Recovery of Fish Habitat along the Poudre River following 2021 Black Hollow Debris Flow

Warner College of Natural Resources




Primary Topic:

Natural Resources and Sustainability

Other Topics:

No additional topic areas, only my selection from previous question

Lead Mentor:  

Ellen Wohl

Professor of Geology

Internship Overview:

Both mentors have extensive experience mentoring and advising students. We will provide hands-on training, guidance, and support for self-motivated and curious students interested in problems that bridge important environmental and societally relevant issues.

Goals, Scope and Objectives:

The 2021 debris flow in Black Hollow created numerous effects in the mainstem Poudre River. The mainstem flood associated with the tributary debris flow killed an estimated 70% of the salmonid fishes in the Poudre River. The flood also left extensive deposits of fine sediment (sand, silt, clay, ash, charcoal) along margins of the Poudre River throughout the length of Poudre Canyon. These deposits, which can be up to 50 cm thick in places, have proven to be persistent and are still present as of the end of the 2022 runoff season. Channel-margin environments are important for native fishes as resting and nursery habitat, but fine-sediment accumulation reduces habitat abundance and impedes the hyporheic exchange flows through the bed that help to maintain water quality and provide habitat for benthic macroinvertebrates on which salmonids feed. We will (i) map the location of fine sediment deposits along the mainstem Poudre and the mouths of larger tributaries and use the map to identify reach-scale characteristics that facilitate fine sediment retention, (ii) select a subset of 10 sites for detailed field assessment and monitoring (drone-based mapping, ground surveys and sediment sampling), and (iii) select a further subset of 5 sites for 2D numerical modeling of hydraulics and sediment dynamics in order to estimate the flows needed to mobilize fine sediment from storage.

With which stakeholder group(s) will the intern work?

Colorado Water Conservation Board, South Platte Basin Round Table, Colorado Parks and Wildlife, City of Fort Collins, Coalition for the Poudre Watershed, City of Greeley, and private landowners.

What student learning outcomes do you anticipate and what are the opportunities for professional development?

The student intern will gain proficiency in mapping channel characteristics from drone imagery (including generating digital elevation models using Structure from Motion software), sediment collection and grain-size analyses, topographic surveying using state-of-art equipment, and collaboration with diverse stakeholders. Professional development will occur through exposure to applied, interdisciplinary research, interactions with diverse faculty and extension mentors, graduate students and stakeholders, opportunities for continued involvement with the project including sediment analyses, GIS-based analyses, and communicating the results to the broader community.
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