Using the Fiber Optic Distributed Temperature Sensing (DTS) System to Determine Temperature Dynamics and Groundwater Spring Influences due to Channel Relocation and Habitat Enhancement in a Mountain Stream
Big Boulder Creek is a major tributary to the Middle Fork John Day River near John Day, Oregon. During the summer of 2008, the channel was relocated to its historic alignment and reconnected with the flood plain as well as spring-fed ground water springs throughout the new reach. Large woody debris (LWD) was installed at designated locations as well as in the vicinity of the springs to enhance steelhead and salmon habitat opportunities.
* Can realigning a steep mountainous stream, installing woody material, and reconnecting it with springs aide in lowering temperatures and creating pocket pool habitat such that summer/fall steelhead, Chinook, and trout habitat is enhanced?
If increased chemical (dissolved oxygen improvement, etc), biological, and physical (temperature decrease, pools, spring re-introduction, holding areas, etc) integrity can be observed through these type of projects, then we can show an increase of available habitat to multiple species.
Need and Benefit
Reclamation uses time-series data collectors that measure data at intervals in space. Because this existing technology is location-specific, it does not provide information between sensor locations, resulting in data gaps that can be significant and that can only collect temperature flux data at a specific location. This limits full understanding of what drives temperature flux in between the sites.
In comparison, DTS combines the ability to read temperature, at each location, over length of the fiber-optic cable up to 10 km at 0.01degrees Celsuis resolution. The DTS sends an intense laser pulse down the fiber, with temperature computed from the backscattered light. Although most of the light travels unimpeded, a small fraction of the light interacts with the glass, bouncing back toward the source. This faint optical echo is composed of three wavelengths: that of the injected light, and just above and just below this frequency (so-called Stokes and anti-Stokes bands). The ratio of the intensity of the two Stokes bands reveals the temperature of the glass at the source of the backscattering. The arrival time of the backscattered pulse indicates the distance along the fiber of the source of the backscattered light.
Dr. Selker has been working directly with the fiber optic cable producers in the United States and Europe to optimize cable for the stream environment. Having now installed cables in streams in Holland, Switzerland, Luxembourg, and across Oregon, as well as having lead two workshops on environmental sensing using DTS, Dr. Selker's lab is the leader in the application of DTS to environmental monitoring. The instruments available to this project include two SensorTran M4-5100s (dual-channel, 4-km range, 1 m-0.01C resolution), a SensorTran M10-5100A (quad-channel, 10-km range, 1 m-0.01C resolution), and an Agilent N4386A (dual-channel, 4-km range, 1 m-0.01C resolution). These are state-of-the-art instruments purchased in the last 20 months, representing over half a million dollars in instrumentation. Supporting equipment, including fusion welders, solar power systems, and a 4-wheel-drive field support vehicle, are also owned by Selkers lab, and will be employed in this project.
The low-flow of many streams grows from upwelling from aquifers. The water that emerges carries with it the stable temperature of the deep rock, quite distinct from fluctuating surface water temperatures following the daily rhythm of the atmosphere. By observing the temperature of the stream along its whole length with an optical fiber connected to a DTS, it is possible to identify the location and amount of each (otherwise invisible) ground water contribution. In addition, hyporheic exchange through the gravel that forms the channel bed can act as a thermal flywheel, soaking up the peak daily heat as the stream water filters through, and recooling as the nighttime water carries this heat away. By observing, meter-by-meter with 0.01 degrees Celsuis resolution, the daily fluctuations in temperature, combined with numerical modeling of the thermal processes of the system (e.g., the HeatSource model by Boyd), the location and magnitudes of ground water upwelling and hyporheic flow can be determined. The temperature data directly reveal the location, size, and thermal stability of cool water refugia created by these stream processes.
In the John Day Basin and in much of Oregon streams, temperature is an ecological limiting factor. The study of temperature has advanced substantially in the last two decades, with Oregon in the forefront of this research. Robust methods for simulating stream temperature and thermal controls are now available. However, a persistent gap in understanding stream thermal restoration is the ability to the estimate changes in hyporheic exchange associated with fluvial morphologic and textural modification. The DTS technology has great potential to fill that gap.
Columbia Cascades Area Office, Pacific Northwest Region
Pacific Northwest Regional Office, Pacific Northwest Region
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