5 research outputs found
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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 A3- Stream Simulation Desing: Providing Unimpeded Aquatic Organism passage at Road-Stream Crossings
The stream simulation approach for designing road-stream crossing structures developed and used by the U.S. Forest Service provide a pragmatic and sustainable long-term solution to maintain passage for all aquatic organisms at all life stages, while meeting vehicle transportation objectives. The premise of stream simulation is that by creating similar channel dimensions and characteristics in the structure as those in the adjacent natural channel, fish and other aquatic organisms should experience no greater difficulty moving through the structure than if there were no crossing. The stream simulation design approach is an interdisciplinary process, integrating concepts of fluvial geomorphology with engineering principles to design a natural and dynamic channel through a rigid structure. Using channel characteristics from an adjacent representative reach as a starting point to develop the stream simulation design channel width, bed material sediment sizes, and bedform types and spacing are verified and adjusted to provide continuity of flow hydraulics, sediment transport, and ultimately aquatic organism movement through the crossing for a wide range of flows. Because the dimensions and characteristics of stream simulation designs are similar to those in the adjacent natural channel, stream simulation channels are capable of laterally and vertically adjusting to a wide range of floods and sediment/wood inputs without compromising the movement needs of fish and other aquatic organisms or the hydraulic capacity of the structure. Additionally, stream simulation structures are less susceptible to damage by high flows and debris blockage because they do no constrict the channel until flows substantially exceed bankfull flow conditions
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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