A CFD model to assess lower Granite Dam operations under stratified conditions

Abstract

Elevated water temperature has deleterious effects on cold-water fish. Lower Granite (LWG) is a run-of-the river dam in the Pacific Northwest, USA. LWG impounds a reservoir, with capacity of 5.7×10⁸ m³, that often become stratified. This paper presents a numerical model to assess LWG selective withdrawal operations to minimize thermal effects on fish. The model accounts for buoyancy forces, which are dominant at low river flowrates. The thermal model was validated against forebay temperature profiles and tailrace temperature on 3 July 2015. Twenty-six simulations were performed under different dam operations, stratification intensities and river flowrates. Numerical results indicate that the thermal stratification has a strong effect on the withdrawal region. Under stratified conditions, a high velocity layer at the intake elevation impacts the hydrodynamics and thermal capacity of the reservoir. According to the simulations, flow uniformly distributed across odd numbered powerhouse units is the best configuration to reduce downstream temperature.

KEYWORDS:

• Temperature
• reservoir
• CFD
• stratification
• dam operation
• selective withdrawal

Acknowledgements

The authors thank our colleagues from CH2M who provided files with updated bathymetry, location of the trash boom, geometry of the powerhouse intakes and removable spillway weir.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental data for this article can be accessed at https://doi.org/10.1080/23249676.2020.1831973

Additional information

Notes on contributors

Marcela Politano

Marcela Politano is an Associate Research Engineer at IIHR-Hydroscience& Engineering, University of Iowa, USA. She holds a PhD from Instituto Balseiro, Argentina. Her background includes modelling of multiphase flows, total dissolved gas, and heat and mass transfer. She has expertise in numerical modelling of the hydrodynamics and water quality in rivers, tailraces, reservoirs and fish passage facilities. She has over 17 years of experience developing and using numerical codes and algorithms for multiple applications, including modeling of environmental flows for the hydropower industry.

Ryan Laughery

Ryan Laughery is a registered professional engineer that serves as the Regional Fish Passage Technical Specialist within the Northwest Division Corps of Engineers, Walla Walla District.Obtained his bachelor's degree in civil engineering from Washington State University in 2002. From 2002 to current has primarily been involved in the design and development of hydraulic structures for Lower Columbia and Lower Snake River hydropower projects. For the past several years he has served as technical lead for the development of physical and numerical models for the evaluation of configurations and operations of hydropower projects to improve fish survival.