May 29, 2010 (7:30 a.m. approximate start time) to May 30, 2010 (12:00 p.m. approximate stop time)
Heavy rain event summary
Heavy rain and high river levels put many unprotected homes at risk of basement flooding on May 28 and 29, 2010.
Heavy rain passed through the city on Saturday, May 29 (pdf - 97kb). The east side of the city was hardest hit with over 100 millimetres of rain. Saturday’s rain drenched ground that was already saturated by significant rainstorms on May 27 - 28 (pdf - 89kb) and May 24 - 25 (pdf - 122kb).
During Saturday’s rainstorm the Red River was between 12.7 and 15.3 James Avenue datum and rose to 18.3 feet James by June 1 – an increase of 9.2 feet in five days. This is 11.8 feet above normal summer water levels at James and close to 18 feet above normal in the south end of the city. Creeks and streams were also noticeably higher – Sturgeon Creek overtopped Ness Avenue for a number of days and Ness had to be closed.
With heavy rains every summer, there is a significant risk of overloaded sewers backing up through house sewer lines and flowing into basements that aren’t protected. Although basement flooding is a risk at any time of the year, the risk increases with high river levels because the sewer system must then rely more heavily on pumping stations rather than gravity to carry the rainfall runoff.
The wastewater system operated at full capacity (given river levels) during the storm. We maintain all the systems, including 74 lift stations and 30 plus flood pumping stations regularly on a year round basis. We respond to high level and other alarms and during storms on a priority basis. Crews worked around the clock monitoring the land drainage and wastewater systems and correcting any problems. There were some brief interruptions in the operations of a few sewage lift stations and flood pump stations during the rainstorms, largely due to power interruptions or clogged pumps caused by debris washing into the pumps. These types of issues are common during major rain events and not unexpected. We rely on mechanical and electrical systems that can fail and/or have their capacity exceeded. These problems are a result of the storm and not from a lack of maintenance as some have alleged.
The intense downpours on Saturday, May 29, 2010, temporarily also exceeded the capacity of our street land drainage systems and as a result, there were flooded streets and underpasses, and overflowing drainage ditches. The majority of the streets and underpasses were passable within a few hours of the event; however there were some exceptions that had street flooding until Monday.
With total rainfall across the city varying between 100 and 130 millimetres from the storms on Friday and Saturday, the majority of the City’s stormwater retention ponds were at or above their design high water level and into their additional 0.6 m of freeboard. This is not surprising since they are designed for lesser storm amounts. A few of the City’s ponds in residential neighbourhoods did exceed their 0.6 m freeboard range (e.g., Kildonan Meadows and Lake Side Meadows retention ponds in Transcona, a pond off Lee Blvd in Fort Richmond). Investigations are currently underway to assess the hydraulic performance of these lakes. All lakes are now back to their near normal level.
This type of significant basement flooding is not new in Winnipeg. Residents will recall major basement flooding events in July of 2005 (pdf - 595kb), in June and July of 2000 (pdf - 433kb), as well as July (pdf - 92kb) and August (pdf - 91kb) of 1993, and to a lesser extent in other years. Moreover, storms that exceed the capacity of the system will occur again. Our sewer systems, like others everywhere, are not designed for this kind of heavy long duration rain event. Residents should be aware that their basement is connected to many other basements through the sewer system. Residents can protect their homes from sewer backup if they:
- Have a properly installed backwater valve to protect all basement plumbing fixtures. This device, if properly installed, automatically closes if sewage backs up from the main sewer.
- Have a sump pit drainage system (includes a sump pit, a sump pump and a pump discharge pipe.
- Check and maintain their backwater valve and sump pit drainage system regularly.
- Have proper drainage around the foundation of their home.
- Extend downspouts so that water flows away from their home or building.
New homes built since 1979 are required to have backwater valves and new homes built since 1990 are required to have sump pits with pumps. Next time we experience similar circumstances (e.g., extreme rain event and high river levels), all homes that predate these building requirements and have not added this protection will again be vulnerable and at risk of basement flooding.
Our City wastewater and land drainage systems, much like any other city systems, function according to their design, but this isn’t enough to completely protect unprotected properties.
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A concern has been raised by residents in the vicinity that the failure of the Hawthorne lift station resulted in basement flooding. By understanding how the system works as described below, it is easy to show that the basement flooding is not related to the lift station.
The Hawthorne lift station is within a combined sewer area as shown on the map to the right. A combined sewer is fundamentally a land drainage sewer to carry runoff to the river. It is "combined" in that it also carries wastewater to the lift station. The wastewater flow is very small (1% - 3%) when compared to the land drainage flow. Hence the lift station that pumps wastewater has very small pumps compared to the capacity of the system to carry flows to the river.
