CaracterizaciĆ³n de la resuspensiĆ³n de sedimentos en el lago Llanquihue
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2022
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es
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Universidad AndrƩs Bello
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El presente documento corresponde a un estudio numĆ©rico de la resuspensiĆ³n de sedimentos en el lago Llanquihue, utilizando para ello el software STWAVE. Se recopilaron mediciones de campo con dos instrumentos ubicados dentro del lago, a unos 3 km de la costa sur del lago Llanquihue. El primer instrumento corresponde a una estaciĆ³n meteorolĆ³gica la cual registra direcciones y velocidades de viento, mientras que el segundo instrumento es un medidor de onda direccional (AWAC)que provee informaciĆ³n de alturas y periodos significativos de olas. Una tercera fuente de informaciĆ³n se obtuvo de la DirecciĆ³n MeteorolĆ³gica de Chile (DMC) con datos de direcciones y velocidades de vientos, valores registrados en tierra, a unos 250 m de la ribera sur del lago. Las velocidades y direcciones de vientos entregadas por el primer instrumento se utilizaron como variables de entrada en STWAVE para obtener alturas y periodos significativos de olas. Estas dos propiedades de las olas fueron comparadas con los registros provenientes del segundo instrumento (AWAC). Se llevaron a cabo simulaciones numĆ©ricas para caracterizar las olas en el intervalo de tiempo comprendido entre el 21 de marzo y el 7 de abril de 2022. Al ser STWAVE un modelo de estado estacionario, reprodujo bastante bien las caracterĆsticas de las olas cuando los vientos eran mĆ”s bien constantes. Sin embargo, el modelo no fue capaz de capturar los atributos de las olas bajo cambios abruptos de velocidad o direcciĆ³n de vientos. Los datos de velocidades y direcciones del primer y tercer instrumento fueron comparados para verificar la validez de la informaciĆ³n de la DMC, y asĆ determinar si las estadĆsticas de las DMC podrĆan ayudar a estudiar olas de vientos en periodos de tiempo previos a la instalaciĆ³n dela estaciĆ³n meteorolĆ³gica. Se encontrĆ³ que las direcciones de vientos de la estaciĆ³n meteorolĆ³gica y de la DMC seguĆan un patrĆ³n similar. Respecto a las velocidades, los registros de la DMC, eran bastante mĆ”s pequeƱos que los valores obtenidos con la estaciĆ³n meteorolĆ³gica, aunque ambos seguĆan un patrĆ³n proporcional. Se obtuvo un factor igual a 2,69, con el cual se podrĆan amplificar los datos de la DMC para modelar los vientos en el lago Llanquihue, en periodos anteriores a la instalaciĆ³n de la estaciĆ³n meteorolĆ³gica. Por medio del software STWAVE se ingresaron los datos de velocidades y direcciones de viento para modelar las alturas y periodos de olas y el esfuerzo de corte de fondo en un intervalo que va desde el 14 de octubre de 2021 hasta el 16 de marzo de 2022. Las tres zonas de interĆ©s del lago Llanquihue que fueron analizadas corresponden a los sectores de Puerto Octay, Las Cascadas y Llanquihue, respectivamente. La resuspensiĆ³n ocurrirĆa una vez que el esfuerzo de corte de fondo supera el esfuerzo de corte crĆtico, el cual se estimĆ³ con la ecuaciĆ³n de Shields obteniendo un valor de 0,21 Pa. Los resultados numĆ©ricos indican que, para el sector de Las Cascadas, el 10,7%de los vientos tendrĆa asociado resuspensiĆ³n de partĆculas, mientras que para Puerto Octay la resuspensiĆ³n de partĆculas ocurrirĆa para un 7,2%de los vientos. Para el sector de Llanquihue, se obtuvo que tan sĆ³lo el 1% de los vientos logra sobrepasar el esfuerzo crĆtico, indicaciĆ³n de que la resuspensiĆ³n de partĆculas en ese sector es poco frecuente.
