Climate

The mean annual temperature at Elk/Beaver Lake watershed from 1981-2010 is 10.3°C. The warmest months are July and August (average 17°C), and the coldest months are on average December, January, and February (5°C). Annual water temperatures in the lake range from 6° C to 24° C.

The watershed receives an average of 908 mm of precipitation annually, 98% as rainfall (~2% snow), with most precipitation between October and February. Annual precipitation can vary greatly from year to year. For instance, in 2012 (January - December) the watershed received approximately 1024 mm, whereas, in 2013 precipitation was approximately 729 mm.

Topography and Geology

Land elevation within the Elk/Beaver Lake sub-watershed varies from a maximum of 220 m above mean sea level in the north end to 60.5m at the crest of the dam that separates Beaver Lake from the Colquitz River. Maximum elevation on the west side of the watershed is 130 m and 100 m on the east side.

The geology of the watershed is volcanic rock on the south, west, and north sides of the lake, and Cordova sands and gravels to the east.

Lake Hydrology

Coastal lakes receive most of their water from precipitation between October and March. Unlike lakes in colder climates where the surface of the lake freezes in the winter, lakes on southern Vancouver Island rarely freeze. Warmer winter air temperatures mean that lake water temperatures are relatively uniform at all depths during the winter. However, in the summer it’s a different story. Like other lakes in the region, Elk Lake “stratifies” in the summer when the surface of the water is much warmer than the cooler deep water. This stratification forms a thermocline, a zone of rapid temperature change, that separates the surface waters from deep waters, and allows very little mixing of nutrients and oxygen.

As fall approaches and air temperatures cool, the surface of the lake also cools down and the lake no longer stratifies. The deeper, cool water mixes with cool surface water, mixing nutrients and oxygen throughout the water column. Elk Lake basin is 19 m deep, and is known as a “monomictic” lake because it stratifies in the summer and mixes in the fall during lake turnover. Beaver Lake basin, 8 m deep has a very weak stratification that forms periodically throughout the summer, which can be disrupted during high wind events and is often fully mixed by the fall as air temperatures cool. Lakes in colder regions with freezing temperatures typically mix in fall and spring following ice melt, and are called “dimictic” lakes.

Groundwater

Elk/Beaver Lake sits above a groundwater aquifer which extends from the lake to Cordova Bay to the east, and underlies an area of 7.8 km2. The lake is connected to the underlying aquifer, and is a source of discharge and recharge to/from the aquifer due to the predominance of sands and gravels overlying the glacio-fluvial deposits. The median depth to water in this aquifer is 7.3 m, but can range from 30 cm to 18 m. The aquifer is isolated from above by a confining layer in most of the area, and thus has low vulnerability to human activities. The aquifer exhibits moderate productivity and has moderate demand by water users.

Surface Water

Stormwater enters Elk/Beaver Lake from up to 25 points around the lake. The watershed includes O’Donnel Creek, flowing into Elk Lake from the northwest, Hamsterly Creek flowing into Elk Lake from the north, Haliburton Brook flowing into Beaver Lake from the east, Linnet Creek flowing into Beaver Lake from the northwest. Numerous stormwater drainages also carry water to the lake. Water flows out of the lake through the Beaver Lake Dam, into the Colquitz River to the south.

O’Donnel Creek

O’Donnel Creek originates in the northwest section of the watershed draining into Elk Lake basin. Portions of the creek have been diverted from their natural course into roadside drainage ditches to accommodate the subdivision of lands into low-density residential and small agricultural parcels. Numerous drainages and roadside ditches join the main channel of the creek, which crosses approximately 2 km from northwest to southeast. Tributaries of O’Donnel Creek and the creek itself drain a land area totalling 2.6 km2.

Whiskey Creek (aka Hamsterly Creek)

Whiskey Creek is also known as Hamsterly Creek. This creek originates in the northeast section of the watershed, and flows primarily from north to south. The creek flows along the east side of the Patricia Bay Highway for about 400 m, then crosses under the highway in a culvert, flows another 200 m, and enters the lake near Hamsterly Beach. The creek mostly collects runoff from the highway and 0.046 km2 of land east of the highway.

Haliburton Brook

Haliburton Brook originates on the east side of the Patricia Bay Highway and crosses under the highway in a culvert where it receives water from two small roadside drainages. The brook then flows west through a forested area in Elk/Beaver Lake Regional Park and flows into Beaver Lake. Tributaries to Haliburton Brook, and the brook itself drain a land area totalling 0.112 km2, mostly collecting water from highway runoff and drainage from a medium-density residential area east of the Patricia Bay Highway.

Linnet Creek

Linnet Creek originates on the southwest side of Elk Lake and flows southeast into Beaver Lake. Two small tributaries drain into Linnet Creek from the south near the main stem origin. The main stem of the creek flows from a low-density residential area, and through forested lands before entering the northwest corner of Beaver Lake. The small tributaries and Linnet Creek collect runoff from a land area of approximately 0.057 km2.

Colquitz River

Water from Elk/Beaver Lake flows over a dam at the south end of Beaver Lake. The Colquitz River collects water from numerous tributaries throughout the District of Saanich and enters the ocean via Portage Inlet and the Gorge Waterway. Despite creek obstructions in the upper reach, there continues to be a run of 200-400 coho salmon that enter the Colquitz system each fall, as well as several dozen chum salmon.