Tech Briefs

Low-elevation orthophotos used to track river changes

Seattle City Light is using low-elevation orthophotography to track large woody debris movement in the South Fork Tolt River. The utility has a 15-MW project on this river, which provides important spawning area for chinook salmon and winter steelhead. Both fish are listed as threatened under the Endangered Species Act.

An orthophoto (or ortho-rectified photo) is an aerial photograph that is geometrically corrected for topographic relief, lens distortion, and camera tilt. The result is a photo with a uniform scale that can be used to measure true distances.

Seattle City Light investigated many methods to achieve its monitoring goals after the placement of large woody debris in the river in 2005 to create log jams, including taking images using helicopters, balloons, and poles with cameras mounted on top. This placement work was intended to improve access of fish and other organisms to historic side channels in the river, recruit and capture gravel from existing deposits, bolster decaying jams, and increase the distribution of salmon spawning, says Elizabeth Ablow, senior environmental analyst with Seattle City Light.

Monitoring was intended to provide data on the effectiveness in recruiting gravel and accessing side channel habitat, movement of placed wood, any physical channel changes, and chinook salmon spawning distribution.

To capture these images, the utility used a precision aerial mapping camera attached to a fixed wing plane. The camera features a 6-inch focal length lens and is gyroscopically stabilized and equipped with forward motion compensation. The film was color, and photo scale was 1 inch equals 350 feet. Previously, aerial photographs available to Seattle City Light, primarily obtained from the county, had a scale of 1 inch equals 1,600 to 2,000 feet. The choice of scale was a balance between the goals of the aerial photography, cost (the finer the sale, the more photos and flight lines required), and limitations due to topography (steep forested terrain limits how close a plane can fly to the ground).

The utility hired Aero-Metric Inc. to fly the same area in 2006, 2008, and 2010. Care was taken to perform this work when the leaves were off the trees, river flows were at their lowest during the time period, and conditions were overcast (to reduce glare that limits river visibility). The digital images, produced at 0.25’ pixel (rather than the typical 1’ pixel scale) to maintain clarity when zooming in, were orthorectified and incorporated into the company’s geographic information system (GIS).

Results show low-elevation orthophotos are helpful and informative in tracking channel change, wood movement, and substrate change over time. For example, the utility was able to determine channel access at small and large scales, quantifying both linear distance and area of reconnected active channel. This method also allowed Seattle City Light to capture log movement and log jam development at both a specific site and over a river reach.

Rodney Hunt Co. receives ISO 9001:2008 certification

Flow control products firm Rodney Hunt Co. has received ISO 9001:2008 certification, the company reported.

The certification is an internationally recognized quality management standard.

The certification was authorized by TUVRheinland, a global provider of independent testing and certification services.

ISO 9001:2008 provides a set of requirements that must be in place to have a quality management system — regardless of the organization’s size, product or service line, or public or private status. Certification to the standard is voluntary, and organizations must complete a rigorous auditing process by a third-party registrar.

Rodney Hunt has been in operation since 1840, designing and manufacturing engineered flow control products for the hydropower markets and other sectors.

Spawning beds provide habitat for sturgeon

Two spawning beds installed by New York Power Authority (NYPA) in the St. Lawrence River are successfully providing habitat for threatened lake sturgeon. The number of sturgeon observed on or near the beds in 2010 was lower than in 2009 but higher than in 2008. During the peak day in 2010, 261 sturgeon were observed on the beds, compared with 395 in 2009 and 116 in 2008.

During the Federal Energy Regulatory Commission (FERC) relicensing process for the 800-MW St. Lawrence-FDR Power Project, improving lake sturgeon spawning opportunities became one of the habitat improvement projects incorporated into the new operating license for the project. The New York Department of Environmental Conservation puts great value on trying to expand the existing population through natural reproduction, says Thomas R. Tatham, director of the relicensing and implementation division of NYPA.

To achieve this goal, NYPA worked collaboratively with representatives from state and federal resource agencies, the St. Regis Mohawk Tribe, and others to incorporate data into the siting and design of the spawning beds.

NYPA used underwater videography and gill netting to determine where sturgeon were active during the spawning season and to characterize the structure of the river bed and vegetation. Results from near Iroquois Dam, a water control structure, indicated that sturgeon ready to spawn were in the area but there as no apparent egg laying activity. This provided an ideal opportunity to provide spawning habitat without disrupting existing spawning activity, Tatham says.

To determine the exact site for the beds, NYPA used an acoustic Doppler current profiler to study flow rates. Water depths at the two beds range from 9 to 12 meters, and current velocities are 0.8 to 1.5 meters per second. Each bed is about 30 meters wide and 30 meters long.

For material, NYPA selected a processed coarse gravel with rock sizes primarily in the 2- to 4-inch range, placed using a bottom-opening hopper barge. Contractors devised a heavy steel rake that could be lowered from a work boat on a small crane and dragged along the riverbed to level the piles of gravel dropped from the hoppers. Divers were used to inspect the beds and identify areas that needed to be further leveled. In addition, ten large boulders were placed at the downstream end of each spawning bed to act as velocity breaks. This work was completed in late 2007.

Video monitoring was conducted in 2008 to check for the presence of fish near the beds. On the first day, sturgeon were observed on or near the beds. Their numbers increased gradually, then dramatically. Egg traps were then deployed to determine if spawning was occurring. Once spawning was confirmed and the incubation period had passed, drift nets were deployed and larvae were collected. Production levels from these spawning beds approached those found at very productive natural spawning beds.

To ensure the success of the spawning beds, NYPA installed them using a phased approach. Lessons learned from the first phase could be incorporated into later stages. The authority has agreed to install a total of six beds.

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  • Renewable Energy World's content team members help deliver the most comprehensive news coverage of the renewable energy industries. Based in the U.S., the UK, and South Africa, the team is comprised of editors from Clarion Energy's myriad of publications that cover the global energy industry.

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Renewable Energy World's content team members help deliver the most comprehensive news coverage of the renewable energy industries. Based in the U.S., the UK, and South Africa, the team is comprised of editors from Clarion Energy's myriad of publications that cover the global energy industry.

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