The present documentcorresponds to a numerical study of sediment resuspension in lake Llanquihue, using STWAVE software. Field measurements were collected with two instruments located within the lake, about 3 km from the southern shore of lake Llanquihue. The first instrument corresponds to a meteorological station which records wind directions and velocities, while the second instrument is a directional wave gauge (AWAC) that provides information on wave heights and significant wave periods. A third source of information wasobtained from the Chilean Meteorological Direction (DMC) with data on wind directions and velocities, values recorded on land, about 250 m from the southern shore of the lake. The wind velocities and directions provided by the first instrument were used as input variables in STWAVE to obtain significant wave heights and periods. These two wave properties were compared with the records from the second instrument (AWAC). Numerical simulations were carried out to characterize the waves in the time interval between March21 to April7 2022. Since STWAVE isa steady-state model, it was able to reproduce the wave characteristics when the winds were in steadystate. However, the model was not able to capture wave attributes under abrupt changes in wind velocity or direction.The velocity and direction data from the first and third instruments were compared to verify the validity of the DMC data, and to determine if the DMC statistics could help to study wind waves in time periods prior to theinstallationof the meteorological station. It was found that the wind directions from the meteorological station and the DMC followed a similar pattern. Regarding velocities, the DMC records were significantly smaller than the values obtained with the meteorologicalstation, although both followed a proportional pattern. A factor equal to 2.69 was obtained, with which the DMC data could be amplified to model the winds in lake Llanquihue in periods prior to the installation of the meteorological station.Using the STWAVE software, wind velocity and direction data were entered to model wave heights, wave periods and bottom shear stress in a time interval from October 14,2021, to March 16,2022. Three areas in lake Llanquihuewere analyzedcorrespondingto the villages of Puerto Octay, Las Cascadas and Llanquihue, respectively. Resuspension would happen once the bottom shear stress exceeds the critical shear stress, which was estimated with the Shields equation obtaining a value of 0.21 Pa. The numerical results indicatethat, 10.7% of the winds in Las Cascadas areassociated with particle resuspension;whereas inPuerto Octay particle resuspension would happen for 7.2% of the winds. For the Llanquihue sector, only 1% of the winds exceeded the critical stress, indicating that particle resuspension in this regionis infrequent.The results also show that the wind velocities contributingto sediment resuspension are those higher than 5.5 m/s. The preferred directions for particle resuspension in the lake are in the range of values from 42Ā° to 310Ā°. Finally, the numerical results indicate that the wave associated with resuspension are at least 0.38 min height,with minimum periods of 3.8 s.
The present documentcorresponds to a numerical study of sediment resuspension in lake Llanquihue, using STWAVE software. Field measurements were collected with two instruments located within the lake, about 3 km from the southern shore of lake Llanquihue. The first instrument corresponds to a meteorological station which records wind directions and velocities, while the second instrument is a directional wave gauge (AWAC) that provides information on wave heights and significant wave periods. A third source of information wasobtained from the Chilean Meteorological Direction (DMC) with data on wind directions and velocities, values recorded on land, about 250 m from the southern shore of the lake. The wind velocities and directions provided by the first instrument were used as input variables in STWAVE to obtain significant wave heights and periods. These two wave properties were compared with the records from the second instrument (AWAC). Numerical simulations were carried out to characterize the waves in the time interval between March21 to April7 2022. Since STWAVE isa steady-state model, it was able to reproduce the wave characteristics when the winds were in steadystate. However, the model was not able to capture wave attributes under abrupt changes in wind velocity or direction.The velocity and direction data from the first and third instruments were compared to verify the validity of the DMC data, and to determine if the DMC statistics could help to study wind waves in time periods prior to theinstallationof the meteorological station. It was found that the wind directions from the meteorological station and the DMC followed a similar pattern. Regarding velocities, the DMC records were significantly smaller than the values obtained with the meteorologicalstation, although both followed a proportional pattern. A factor equal to 2.69 was obtained, with which the DMC data could be amplified to model the winds in lake Llanquihue in periods prior to the installation of the meteorological station.Using the STWAVE software, wind velocity and direction data were entered to model wave heights, wave periods and bottom shear stress in a time interval from October 14,2021, to March 16,2022. Three areas in lake Llanquihuewere analyzedcorrespondingto the villages of Puerto Octay, Las Cascadas and Llanquihue, respectively. Resuspension would happen once the bottom shear stress exceeds the critical shear stress, which was estimated with the Shields equation obtaining a value of 0.21 Pa. The numerical results indicatethat, 10.7% of the winds in Las Cascadas areassociated with particle resuspension;whereas inPuerto Octay particle resuspension would happen for 7.2% of the winds. For the Llanquihue sector, only 1% of the winds exceeded the critical stress, indicating that particle resuspension in this regionis infrequent.The results also show that the wind velocities contributingto sediment resuspension are those higher than 5.5 m/s. The preferred directions for particle resuspension in the lake are in the range of values from 42Ā° to 310Ā°. Finally, the numerical results indicate that the wave associated with resuspension are at least 0.38 min height,with minimum periods of 3.8 s.
Notas
Trabajo de TĆtulo (Ingeniero Civil)
Palabras clave
Sedimentos (GeologĆa), Investigaciones, Lago Llanquihue