Engineering Design

Alden’s engineers and biologists conducted extensive CFD modeling and biological evaluations to help the Holyoke Gas & Electric Department (HG&E) develop an effective downstream passage solution for endangered shortnose sturgeon at the Hadley Falls Station on the Connecticut River. The results of these studies produced engineering and hydraulic design criteria for an exclusion rack and downstream bypass.  The CFD modeling examined flow conditions for several alternative rack designs, as well as the bypass discharge to ensure safe downstream passage of fish and minimal interference of upstream migrants trying to locate the entrance to a fish lift.  Alden also developed conceptual designs and preliminary cost estimates for the preferred alternatives and conducted biological testing in a large laboratory flume with various configurations of bar racks and bypass entrance designs with juvenile shortnose sturgeon.  Agency acceptance of the final design was obtained by HG&E after Alden completed a desktop analysis of total downstream passage survival using the laboratory bypass efficiency data and theoretical estimates of turbine survival.

On startup, the air quality control system (AQCS) at Deerhaven Generating Station was not able to meet its guarantees for SO capture and reagent usage.  Also, the material handling systems were not operating properly, forcing the units to shutdown.  To identify and solve these problems, Alden built three scaled physical flow models to simulate the complex gas-solids interactions in each component of the Turbosorp system.  The design solutions that were found during model testing were implemented in the field with great success.  As a result, the Deerhaven AQCS was able to meet all the performance guarantees within its contract, and has since been host to a dry scrubbers users group as an example of how these systems should operate.

Alden performed design studies and field startup testingof PSE’s Upper and Lower Baker Dams Floating Surface Collector (FSC) systems. The FSC concept is well-suited for downstream fish passage in deep reservoirs with large variations in water level. Guide nets stretching from the water surface to reservoir bottom funnel migrant fish to the FSC, which provides attraction flow through high-flow submersible pumps. As flow is drawn into the FSC, dewatering screens funnel the fish to holding pens for transportation around the dam.

ALDEN conducted a 3-D Computational Fluid Dynamics (CFD) model study of the reservoir hydraulics, guide nets, and FSC to optimize the location, orientation, and discharge of the Upper Baker FSC. Alden then developed a physical model of a preliminary version of the FSC dewatering screens and pumps to improve pump performance and screen channel hydraulics. After construction, ALDEN provided comprehensive field startup testing of the hydraulic performance of the FSC, balanced the dewatering screens, and provided critical operations information to PSE.

During periods of spill, Cabinet Gorge Dam was generating total dissolved gas (TDG) concentrations in excess of water quality standards. Through a series of feasibility studies, design evaluations, retrofits and/or modifications, Alden engineers worked to help Avista Corporation meet their FERC licensing requirements for the hydroelectric project located in Idaho on the Clark Fork River.

In early studies, the Alden team performed a 1:50 scale physical hydraulic model study to investigate re-commissioning of diversion tunnels used during construction of the project as bypass tunnels to pass spill flows at lower TDG levels than are generated during spillway operation. Studies revealed that the reduction in TDG afforded by the bypass tunnels was less than originally expected.

Additional feasibility studies were conducted to evaluate two alternatives for TDG reduction. One idea was the creation of off-stream “gas stripping” channels downstream of the dam, which ultimately proved to be fish passage un-friendly. Ultimately, modification of the existing spillway crest was found to be most feasible.

Full hydraulic and structural engineering services from feasibility through design and construction have been completed for the modifications to five of the eight spill bays in order to reduce TDG. Construction plans and specifications were prepared, and documentation for submittal to FERC was produced. Alden also provided construction technical support.

In addition to the work done to reduce TDG, Alden engineers also performed several structural projects for Cabinet Gorge Dam:

• A Stoplog Deployment Crane was designed and fabrication-level drawings developed for the deployment crane system for lifting 10-ton stoplogs. The steel frame was designed to allow assembly and disassembly at each of the eight spill bays. Performance specifications for the 15-ton top running hoist were also provided
• The FERC Supporting Technical Information (STI) Documents were reviewed and updated for Section 6—Hydrology/Hydraulics and Section— Stability/Stress Analysis.

In further compliance measures, the development of a fish trap design in the project tailrace for the expedited transmissivity of ESA listed bull trout past the project was supported. This effort also used the 1:50 scale model for initial site selection studies. Alden also provided a fisheries and hydraulic engineering representative on a “panel of experts” who advised on the best approach for trap site selection and design. Computational Fluid Dynamics (CFD) modeling of the project tailrace was performed to confirm satisfactory location and performance of the selected trap design. The CFD model developed for the fish trap studies also confirmed compatibility of the TDG mitigation measures with the fish trap operations and to guide future development of the TDG mitigation.

Dive in Deeper

Read more about Total Dissolved Gas at High Head Dams in this three-part blog series.

1. Improving Water Quality: Total Dissolved Gas (TDG) Production at High Head Dams [Part 1]
2. Air Supply Ramps and Cavitation: Total Dissolved Gas (TDG) Production at High Head Dams [Part 2]
3. Energy Dissipating Devices: Total Dissolved Gas (TDG) Production at High Head Dams [Part 3]