Water Balance

Since 1995, TransAlta has retained an independent consultant to develop and manage a water balance model for Lake Wabamun. The model is used to complete annual licensing requirements for Alberta Environment, but more importantly, it allows one to understand: various inflows and outflows to the Lake; the effect of natural cycles – that being wet and dry years; TransAlta’s impacts on the Lake; and forecasting water treatment plant requirements and debt repayment to the Lake.

The model is a large multi-sheet Excel spreadsheet that has numerous inputs, including measured data and assumptions. In order to calibrate the model or to confirm its estimates, it is compared against reality – in this case the Lake level.

Factors that influence the water balance include:

In a comparison between 2002 and 2003, the amount of precipitation in the Lake Wabamun area was approximately 25 million cubic metres (m³) in 2002 versus 39 million m³ in 2003. Ironically the estimated runoff into Lake Wabamun accounted for approximately 20 million cubic metres (m³) of water, versus 11 million m³, for the same periods. This significant difference in runoff volume as compared to the estimated volume of precipitation would be attributed to the lack of soil moisture in the region, as the soil actually acted as a sponge, adsorbing a large volume of water. Overall for the periods, the inflow to Lake Wabamun was 61 million m³ in 2002 and 74 million m³ in 2003.

Conversely for the same period of time, total outflows calculated for Lake Wabamun were 75 million m³ in 2002 and 62 million m³ in 2003. With the increased inflows and lower outflows in 2003 a net water level change of 18 cm was calculated for the Lake. A review of Alberta Environment’s water level report (click here to link to AE water level report) supports this conclusion as overall, the Lake water level increased in 2003.

Overall, natural evaporation off of Lake Wabamun continues to be the single largest factor contributing to overall outflows. To put the evaporation numbers into perspective, the volume of water that TransAlta is required to pump into Lake Wabamun currently is 20 million m³ per year (8300 gallons per minute). In 2002, natural evaporation accounted for approximately 62 million m³ of water or 25,000 gallons per minute – three times the amount that TransAlta is required to pump into the Lake.

Some of the impacts from evaporation were certainly evident during the summer of 2002 when we experienced a record number of days above 30oC. Conversely in 2004 we have experienced a considerable amount of precipitation and water levels have remained relatively static, despite the warm weather.

On average (over a 51 year period – assuming average precipitation and runoff), Lake Wabamun’s water level should rise 10 inches (25 cm) per year. However with lower direct precipitation and runoff, the overall inflow to Lake Wabamun will be lower, thus resulting in lower water levels. Outflows as they relate to TransAlta’s operation are minimal as compared to the natural evaporation off Lake Wabamun.

There is no doubt that TransAlta’s activities have an impact on Lake Wabamun, however natural cycles on the lake are extremely powerful and cannot be overlooked.