Update on Lake Ontario Regulation
Reductions in Lake Ontario Outflows Made
to Relieve Downstream Flooding
Exceptionally warm weather, beginning this past weekend, resulted in rapid snow melt, high inflows and a sudden rise in water levels on Lake
Ontario and the St. Lawrence River. Heavy rainfall during the week also
compounded the flooding problem in the Montreal area. To provide a
measure of relief from the serious flood conditions on Lake St. Louis and
elsewhere in the Montreal area, the International St. Lawrence River
Board of Control directed a series of large reductions in Lake Ontario
The rapid snow melt caused record high flows in some of the tributaries
to Lake St. Louis and Lake St. Peter near Montreal. Lake St. Louis began
to rise abruptly late on March 27 and exceeded flood stage the next day.
The spring melt in the lower portion of the Ottawa River basin, which
was also brought on by the warm weather, has resulted in high flows to
the Montreal area that have come much earlier than usual. Heavy rainfall
during the week also exacerbated flooding conditions on Lake St. Louis
and brought significant moisture to the Lake Ontario and the Ottawa
Since late December 1997, the International St. Lawrence River Board of
Control has been releasing as much water as possible from Lake Ontario
without causing ice jams or flooding downstream. A short ice season
this winter has allowed the Board to achieve record outflows during the
month of March of 10,200 cubic metres per second (360,000 cubic feet
per second), which was the flow until March 27. Beginning on March 28,
the series of large flow changes was initiated, which brought the
outflow to a record low of 4,700 cms (166,000 cfs) by March 31. In spite
of the drastic flow reductions, the levels of Lake St. Louis and the
Montreal Harbour rose above flood stage.
The large Lake Ontario outflow reductions also resulted in high water levels on Lake St. Lawrence. To prevent the water from rising above
flood stage on Lake St. Lawrence, gates at the Iroquois Dam have been
set at an all time minimum open setting.
The level of Lake Ontario has risen nine centimetres (3.5 inches) since March 28 when Lake Ontario outflows were reduced to alleviate flooding
in the Montreal area. The lake is presently at 75.26 metres (246.92 feet)
above sea level, 50 centimetres (20 inches) above average. The
International Joint Commission notes that the flows to Lake Ontario from
Lake Erie will remain high for the foreseeable future. Depending on
precipitation during the next few weeks, Lake Ontario could rise another
10 to 30 centimetres (four to 12 inches).
The International Joint Commission advises shoreline communities to prepare for the potential continuation of high water levels and other
users of the system to prepare for the potential of high flows in the St.
The Board continues to monitor conditions closely on a continual basis
and will adjust the flows as needed to provide all possible relief from
high water on Lake Ontario and the St. Lawrence River.
The International Joint Commission was created under the Boundary Waters Treaty of 1909 to help prevent and resolve disputes over the use of waters along the Canada-United States boundary. Its responsibilities include approving certain projects that would change water levels on the other side of the boundary. If it approves a project, the Commission's Orders of Approval may require that flows through the project meet certain conditions to protect interests in both countries. For more
information, visit www.ijc.org on the Worldwide Web.
The International St. Lawrence River Board of Control was established
by the Commission in its 1952 Order of Approval. Its main duty is to
ensure that outflows from Lake Ontario meet the requirements of the
Commission's Orders. The Board also develops regulation plans and
conducts special studies as requested by the Commission. For more
information, visit www.islrbc.org/ on the Worldwide Web.
Provisional water level gauge readings, updated every three hours, can be found at www.opsd.nos.noaa.gov on the Worldwide Web.
Reported by: John Whitehead