18 research outputs found
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Landscape Approaches: Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings
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Session A9: To Fill or Not to Fill: Stream Simulation and Embedded Aquatic Organism Passage Structures
Abstract:
Throughout North America stream simulation and embedded / recessed culverts are used to facilitate the passage of aquatic organisms thru road stream crossings. Although the concept of naturelike streambeds inside these structures is widely embraced, the design methodology and construction practice varies widely between state and federal agencies. Much debate has occurred with one specific requirement, whether or not to place stream bed material inside these structures. Not placing bed material inside structures assumes on going sediment transport processes will fill the structure’s interior with streambed materials. This is assumed to be a cost saving measure from both a design and implementation standpoint. Recent research, monitoring, and historic installations provide evidence that not placing streambed material can produce deleterious effects to the stream and aquatic habitat, cause low flow barriers, may not retain bed material, and potentially cause long term structural failure. Conversely in some channel types or site condition infilling may not be necessary and produce satisfactory results. Casual mechanism of success and failure, stream impacts, and design considerations will be discussed along with recommendations for site specific conditions where infilling structures is required or allowing structures to fill naturally would be successful
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Session B1: Lessons Learned from Tropical Storm Irene 2.0: How Flood Resiliency Benefits of Stream Simulation Designs Are Changing Policy within the U.S.
Abstract
Stream simulation design is a geomorphic, engineering, and ecologically-based approach to designing road-stream crossings that creates a natural and dynamic channel through the crossing structure similar in dimensions and characteristics to the adjacent, natural channel, allowing for unimpeded passage of aquatic organisms, debris, and water during various flow conditions, including floods. A retrospective case study of the survival and failure of road-stream crossings was conducted in the upper White River watershed and the Green Mountain National Forest in Vermont following record flooding from Tropical Storm Irene in August 2011. Damage was largely avoided at two road-stream crossings where stream simulation design was implemented, and extensive at multiple road-stream crossings constructed using traditional undersized, hydraulic designs. Cost analyses suggest that relatively modest increases in initial investment to implement stream simulation designs yield substantial societal and economic benefits. Numerous other examples across the country of stream simulation designs surviving large flood events underscore these benefits. Four years after the historic Irene flood event, policy changes at state and federal levels across the U.S. suggest that the flood resiliency of culverts is gaining momentum as a policy driver amid growing public sensitivity to climate change risks and the importance of restoring ecological connectivity and protecting investments in transportation infrastructure
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Session C2 - Stream Simulation: Analytical versus Standards based design methodology
Stream simulation by USFS definition is a channel that simulates characteristics of the adjacent natural channel (reference reach), and presents no more of a challenge to movement of aquatic organisms than the natural channel. How to design the channel and road crossing varies in detail widely from state to state. Standard requirements can force a design rather than inform it. Analytical based design provides the designer with an understanding of potential channel adjustments and risks at the site based on differences in channel types and geomorphic context on which to base design decisions. Common pitfalls in stream simulation design and application will be discussed along with recent stream simulation flood response from Hurricane Irene
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Concurrent Sessions A: Co-Benefits of Barrier Removal: Fish Passage and Public Safety - Flood Resiliency, Aquatic Organism Passage, Critical Infrastructure, and Economics
A retrospective case study was conducted in the Upper White River subbasin in Vermont (Unthank et al 2012) that examined persistence of traditional hydraulic and stream simulation designs following the record flood flows from Tropical Storm Irene that occurred in August 2011. Analysis indicated that extensive damage to road infrastructure in this study area was largely avoided in areas where the stream simulation design approach was implemented, as did several other localized case studies from across New England. Benefit/cost analyses suggest that a relatively modest increase in initial investment to implement stream simulation designs to provide aquatic organism passage yield substantial societal benefits. When considering the overall comparative economic, social and natural resource costs to communities caused by crossing and/or road failure due to undersized road-stream crossings, adoption of stream simulation design is comparatively inexpensive when examined over a multi-year time frame. Hydraulic analysis results of stream simulation designed structures surviving Tropical Storm Irene will be presented along with a series of regulatory, policy and funding recommendations to help agencies, municipalities and communities make smart infrastructure and aquatic resource investments that reduce future road and stream crossing failures and associated impacts, and to help provide biological resilience and infrastructural persistence in the face of increased frequency and severity of flood events modeled under climate change