Tracking thermal structure evolution: An objective practice in a stratified reservoir based on high-frequency measurements

Abstract

Study region: Daheiting Reservoir, Tangshan, China Study focus: Based on the recently sprouted high-frequency measurement of water temperature, an objective identification method for thermal structures is proposed, and the optimal thermal threshold of the Daheiting Reservoir is further determined. Then, this optimal threshold is adopted to identify the temporal and spatial evolutions of thermal structures combined with routine measurements. New hydrological insights for the region: The optimal thermal threshold of the Daheiting Reservoir is determined to be 1.5 °C·m−1. The identification result suggests that the thermal stratification lasted from early May to late October and reached its peak in late July, following the rule of three stages. The temperature differences between air and each stratified layer are decisive for the development direction of thermal structures, and thermocline thickness and average strength could transform into each other during a period ranging from a week to half a month. Moreover, the thermal structure is greatly influenced by the cascade reservoir operations. The cold water discharged from the upper reservoir could significantly alter the thermal structures in the tail region of the study reservoir, where abnormal thermoclines with extraordinary strength occur. In contrast, the water supply operation gently weakens the thermal stratification in the head region of the study reservoir by triggering continuous advection near the outlet.

Keywords

• Thermal structure
• High-frequency measurement
• Objective identification
• Thermocline transformation
• Cascade reservoir