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INSTRUCTOR: F. Douglas Shields, Jr, Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
Sponsored by ASCE Continuing Education and the Environmental & Water Resources Institute (EWRI).
Purpose and Background
Recent developments in river restoration science highlight the complex condition of stream corridors prior to European settlement. In many North American ecoregions, streams were dominated by large wood and beaver dams to the extent that they exhibited multithread braided or anastomosing channel forms. Use of simple structures (beaver dam analogues) made of primarily of posts, willow branches and stream bed materials to mimic or facilitate beaver activity is rapidly increasing in popularity as a stream restoration strategy. Some workers report reversal of channel incision and transition from ephemeral to perennial flow in smaller streams treated with beaver dam analogues. Early experiments with beaver dam analogues were planned with little input from basic engineering disciplines and relied on intuition and experience. Engineers are now being asked to assist in planning and design of beaver dam analogue projects in order to address concerns of regulators, riparian landowners and project sponsors regarding structure design life and impacts on flooding, erosion and sedimentation. However, budgets for most of these projects are not large enough to support sophisticated design approaches. Under the aegis of the National Marine Fisheries Service a macro-enabled Excel© file has been developed to facilitate design. This webinar introduces students to the beta version of this tool and demonstrates its use with a simple example project. It includes sheets for hydrologic and hydraulic design including selection of a design event, estimation of downstream scour depth, and computation of required embedment depth for posts. It includes rough estimates of required material quantities and project costs.
Primary Discussion Topics
- Review of information resources for learning about beaver dam analogues (BDAs)
- Three approaches for determining design discharge for BDA projects
- Selection of appropriate design type and dimensions for BDA
- Computation of forces acting on BDA
- Design for BDA posts (pilings) including embedment depth
Learning Outcomes
- Identify information resources (design handbooks and spreadsheets) for BDAs
- Compute design discharge for BDA three ways; compare selected discharge with desired design life
- Select appropriate sizes for materials and dimensions for BDA
- Compute hydraulic forces acting on BDA
- Create estimates for scour depth downstream from BDA
- Compute post embedment depths
- Compute and understand safety factors for failure through vertical movement, post breakage, and post overturning
Webinar Benefits
- Learn sources for scientific background for BDAs
- Avoid costly failures or overdesign of restoration projects that include BDAs
- Communicate reasonable expectations for BDA performance to project stakeholders
Intended Audience
- Hydraulic engineers
- Hydrologists
- Planners and project managers
- Geomorphologists
- Biologists and ecologists
Webinar Outline
- Review of information resources for BDAs
- Acquisition and use of BDA design tool 1.0 beta version
- BDA tool workflow
- Hydrologic analysis
- Selecting BDA dimensions
- Hydraulic analysis/flow force computations
- Post embedment depth
- Material volumes and cost estimation
- Summary