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Realization of the Holtwood Expansion Project

Project TimelinePlanning Phase

August – December 2004-Brainstorm Session-Discerning Key Factors-Turbine Size/Type Selection-Feasibility Study

Concept Refinement

February – December 2005-Agency Outreach-Detailed Hydraulic Analysis-Value Engineering-Cost Refinement

Final Design and Relicensing

2006 - 2009-Ongoing Agency Negotiationsand StudiesMarch 2006 – May 2008-Civil/Mechanical/Structural DesignAugust 2010 – June 2011-Electrical Design

License/Permits

-401 Water Quality CertificationIssued June 2009-FERC License Amendment Issued October 2009-More than 20 Permits and Approvals needed for Construction

General Construction Bidding

-June – October 2008-December 2008 Project Cancelled-Rebid June to September 2009

Construction

October 2009 – February 2013

Past, Present & FutureEnvironmental and Public Concerns•Fish Passage EnhancementsThe existing fish elevator is modified to provide an additional800 cfs attraction flow for the three entrances. The tailrace crowder mechanism travel is extended to mitigate objectionable shadows, and the spillway side Entrance C gate guides modified to minimize future damage.

•Bald EaglesThere are two active bald eagle nests, three osprey nests and a peregrine falcon nest located in the Holtwood project area. An eagle observation tower equipped with real time remote video observation and audio recording equipment was constructed to observe eagle nesting behavior during blasting operations. Blasting near the nest was scheduled to avoid sensitive egg laying and nesting periods.

•Endangered Plant SpeciesFour threatened and endangered plant species at the site, including American Holly trees. Mitigation included designing the site construction and permanent site plans to avoid or minimize disturbances, and providing an American holly tree nursery.

•Whitewater RecreationThe existing Piney Channel and river area below the dam is a popular whitewater recreational feature during various river flow levels. Consequently, the Piney Channel excavation modifications are designed to enhance the natural features. Changes in spill conditions due to the new powerstation are being addressed by incorporating two whitewater boating features into the lower end of the Piney Channel excavation combined with future scheduled water releases.

Authors:N. Christian Porse, P.E. MBA, Site Supervisor, Peaking Power, PPL Generation, USA

Thomas L. Kahl, P.E., Senior Engineer, Kleinschmidt, USA

Project Location: Lower Susquehanna RiverHoltwood, PA

Key Project DecisionsEconomic Tailrace Excavation - The long 6,700 foot long tailrace was hydraulically undersized and resulted in a 10.5 ft rise from zero to full load operation. Unlike previous studies that projected straight tailrace excavation channels, particularly at the lower portion of the existing tailrace channel, we implemented tailrace excavations within the existing serpentine natural channels. The advantages of this approach were that it reduces the total quantity and cost of excavated rock, is more environmentally sensitive, fish friendly, and is more aesthetically attractive.

•Fish Passage Improvements Incorporated Into Design - The new powerstation was located so that it will provide additional attraction flow to the existing fish elevator to improve its performance without the need to construct an additional fish elevator. The new tailrace excavation will provide velocities needed to accommodate shad and river herring upstream swimming strengths. The 2004 lower tailrace downstream of the highway bridge showed extended reaches of high water velocities up to 11 feet per second (fps), that produced a velocity barrier to upstream fish passage. The new excavations will provide an upstream fish passage shelf along the west shore of the Main Tailrace that is approximately 12 ft wide, with a maximum velocity of 6 fps, and nominal 3 ft depth.

•Innovative Minimum Flow Discharge – Agency concerns for minimum flows in the Piney Channel bypass reach were addressed by an innovative draft tube extension of the existing Unit No. 1. The Piney Channel excavation was also designed to provide velocities suitable for an alternative fish passage zone to the spillway side entrance of the existing fish elevator.

•New Station Location – Locating the new station at the downstream end of the existing forebay (Option 1) provided the highest revenue to tailrace excavation ratio which was a significant portion of the redevelopment cost. Additional advantages of this location included:

•Convenient and less costly new station access requiring the least site civil modifications.•Presents the least exposure to the Susquehanna River’s severe ice and debris conditions and offers the protection of the forebay skimmer wall.•Does not reduce the effective spillway discharge length that would require additional measures to compensate for any decrease in spillway flood discharge capacity.•Reuse of the former steam station transmission line right-of-way.•Continued long term operation of the existing station, and minimal interference with existing station operation during new power station construction.

•Turbine Selection - The lowest capital cost to provide the anticipated large increases in hydraulic capacity of 15,000 to 60,000 cfs for any Holtwood redevelopment would be to use the smallest number of the largest practical machines. Based on this station’s 54 ft. head the largest practical turbines at Holtwood were 7 to 9 meter diameter runners with approximately 15,000 cfs hydraulic discharges, resulting in 57-62 MW per unit depending on the design head. These are the largest practical turbine size that could be cost effectively manufactured for this site’s head was 15,000 cfs. The new large turbines operate at a slow 85 rpm resulting in very high (95% to 98%) survival rate for entrained fish. The Holtwood turbines also incorporate fish friendly features such as a cylindrical runner hub, semi-cylindrical discharge ring to minimize blade gap, and limited wicket gate protrusion inside the lower stay ring to prevent fish harmful turbulence.

Project History and BackgroundPPL Generation’s Holtwood Hydroelectric station on the lower Susquehanna River in south central Pennsylvania began generating electricity in October 1910. After the last of the existing 10 turbines were placed in service in 1924 the station had a generating capacity of approximately 108 MW. Although this was one of the largest North American hydroelectric stations at that time, river flows exceed the station’s 31,000 cfs hydraulic capacity 40% of the time. Since the early 1930’s numerous schemes for further site development were studied but never implemented. Other significant site conditions include:

New Site PlanDesign-Excavation -RR Overpass Bridge -Innovative Unit 1 -Powerstation-Draft Tube Extension -Site Layout-Skimmer Wall -Inflatable Flashboards-ADA Fishing Access

Excavation1.5 Million cu yds

Holtwood

Harrisburg

Philadelphia

•An adjacent 110 MW anthracite coal fired steam electric generating station that operated from 1925 to 1999 before being decommissioned and demolished.

• Increasing concern for fish passage since the 1980’s resulted in the construction of an upstream fish elevator in the tailrace that was commissioned in 1997.

•The 1980 issued FERC license was set to expire in 2014.

ConstructionPowerstation-57,000 cubic yards of concrete-5.4 million pounds of rebar-2,500 rock anchors & dowels

New 125 MW Powerstation

Innovative Unit 1 Draft Tube Extension