The GRCA owns and operates seven dams and reservoirs. They play a vital role in protecting the health and safety of the residents of the watershed.
The dams were built between 1942 and 1976 to address major, long-standing problems:
Sometimes, these goals compete with each other. The GRCA's reservoir operations must find the right balance to meet all the objectives.
The reservoirs are managed to provide maximum flood storage when it is needed most - in the spring to handle the spring melt and in the fall to deal with remnants of tropical storms.
Water levels are lowest in the winter. In the spring, melting snow and rain result in higher flows in rivers and streams. Some of that water is held in the reservoirs, reducing the amount that flows downstream. This helps to reduce flood peaks in the cities and towns along the rivers.
After the spring melt, the reservoirs are full. The water in the reservoirs is released gradually during the summer and fall to ensure there is water to support the operation of municipal drinking water plants and wastewater treatment plants. This is called flow augmentation.
In a dry year, natural flows can be only a small fraction of normal. Sometimes, more than 90 per cent of the water in the Grand River at Kitchener is water from the GRCA's reservoirs.
More than 15 wastewater treatment plants, treating 90 per cent of the sewage of watershed residents, are downstream of the reservoirs.
The plants provide a high level of treatment. However, even the newest and most advanced plants release treated effluent containing small amounts of pollutants, notably nitrogen and phosphorus.
Natural processes in the river will take care of some of these materials. However, there must be enough water in the river to let the process work. Water discharged from the GRCA's reservoirs ensure there is enough flow to allow these processes to happen.
The two principle functions of the reservoirs - flood damage reduction and flow augmentation - sometimes conflict with each other.
That requires careful managing of discharge rates by reservoir operators to find the right balance in an effort to meet both objectives.
The most challenging period is in late spring and early summer when reservoirs are fullest. There is very little space left in the reservoirs to handle the water from a big storm. When that happens, the operators have to release some water from the reservoirs to protect the dam. If water were to flow over the top of the dam, it could weaken it to the point where it would collapse.