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Characterizing environmental flows for maintenance of river ecosystems; North Fork Cache la Poudre River, Colorado

Sara L. Rathburn, David M. Merritt, Ellen E. Wohl, John S. Sanderson and Heather A. L. Knight
Characterizing environmental flows for maintenance of river ecosystems; North Fork Cache la Poudre River, Colorado (in Management and restoration of fluvial systems with broad historical changes and human impacts, L. Allan James (editor), Sara L. Rathburn (editor) and G. Richard Whittecar (editor))
Special Paper - Geological Society of America (2009) 451: 143-157

Abstract

Streamflow on the North Fork Cache La Poudre River, a tributary of the South Platte River in north-central Colorado, has been modified by impoundments for a century. A proposed expansion of the largest reservoir on the North Fork, Halligan Reservoir, presents an opportunity to modify dam operation to achieve environmental flows that sustain the river ecosystem while augmenting municipal water supplies. Over the past century, decreases in flood-related disturbances have resulted in reduced bed scouring through sediment transport and significant shifts in community composition and population structure of the dominant woody species present along the North Fork. We propose a four-step method to characterize environmental flows that maintain sediment mobility and riparian vegetation composition and structure. Our environmental flow standards explicitly address the fundamental role of sediment in creating and maintaining riparian habitat. Environmental flows to transport bedload are lower magnitude, higher frequency events (2 yr recurrence interval) that serve many in-channel functions, whereas environmental flows directed at riparian vegetation respond over longer time scales to high magnitude, lower frequency events (10 yr and 25 yr floods). Field evidence suggests the need for a 10 yr flood to saturate over-bank areas and exclude xeric species near the channel. Managed 25 yr floods serve as a target flow for generating canopy gaps, creating regenerative habitat, enhancing biogeochemical processes, maintaining habitat heterogeneity, and possibly disrupting the coarse bed-surface layer and scouring pools to maintain fish overwinter habitat within the North Fork. Where field evidence is lacking, selection of target flows can be guided by daily discharge exceedence values.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 451
Title: Characterizing environmental flows for maintenance of river ecosystems; North Fork Cache la Poudre River, Colorado
Title: Management and restoration of fluvial systems with broad historical changes and human impacts
Author(s): Rathburn, Sara L.Merritt, David M.Wohl, Ellen E.Sanderson, John S.Knight, Heather A. L.
Author(s): James, L. Allaneditor
Author(s): Rathburn, Sara L.editor
Author(s): Whittecar, G. Richardeditor
Affiliation: Colorado State University, Department of Geosciences, Fort Collins, CO, United States
Affiliation: University of South Carolina, Geography Department, Columbia, SC, United States
Pages: 143-157
Published: 2009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Meeting name: 2007 GSA annual meeting
Meeting location: Denver, CO, USA, United States
Meeting date: 20071028Oct. 28-31, 2007
References: 45
Accession Number: 2009-074393
Categories: Environmental geologyGeomorphology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N40°52'45" - N40°52'45", W105°20'14" - W105°20'14"
Secondary Affiliation: Colorado State University, USA, United StatesOld Dominion University, USA, United StatesU. S. Forest Service, USA, United StatesNature Conservancy, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200940
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