Alden designed, constructed and tested a ~1:7 Froude scale physical hydraulic model to evaluate the hydraulic performance of the Tarrant Regional Water District Integrated Pipeline Project Joint Cedar Creek Pump Station in accordance with the Hydraulic Institute Standards (HIS).
The pump station consists of six 66 inch tee screens and 7 vertical pumps, each with a rated capacity of 27 to 49.4 million gallons per day (mgd). The maximum total flow for the pump station is 277 mgd, which corresponds to all seven pumps operating. The design requires each of the seven pumps to be placed into a depressed pump can located in the wet well floor.
Baseline tests were conducted to evaluate the pump hydraulic performance in terms of vortex formation, swirl at the pump impeller, and the velocity distribution approaching the pump impeller. The tests were conducted at two water levels; the normal water surface elevation and the maximum pool elevation. The test results identified the presence of unacceptable dye cAre subsurface vortices emanating from the can walls.
Two design modifications were developed and evaluated each of which met the HIS acceptance criteria. The first design modification included can-wall roughness vanes at 10 degree intervals to dissipate the unacceptable vortices. The second design modification included an inverted torus dish installed on the can floor (under the pump suction) as well as shortening the existing vertical can vanes. The dish modification was selected as the preferred modification since it demonstrated the most streamlined flow entering the pump.
- Baseline design was an innovative combination of a traditional wet well configuration with recessed pump suction cans to minimize overall excavation costs.
- Two design modifications were provided to the client that satisfied the HIS acceptance criteria and the most cost-effective design was selected.