Hydraulic Management Drives Heat Budgets and Temperature Trends in a Mediterranean Reservoir

Abstract

By contrast to the more regular and predictable temperate lakes, heat budgets and temperature dynamics in Mediterranean reservoirs are characterized by a marked interannual variability. In the present paper, the heat content, annual Birgean heat budget (ABHB), and thermal structure of Sau Reservoir were examined during a period of hypolimnetic withdrawal between 1980 and 1985, and during a period of withdrawal at intermediate depths between 1996 and 2003. The two study periods were also characterized by a wide range of stored water volume fluctuations. Results were used to develop and validate an empirical model to predict annual and monthly heat dynamics statistics and mixed layer depth as a function of hydraulic management parameters such as water volume and selective withdrawal depth. During the hypolimnetic withdrawal period elevated ABHB and deep mixed layer depths were recorded in the reservoir, which behaved as a heat trap. By contrast, intermediate depth withdrawal promoted a shallower and more stable thermocline, thus increasing the cold hypolimnetic water volume and decreasing heat content and ABHB. The study reveals that hydraulic management constitutes the main driver of the heat and thermal dynamics in reservoirs with multiple withdrawal outlets. By contrast with the increasing temperature trends recorded in many natural lakes, the hydraulic management in Sau Reservoir induced a progressive reduction in water temperature and heat content in the system, thus partially counteracting the possible deleterious effects of global warming. Our intensive study in a single, highly-dynamic ecosystem constitutes a new approximation to the study of thermal structure and heat dynamics in water bodies.

Simulation of the hydrodynamic behaviour of a Mediterranean reservoir under different climate change and management scenarios

“…In reservoirs, climatic warming trends can be modified by hydraulic N o n -c o m m e r c i a l u s e o n l y management (Moreno-Ostos et al, 2008;Kerimoglu and Rinke, 2013). Important warming rates may appear because of the reduction of the cloud cover, resulting in higher temperatures and incoming solar radiation .…”

“…Since epilimnion temperature and hypolimnion temperature trends are similar for the reservoir of Bimont, it seems reasonable that the stability and stratification period do not change in the projected scenarios. In addition, given the great importance of hydraulic management on stratification (Moreno-Ostos et al, 2008), we expect stratification patterns in reservoirs to be less affected by climate.…”

Contributions from limnology to reservoir management

“…La estructura térmica del embalse y el calor almacenado en él dependen de la profundidad de la que se toma el agua (Han et al, 2000;Moreno-Ostos et al, 2008). Los sistemas de captación múltiple pueden ofrecer una solución para evitar las bajas temperaturas en primavera y verano, permitiendo la descarga de agua con una temperatura adecuada (Sherman et al, 2007).…”

La gestión de los embalses en relación a la calidad del agua en condiciones de sequía extrema

“…En la península Ibérica los embalses están aproximadamente 9 meses estratificados, de marzo a noviembre y empiezan a detectarse casos en los que este periodo se alarga en la medida que las temperaturas invernales se suavizan. En el embalse de Sau ya se ha detectado un aumento de la estabilidad térmica en los meses de verano como consecuencia de la gestión de la profundad a la que se extrae el agua (Moreno et al, 2008) y en el invierno 2006-2007 por primera vez en toda su historia no se produjo la mezcla completa del embalse (Figura 2). Estas condiciones no deben suponer un cambio importante en la calidad del agua superficial en años hidrológicos normales o húmedos, pero si se combinan estas condiciones con las de años secos, que obliguen a utilizar toda el agua almacenada, incluyendo la anóxica, con elevadas concentraciones de compuestos reducidos, amonio,ácido sulfhídrico, materia orgánica disuelta y metales disueltos el coste de la potabilización del agua aumentará considerablemente.…”