Forum questions: 1) Divers are often used for dam inspection and maintenance jobs. What standards do you use to select qualified diving contractors? 2) Remotely operated vehicles (ROVs) are now doing many dam inspection maintenance jobs once done exclusively by divers. What experience have you had with ROVs?
Tom Spicher replies:
I was one of the original US Bureau of Reclamation inspection/engineering divers in Sacramento in 1965. Subsequent to that, I headed up the dive team for the Northwest Region USBR, based at Grand Coulee. We discovered that the commercial divers often did not use an engineering perspective to identify the conditions encountered. Many are very fine firms, but the individual divers vary significantly.
ROVs are excellent where visibility and appropriate interpretive engineering review are available. Personal interviews with the potential contractor are essential prior to the need arising for their application. If competitive bidding is required, pre-qualify the potential bidders.
Safety is a primary concern when divers or manned vehicles are involved. Individual experience with black water, high currents or other nasty situations that may be present is an essential. With diver applications, a compact TV is often very helpful. Preparation is the most important aspect of underwater inspection applications.
Sean Horgan, strategic asset manager of Meridian Energy Limited in New Zealand, writes:
In May of last year we completed an ROV inspection of a 10km tailrace tunnel at our Manapouri power station. (See IWP&DC, November 2000, pp16-17). The ROV was our only real option due to time constraints (only a 48-hour window was available) associated with dewatering a tunnel that has been in service for 30 years, along with a number of other constraints.
The contractor we employed was Aquatic Sciences Inc of Canada because of their proven track record and fit-for-purpose technology (eg 10km umbilical, profiling sonar, high res cameras).
Chuck Hutton, vice president of ECI in Colorado, US, writes:
The ASCE is in the process of finalising a Manual of Practice for Underwater Inspections that should be available later this year. For more information contact:
Patricia S. Brown, P.E, Director, COPRI of ASCE, 1015 15th St. NW, Suite 600, Washington, DC 20005, US, tel: 202-326-5237, fax: 202-789-0212, email: email@example.com
Another source that will be useful with respect to diving standards is the US Department of Transportation, Federal Highway Administration, Bridge Inspector’s Training Manual. Chapter 17 on underwater inspections includes a section on qualifications of Diver-inspector.
Remotely operated vehicles (ROVs) are useful but cannot replace the experience of a diver with a video camera if there is good visibility. For zero visibility, a diver is the only choice.