Stream power framework for predicting geomorphic change: The 2013 Colorado Front Range flood
Introduction
Predicting the settings where geomorphic change can be expected as a result of flooding is valuable for informing environmental management and policy, as well as specific project designs. Human encroachments into stream corridors, including roadway and railroad alignments, commercial developments, and private residences, are key drivers of flood hazards. Geomorphic change and subsequent flood hazards include localized streambank erosion, hillslope and terrace failure, reach-scale channel widening, sediment deposition and associated loss of channel and floodplain capacity, rapid downstream meander migration, and channel avulsions and braiding. Where allowed by the valley form, sufficient floodplain extent and connectivity is needed to diminish the effects of erosive forces on streambanks, floodplain and terrace surfaces, infrastructure and property, and riparian and aquatic habitats. The identification of hydraulic thresholds beyond which a substantial potential exists for geomorphic change of channel and floodplain form are consequently quite valuable, but hindered by variability in driving mechanisms (peak discharge, flow duration, channel and floodplain slope, stream power, etc.) and resisting mechanisms (flow resistance, bank composition, vegetation type and extent, rip rap, etc.).
The 2013 Colorado Front Range flood provides an opportunity to assess geomorphic changes associated with a large flood in a semiarid landscape. This event, which impacted a substantial geographic extent and numerous streams in and adjacent to the Colorado Front Range foothills, allows us to relate diverse geomorphic changes to unit stream power (ω) and other variables. Observed responses ranged from undetectable or minimal impacts upon cross sections and planforms to major changes including widening, braiding, overwhelming erosion of road embankments, hillslopes and terraces, and extensive aggradation. Numerous avulsions were also observed. Additionally, a large number of landslides and debris flows occurred (> 1100; Coe et al., 2014), contributing large point sources of sediment and water to many of the most-impacted streams. The largest rainfall accumulations were observed on the mid-elevation foothills (elevations primarily from 2000 to 3000 m; Fig. 1). The flood response extended from confined, high-gradient reaches within canyons of the foothills to wide and lower-gradient high plains stream valleys; thus, the geomorphic variability and extent of affected reaches provide a valuable opportunity to explore relationships between hydraulic descriptors such as ω and observed geomorphic changes.
Given the limited available guidance for predicting varying types and degrees of geomorphic change resulting from large floods, we initiated a project with the following objectives:
- •
develop an ordinal classification scheme describing diverse types of geomorphic change and apply it to stream reaches impacted to varying degrees by the 2013 Front Range flood;
- •
assess reach-specific hydraulic variables that quantify driving mechanisms of geomorphic change and assess their effectiveness for predicting observed responses; and
- •
identify ω thresholds associated with specific types of geomorphic change and compare these results to previously published findings from floods in other regions.
Section snippets
Background
Floodplain mapping based on flood-frequency relationships and hydraulic modeling of inundation extent and elevation is the standard method for characterizing flood hazards and informing floodplain management (e.g., Federal Emergency Management Agency, FEMA, floodplain planning and mapping). However, the area within stream corridors subject to flood hazards caused by geomorphic change typically is not considered. Flood hazard maps based on inundation alone can underestimate compounding threats
Study area
During this flood, large portions of the Colorado Front Range foothills (Fig. 1) received heavy rainfall, with up to 460 mm falling in 10 days. The majority of the precipitation in and along the Front Range fell during 36 h on 11–12 September 2013. Rain gauge data from the most severely affected areas of the foothills indicate that up to 380 mm fell in Larimer County, 460 mm fell in Boulder County, and 410 mm fell in El Paso County (Community Collaborative Rain, Hail and Snow Network (CoCoRaHS), 2013
Results
A total of 531 reaches were assessed on 226 km of streams impacted to various extent by the 2013 flood event in the Cache la Poudre River, Big Thompson River, Little Thompson River, Saint Vrain Creek, Left Hand Creek, Boulder Creek, and Coal Creek watersheds, which are all located in the South Platte River basin in and adjacent to the Colorado Front Range foothills. Reach lengths varied from 71 to 500 m, with an average of 426 m. A variety of stream channel scales and types were included in the
Discussion
The Colorado Front Range flood impacted streams along a substantial extent of the foothills and high plains in September 2013, from Fort Collins south to Pueblo. Infrastructure, homes, businesses, stream functions, and ecosystem services were disturbed by the flooding and negatively impacted by emergency response measures within the riparian corridors. Owing to the large spatial extent of flooding induced from this event, from narrow foothill valleys to wide high plains stream corridors,
Summary and conclusions
This study has utilized an extensive data set from the 2013 Colorado Front Range Flood to relate channel adjustments to descriptors of driving processes and geomorphic setting. We defined six classes of geomorphic change related to stream power and valley confinement for 531 stream reaches over 226 km, spanning a gradient of channel scales, slopes, and watershed areas. The geomorphic change classes (and median ω values) were: (1) no detected geomorphic change; (2) infrequent eroded streambanks
Acknowledgements
We thank Sara Rathburn and John Moody, as well as an anonymous reviewer, for constructive reviews that substantially improved the manuscript. Additional review and editorial work by Richard Marston, Gene Bosley, and David Levinson is also greatly appreciated.
