Report prepared for Alta Vista Ward based on the flooding event of August 10, 2023

Affected Areas are organized by clusters – Scroll down to find your area. General information is provided at the beginning and end of this report.

Introduction

On August 10, 2023, the City of Ottawa experienced a significant weather event that produced an average of 60 millimeters of rain throughout the city over a period of five hours, with a peak recorded volume of 107 millimeters at the Colonnade Road gauge. The intensity of the storm reached a peak rate of 190 millimeters/hour at the Colonnade rain gauge.  The storm moved from West to East band in the south portion of the City Core. Due to the nature of the storm (high peak intensity and high volume), sanitary sewers, storm sewers and overland drainage systems were all affected. 

There are 474 reports of flooding reported through 311 on August 10, 2023. Flooding reports were also collected by the way of a resident survey and a public meeting for residents held on August 23, 2023. 

Reports of flooding shows the source of flooding varied by neighbourhood depending on the age and configuration of the sewer system. Most of the homes in the hardest hit areas of the City were constructed in the early to mid-1960s when the design standard was quite different than today’s.

For many homes constructed before the mid-1960s, flooding occurred via floor drains and basement plumbing, indicating that the sanitary sewer system was overwhelmed due to high flows from weeping tiles/foundation drains connected to the sanitary system. 

For homes constructed after the mid-1960s flooding was caused by surcharging of the storm sewer system, which backed up water into the weeping tiles. 

Many areas experienced, overland flooding, where the water flows and seeps into buildings through windows, doors, and cracks.  

Flood reports are grouped into clusters. A cluster is defined as a grouping of homes that have flooded in a particular area. For Ward 18, there are nine clusters accounting for approximately 137 flood reports.  

Types of Sewer Systems

The City of Ottawa is serviced by various types of sewer systems. Prior to 1948, the

City constructed combined sewers in urban areas, in which both domestic sewage, (used water from kitchen, bathrooms) and surface runoff (precipitation including rain snow and sleet), were conveyed in the same pipe.  

Such systems were prone to surcharging (when a pipe reaches it’s capacity) during large rainfall events and overflows to surface water bodies often occurred. The surcharging of these systems also caused sewage to backup into some basements.  

From 1948 to 1961 the City constructed sanitary sewers and surface runoff was conveyed using ditches and shallow storm sewers. The practice at the time was to use the deeper sanitary sewer pipes to capture foundation drain flow, thereby eliminating the need for sump pumps in homes. This practice unfortunately led to excess flow in the sanitary system during large rainfall events.

In 1961, the City of Ottawa passed a bylaw that required that all new sewer systems be fully separated. In other words, a sanitary sewer system would be designed for domestic flow only and a deeper storm system would capture surface runoff and weeping tile/foundation drain flow.  The City even proceeded to separate sewers in some of the combined areas, however due to outlet restrictions, the storm sewers were shallow and foundation drains remained connected to the sanitary sewers. Also, in many areas where ditch drainage existed, the City constructed storm sewers, but again due to various drainage conditions or limitations the sewers were shallow and foundation drains remained connected to the sanitary system.  

All areas that have foundation drains connected to the sanitary sewers are referred to as partially separated. 

Figure 1.0 below, shows an approximate outline of the partially separated systems (in yellow) and fully separated systems (in orange) in the southern portion of the City core, which was most affected by the storm.

Figure 1 – System Type and Flooding Clusters

The rainfall of August 10, 2023, had both high volume and high intensity, thus impacting the sanitary sewers, the storm sewers and the overland drainage system. Various areas were impacted differently depending on the type of sewer system.

Partially Separated Sewer System

Partially Separated Systems: Partially Separated systems were constructed prior to the early-mid 1960s and have weeping tiles connected to the sanitary sewers. When a high – volume critical event of rain falls over an extended period of time, much of the rainfall infiltrates into the ground and reaches the weeping tiles. This flow then enters the sanitary system causing surcharge since the flow contribution from weeping tiles is much greater than the domestic flow and can exceed the capacity of the sanitary sewers during an extreme storm. This surcharged water then flows back into basements via floor drains and basement plumbing. Many of the flooded areas on August 10, 2023, flooded due to surcharging from the sanitary sewer system.

Fully Separated Sewer System

Fully Separated Systems: In fully separated systems, foundation drains (weeping tiles) are connected to the storm sewer and not the sanitary sewer. However, these systems are also prone to surcharge when too much surface water enters the storm sewer via catch basins. Storm sewers are design to capture frequent rainfall events, so when a critical event occurs, these systems can surcharge. In newer subdivisions (post 1990), the flow entering the system is restricted and excess runoff is managed on the surface, but most older areas (prior to 1990) do not have these types of controls as to not exacerbate surface flooding. When the storm sewer surcharges, water can backup around the weeping tiles and enter the basement via foundation joints and cracks.

Left: Separated Sewer System with Roadside Ditch. Right: Partially Separated System with Roadside Ditch

Ditch Systems: Ditch systems are often like Partially Separated system in that weeping tiles can be connected to the sanitary sewers (prior to mid 1960’s). In many instances, residents may redirect their sump pumps to the house’s internal pluming if there is no adequate outlet outside the building. Like storm sewers, ditches are designed to convey runoff from smaller frequent events with excess flow being directed to the street or even onto private property. 

