— Dearborn Dam Diversion for the Revitalization of the Local Economy, presented by Tim Huffman, Duke Energy
— LADWP Haiwee Power Plant: Innovative CFRP Renewal Method Streamlines Penstock Replacement Project, presented by Anna Pridmore, Structural Technologies
— Instream Bypass during Construction, presented by Joji Cherian, Black & Veatch
Details about each presentation and the speakers are below.
Dearborn Dam Diversion for the Revitalization of the Local Economy, presented by Tim Huffman, Duke Energy
The diversion is a requirement of the new Federal Energy Regulatory Commission (FERC) license for the Catawba Wateree Project to divert flow from three existing concrete dams in order to re-establish flow to two historical river channels removed in 1906 during the construction of Dearborn/Great Falls Hydro projects. While there is environmental importance in restoring the two river channels, this project is particularly important because the recreation flows will be tied to the future state park at Dearborn Island. This will help revitalize the Town of Great Falls with an influx of tourism for the local community.
The complexity of the project involves significant effort in the engineering and analysis phase to determine the most cost-effective solution to provide the required diversions in a manner safest for the general public while minimizing future risk to Duke Energy.
This project has been in engineering since 2014 with the first phase including geotechnical exploration of the Headworks and Canal dams. The final concept was developed at the end of 2016 and this was followed by extensive work to detail the concept and to conduct analytical and physical modeling to prove it out. Long lead permits have been evaluated and secured through the Army Corps of Engineers. Engineering was completed in June 2020 and submitted to the FERC. Construction is in progress as of today.
LADWP Haiwee Power Plant: Innovative CFRP Renewal Method Streamlines Penstock Replacement Project, presented by Anna Pridmore, Structural Technologies
The Haiwee Penstock Replacement Project, an ENR Best-of-the-Best awardee, is a powerful example of how combining technologies can deliver the best value for the Owner. This design-build penstock replacement project was streamlined by utilizing an innovative trenchless renewal method – carbon fiber-reinforced polymer (CFRP) – at penstock locations where excavation was not feasible. CFRP is a widely used pipeline repair and upgrade material that can be designed and installed at targeted segments, or for extended runs of penstocks and pipelines, to deliver a fully structural 50-year lifecycle extension.
The original Haiwee penstock was riveted steel pipe and built in the 1920s as part of the Los Angeles Aqueduct system. The penstock runs approximately 10,000 feet south from the dam to a powerhouse at the bottom of Haiwee Canyon. In 1968, the Rose Valley Los Angeles Aqueduct 2 (LAA-2) penstock was constructed, and a wye branch connection was made to the Haiwee penstock. Approximately 1,700 feet of the Haiwee penstock located upstream of the wye branch connection collapsed due to a vacuum event in 1984. The penstock was then pressure inflated, but the section affected by the vacuum event was extremely distorted and had many longitudinal creases and folds.
The Haiwee Project included replacement of the outdated and distorted steel penstock, along with CFRP lining of multiple segments that were to remain in service. This presentation will include detailed information on the selection of CFRP for these segments, design of the stand-alone system to be fully structural and vacuum-resistant, and an overview of the installation process and how it is completed with no excavation necessary. Attendees will benefit from learning about this state-of-the-art repair and renewal method used to deliver long-term lifecycle extension for existing penstocks.
Instream Bypass during Construction, presented by Joji Cherian, Black & Veatch
Preserving reservoir storage capacity and the normal operating range with ongoing sediment inflows is commonly one of dams’ greatest lifecycle challenges. While techniques like sediment sluicing and drawdown flushing can reduce reservoir sedimentation, mechanical removal of accumulated sediment by dredging or dry excavation is often necessary to maintain reservoir storage capacity and dam and reservoir facilities. Dry excavation is typically less costly per cubic yard, but usually requires extensive multi-year permitting and conveyance of instream flows through, or around, the reservoir to the downstream watercourse.
The special challenges of instream bypass during sediment removal, intake maintenance, and low-level outlet (LLO) rehabilitation or other work requiring a dewatered area are discussed in this presentation based on lessons learned from several recent California hydropower projects.