How can reservoirs help flooding?
Both the Glenmore Reservoir (The City) and the Ghost Reservoir (TransAlta Utilities) are operating to maintain additional flood water storage, from May to July, should potential flooding occur. This will help protect Calgary from potential flood damage when the risk of flooding is the greatest.
Why can't reservoirs be lowered for floods?
We are often asked why reservoir operators cannot simply lower the reservoirs when we know a flood is coming. As we know from recent flood events, flooding in our watersheds happens quickly and with little warning because of the short, steep distance the rivers travel from the mountains to Calgary.
However, having the reservoirs maintain lower water levels from May to July allows them to have more capacity to help store flood water when it's needed and it also allows us the flexibility to reduce levels lower should we need to optimize flood protection for large flood events.
The Glenmore Reservoir will have about 10 million cubic meters and the Ghost Reservoir will have about 65 million cubic meters of storage available for flood mitigation. With additional flood water storage possible at the reservoirs, we gain time to construct temporary mitigation measures to protect Calgary further from flood damage.
About the Glenmore Reservoir
To achieve and maintain an optimal minimum level of the Glenmore Reservoir, we monitor weather conditions and flow rates in order to make operational adjustments 24/7 and ensure stable and normal flow rates occur downstream on the Elbow River.
Flood mitigation is only one of the many important functions of the Glenmore Reservoir and Dam. First and foremost they were constructed to provide Calgarians a safe and sufficient supply of drinking water with the reservoir also providing recreational opportunities during the summer months. Calgary's treatment plants incorporate advanced technology that can treat highly turbid (cloudy) water while still meeting demand.
About the Ghost Reservoir
TransAlta Utilities manages water at its Ghost facility on the Bow River to aid in potential flood mitigation efforts for 2015. They have agreed to reduce the Ghost facility's operational levels from May 15 to July 7 and to not operate the reservoir below the minimum level of 1184.2 metres.
Water levels in the Ghost Reservoir can only be lowered by 0.3m/day for geotechnical reasons, so if a major event is in the forecast, the TransAlta team requires a three-day period to prepare. The reservoir will begin refilling no later than July 7 and probably sooner.