The runoff from the rainfall event at the end of May exceeded the combined sewer's capacity to carry runoff to the river. This caused levels to rise in the sewer system, resulting in sewer backup.
The loss of the lift station would reduce the carrying capacity of the pipe by an extremely tiny amount. In other words, the storm would have overwhelmed the sewer system whether or not the lift station was operating. In addition, the high river levels further reduced the pipe's capacity.
Runoff and wastewater are carried in the same pipe to the Hawthorne outfall (the point at which it drains into the river). When there is no runoff, minor wastewater flows are diverted to the Hawthorne lift station and to the North End wastewater treatment plant. However, when it rains, major flows overflow a weir (a device used to regulate the flow) and are discharged to the river. When gravity capacity is not available due to high river levels, the flood pumping station is used to pump the runoff to the river. The relevant capacities of the sewer system at this location are as follows:
- The approximate gravity capacity given river levels on May 29 was 6.0 cubic metres per second.
- The capacity of each of two flood pumps is 1.4 cubic metres per second.
- The capacity of the each lift station pump is 0.06 cubic metres per second.
The system is constructed with a flap gate to take advantage of the maximum gravity or pump capacity depending on river levels. In this case, this means the system capacity on May 29 was about 6.0 cubic metres per second.
We can conclude that the sewer system flow was much higher than 6.0 cubic metres per second because levels in the sewer system rose rapidly. Whether or not the lift station with a capacity of 0.06 cubic metres per second was operating would not have impacted sewer levels.
A crew attended the Hawthorne station at 17:42 hours on Saturday May 29 and "activated" the flood pump station in response to rising river levels and in accordance with the flood manual. At this time, levels were normal in the system. The flood pump came on at this time and reduced levels in the sewer and was cycling normally by 18:30 hours.
In response to the major rain fall that started about 18:30 hours, the water levels in the sewer system (as measured at the lift station) rose quickly and to a very high level. At 18:52 hours, the level exceeded the floor level in the lift station of 226.84 metres. At this point, the water level was already above the level of the low basement in the system (226.5 metres). A "station flood" alarm was triggered at 19:00 hours. Before crews could respond to the "station flood" alarm, the sewage lift station motor floor flooded and the two pumps switched off automatically at 19:03 and 19:24 hours respectively. In effect, the storm runoff flooded the lift station.
The peak recorded level in the sewer system at the lift station was 227.4 metres at about 19:30 and remained high for several hours as the flows into the combined system exceeded the capacity of the outfall. Levels in the sewer system away from the station would have been higher. The level at the lift station came down to 226.5 metres at about 22:30 hours and returned to normal at 01:30 on May 30.
In the meantime, staff came to the lift station and removed the motors for the pumps and had them repaired so that the wastewater could be directed back to the wastewater system. The lift station was put back in service with one pump on Sunday May 30 at 15:38 hours.
The magnitude of this storm event caused rainfall runoff far in excess of what our sewer piping systems can manage. As a result, the peak water levels in the sewer system rose well above many basement floor levels in the district. This is not unexpected in Winnipeg and is why we promote backwater valves, sump pumps and drainage away from foundations to protect each home.
As the sewer continued to function by gravity during the peak of the event and because our flood pump station was activated, the system functioned at capacity. The loss of the small sewage lift pumps during this event would have had no effect on levels in the sewer system.
As is our practice after a major storm event, we are reviewing many of our pumping procedures and piping systems to determine if improvements can be made. We also inspected the outfall at this location to ensure it is functioning as expected and found it to be in good condition.
In addition, the City has an ongoing program to increase the capacity of our combined sewer system. The information from the May event will be used to update priorities in that program.
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The Bournais sewage lift station serves the Mission Garden area as shown on the map to the right. The Bournais lift station is known to have stopped pumping during the event due to partial clogging of the pumps and submergence of the pump control system. A concern has been raised by residents in the Mission Gardens area that the City should have maintained the system so that the problem with the Bournais lift station would not have occurred.
The City does routinely maintain all of its 74 sewage lift stations. The stations are monitored remotely at all times and at least every two weeks, a crew goes to each station and checks that the station is operating normally. Even with monitoring and maintenance, an event like the one on May 29 can overload the system and result in backup into the sewer system and into unprotected basements. This is not unexpected in Winnipeg and is why we promote backwater valves, sump pumps and drainage away from foundations to protect each home.
On May 29, the station failed to keep up with the flow and eventually stopped pumping as described below. The high level overflow pipe that is intended to function in this case was also overwhelmed as levels in the interceptor sewer were very high. The system was overwhelmed by flows exceeding capacity.
