75 research outputs found
The influence of large woody debris on post-wildfire debris flow sediment storage
Debris flows transport large quantities of water and granular material, such as sediment and wood, and this mixture can have devastating effects on life and infrastructure. The proportion of large woody debris (LWD) incorporated into debris flows can be enhanced in forested areas recently burned by wildfire because wood recruitment into channels accelerates in burned forests. In this study, using four small watersheds in the Gila National Forest, New Mexico, which burned in the 2020 Tadpole Fire, we explored new approaches to estimate debris flow velocity based on LWD characteristics and the role of LWD in debris flow volume retention. To understand debris flow volume model predictions, we examined two models for debris flow volume estimation: (1) the current volume prediction model used in US Geological Survey debris flow hazard assessments and (2) a regional model developed to predict the sediment yield associated with debris-laden flows. We found that the regional model better matched the magnitude of the observed sediment at the terminal fan, indicating the utility of regionally calibrated parameters for debris flow volume prediction. However, large wood created sediment storage upstream from the terminal fan, and this volume was of the same magnitude as the total debris flow volume stored at the terminal fans. Using field and lidar data we found that sediment retention by LWD is largely controlled by channel reach slope and a ratio of LWD length to channel width between 0.25 and 1. Finally, we demonstrated a method for estimating debris flow velocity based on estimates of the critical velocity required to break wood, which can be used in future field studies to estimate minimum debris flow velocity values.</p
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Geologic Map of the Somerton 7 1/2' Quadrangle, Yuma County, Arizona
The map area is comprised entirely of late Cenozoic sediments. The map area can be divided into two geomorphic settings. The NW half of the quadrangle includes Yuma Valley and consists of Holocene Colorado River deposits. Approximately 12m (40 feet) above the river valley is Yuma Mesa which occupies the SE half of the quadrangle and is composed of late Pleistocene Colorado River sediments called the Chemehuevi Formation.These GIS data adhere to the standard format supported by the US Geological Survey's National Cooperative Geologic Mapping Program (NCGMP09). NCGMP09 recommends distributing geologic map data using the proprietary ESRI File Geodatabase format. We follow this convention, but also provide open-source geojson and csv data as part of this collection.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Ruby Road Washout, Atacosa Canyon, Arizona (27-28 July 2012)
Ruby Road washout associated with monsoon storm runoff of 27-28 July 2012. Visual narrative includes images of the washed out road, location maps, and rainfall from ALERT gauge at Pena Blanca Lake.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Methods for Evaluating Alluvial Fan Flood Hazards From Debris Flows in Maricopa County, Arizona
This study evaluated methods to quantify the risk of debris-flow initiation and runout potential to impact alluvial fan flooding hazards in Maricopa County. Debris flows are unsteady, non-uniform, very poorly sorted sediment slurries that are generated when hillslope soils become saturated and fail. While there is some evidence that debris flows have occurred in Maricopa County on very steep slopes of mountainous watersheds, there are no documented cases of historic debris flows impacting flood hazards on mid-piedmont alluvial fans. Based on known general characteristics of debris-flow behavior, as well as on the specific climatic and geologic conditions in Maricopa County, the expected recurrence interval for debris flows in Maricopa County probably exceeds 1,000 years. Furthermore, because of the regional physiography and watershed characteristics, it is likely that future debris flows will have low volumes because of limited sediment supplies, will travel only short distances from their point of initiation due to their coarse sediment composition and low clay content, and that most will not reach the active areas of alluvial fans, particularly the fans that are located away from the mountain front. To assess potential debris flow impacts on alluvial fan flooding, a combined approach of geologic reconnaissance and mapping, with a two-phase application of the LAHARZ debris-flow runout hazard model is recommended. Geologic reconnaissance will confirm the presence or absence of relatively young debris-flow deposits, and provide details of the basin and piedmont conditions which will be useful for calculating and evaluating potential debris-flow volumes. Geologic mapping will provide data regarding minimum number of deposits, relative ages, and travel distances of past debris flows. Debris-flow runout models will provide hazard information regarding potential travel distances, and the volumes required to reach those distances.This report is part of a larger product, Refinement of Methodology: Alluvial Fan Flood Hazard Identification & Mitigation Methods, by J.E. Fuller on behalf of the Flood Control District of Maricopa County.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Ruby Road Washout, Atacosa Canyon, Arizona (27-28 July 2012)
