Calculates volumetrically weighted average epilimnetic temperature using the supplied water temperature timeseries. If the lake is not stratified, the bottom of the epilimnion is calculated as the full depth of the lake.
epi.temperature(wtr, depths, bthA, bthD)a numeric vector of water temperature in degrees C.
a numeric vector corresponding to the depths (in m) of the wtr measurements
a numeric vector of cross sectional areas (m^2) corresponding to bthD depths
a numeric vector of depths (m) which correspond to areal measures in bthA