Bathymetric Data Collection Techniques around Large Wood
Large wood installations are an important element of Reclamation's overall river restoration strategy due to the many realized benefits of large wood structures. These structures, however, can be dangerous to collect bathymetric (the measurement of water depth at various places in a body of water) data around, and there is no known amount of guidance available for data collection around wood. In addition, there is a lack of field data/information of depths around Large Wood structures to resolve technical data gaps in the design, monitoring and installation of these structures. The following research questions are posed to address this issue of safe data collection techniques are posed:
1. What technologies and associated guidelines/methodologies are currently available for collecting bathymetric data around large wood structures?
2. What new technologies/methodologies (e.g. Side-Scan Sonar) are available that can potentially be used to collect bathymetric data around large wood structures?
3. What are the relative applicability, performance ability, and accuracy, between various bathymetric data collection techniques around Large Wood structures?
The goal of this research is to scope out what documentation/guidance is available on the safe and accurate collection of bathymetry data around Large Wood structures.
Need and Benefit
One of the many data gaps in the design, implementation, and monitoring of large wood that was identified at a Large Wood Workshop in February 2012 (funded through the S&T office) is a means evaluating the performance of large wood structures to resolve technical data gaps (High Priority). Collecting bathymetry data around these features in a safe and reliable manner is paramount in gathering a dataset to resolve any outstanding technical data gaps. This research aims to primarily fill in the gap of safe and reliable data collection. Information compiled during this research can be incorporated into the Large wood design manual (outline currently funded through the S&T office).
Using large wood structures for the purposes of reducing stream bank erosion, while at the same time adding in-stream habitat, is a fairly recent concept. The concept began with the observation that natural logjams not only introduce physical complexity to rivers, which creates productive fish habitat, but can also control the morphology and grade of fluvial systems. As opposed to the engineering rigidity of its predecessors such as rock barbs, spur dikes, and bulkheads, large wood structures are unique in that they are engineering structures that replicate the complexity found in the natural system. The structural complexity and hydraulic diversity associated with log jams provide ideal habitat for a variety of life stages and species of fish. Large wood in the channel provides cover for fish, slows water velocities, creates pool habitat, enhances hyporheic flow, provides nutrients for invertebrate populations, and gathers spawning gravels. These project features also provide shading for the river, which decreases summer maximum water temperatures. This technology is an evolving science as lessons learned from ongoing monitoring activities are continually being incorporated into design. Various federal and state agencies are advocating that Reclamation use these types of "soft" engineering approaches to meet endangered species requirements while maintaining water delivery needs.
An understanding of the importance of large wood in river systems has gained significant strength in the research and applied studies of eco-hydraulics within recent history. One major ecological benefit of the use of large wood in rivers is the improvement to floodplain connectivity and creation of habitat and cover for endangered fish species. These improvements to habitat may reduce in-stream flow requirements, thereby increasing the amount of water delivery to downstream water users. Design of large wood structures that can sustain habitat features and meet program objectives for water users are essential components of successful project implementations.
Large wood structures are being incorporated into projects at Reclamation at a more frequent rate today than ever before. The Trinity River Restoration Program is incorporating 400-500 pieces of wood into the river annually. There are 22 large wood structures, each with several hundred pieces of wood, currently being implemented on the Elwha River. There is a habitat restoration project on the Entiat River that includes the placement of 13 large wood structures on a stretch of river less than a mile in total length. The list goes on. Rivers such as the Columbia tributaries, Trinity, Klamath, Yellowstone, Bighorn, and Colorado headwater streams all have a need for a better understanding of the effects of implementing these types of structures, which is what this research intends to provide.
A technical memorandum describing the research efforts and results will be composed. In addition, as appropriate, S&T progress reports and a research bulletin will be prepared and the results will be presented at a professional conference. Non-labor for professional conference will be funded in-kind (not by S%26T funds).
This information was last updated on December 10, 2013
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