Ruby Road washout associated with monsoon storm runoff of 27-28 July 2012. Visual narrative includes images of the washed out road, location maps, and rainfall from ALERT gauge at Pena Blanca Lake.Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected])
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Geologic Map of the Thatcher 7 1/2' Quadrangle, Graham County, Arizona
Quaternary geology of the Safford Basin, Graham County, Arizona, was mapped in three 7 1/2' minute quadrangles: Artesia, Safford and Thatcher. The geologic mapping is original but informed by previous works in the Gila River Valley. Holocene geomorphic boundaries of the Gila River were based on work by Klawon et al. (2004). Bedrock geology was derived from Thorman and Naruk (1987).The Thatcher geodatabase file for v. 1.0 was added to the repository on 15 April 2016.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Southwest Wildfire Hydrology & Hazard Workshop Proceedings
This open-file report (OFR) presents materials from the 2012 Southwest Wildfire Hydrology & Hazards Workshop, including the workshop schedule, presentation abstracts, and a list of attendees. The oral presentations and posters are part of this OFR and are available for viewing from the Arizona Geological Survey Document Repository (http://repository.http://http://azgs.arizona.edu///). A second OFR scheduled for fall 2012 will host white papers produced by the working groups. Approximately 70 participants, representing various federal, state, and local agencies, researchers and practitioners, gathered at the University of Arizona’s Biosphere 2, north of Tucson, between April 3rd-5th for the 2012 Southwest Wildfire Hydrology and Hazards Workshop. The purpose of the workshop was two-fold: 1) share the most recent research regarding post-fire hydrology and hazard assessments and mitigation and warning systems; and 2) discuss ideas for bridging funding gaps for research and warning system implementation. Representatives from the U.S. Forest Service kicked off the 3-day workshop with a discussion of the philosophy and policies of the Burned Area Emergency Response (BAER) program, which is responsible for rapid post-fire assessments of forest service lands burned by wildfires. Included in this presentation was a discussion of the operations, restrictions and limitations of BAER, along with examples from the BAER assessments for the 2011 Wallow, Monument and Horseshoe 2 Fires. Subsequent presentations addressed modeling of post-fire hydrologic processes, warning systems, and current research. Dr. Peter Robichaud’s lunchtime keynote address focused on recent research regarding the effectiveness of hillslope mitigation treatments used by BAER teams. The day was rounded out with an evening keynote talk by Dr. Thomas Swetnam on historical and current fire regimes in the Southwest, and the implications of climate change. The second day of the workshop consisted of a field trip to the 2011 Monument Fire near Sierra Vista, Arizona, to see post-fire flood warning systems installed by the USGS, hillslope treatments implemented by the BAER team, channel mitigation measures implemented by county and federal agencies to protect downstream private residents, and to observe evidence of, and damages from, post-fire floods and debris flows. The workshop closed with final presentations on post-fire research and a roundtable discussion on key issues, such as pre-season readiness, during-incident support, post-fire responses for hazard warnings and research, and identification of steps needed to address those issues. Working groups formed to synthesize the workshop findings, and to recommend actions to effectively address the issues.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Geologic Map of the Somerton 7 1/2' Quadrangle, Yuma County, Arizona
The map area is comprised entirely of late Cenozoic sediments. The map area can be divided into two geomorphic settings. The NW half of the quadrangle includes Yuma Valley and consists of Holocene Colorado River deposits. Approximately 12m (40 feet) above the river valley is Yuma Mesa which occupies the SE half of the quadrangle and is composed of late Pleistocene Colorado River sediments called the Chemehuevi Formation.Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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