The Bournais lift station is part of a separate wastewater system servicing Mission Gardens. In addition to the wastewater sewer system, there is a separate land drainage system which conveys runoff to the deep pond on Ravelston Avenue north of Mission Gardens. Runoff in the deep pond is then pumped by the Ravelston deep pond pumping station to the Kildare land drainage system and eventually is discharged into the floodway at the end of Kildare Avenue.
The Bournais lift station contains three submersible pumps with capacities ranging from about 21-28 litres per second. The station receives wastewater from its catchment area through a 600 millimetre diameter inflow pipe. The wastewater is then pumped to a 1200 millimetre interceptor sewer located on Bournais Drive.
There is also a high level overflow at elevation 227.48 metres designed to discharge sewage into the interceptor in the case of total station failure (e.g., loss of power, loss of pumps) as happened in this case. The overflow is intended to be the backup for the station. The low basement in the area is at 227.76 metres.
The station contains a level sensor that turns the pumps on and off as required. The level sensor is also a source of information for at least part of this event. In addition staff were able to determine maximum levels in the system by observing the water lines on the walls of the station and manholes near the station.
The station is monitored continuously and is routinely inspected by a crew. The last inspection prior to event took place on May 24, 2010.
Rainfall started in the area of the Bournais sewage lift station on Saturday May 29 at about 08:10 hours. The records we have since retrieved show that the pump station was operating normally with one pump cycling on and off and keeping up with the flow.
At about 09:00 hours, levels rose quickly and actually went above the sensor that controls the pumps. At 09:03, a high level alarm was received at our operations centre. A high level alarm indicates that the pumps are not keeping up but does not tell the operator that the pumps are not operating, only that they are not keeping up with the inflow. A crew was notified of this low priority alarm; however crews were busy attending high priority alarms where it was known that there were power failures or that pumps had actually stopped working.
This continued through the day and at 22:01 hours, an alarm was received at Bournais that pump number 2 had failed. A crew arrived at the station shortly after midnight on May 30. They observed that all three pumps were not pumping and that the wastewater level in the station was very high. They attempted to start and run the pumps manually but were unsuccessful as the pumps would not run to their satisfaction. They concluded that the pumps were partially or completely clogged and called for assistance. A second crew arrived at 02:00 hours. The sewage level in the station was several metres above the floor level where they could get at the pumps. They closed the inlet valve to the station at 03:35 hours and cycled the pumps manually to reduce the level in the wet well low enough for the pumps to be retrieved.
They removed and serviced the pumps which were clogged with debris and reopened the intake gate at about 04:55 hours. The level at the station rose again above the level alarm set point due the large inflow. However the station operated without incident until levels returned to normal at about 20:40 hours on May 30.
After the event, data was collected by observing water marks in the station and at the interceptor. In addition, pump run records were retrieved from a monitoring system just being installed at the station. We found that the:
- the pumps in the station were off for much of the day as the level sensor controlling the pumps was submerged – however, even if the sensor was working, the pumps couldn’t have functioned properly because they were clogged
- level in the station at some point reached 229.2 metres well above the overflow elevation of 227.48 metres
- interceptor sewer level at Bournais was as high as 230.61 metres indicating the interceptor sewer was also overloaded and surcharged rendering the overflow useless – in fact, wastewater in the interceptor could have flowed back into the Mission Gardens system.
These levels are well in excess of the low basement elevation of 227.76. It is important to note that staff were not aware of this information during the event.
The magnitude of this storm event caused flows in the wastewater system in excess of what our sewer piping systems can manage as evidenced by the high levels in the interceptor sewer. As well, the Bournais lift station was overwhelmed and eventually failed as a result of the pumps being partially clogged with debris and submergence of the pump controls. As a result of the flows exceeding the system capacity, the peak water levels in the sewer system rose well above many basement floor levels in the district. In fact this happened in many areas of Winnipeg and is why we promote backwater valves, sump pumps and drainage away from foundations to protect each home.
As is our practice after a major storm event, we are reviewing many of our pumping procedures and piping systems to determine if improvements can be made.
At this location, we have added a check valve on the overflow so that if the interceptor is overloaded again in the future, wastewater cannot flow back into the Bournais lift station.
We are also reviewing the level monitoring system that controls the pumps at Bournais to ensure controls will not be overwhelmed again in an event like this one.
For more information, contact 311.
This information has been gathered and compiled by the City of Winnipeg for its own use. Although it is the best information available to the City at this time, the City assumes no responsibility for its accuracy and will not accept liability for any use made of it or actions taken in reliance on it.
This page was last updated on June 29, 2018