Innovation-March_April 2013

Areas of karst or potential karst

more CO 2 . This slightly acidic water solution then exploits any existing joints or fractures in the carbonate bedrock. Over thousands of years this process leads to the development of a solutionally weathered landscape linked by near-surface openings to a subterranean drainage system with conduits and other cavities. Some of these cavities are enlarged by mechanical erosion or other pro- cesses to form caves. Solutionally rounded, grooved or pitted bedrock surfaces characterise the surface of a karst landscape along with distin- guishable features such as sinkholes, shafts, dry valleys and grikes (a linear opening or fissure formed along a solutionally enlarged fracture in a limestone outcrop). Karst landscapes often lack surface streams, or may

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have surface streams that disappear at discrete openings or sink points and reappear elsewhere as springs. The lower and mid elevation karst areas of the BC coast and interior are frequently forested and covered by varying thicknesses of glacial materials. This surficial cover can sometimes mask the presence of karst, making it harder to identify. Carbonate bedrock underlies approximately 10% of BC’s land mass, providing an extensive area for karst to develop. Reconnaissance scale karst potential maps completed for the province in 1999 provide a first approximation of where karst might occur in BC and its potential intensity of development. The intensity of karst development primarily depends on the host bedrock type and its purity, unit thickness, physiographic location, and biogeoclimatic setting. Well-developed karst areas on the BC coast are associated with almost all of the limestone units on Vancouver Island (approximately 4% by area) and Haida Gwaii (less than 2% by area); many of which are for- ested. Smaller, isolated forested karst areas are present along the Central and North Coast, as well as on the Sunshine Coast and near Chilliwack. Karst also occurs in Northwest BC (e.g., near Atlin, Stuart and Babine Lakes, and along the Stikine, Nakina and Taku Rivers), Northeast BC (e.g., Chetwynd) and in the BC Interior (e.g., Marble Range and Purcell Mountains). Major areas of alpine and subalpine karst occur in the Rocky Mountains within extensive units of both limestone and dolomite. Karst landscapes are important for a variety of reasons: they can host sensitive ecosystem elements both on the surface and underground; and some provide scientific material related to paleontology, climate change and archaeology. Karst aquifers contribute to many important fish-bearing streams, and are used occasionally for domestic water supply in BC. Karst scenery, both

Above: Karst in BC and Vancouver Island. The distribution and extent of carbonate bedrock in BC is shown in blue. Not all of these areas have well-developed karst lands. However, most areas of carbonate bedrock along the coast have well developed karst lands, primarily due to the high rainfall in this region. Left: Sink points and their associated surface streams require careful assessment and management as they have the ability to transfer excess sediment, fine organics or contaminants to the subsurface, which are impacts that are difficult to remediate. Dye tracing, shown at this karst sink point on Quadra Island, is a technique used to use to delineate subsurface flow paths in karst lands.

the surface and subsurface conditions of the karst landscape— integrating a broad understanding of the rock, soil, air, water and biota attributes of the site into the overall evaluation. Karst lands can also pose a number of geological and engineering hazards to projects such as subsidence, unpredictable subsurface cavities and unusual groundwater flow conditions. The Nature, Distribution and Importance of Karst Lands in BC The evolution of karst landscapes fundamentally involves rain- fall, which picks up CO 2 as it falls through the atmosphere and starts to form a weak solution of carbonic acid. After the rain infiltrates the ground it percolates through soil and picks up

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