Observations of vertical eddy diffusivities in a shallow tropical reservoir
Fong, Derek A.
Monismith, Stephen G.
Tan, Kok Meng
Lo, Edmond Yat-Man
Date of Issue2014
School of Civil and Environmental Engineering
Tropical lakes are of key importance as fresh water supply sources in tropical regions. One of the biggest threats to tropical lakes is nuisance algal blooms which at times can be harmful to human health. Research shows that thermal and flow dynamics, through their effects on the light and nutrient accessibility to phytoplankton, have a strong bearing on the growth of phytoplankton. We report herein results combining long-term and short-term observations of vertical diffusivities which impact the evolution of the surface mixed layer and the vertical transport of nutrients for a shallow tropical reservoir, Kranji Reservoir in Singapore. The one-dimensional heat flux method (Jassby and Powell, 1975; Henderson-Sellers, 1985) is applied to obtain estimates of the vertical mixing in Kranji Reservoir using water temperature and meteorological data collected during a two month field experiment conducted in 2007. To fit the assumptions of the method and particularly the heating duration, a time period of 11:00–15:00 is selected for heat flux method when the water body is strongly stratified. The vertical eddy diffusivity, Kz varies with depth and spans two orders of magnitude, from 10−5 to 10−3 m2/s. In addition, short-term observations from two 24hr turbulence microstructure measurements conducted in 2011 are considered. The heat flux method derived diffusivities are compared directly against those derived from the microstructure measurements with reasonable agreement with the latter when the system fits a one-dimensional assumption. The microstructure measurements further provides Kz observed values over the entire day and this is discussed in the context of the thermal forcing regimes in Kranji reservoir.
DRNTU::Engineering::Civil engineering::Water resources
Journal of hydro-environment research
© 2014 International Association for Hydro-Environment Engineering and Research (IAHR). This is the author created version of a work that has been peer reviewed and accepted for publication in Journal of Hydro-environment Research, published by Elsevier B.V. on behalf of International Association for Hydro-Environment Engineering and Research (IAHR). It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [http://dx.doi.org/10.1016/j.jher.2014.09.004].