It cautions residents along the shores of the Ottawa River from Mattawa down to the Montreal Region that throughout the spring freshet period water levels can rise rapidly at times and cause minor flooding in low-lying areas. Spring started early this year and the snow cover has slowly melted away from the central and southern parts of the basin over the last few weeks. However, heavy rainfall events in parts of the watershed may cause levels and flows to change rapidly in downstream river reaches and the Regulating Committee will be closely monitoring the effects of precipitation over the next few weeks. Further bulletins will be published if flood risks increase.
Refer to the River Conditions Forecast message at www.ottawariver.ca for frequent updates on river conditions throughout the freshet.
River Conditions Forecast / Flooding Risk*: A large weather system from Texas brought 15 to 75 mm of precipitation over much of the Ottawa River basin between April 11 and 13, with the highest amounts received in the Timiskaming area. This system brought considerable warmth that quickly melted the remaining snow upstream of Lake Timiskaming, which added up to 60 mm of water in some areas. No significant precipitation is forecast over the next few days. With normal daytime temperatures now above zero, runoff from recent precipitation is combining with the remaining snowmelt in the northern portion of the basin. Spring runoff into the Ottawa River is thereby increasing, causing levels to rise on the Ottawa River between Mattawa and the Montreal Region. Although March brought close to average precipitation amounts, part of it fell as rain and the snow cover that remained in the upland areas and the northern part of the watershed continued to melt slowly with daytime temperatures above zero. As seen in the figure, the snow water content (that is the amount of water held in the snow cover) at the end of March and early April was significantly below normal everywhere, with snow water equivalent varying between 40 and 120 mm in the central and northern parts of the basin respectively. While the absence of snow in a large portion of the basin reduces the risk of significant flooding, it is important to remember that spring water levels depend also on the timing and amount of rainfall during the months of April and May. Weather conditions that bring heavy rainfall events can only be known a few days in advance. Rising levels along the main stem of the Ottawa River could create possible flooding in low-lying areas over the coming weeks. Low-lying areas are those that are regularly flooded during the spring
