Loch Garry

Background
Loch Garry is the first (and largest) lake of three which comprise the Garry River sub-watershed.  The water from Loch Garry travels through Middle Lake to Mill Pond and then into the Delisle River. The proper management of all three lakes is critical to ensuring an adequate supply of drinking water for the Town of Alexandria. The Raisin Region Conservation Authority (RRCA) manages the water levels in the lakes by adjusting the dams at the outflows of the three lakes.

Loch Garry Facts
Surface Area: 3.8 km² (939 Acres)
Depth: varies between 1m to 5m
Drainage area: 16 km² (4,000 Acres)

Where does the water come from?
There are no rivers supplying water to Loch Garry. Water in the lake is supplied through the hydrologic cycle within the local drainage area. The water in Loch Garry comes from precipitation: snow melt and rain. When it rains, a portion of the water runs off the surrounding 16 square kilometers of land and enters the lake; another amount of water percolates through the ground and discharges into the lake.

Where does the water go?
Approximately 50% of the water leaves through evaporation. A small amount migrates naturally through the ground. The remaining water flows through the dam on Lakeshore Road. If more water leaves the lake than enters, the water levels drop. Conversely if more water enters the lake than leaves, the water levels rise.

The Garry River Watershed
The entire watershed area is relatively small, only 34 square kilometers. Rain and snow falling inside the red line below is the primary source of new water in the lakes.

Management of the Lakes
The three lakes work as a system: an adjustment to the outflow of one lake will affect the water levels of all three lakes. Water leaving Mill Pond enters the Delisle River just downstream of the Town of Alexandria. The RRCA’s primary concerns for managing the lake system are:

• Ensure sufficient water supply for the Town of Alexandria
• Ensure a sufficient water supply to the Delisle River (The Ministry of the Environment compels a minimum specified amount of flow every day)
• Flood prevention and protection (around the lakes and dams)
• Environmental considerations
• Recreational considerations

Operational Considerations
The RRCA sets and reviews operational guidelines to ensure the lakes are operated to meet the management objectives, while considering the following:

• The majority of outflow through the dams is during the spring months (the Spring Freshet)
• The majority of evaporation occurs during the summer months

For Loch Garry, the operational guidelines include making adjustments to the water level throughout the year.  During the summer months, the target water level elevation is 89.1 masl (meters above sea level) *.  The RRCA strives to maintain water levels above a minimum of 88.9 masl during the summer.

*Water Elevations are generally measured to a standardized datum. Meters above Sea Level (masl) is a common datum. A water level of 88.9 masl does not mean that the water is 88.9 meters deep. To compute the depth, you would need to know the elevation of the bottom of the lake, and subtract it from the water level elevation.

Historic Records
The RRCA maintains detailed records of water levels in all of the lakes. The minimum levels since 2003 for the period between June 1 and August 31 are listed below.

Current Conditions (as of June 17th, 2011)
· Water levels have been slowly dropping since May 25th. Since then the water level has dropped about 4 inches in 29 days

Information provided by the Raisin Region Conservation Authority