Getting to the bottom of it15 June 2010
IWP&DC takes a look at the latest products and technologies available for underwater applications at dams and reservoirs
When it comes to underwater inspections there are a number of products on the market to meet the differing requirements of hydroelectric and dam projects. Below we take a look at some of the most recent releases to hit the marketplace.
Sawfish helps hydro harvesting
Combining elements from timber harvesting and marine vehicle technology, Triton Logging’s Sawfish underwater harvester is an innovative deep water logging machine.
Canadian company Triton Logging researches, develops and markets logging equipment to recover millions of trees flooded by hydro dams worldwide, helping to manage large scale reservoir harvest projects.
Sawfish can navigate precisely by a remote pilot and is capable of operation at any depth. In comparison, grapples and divers are claimed to be limited to approximately 25m, even though 80% of submerged timber resources are found at greater depths.
Efficient operation is made possible by Sawfish’s de-coupling cutting and surfacing processes, which enable it to perform multiple cuts without having to return to the surface.
Features of the product include:
• Fully remote control with eight video cameras and sonar.
• Powered by a 75hp electric motor, using biodegradable and vegetable oil-based hydraulic fluids.
• Inflatable/reusable air bags to float trees to the surface.
In 2009 Triton Logging was recognised by the National Research Council of Canada as a Canadian innovation leader, demonstrating specific advances in research and development within its industrial sector.
Broadband developments for underwater application
Two advanced broadband acoustic systems have been developed by researchers at Woods Hole Oceanographic Institution (WHOI) in the US. This could mean a major advance in the ability to count and classify fish and identify turbulence.
The two systems have been tested off the east coast of the US and measure sound over a continuous range of frequency, generating broadband acoustic spectra. In broadband spectrum the scattering signal generated by fish centres at a frequency of 1-10Hz for small fish, and since most echo sounders measure frequencies at 38-120Hz they miss this key indicator. Ultimately broadband signals can be used to discriminate between fish and other marine organisms, as well as to identify both sizes and densities of fish.
The continuous range of frequencies used by broadband systems will help to improve interpretation of data, providing more information so sophisticated algorithms can be used and accuracy improved.
The work has been supported by the US Office of Naval research, National Oceanic and Atmospheric Administration and WHOI. Fisheries managers can use the system to determine stock sizes, while the navy has been using the technology to learn how fish interfere with underwater equipment. The hope is that other major companies who manufacture acoustic systems will pick up on the broadband technology and apply it to other industries.
Spotlight on inspection
US-based JW Fishers has developed an external light system for its MC-1 mini camera which is designed for underwater applications. The new light system provides high intensity lighting to optimise picture quality. An internal ring light with high intensity LEDS provides the lighting when performing internal pipe inspections with the mini cam. One or two lights can be attached directly to the camera housing. The 6” long, 2” diameter camera housing can be easily mounted to a diver’s helmet or lowered into a pipe for internal inspections.
The mini camera is currently in use by diving companies worldwide, although two companies have recently reported new and unique uses for the product. A company based in Rhode Island that manufactures sediment sampling devices, attached an MC-1 to its equipment so the operator could view the area being sampled. While a dredging company in Florida attached the camera to its equipment allowing the operator to view the bottom before and after dredging operations.
See www.jwfishers.com for more information.
Zooming in underwater
New from EZspycam is a telephoto zoom camera on a pre-assembled retractable pole designed to support good portability for underwater inspections. The remote control unit allows you to configure the camera and view close captured images magnified up to 22x optically and up to 176x digitally. Night vision white LED lights means that the product is ideal for use in dark, hard to reach areas as are often found in dam inspections.
The acetyl coated housing for the camera is corrosion-free for saltwater and chemical use.
For more details see www.ezspycam.com/ENC-130.htm.
Rotating head sonar puts spin on inspections
AquaCoustic has collaborated with a leading sonar manufacturer in the development of a specialised profiling sonar system. The use of a rotating head sonar can provide accurate information about critical dam and reservoir features which could compromise structural integrity if left unaddressed. The system can provide accurate visualisation and measurement of underwater features of up to 2mm resolution at close range.
Advantages of the sonar include accurate data collection and real time field observations which allow on-site assessment of unusual features that may require further investigation. Real time on-screen review of the sonar profiles allows modification of the survey and data can be used in AutoCAD or other modelling software. The system can also be deployed from a small vessel, a fixed structure such as an intake or spillway, or through ice.
The profiling sonar technique has the following applications in dam inspections:
• Detailed investigating and monitoring of sink holes.
• Identify and measure retrogression of scour and undermining towards the dam structure from plunge pools.
• Determine earthquake values by accurate measurement of dam slope profile from a single point.
• Gather detailed data from hard to reach areas such as under overhangs, vertical dam faces and structures, and across the bottom.
• Accurate data can be obtained up to the shoreline or beside vertical structures where boat soundings are not reliable.
• Volume measurements for water inundation studies.
• Siltation volume measurement.
• Debris identification.
• Pre- and post-dredging quality control.
• Internal tunnel and pipe surveys.
DCN Diving BV is based in the Netherlands and utilises a selection of different techniques and systems for underwater inspections. The use of a self-propelled habitat can minimise diver excursion distances during dam inspections. Based on an inhouse concept the system is operated either by divers or from the surface.
The habitat is connected via the main umbilical to the habitat control room and live support systems and divers are connected to the habitat via short 20m length excursion umbilical. This concept creates a safe and dry working environment which allows divers to work over long distances in confined spaces. It can cover distances up to 400m with a minimum width of 2500mm and a maximum width of 2800mm.
The company also uses a remotely operated cleaning machine (ROCM) which is described as the ideal platform for cleaning and removal of debris and sediment inside pipelines, culverts and outfalls.
The system removes debris by using hydraulically operated brushes and the debris is pumped through a flexible hose to a discharge location. The vehicle is mounted on tracks and controlled from the surface.
Advantages of the ROCM include:
• Low risk, no human (diver) intervention for normal cleaning operations.
• Shut down periods can be kept to a minimum.
• Video and photographic images can be displayed in real time.
• No dewatering required.