Red River Floodway Siphon
You may wonder what the Red River Floodway has to do with the Seine River. You are not alone. In fact, very few people are aware that the floodway cuts the Seine River in two. In exchange for this flood protection, there have been tremendous impacts on both the upper and lower Seine River.
In order to understand this impact, it is first necessary to understand the siphon structure that allows the river to cross under the floodway and into the city. The Seine River was diverted to flow into an inlet structure; some of the river water is directed into the floodway channel, while the remaining water flows down an underground pipe underneath the floodway and to an outlet structure to "reconnect" with the river.
The Trouble with the Original Siphon
In the mid 1990s, it appeared that the siphon was leaking into the floodway, bleeding precious water from the portion of the Seine that runs through the city. SOS lobbied the province to investigate and repair the siphon for many years. In 1999, the siphon was relined to prevent leakage, but was leaking again by the early 2000s, as evidenced by pools of water appearing above areas where the river ran underground. The river again began to suffer during periods of low rainfall, with a steady stream entering the siphon but a pitiful trickle exiting.
The inlet structure also suffered many deficiencies. Its trash rack of a vertical steel grate was prone to being plugged with woody debris, cattails, weeds, and garbage. A plugged grate resulted in a greater volume of water being diverted into the floodway. Turtles had been found impinged and killed on the grate.
In 2004, SOS was granted research funding from Manitoba Conservation to study the Seine River Crossing. The study was conducted by Cochrane Engineering Ltd and Green Spaces Environmental Consulting. The conclusions were shocking: it was found that the crossing was a total barrier to upstream fish passage, denying fish and other aquatic species access to the 300+ kilometers of river upstream. It was considered an "illegal crossing" under the Federal Fisheries Act.
It was also discovered that 75% of the river's natural water, derived from 90% of the Seine's watershed, was pouring directly into the floodway. This resulted in low river levels along the lower 26 kilometers of the river, impacting both water quality and quantity, and damaging the health of the aquatic habitat.
From October 2009 until March 2010, the Manitoba Floodway Authority carried out an improvement project on the floodway siphon at a cost of nearly $2.5 million. Some of the improvements included:
Installation of a new track rack: The new trash rack is much larger and less prone to clogging.
Installation of a new backup gate: Three of the four original culverts that diverted water from the Seine River into the floodway are no longer used. The remaining culvert was upgraded with a gate that can be closed during periods of flooding when the floodway is in use, thus protecting the community of Grand Pointe from floodwaters backing up out of the floodway.
Raising the elevation of the overflow weir: This work resulted in an increase to the maximum flow in the Seine River from 1100 liters per second to 2500 liters per second and an increase to the average flow from 700 liters per second to 1200 liters per second.
Installation of additional guard rails and metal grate: This improves safety by preventing people and wildlife from falling into the floodway culverts.
Although it took many years of lobbying, SOS is very grateful for the siphon improvements and the vast difference that it has made to the quality and quantity of the river water and aquatic habitat in Winnipeg.