|
Canadians have a strong cultural link with water, which is a major facet of our heritage, our spirituality and our economy. From the earliest settlements, people built their homes along rivers and lakes.
Apart from being a source of drinking water, the water of watersheds is used for irrigation, the production of hydroelectricity and as a means of transportation. The riverbanks and floodplains provide aesthetically pleasing sites for housing and recreational activities. Unfortunately, water is also used as an egress for industrial discharge.
Major water consumers are municipalities, agriculture, mining, manufacturing and thermal power generation. Consequently, there are huge demands from these activities for all water reserves.
The map layers show different human and economic components of a watershed. The following descriptions of each layer demonstrate the importance of each component to watersheds.
Human Components
Population
The highest demand for freshwater arises from the southern areas of Canada within 200 kilometres of the United States, where the population density is highest. Many of the major river systems in the south, however, flow northwards away from the major cities.
The rapid growth of population in southern areas has resulted in an increasing gap between the availability of freshwater resources and the demand from economic and human activities (such as municipalities, thermal power generation, manufacturing, mining and agriculture).
Continued urban development causes stress on watersheds. It alters the hydrological cycle by modifying the fluxes of water and sedimentation and by decreasing the water quality, affecting the biodiversity and bringing a general degradation of water resources. Also, groundwater recharge may decrease due to decreased permeability of the aquifer and the overlying materials. Compared to watersheds with little or no population, watersheds in urban areas are subjected to changes in local meteorological phenomena and microclimate, leading to increased precipitation downwind of cities, higher incidence of fog and higher air temperatures, which favour evaporation.
Growing urban populations also impose increasing demands for provision of water services, including water supply, drainage and wastewater collection and treatment. Also, the increased wastewater discharge that results from this growth causes chemical and thermal pollution, a decrease of oxygen, eutrophication, restrictions on fish and shellfish consumption, degradation of aquatic and wildlife populations and their habitat, beach closures and added costs to agricultural, industrial and municipal users for treatment of water.
Aboriginal Population
Water for Aboriginal peoples is the basis of all life. For them, it is necessary to understand and respect the water and its role. Knowing how water can be used for nourishment and transportation can be life-saving skills.
Aboriginal populations are profoundly linked to water and waterways for both physical and spiritual health. Today, the water quality of many watersheds is degraded by the pressures of human development. To many Aboriginal people, this degradation of the land and the water results in the deterioration of their health and way of life.
Economic Components
Dams and Diversions
There are a number of dams and diversions in most provinces in Canada. Water is stored behind a dam, and then withdrawn from its natural course for transfer elsewhere in the same, or to another, drainage basin. Dams and diversions redistribute the streamflow toward areas that have greater demand.
The vast majority of large dams in Canada were constructed solely for hydroelectric production. The others were constructed primarily for water supply and for irrigation, mainly in the Prairie provinces, whereas others serve a variety of purposes, including flood control, navigation, recreation, or a combination of these. The more recent and largest dams are the La Grande (James Bay) Project in Quebec, the Churchill–Nelson diversion in Manitoba, and the Churchill Falls Project in Labrador, all publicly administered hydroelectric power programs.
Hydro developments have had a substantial effect on rivers and lakes in Canada. There have been relatively few large hydro sites developed since the 1970s because the environmental and human effects to be avoided or mitigated in such large projects make them increasingly difficult and costly to plan and build.
Agriculture
As agricultural land use in Canada has increased, the natural hydrology of watersheds has changed, affecting the relative availability, and in some cases the quality, of water. Agriculture is one of the largest water consumers and withdraws water supply from rivers, streams, reservoirs and wells for land irrigation and watering livestock.
Irrigation is defined as the provision of water to crops beyond what is provided by local rainfall. Irrigation is a vital part of agriculture in certain areas of Canada, such as the southern Prairies and the interior of British Columbia. The amount of water that needs to be withdrawn for irrigation varies annually. It depends on winter precipitation and weather and soil moisture during the growing season. In fact, dry regions in the southern Prairies and in the interior of British Columbia have severe moisture deficits at some time during most summers. Dry areas are also more prone to long-term drought conditions as well. These areas (especially southernmost Alberta) hold most of the one million hectares of irrigated cropland in Canada.
Forests
Forests play a vital role in the hydrological cycle, influencing patterns of evapotranspiration, runoff and soil moisture. In fact, forest cover maintains stability of the infiltration capacity of the soil, decreases runoff, lowers wind speed and increases precipitation interception, thereby significantly affecting the local microclimate and hydrological cycle.
Disturbances caused by forestry operations, fires and infestation, however, exert significant impacts on streamflow, water quality, sediment discharge and groundwater recharge. The removal of vegetation produces short-lived, significant decreases in water losses through evapotranspiration and decreases in precipitation interception, which together lead to increase in soil water content in disturbed areas. Removal of vegetation also increases the flow of water out of the watershed.
Mining
Large volumes of water are used by the mining and petroleum sectors for extraction and concentration of metals and nonmetallic minerals, extraction of light and heavy crude, and generation of the electricity required for crushing ore, on-site processing, smelting, refining and other aspects of treating resources to improve their properties. Demand for water by the mining industry is limited and localized but becomes high when associated refining, smelting and manufacturing operations are considered.
Furthermore, the release of substandard water from abandoned mines is a significant threat to freshwater availability in some watersheds of the country.
|
