|Photo courtesy Grant County Public Utility District|
Processing important aspects of dam-related modeling means using a computer and hard-earned work experience.
By Gregory B. Poindexter
Designing and constructing dams in a timely and cost-effective manner, many think, is as important as the social and economic factors that directly result from the presence of a dam in a given environment.
Dam design and construction in its simplest form attempts to utilize man’s ability to harness, contain, divert and monetize one of the greatest natural resources on Earth — water.
In an effort to assist dam engineers in processing information related to design, construction and monitoring facilities, the International Commission on Large Dams (ICOLD) issued Bulletin No. 155, “Guidelines for Use of Numerical Models in Dam Engineering,” in 2014.
In part, the bulletin offers guidance to help engineers deal with issues surrounding the immense amount of data designers must digest when undertaking the monumental task of dam design and construction.
ICOLD is a non-governmental international organization that provides a forum for the exchange of knowledge and experience in civil engineering and at its core has a membership of international professional engineers. Through academic research, empirical studies and real-world experience, ICOLD helps set standards and guidelines to ensure that dams are built and operated safely, efficiently and economically and are environmentally sustainable and socially equitable.
“The objective of [Bulletin No. 155] is to help the engineer in establishing a sound computation strategy based on a careful analysis of the problem to be solved, selecting the adequate software options needed, then carrying out the analysis in a progressive way with frequent checks, and finally using adequate outputs to make rational interpretation of the results achieved, so as to translate them into engineering decisions,” ICOLD said.
Said another way, the bulletin will help dam designers make sure their computer-assisted designs actually measure what they intended to measure, check the process along the way and then easily translate their data into real-world engineering.
Prior to designing and constructing a dam, countries, states and provinces, and municipalities request site-specific data on which to make decisions on the viability of a proposed dam. The key word here is “data.”
“The need for the present bulletin arose from observation by several members of the committee, in the frame of their professional experience, that even good engineers, using well-validated software in a pertinent field of application, may lose much time and sometimes miss the objective of their computational activity,” according to the bulletin.
ICOLD recognizes that the amount of data an engineer can amass ahead of dam design is overwhelming. “The main reason seems to be that software now available has more and more capabilities and offer a wide range of options,” ICOLD said, “which require users to make adequate choices when preparing and operating their models.”
Not only is an array of tools available to gather and process data, once the data are gathered, engineers must decide what information is important to their specific endeavor.
“The use of numerical tools, such as finite element, boundary element and finite difference methods, has become standard practice in dam engineering,” according to the bulletin. “The significant advances in software and hardware technology allow dam engineers to perform a variety of quick and efficient numerical analyses for usual or very complex problems in dam design, construction and operation.”
ICOLD enumerates in the following exactly why numerical simulation models of dam-foundation-reservoir systems have been developed and used for different purposes:
— Prediction of the structural stability and simulation of any possible failure mechanisms under all types and the whole range of loading scenarios (typically normal operation, flood and earthquake);
— Pre-design and optimization of new dams at different project stages;
— Interpretation of the behavior of dams under operation by comparison of results of the monitoring system with theoretical computed values, and assessment of their safety;
— Design and optimization of remedial works, corrective measures, and most efficient rehabilitation methods of existing dams; and
— Learning from real cases and back analysis of different problems.
Bulletin contents reflect need
Several countries are seeking or have sought requests for study of proposed dams, resuming halted construction at partially constructed dams and answers to why design-related mishaps occurred at existing dam construction sites.
Though specific examples are not identified in the bulletin, the types of issues the bulletin addresses ultimately reflect the need for the document and a number of examples of real-world situations follow.
In 2014, the government of Nigeria requested dam safety experts to serve on a panel to review and advise Nigeria’s Ministry of Water Resources on dam safety and other critical aspects of seven dams and a reservoir in Nigeria.
The dam safety experts, under the Transforming Irrigation Management in Nigeria Project, will review remedial design considerations for several dams in Nigeria that include Dadin Kowa, Tiga, Challawa Gorge, Bakolori, Zobe, Goronyo and Hadejia dams as well as Ruwan Kanya Reservoir.
Nigeria’s Kano State and India’s Skipper Group signed an agreement in 2013, to develop small hydro projects at the Tiga and Challawa Gorge totaling 35 MW.
Early last year the Grant County Public Utility District said a crack, 65 feet-long by 2 inches-wide, was found by divers at Washington’s Wanapum Dam. The discovery led Grant PUD to coordinate with the Federal Energy Regulatory Commission and upstream dam operators, dropping the Columbia River forebay levels to the lowest they have been since the reservoir was filled in 1964.
The affected spillway is one of 12, which, combined, are capable of releasing 80,000 cubic feet of water per second based on current river conditions.
Misicuni Dam is a concrete-faced rockfill dam about 30% complete, being constructed on the Misicuni River near Cochabamba, Bolivia.
Empresa Misicuni, Bolivia’s special-purpose company to develop the Misicuni multi-purpose project, sought to resume construction of Misicuni Dam, spillway and related underground construction works in June 2014. The company resumed the dam’s development, but more than four years has elapsed since the project’s initial construction.
A contract originally awarded in 2009 for the second phase of the dam project was rescinded because of contract disputes. However, to continue the construction of the 120 meter-tall dam, water conduit and related structures for the 80 MW hydroelectric plant, the developer had to re-examine data obtained prior to 2009 through the lens of updated technical capabilities.
Bulletin offers sage advice
Authors say the bulletin could help the engineer in establishing a sound computation strategy based on a careful analysis of the problem to be solved, selecting the adequate software options needed, carrying out the analysis in a progressive way with frequent checks, and finally using adequate outputs to make rational interpretation of the results achieved, so as to translate them into engineering decisions.
“Whether applied to the design of a new structure or to the verification of an existing one, each project that makes use of a numerical model includes a certain number of steps that complete one another to reach a successful result,” said the bulletin. The authors remind readers to try to order their engineering processes in the most logical and pragmatic way. But, the most poignant advice is offered to reduce dependence or abject trust in computer assisted design.
“A contributor to this bulletin on numerical analysis applied to dam engineering once heard, at the early era of the finite element models, one of his colleagues to declare, concerning the design of a relatively complex project: ‘since this problem is complicated, let’s put it in the computer,'” said the bulletin.
“This expression of faith in the capabilities of computer analysis is to be taken with caution: the results of computations are not guaranteed to be reliable simply because they come out of computer analysis.”
To access ICOLD Bulletin No. 155, log on to www.icold-cigb.org/GB/Publications/bulletin.asp.
Gregory Poindexter is associate editor of HRW-Hydro Review Worldwide.