Sylvan Lake exists because the last ice age created the watershed basin and because today the amount of water that enters the watershed is about the same as the amount that leaves it. The following diagram shows the inputs and outputs of water that determine the lake level and its fluctuations from year to year:
Water Balance for Sylvan Lake (AXYS 2005)
The inventory of water in the Sylvan Lake watershed is controlled by the balance between input precipitation and losses by evaporation and export. According to the analysis of multi-year data presented in the AXYS 2005 report the lake annually receives about 20 million cubic metres (Mm3, or tonnes) of precipitation. Surface runoff adds about 11 Mm3 and subsurface groundwater flow contributes about 3 Mm3 of water.
The major loss of 31 Mm3 is by surface evaporation. Stormwater diversion easterly to Cygnet Lake and overflow through the Outlet Creek removes about 3 Mm3 of water.
Hot dry summer months accelerate evaporation and the historic record shows that the lake level can drop by up to one foot within a few weeks. Periods of cool weather and high precipitation reduce the evaporation rate and raise the lake level. In the future, increased well water extraction of groundwater for domestic use combined with pipeline export downstream to Cygnet Lake and then on to the Red Deer River has potential to disrupt the Sylvan Lake water balance. In addition, increased collection and diversion of stormwater outside the watershed by the Town of Sylvan Lake will reduce the volume of surface water entering the lake.
The figure above also includes data from the AXYS 2005 report on the input of the plant nutrients nitrogen (as the analysis Total Nitrogen, TN) and phosphorous (Total Phosphorus, TP) both of which can cause the undesirable growth of algae in the lake.
The 1978 Alberta Environment report on the regulation of the Sylvan Lake water level may be downloaded using this link: Sylvan Lake Regulation Study-AE-1978.