Thermal structure and variability of a shallow tropical reservoir

Abstract

The structure and mixing dynamics of shallow tropical reservoirs was investigated using data collected in the Kranji Reservoir in Singapore. Water temperature data spanning a 2 month period in 2007 shows that diurnal cycles of stratification and destratification were formed in various locations in the reservoir. Temperature stratification of 0.5°C to 3.5°C was formed during the daylight hours and reduced nightly when cooling occurred. Substantial horizontal redistribution of heat was also observed between the side arms and the main body of the reservoir. The Kranji's dynamics can be summarized in terms of three physical forcing regimes: a solar radiation—dominated regime, a windy regime, and a cold inflow regime. We delineate the three physical forcing regimes by two potentially useful dimensionless numbers that quantify the relative influences of surface heating, wind stirring, and inflow buoyancy fluxes. For most of the measurement period (88% of the data record), the solar radiation—dominated regime characterized the hydrodynamics. In spite of the dominance of solar radiation in setting local stratification, it is shown that Kranji Reservoir is a three‐dimensional system in which there can be significant variations in temperature in the vertical and along‐reservoir directions, as determined by cold inflow events, differential heating, and reservoir releases. Moreover, the data suggest that the dynamical balance of the Kranji system is sensitive to small forcing events, with the timescales of stratification and mixing as short as a day or less.

Extreme weather events: Should drinking water quality management systems adapt to changing risk profiles?

“…Extreme cold333Ambient air temperature, in general, plays a significant role in establishing and maintaining 334 thermoclines and stratification in drinking water reservoirs(Butcher et al 2015). Sudden switches 335 from warm to cold air temperatures can rapidly disrupt thermoclines, leading to the mixing of surface 336 water stored at deeper depths(Xing et al 2014). Similarly, an influx of very cold water into 337 a weakly-stratified reservoir can cause destratification(Brookes et al 2005).…”

Robotic mapping of mixing and dispersion of augmented surface water in a drought frequent reservoir

“…Laboratory (e.g., Horsch and Stefan ), field studies of convective flows in side‐arms of reservoirs (Monismith et al ; James and Barko , b ), and numerical modeling work (Horsch and Stefan ; Horsch et al ) have helped identify the mechanisms initiating these downslope gravity flows. More recently, well‐designed studies incorporate multiple thermistor arrays, acoustic Doppler Aurrent Profilers (ADCPs), and meteorological stations to quantify convective flows in lakes or reservoirs (e.g., Xing et al , ; Kirillin et al ; Yang et al ). These studies utilize multiple moored arrays to quantify horizontal convection, but mapping short timescale horizontal variability remains a challenge especially in reservoirs that can undergo rapid changes in horizontal density gradients (e.g., surface wind shear).…”

Mean diel variability of surface energy fluxes over Manso Reservoir

“…With evaporation peaking at night, we should expect nighttime increases in the mixed layer deepening, or even total water column mixing in shallower places, with consequently larger fluxes of GHGs (Crill et al 1988). We anticipate that studies at additional locations within Manso Reservoir would show similar patterns but could show some spatial differences in heating and cooling, particularly in secondary sidearms of the reservoir, inducing exchange flows within the reservoir (Monismith et al 1990, Xing et al 2014. Studies in other seasons combined with time-series temperature measurements within the reservoir are still needed to describe the seasonal variability in the surface energy budget and how this changing budget moderates mixed-layer dynamics and controls the variability of GHG emissions by the reservoir.…”