Water Quantity Issues

Like many watershed in southern Ontario, urbanization and the associated density of population translates to significant water quantity issues in the Lake Simcoe watershed. These issues are; flooding, drought and the related competition for water resources.

Flooding

Flooding issues can be related to the development of an area for a number of reasons; urbanization can significantly change the nature of stormwater runoff, roads and other infrastructure impose artificial impedances to streamflow, and historical development was often preferentially located in floodplains as proximity to water was of primary concern.

These issues are all relevant in the Lake Simcoe watershed. Until recently, urban development diverted stormwater runoff directly to watercourses and the impervious nature of the developments significantly increased surface runoff and decreased infiltration. The net result of this combination is a very rapid response to precipitation events causing large surges in streamflow that can result in flood events. Compounding this problem, road crossings of watercourses utilizing culverts or bridges represent obstructions to high flows. If the structures are not sized appropriately, they can act as dams flooding areas upstream. The areas most at risk are obviously those structures located within the flood plain. The flood plain in the Lake Simcoe watershed is defined for planning purposes by the flood level under Hurricane Hazel conditions or a 1 in 100 year flood event.

Drought

While not as severe as those experienced in the Prairie Provinces, drought conditions are not uncommon in the Lake Simcoe watershed. The implications of drought affect not only the agricultural community but also urban centers in the form of water use restrictions or outdoor water bans imposed by the municipalities in an effort to conserve the municipal sources of potable water.

Drought can also have significant impacts on stream ecosystems. In the absence of surface runoff contributions during extended dry periods, groundwater discharge maintains streamflow. Without recharge to sustain groundwater levels, the effects can be reduced groundwater discharge to streams or no discharge with obvious consequences to aquatic habitat.

Competition for Water Resources

As the population density in the watershed increases, so does the demand for water resources. The major uses of surface and groundwater in the watershed include; potable water, livestock watering, crop irrigation, and industrial and commercial activity. The competition for water resources is exacerbated under low water or drought conditions when irrigation, including urban lawn watering, is most necessary or desirable.

The challenge for water managers is to balance the needs of each community in the watershed including groundwater discharge/stream baseflow that is vital to the maintenance of stream habitat during dry periods. Monitoring data from the LSEMS program is shared with the York Region Low Water Response Team whose mandate is to monitor for low water conditions and to recommend strategies to deal with such conditions.