Poudre River Drop Structure Replacement
Alden was retained by the Northern Water Conservancy District (Northern Water) for the Hansen Supply Canal Poudre River Drop Structure Replacement Project. Alden was the prime consultant for the Project and provided complete structural and hydraulic engineering services, including hydraulic modeling for the design of the replacement drop structure and overall site improvements. The new structure included a stepped spillway, stilling basin, and retaining walls.
Alden performed Computational Fluid Dynamics (CFD) modeling of the existing structure and the proposed structure. The new structure is designed for a peak discharge of 1,500 cfs. Alden also performed 3D finite element modeling for the structural design. Alden collaborated with Northern Water staff to identify maintenance needs and preferences for the new structure. The stilling basin includes an access bridge, jib cranes, and stoplogs to isolate the structure for future maintenance and inspections. The existing site featured extremely steep slopes at 1V:1H with poor surface drainage. The final grading established stable slopes and improved surface drainage to keep water away from the new structure.
Details of the project included:
- Concrete structure demolition, removal, and repair
- New concrete stepped spillway, concrete stilling basin, and concrete retaining walls
- Foot bridge with access stairs
- Subsurface drain system and surface drainage improvements
- Temporary construction cofferdam and dewatering
- Site grading and access road
- Trapezoidal channel restoration and riprap sizing
The project also required coordination regarding the environmental impacts to the Preble's mouse habitat and an adjacent eagle's nest. Design was completed in July 2019. Construction was completed in March 2020 with the first water flowing through the structure on April 1, 2020.
2020 H2O Project Award
The Poudre River Drop Structure Project was the recipient of The Colorado Contractors Association's 4th Annual H2O Awards. The Project won in the category of Open Concrete Flow Structures under $6 million.
The overall Project Team included:
- Design Team – Alden and geotechnical subconsultant, Lithos Engineering
- Client – Northern Water
- Contractor - Zak Dirt
Capability
Civil InfrastructureServices
Structural DesignHydraulic Structure Engineering Design
Related Projects
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.