantial uncertainty in our approach of using daily satellite imagery to monitor the surface impact of flood flows, there is great potential in leveraging these new platforms to observe streams through time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10329

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