Mixed‐Layer Hydrothermal Reservoir Model

Abstract

This paper describes a new epilimnetic mixing formulation for two‐dimensional reservoir models. This formulation incorporates a wind‐mixing algorithm based on a mixed‐layer theory developed previously for the upper ocean. Given an input of relevant meteorological parameters, the algorithm computes a heat‐flux source term and a mixed‐layer thickness using a mechanical energy balance approach. The computed heat‐flux profile is used as a source term to the two‐dimensional (longitudinal‐vertical) transport equation for temperature. This transport equation is coupled with a corresponding laterally averaged hydrodynamic model developed previously. The combined formulation is solved using a semi‐implicit, central‐differencing scheme. Overall, this modeling approach requires minimal parameterization of wind‐mixing processes. The combined model was adapted to an elongated (10.6‐km‐long, 0.8‐km‐wide) reservoir system, the Wanaque Reservoir, New Jersey. Wanaque Reservoir data were collected semimonthly during a calibration period (August 1983 through November 1983) and a year‐long verification period (November 1985 through November 1986). The model adaptation successfully reproduced salient features of the vertical structure, including a warm, well‐mixed epilimnion, a relatively thin and abrupt metalimnion, and a cold, nearly isothermal hypolimnion.