Reclamation, DWR study effects of climate change on hydro
The U.S. Department of the Interior’s Bureau of Reclamation is working with the California Department of Water Resources (DWR) to explore how a risk-based framework might be used to illustrate the implications of climate change for reservoir operations.
This research project has two main parts:
– Studying the application of risk assessment and sensitivity analysis. This part focuses on the effects from 22 climate projection scenarios on the runoff and operations in the California Central Valley Project and State Water Project systems. Risk metrics being analyzed include long-term average annual water deliveries and carryover storage. Analyses are being repeated to explore the significance of different analytical design decisions, such as usage of precipitation projection information, assumptions about future flood control, and assumptions about relative scenario probabilities.
– Developing a method to estimate relative probabilities for climate change scenarios. This part focuses on how to estimate relative probabilities for the 22 projection scenarios, given a larger set of contemporary climate projections (75 projections representing 17 climate models). Reclamation is performing frequency-based assessment of climate projections, constructing projection distribution functions, and then using these functions to estimate relative probabilities for the 22 projection scenarios analyzed in the first part of the research project. The analyses are repeated with and without considering apparent climate model skill, based on how well the 17 models simulated 20th century regional and global climate conditions.
Results of this research project are expected to be available in fiscal year 2008.
Reclamation and California DWR are exploring the possibility of applying the results for both project-specific planning and research prioritization. Methods might be used to evaluate contemporary climate project information, define sensitivity scenarios, and assess scenario-specific effects on runoff and operation. With regard to research, the results from the risk sensitivity analyses offer some insight into which analytical design choices introduced relatively more uncertainty about the perceived risk. This topic might then warrant greater research attention.
– For more information about this research, contact Levi Brekke, Science and Technology Division, Bureau of Reclamation, U.S. Department of the Interior, (1) 303-445-2494; E-mail: [email protected]
Study assesses RCC performance for overtopping protection
Roller-compacted concrete (RCC) exhibits excellent abrasion resistance and durability when used to provide spillway and overtopping protection for dams. This is the finding of a review conducted by the Portland Cement Association to determine the performance of RCC structures that have been exposed to flooding, freeze-thaw cycles, and intermittent flows carrying heavy abrasive sediment loads.
RCC has been used to provide spillway and overtopping protection for more than 130 dams over the past 27 years. However, because these RCC structures are designed to operate infrequently, limited information is available on actual performance.
Portland Cement Association compiled findings from several RCC projects that have experienced multiple flows during their service lives. Results show that these RCC overtopping protection and spillway structures have performed satisfactorily, with no evidence of excessive wear or structural distress.
Some projects where the RCC protective structures have operated satisfactorily, and that were included in the review, are:
– Ocoee Dam #2 in Tennessee, where RCC was added in 1980 for overtopping protection. The dam is subjected to more than 80 days per year of regularly planned overtoppings to accommodate white-water rafting downstream. Although inspections show that the compacted RCC farthest downstream has suffered erosion of several inches, the dam continues to perform well;
– Brownwood Country Club Dam in Texas, where RCC was added in 1984 for overtopping protection. The dam has been overtopped at least once every one to two years, with overtopping events up to 2 feet deep. Although the uncompacted RCC at the lift edges has eroded, the RCC remains durable and the spillway continues to function properly;
– Lower Lake Royer Dam in Maryland, where RCC was added in 1995 to increase spillway capacity. This dam is exposed to a harsh freeze-thaw environment. The spillway shows only minor erosion, mainly at the exposed lift edges; and
– Lake Tholocco Dam in Alabama, where an RCC auxiliary spillway was constructed in 2000 to return the dam to service after two failures of the earthen emergency spillway. Since then, the dam has been overtopped at least twice, once with maximum overflow of 3 feet. An inspection performed in May 2007 showed that the RCC steps are in excellent condition.
As a result of the review, Portland Cement Association determined that several factors contribute to the successful performance of RCC spillways and overtopping protection. These factors include:
- – Proper structural design;
– Proper mix proportioning;
– Use of the hardest aggregate available;
– Sufficient cementitious content and proper compaction;
– Forming and compacting the steps to a high density; and
– Proper bonding of the RCC lifts.
– For more information on this review of RCC performance, contact Fares Y. Abdo, P.E., program manager, water resources, Portland Cement Association, at (1) 205-979-9435; E-mail: [email protected]
CEATI publishes report on debris management
CEATI announces availability of a technology review of debris management at hydro facilities. The review is titled Hydro Plant Debris Management.
CEATI says the review is intended to increase maintenance managers’ awareness of current technologies and equipment related to the management of debris in a hydro plant forebay.
The review has two main focuses:
– Trashrack exclusion, including debris management of hydro intakes, configuration of intake trashracks, and design criteria and considerations; and
– Trash removal, including an overview of trash removal systems and types, debris handling and disposal, and trash rake design and operating criteria.
The report also includes factors to consider when selecting a commercially available trash removal tool. And the review includes a brief section on debris disposal practices, providing some ideas of how owners are coping with debris after it is collected.
Sources of information used to develop the technology review include hydro industry service providers and product distributors, telephone discussions with suppliers of goods and services to the hydro industry, and published papers on the topic.
CEATI’s Hydraulic Plant Life Interest Group compiled the review. This group is comprised of more than 40 power generators who share experiences and address issues pertinent to their day-to-day operations and life-cycle management of various plant assets.
– To purchase this report or for more information about the Hydraulic Plant Life Interest Group, contact Jennifer Forbes at (1) 514-904-5086; E-mail: [email protected]
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