The watershed of Brome Lake
A watershed is a portion of territory bounded by ridgelines, whose waters feed a common outlet: stream, lake, sea, ocean, etc. The common outlet of the Lake Brome watershed is the Yamaska River. The Lake Brome watershed covers an area of 186.7 km². There are approximately 3,375 housing units in the watershed for a population of about 6,000 people. Except for about 2,000 housing units in Lac-Brome, all residences are equipped with private septic systems.
Land use
13,3%
AGRICULTURAL
60,3%
FORESTRY
7,7%
ANTHROPOGENIC
14,4%
AQUATIC
Land use in the watershed partly determines whether rainwater infiltrates, runs off, or evaporates. The part of the water that infiltrates can remain near the surface, where it is partly used by plants for growth or simply evaporated. The other part of the infiltrated water reaches the groundwater table. In areas covered with vegetation, such as forested areas, the soil absorption rate is much higher than in places where the soil surface is bare. In urbanized areas, there is much less infiltration, increasing runoff and especially the pollutant loads that this water carries.
Water that runs off from a watershed disregards administrative boundaries. Thus, the Lake Brome watershed encompasses eight municipalities, in whole or in part. These municipalities are attached to two RCMs, namely the RCM of Brome-Missisquoi and the RCM of Memphrémagog.
Increasingly, public authorities recognize the need to manage water policies according to the characteristics of each watershed. This is known as integrated water management by watershed.
Municipalities in the watershed
Bolton-Ouest
43%
Lac-Brome
31%
Stukely-Sud
18%
Ste-Étienne de Bolton
5%
Canton de Shefford
2%
Bolton-Est
0,5%
Waterloo
0,07%
The sub-watersheds
Each watershed is subdivided into a number of elementary basins (sometimes called "sub-watersheds") corresponding to the catchment area of the tributaries flowing into the main watercourse. The Lake Brome watershed includes 8 main tributaries totaling 278 km and about thirty small tributaries flowing directly into the lake.
The mandate for the characterization and diagnosis of the sub-watersheds was given to a team of scientists from the Regroupement des Associations pour la Protection de l’Environnement des Lacs (RAPPEL). These reports provide valuable sources of information for the officials of the concerned municipalities who wish to apply the necessary corrections to the quality of the water running off in their ditches, on their roads, and in their watercourses.