Caracterización de la distribución de temperaturas en el lago Llanquihue por medio del modelo hidrodinámico SI3D
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2023
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es
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Universidad Andrés Bello
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Licencia CC
Resumen
El presente trabajo incluye una caracterización de la distribución de temperaturas en el lago
Llanquihue, utilizando para ello un modelo numérico tridimensional semi implícito denominado
SI3D, el cual ha sido validado en estuarios, lagos y costas de Estados Unidos. La importancia de
conocer la distribución temporal y espacial de la temperatura en el lago Llanquihue radica en el
hecho que los procesos de transporte y mezcla de nutrientes y químicos que allí ocurren
dependen justamente de la distribución de temperatura al interior del lago, en particular, de la
estratificación por gradientes de temperatura impuesta por la radiación solar.
El modelo numérico se implementó para tres periodos de tiempo en diferentes meses con un
paso de tiempo de 60 minutos. El primer periodo va desde el 18 de octubre al 15 de noviembre
de 2021; el segundo periodo va desde el 12 de diciembre de 2021 hasta el 06 de marzo de 2022
mientras que el tercer periodo corresponde al intervalo del 04 al 24 de abril de 2022. Para dichos
periodos se contó con información meteorológica que incluye la velocidad y la dirección del viento
en el lago, así como también la temperatura, presión atmosférica y humedad relativa del aire. El
primer periodo fue seleccionado de modo de iniciar la simulación con el lago relativamente
mezclado en octubre, para terminar con el lago estratificado durante marzo, condición que se
mantiene durante abril debido a las altas temperaturas del verano.
Para caracterizar el intercambio de calor que ocurre en la superficie del lago Llanquihue entre el
agua y la atmósfera, se utilizó un balance de calor que incluyó el efecto de la radiación solar de
onda corta, la radiación atmosférica de onda larga y la evaporación.
Antes de llevar a cabo las simulaciones que incluyen las épocas de verano y de otoño, se
realizaron tres simulaciones exclusivamente para el periodo de octubre a noviembre utilizando 3
mallados con celdas de 160 m, 200 m y 260 m en el plano horizontal, respectivamente. En la
vertical se utilizó una resolución de 2 m para los tres casos. Dado que la distribución de
temperaturas obtenida en cada uno de estos tres casos fue similar, se consideró que la malla
más gruesa de 260 m era suficiente para correr durante los meses seleccionados.
De los resultados numéricos se observa que, para los meses de noviembre, diciembre y enero,
la termoclina, la cual separa la región del epilimnion con la del hipolimnion, se ubica a una
profundidad media de entre 30 a 50 metros en sectores relativamente cercanos a la orilla del
lago, donde la profundidad del lago es de unos 85 metros. A unos sesenta metros de la orilla y
hacia el interior del lago, donde la profundidad alcanza unos 135 metros, la termoclina se localiza
entre los 20 y 53 metros de profundidad, mientras que en zonas más centrales del lago se
encuentra a los 30 y 60 metros. En este último caso, la profundidad del lago llega hasta 317
metros.
This work is a characterization of the temperature distribution at Lake Llanquihue in the south of Chile, utilizing to that end, a semi-implicit three-dimensional numerical model called SI3D, which has been validated in the study of estuaries, lakes, and coasts of the United States. The importance of knowing the temporal and spatial temperature distribution in Lake Llanquihue relies on the fact that processes of transport and mixing of nutrients and chemicals that take place in that location depend directly on the temperature distribution inside the lake; in particular, they depend on the stratification by temperature gradients imposed by solar radiation. The numerical model was implemented for three periods of time in different months with time steps of 60 minutes. The first period goes from October 18th , 2021 until November 15th , 2021; the second period was between December 12th , 2021 and March 6th , 2022 while the third period corresponds to the time interval April 4th - April 24th , 2022. For such periods we had meteorological information including wind speed and wind direction in the lake, as well as temperature, atmospheric pressure, and air relative humidity. The first period was selected to start the simulation with the lake relatively mixed in October, to finish with the stratified lake during March, condition that is maintained throughout April due to high summer temperatures. To characterize the heat exchange that occurs in the lake surface between the water and the atmosphere, a heat balance was used which included the effect of the short-wave solar radiation, long wave atmospheric radiation, and evaporation. Before running the simulations that include summer and autumn seasons, three simulations were carried out in the October-November period, using three meshes with cells of 160 m, 200 m, and 260 m in the horizontal plane respectively. In the vertical axis a resolution of 2 m was used for the three cases. Since the temperature distribution observed for the three case was similar, it was considered that the coarsest mesh of 260 m was good enough to run the simulation during the selected months. From the numerical results we observed that for the months of November, December and January, the thermocline that separates the epilimnion and the hypolimnion is located at an average depth of between 35 and 55 meters in places relatively close to the lakeshore, where the depth is approximately of 85 meters. About sixty meters from the shore into the lake, where the depth reaches about 135 meters, the thermocline is located at an average depth of between 50 and 75 meters, whereas close to the center of the lake it is located between 30 and 60 meters deep. In the last case, the depth of Lake Llanquihue reaches 317 meters.
This work is a characterization of the temperature distribution at Lake Llanquihue in the south of Chile, utilizing to that end, a semi-implicit three-dimensional numerical model called SI3D, which has been validated in the study of estuaries, lakes, and coasts of the United States. The importance of knowing the temporal and spatial temperature distribution in Lake Llanquihue relies on the fact that processes of transport and mixing of nutrients and chemicals that take place in that location depend directly on the temperature distribution inside the lake; in particular, they depend on the stratification by temperature gradients imposed by solar radiation. The numerical model was implemented for three periods of time in different months with time steps of 60 minutes. The first period goes from October 18th , 2021 until November 15th , 2021; the second period was between December 12th , 2021 and March 6th , 2022 while the third period corresponds to the time interval April 4th - April 24th , 2022. For such periods we had meteorological information including wind speed and wind direction in the lake, as well as temperature, atmospheric pressure, and air relative humidity. The first period was selected to start the simulation with the lake relatively mixed in October, to finish with the stratified lake during March, condition that is maintained throughout April due to high summer temperatures. To characterize the heat exchange that occurs in the lake surface between the water and the atmosphere, a heat balance was used which included the effect of the short-wave solar radiation, long wave atmospheric radiation, and evaporation. Before running the simulations that include summer and autumn seasons, three simulations were carried out in the October-November period, using three meshes with cells of 160 m, 200 m, and 260 m in the horizontal plane respectively. In the vertical axis a resolution of 2 m was used for the three cases. Since the temperature distribution observed for the three case was similar, it was considered that the coarsest mesh of 260 m was good enough to run the simulation during the selected months. From the numerical results we observed that for the months of November, December and January, the thermocline that separates the epilimnion and the hypolimnion is located at an average depth of between 35 and 55 meters in places relatively close to the lakeshore, where the depth is approximately of 85 meters. About sixty meters from the shore into the lake, where the depth reaches about 135 meters, the thermocline is located at an average depth of between 50 and 75 meters, whereas close to the center of the lake it is located between 30 and 60 meters deep. In the last case, the depth of Lake Llanquihue reaches 317 meters.
Notas
Memoria (Ingeniero Civil)
Palabras clave
Temperatura, Modelos Matemáticos, Hidrodinámica, Chile, Lago Llanquihue