The many hydrologists and hydraulic engineers who collected the peak flow data utilized in this analysis are greatly appreciated. This includes individuals with the U.S. Geological Survey and the Colorado Division of Water Resources, for
References (79)
Unbiased plotting positions — a review
J. Hydrol.
(1978)Geomorphic impacts of a 100-year flood: Kiwitea Stream, Manawatu catchment, New Zealand
Geomorphology
(2008)- et al.
Impact of a large flood on mountain river habitats, channel morphology, and valley infrastructure
Geomorphology
(2016) - et al.
Geomorphological impacts of a flood event on ephemeral channels in SE Spain
Geomorphology
(2000) - et al.
Velocity and flow resistance in step-pool streams
Geomorphology
(2002) Thresholds and the spatial variability of flood power during extreme floods
Geomorphology
(1992)- et al.
The efficacy of stream power and flow duration on geomorphic responses to catastrophic flooding
Geomorphology
(2015) - et al.
Geomorphological and sedimentological analysis of flash-flood deposits: the case of the 1997 Rivillas flood (Spain)
Geomorphology
(2009) - et al.
Channel response to extreme floods: insights on controlling factors from six mountain rivers in northern Apennines, Italy
Geomorphology
(2016) - et al.
Geomorphic effects, flood power, and channel competence of a catastrophic flood in confined and unconfined reaches of the upper Lockyer valley, southeast Queensland, Australia
Geomorphology
(2013)
A spatial model to examine rainfall extremes in Colorado's Front Range
J. Hydrol.
Colorado re-emerging from $2.9 billion flood disaster a year later
Riverine Erosion Hazards White Paper
Exhumation by debris flows in the 2013 Colorado Front Range storm
Geology
Stream-channel response to floods, with examples from central Texas
Geol. Soc. Am. Bull.
Flood power
Energy expenditure and geomorphic work of the cataclysmic Missoula flooding in the Columbia River Gorge, USA
Earth Surf. Process. Landf.
Freedom space for rivers: a sustainable management approach to enhance river resilience
Environ. Manag.
The use of stream power as an indicator of channel sensitivity to erosion and deposition processes
River Res. Appl.
Measurement of peak discharge at culverts by indirect methods
The drainage of the Lake Ha!Ha! reservoir and downstream geomorphic impacts along Ha!Ha! River, Saguenay area, Quebec, Canada
Geomorphology
Threshold of critical power in streams
Geol. Soc. Am. Bull.
Impact of reach geometry on stream channel sensitivity to extreme floods
Earth Surf. Process. Landf.
Fluvial riparian classification for National Forests in the Western United States
Geomorphic effects of large debris flows on channel morphology at North Fork Mountain, Eastern West Virginia
Earth Surf. Process. Landf.
Flow hydraulics and geomorphic effects of glacial-lake outburst floods in the Mount Everest region, Nepal
Earth Surf. Process. Landf.
A Tutorial on Fitting Cumulative Link Models with the Ordinal Package
Ordinal — Regression Models for Ordinal Data. R Package Version
Geomorphic thresholds in riverine landscapes
Freshw. Biol.
New insights into debris-flow hazards from an extraordinary event in the Colorado Front Range
GSA Today
R: A Language and Environment for Statistical Computing
Rheologic, geomorphic, and sedimentologic differentiation of water floods, hyperconcentrated flows, and debris flows
Geomorphically effective floods
Measurement of peak discharge by the slope-area method
Physiographically-sensitive mapping of temperature and precipitation across the conterminous United States
Int. J. Climatol.
Controls on spatial variations in flow resistance along steep mountain streams
Water Resour. Res.
Multiple comparisons among means
J. Am. Stat. Assoc.
Creating and evaluating digital elevation model-based stream-power map as a stream assessment tool
River Res. Appl.
Cited by (49)
Spatial and temporal variability of the morphodynamics of a regulated mountain river
2023, Journal of HydrologyWatershed controls and tropical cyclone-induced changes in river hydraulic geometry in Puerto Rico
2022, Journal of Hydrology: Regional StudiesA stochastic model of geomorphic risk due to episodic river aggradation and degradation
2022, Engineering GeologyCitation Excerpt :In recent decades, cases that have been documented in detail include episodes in Canada (Lapointe et al., 1998; Brooks and Lawrence, 1999; Capart et al., 1997), New Zealand (Korup, 2004), La Réunion (Garcin et al., 2005), Taiwan (Hsieh and Capart, 2013), and Switzerland (Turowski et al., 2013; Ruiz-Villanueva et al., 2018). In many recorded cases, rapid changes in river bed elevation have threatened or destroyed bridges and roadways (Korup, 2004; Yochum et al., 2017; Hackl et al., 2018; Ruiz-Villanueva et al., 2018; Seier et al., 2020) or other riverine infrastructure like hydropower plants, run-of-the-river dams and diversion weirs (Lane, 1955; Lapointe et al., 1998; Hsieh and Capart, 2013). When aggradation is severe, such assets may directly get buried by the sediments.
Early detection model for the urban stream syndrome using specific stream power and regime theory
2022, Journal of Hydrology