Why Saint Charles seems dry?
Anyone who frequents the Saint-Charles River will have noticed that it is almost dry in its urbanized portion; an expanse of more or less clean sediment replaced the water mirror. Why?
S ou Samson bridge, one that spans the river near the courthouse and the train station, there is a dam. On Wednesday, it was closed for work that will last for a few days or even weeks, explains the Sun communication consultant Wendy Whittom.
The closure of the dam should raise the water level, right? In fact, the river is currently at “normal” height. It is not surprising that the flow is rather limited in this mild season: “The water supply comes from the rains via runoff and groundwater. In summer, the water supply is at a minimum, but flows at all times to the river. The level of the river is naturally low at this time. ”
So where does the water that usually fills the bed of the Saint-Charles River come from? Of the river. The Samson Dam being closed, the tides can no longer rush. As a result, the stream seems to be very small. And the residues accumulate. “Normally, the valve stays open,” Whittom notes. “This allows the tides to clean up the sediment build-up in the river and the aquatic vegetation to grow.”
Deposits, there are many at the bottom of the Saint-Charles. “For any dam, there is accumulation of sediment upstream, because there is a slowing of water that allows the particles to settle,” explains our interlocutor. “Sediment, often sand, can come from natural erosion of riverbanks and surface runoff [including sewers]. In the case of the St. Charles River and the Samson Bridge, sediment has slowly accumulated since the bridge was built in the late 1970s. ”
Pollution and research
Unfortunately, even if ducks plunge their beak into the accumulated mud, it does not mean that they are pure. The Saint-Charles River has long been an open sewer. Although the City has invested heavily to renaturalize and limit wastewater discharges, it is still common for municipal pipes to spew their soiled contents back into the wild, especially on rainy days.
This justifies the ban on swimming, even navigation. In an ancient article of the Sun , the St. Charles River Society argued that there are too many fecal coliforms to allow canoeing and kayaking .
The city has been looking for a few years to clean the riverbed .
This spring, the National Institute for Scientific Research and its partners received funding to continue work on the contamination of the watercourse, which could guide ecological restoration.
In the meantime, the municipality is continuing the management of the Samson Dam to limit the accumulation of polluted sludge. “Since 2012, we have been following a program to open and close the valve,” notes Wendy Whittom. “There are about 8 or 9 closures a year, depending on activities, jobs and tides. Since that time, the sediment level has been stable, although it is moving steadily and appears to be accumulating. We control sediment accumulation because they can damage ecosystems and clog rainwater outfalls. ”