21 Oct 2015


Neil Goeller & Sylvia Barroso


Forest, Lands & Natural Resource Operations


Precipitation in the Cowichan Watershed in winter has historically been in the form of rain and snow. In higher mountain areas surrounding Cowichan Lake, the snowpack that builds through the winter is a reservoir of water that augments the capacity of the lake, and contributes significantly and critically to the lake in spring and summer.


9 Oct 2014


Ehren Lee


Urban Systems, for the Cowichan Valley Regional District


Groundwater is water which is stored underground - not surprisingly. It can be confined, which means that a deposit of water is surrounded by nonpermeable rock, typically in aquifers or unconfined, in which case it is surrounded by permeable rock, gravel, soil, and other materials. Around 20% of the world's freshwater is groundwater, and groundwater makes up a significant portion of the potable water consumed worldwide, with up to 50% of some populations relying on groundwater.

Supply and Demand

Water in the Cowichan Basin

The Cowichan Watershed can be characterised as having high precipitation/recharge, high storage, and low population/demand in the western and upper half of the watershed, contrasted with low precipitation, low storage, and high population/demand in the eastern and lower half. Supply and demand are not matched regionally, nor seasonally, and the supply-demand gap is pushed to extremes in the late summer and early fall.

The Cowichan Lake Weir

CowichanLakeWeir-labelledThe weir on Cowichan Lake is used to control the outflow from the lake into the Cowichan River. For much of the time between late fall and late spring each year, it does nothing, and the weir is referred to as "off control" - since the lake level is above the top of the weir.

Flooding in the Lower Cowichan

FishNavigatesLakesRoad_DebraBrash_TimesColonist_21Nov2010The lower slopes and floodplain of the Cowichan - Koksilah river system contain significant areas of agricultural land as well as rural, urban and industrial development. Dikes have been built along both banks of the Cowichan River to protect the developed urban core of the City of Duncan and the extensive agricultural and industrialized zones downstream. Dikes have also been constructed on lands of the Cowichan Tribes at various tiines including along the Koksilah River.


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