MEASURE AND MODELING VERTICAL MIXING IN TROPICAL STRATIFIED LAKES
38th IAHR World Congress - "Water: Connecting the World"
Lake's mixing regime affects physical, chemical and biological processes. Each time the vertical stratification is broken an upward velocity is created. But is this velocity strong enough to re-suspend bed material and affect water turbidity? This is a key question in water quality studies, once that turbidity is an important index in those evaluations and bed material could include heavy metals, high load of nutrients or even pesticides, all harmful for the environmental. To respond this
... respond this question turbidity measures and tools of environmental evaluation are needed. In this subject, two stratified tropical lakes, located in São Paulo -BR were used as study sites. Aiming to measure variations on the water turbidity due mixing events and evaluate them according to the temperatures profiles, also assess a model 3D capacity to represent the vertical velocities due to mixing events on the lake. The first lake is called Billings, it is bigger and deeper, than the second site, Hedberg reservoir, different sizes of lakes were chosen to be able to include the size effects on the lakes' mixing regime. Both lakes had their temperature profile and the relative turbidity measured in campaigns that were performed for more than a month and with 1min and 1s time steps, respectively. With the data collected the information were plotted and evaluated looking into specifics moments when the water column mix, and then the lakes were modeled in Delft3D which provided calculated vertical velocities. The measures on the field shows that the relative turbidity, that is, the difference between previous and current turbidity, increase when mixing events begin to happen, proving those events can re-suspend deposited materials. When the same period is modeled in Delft3D the higher vertical velocities are found at same time that turbidity peak occurs, evidencing the efficient of a calibrated model in represent physical conditions and relations in the lake.