Saccarappa Falls Nature-Like Fishway Modeling and Design
As part of project/dam surrender and removal efforts at the Saccarappa Hydroelectric Project (Saccarappa), Alden provided S. D. Warren Company d/b/a Sappi North America (Sappi) with the final design and fish passage analysis for nature-like fishways in the upper channels at Saccarappa Falls. The final design involves reshaping the existing bedrock channel into a form that is more conducive to fish passage while mimicking the morphology of a natural bedrock channel. Alden provided agency consultation while developing the design and will ultimately provide construction support. The proposed design complements a proposed double Denil fishway over the lower portion Saccarappa Falls designed in partnership with Acheron Engineering.
Alden conducted a site visit and reviewed existing geotechnical, hydrologic, site constraints, and other site data prior to developing the final design for the nature-like fishways. The final design was achieved by way of iteration between a 3D CAD representation of the proposed bathymetric surface and a 3D computational fluid dynamics (CFD) model. Expected small-scale roughness of the channel bed was incorporated into the CAD surface through a novel texturizing technique based on a high resolution laser scan of the existing bedrock surface. The CFD model was used to simulate proposed conditions at four discrete design flow rates. Hydraulic data output by the CFD model (e.g., depth and velocity) informed subsequent improvements of the proposed surface in CAD. Sappi and agency review and feedback was provided at 30%, 60%, 90%, and final drafts of the design. Fish passage effectiveness of the final design was analyzed by Alden biologists and engineers using USFWS’s SMath models developed for assessing velocity impediments by estimating fatigue, survivorship, and work. Alden also provided engineering consultation and inspections to support project construction.
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An existing roof vent arrangement was allowing rainwater to enter the Pot Room. Alden supported efforts to develop a roof vent geometry to eliminate the intrusion of rain water. The purpose of the CFD study was to ensure that the roof vent modification did not increase pot room temperature levels beyond specified limits for workers in the plant.
To evaluate the existing and proposed Pot Room arrangements, thermal and fluid flow profiles in the immediate vicinity of the pots were determined based on air flows through the plant floor and wall mounted vents. The detailed CFD model was developed from plant drawings to include all major basement, pot room and roof venting geometries. The surrounding ambient environment was included with quiescent atmospheric conditions and average ambient temperature. Thermal losses form the pots to the pot room air and from the pot room to the environment were included in the analysis. The results of the CFD modeling showed that the proposed modification to the roof venting arrangement was acceptable and would not increase the temperature in the worker-occupied spaces by more than 2 degrees F.
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Civil Infrastructure
Smelter Pot Room Roof Ventilation System
Read how a CFD study ensured that a roof vent modification did not increase pot room temperature levels beyond safe levels
Plant McDonough, owned and operated by Southern Company, has experienced excessive siltation at the makeup water intake. The intake uses cylindrical wedgewire screening within an intake originally designed for much larger, once-through cooling water flows. Flow modeling was performed to provide a viable passive solution to reducing the sediment accumulation at the intake. To model the geometric details of the system accurately, a field survey was performed prior to the flow modeling efforts. The flow study included both CFD modeling and scale physical modeling.
For this investigation, Alden developed a 1:20 scale live bed physical model. This model was extremely well tuned to reproduce the behavior of bed load sediment. Even with the very fine crushed walnut shell particles, however, it was challenging to reproduce the behavior of suspended load. The use of a high fidelity CFD model, therefore, proved extremely useful for this project, in that suspended load is generally very accurately tracked with CFD models, which are not well validated for bed load simulation. By using the two together, the two extremes of sediment transport are captured, and developing a solution that covers this range has a high likelihood of success.
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Civil Infrastructure | Hydrology Hydraulics and Fluids
Plant McDonough Intake Modification
CFD and physical model study to assist in the evaluation of a solution to reduce the sediment accumulation.