Effect of spectral and temporal variation of subsurface irradiance on the heating of lakes

This dissertation illustrates how the vertical distribution of temperature in lakes can be affected by the fact that the attenuation coefficient of light is often strongly dependent on wavelength. The potential importance of this spectral effect is first examined by considering the solar radiation in isolation, and then by including all non–penetrative heat fluxes using a modified version of the numerical model, DYRESM. Comparing the subsurface spectral irradiance of different lakes reveals that the spectral variability of the attenuation coefficient is more significant when calculating the light intensity in relatively clear lakes than in turbid lakes. Comparisons made between field measurements and theoretical predictions of hypolimnetic heating show the importance of accounting for the spectral irradiance for two relatively clear lakes: Pavilion Lake and Crater Lake. A new parameterization that better describes the spectral attenuation coefficient and the distribution of subsurface irradiance is added to DYRESM. The results obtained, when running the original and the modified DYRESM on Pavilion Lake, show a significant improvement in predicting the thermal structure of the lake with the modified version. The effects of the variation in solar angle and the seasonal variation in water quality on the attenuation coefficient are also examined for Pavilion Lake using DYRESM modified to accept a time varying attenuation coefficient. Simulations were performed for Pavilion Lake using the original and modified versions of DYRESM on diurnal and seasonal scales. Results show no significant improvement in the thermal evolution of the lake when considering the diurnal variations, while slight improvement was shown on a seasonal scale.Applied Science, Faculty ofCivil Engineering, Department ofGraduat