Surface drainage:  In newer subdivisions, roadways and easement are designed to convey overland flow to an outlet, consisting usually of a ditch system or watercourse (creek, stream, or river).  Old neighbourhoods (prior to 1980), however, have no clearly defined overland flow system and water can accumulate at low points and spill through private property. If the depth of ponding or flow is excessive, water can enter homes via windows, reverse slope driveways or other openings, and can also damage yards. This flow can also impede traffic and damage vehicles. This was the case in many of the flooding clusters.

Combined impact: If a home floods due to storm sewer surcharge or surface water entering via a window, water will accumulate in the basement and drain back out via the floor drain.  This drain is connected to the sanitary sewer and can lead to surcharging of the sanitary sewer if many flooded homes are all draining at once. This can then impact homes further downstream as the sanitary system becomes surcharged. 

Weeping Tiles and Overland Flow

As we noted earlier in the report, prior to the mid-1960s, weeping tiles were connected to the sanitary sewer system, which can cause surcharging of sanitary sewer during critical events.  Disconnecting all of these weeping tiles would be a significant undertaking that would take a significant amount of time with massive disruption to any given community, and it would also require changes to private property plumbing at the homeowner’s expense. Given the rare occurrence of these events in the past, protective plumbing offered a good solution that provided additional protection. As these events increase in frequency in the future, residents may need to look to additional measures, over and above what the city can do on the sewer system, to protect their properties.

Storm sewers in the 1960s were designed to capture runoff from events that are much smaller than what they are designed for today. This means that excess runoff must be managed on the surface, which is challenging due to overland flow systems that also lack modern design. Roads in new subdivisions are designed to run like rivers during critical events, where water cascades from one street to another until it reaches an outlet. In older areas however, water can accumulate in low-lying areas, cut through private property and pond in rear yards, which occurred during the August 10, 2023, event. Creating a well-defined overland flow system in topographically challenged areas can be very difficult to achieve. Upgrading sewer systems can help with frequent storm events, but such infrastructure upgrades will take decades to achieve since upgrading a local system would only push the problem to the downstream system. Storm sewers are only designed to capture runoff from frequent events, so even if all the sewers are upgraded, the overland flow system during critical events would still be problematic. The City will look at ways of improving the overland system as sewers are upgraded, but the topographical constraints of these older areas will make it near impossible to provide a level of service equivalent to what is provided today in new subdivisions. 

The City is working diligently at upgrading its infrastructure to provide the best level of service feasible, but such changes can take decades to implement. Given the increase in flooding events due to climate change, future works will need to include private property measures. The City cannot implement work on private property, but City engineers can use their knowledge and expertise to help residents find the best way of protecting themselves until the infrastructure is upgraded. 

Potential Causes of Flooding on Private Property

In some instances, it appears that homes with existing protective plumbing reported basement flooding following this event. This could have occurred for four reasons:  

  1. The valve malfunctioned,
  2. Improper maintenance of the valve, 
  3. The storm valve functioned properly and while closed, groundwater overwhelmed the foundation drainage system and water entered through cracks and openings, or 
  4. The sanitary valve functioned properly and while closed, all internal drainage (toilets, tubs, showers, sinks) bubbled out through the floor drain. 

Backwater valves are the responsibility of the owner, and any inspection, maintenance or repairs should be undertaken by the owner.

Ward 18 Cluster Analysis

The following section describes the flooding that occurred on August 10, 2023, on a cluster-by-cluster basis and provides a possible explanation.  The information presented herein is based on analysis of the sewer system using existing computer models and/or historical information. 

Alta Vista/Bank Cluster:

Location and System Characteristics:  

  • 26 properties reported flooding.  
  • The Alta Vista / Bank area was developed in the 1950s and early 1960s and is considered a partially separated area, which means that weeping tiles are connected to the sanitary sewer system.
Figure 2 – Alta Vista/Bank Cluster, August 10 Flooding

Type of Flooding

  • Overland flooding occurred on Wesmar Drive
  • Flooded via basement plumbing and floor drains, indicating that sanitary sewer surcharge was most likely the cause Alta-Vista and Edge Hill Place based on initial information collected

Previous Flooding and Remedial Measures

  • 30 reports of historical flooding in this area, with the majority (20+) having occurred on September 9, 2004 (this was a high-volume critical event)
  • surcharged the sanitary system and caused flooding via floor drains and basement plumbing
  • A 2008 report presented the preliminary design for integrated infrastructure works along Bank Street from Walkley Road to Riverside Drive. This project included the replacement of the sanitary sewer between Alta Vista and the Rideau River Collector at the intersection of Bank Street and Ohio Streets. Construction to begin in 2024

Probable Cause of Flooding

  • Flooding on Alta-Vista and Edge Hill due to surcharging of the sanitary sewer 
  • Flooding along Wesmar  Drive was due to overland runoff from the street spilling into private properties (rear yards and reverse slope driveways) and entering homes via openings
  • The overland drainage issue on Wesmar Drive is currently being investigated

Current Investigation and Next Steps

  • A topographic analysis of Wesmar Drive was undertaken following reports of flooding of a rear yard as well as a reverse driveway; The reverse driveway on Wesmar Drive has been placed on the 2024 list for remediation
  • The section of Wesmar Drive just west of Alta Vista has been added to the list of drainage projects and will be addressed within the next few years to prevent water from spilling into adjacent yards
  • The proposed sanitary diversion work has received budget approval and construction is targeted to begin in 2026
  • Bank Street and Alta Vista – a review of the sanitary sewer model showed significant surcharge, which would have impacted homes in that area; it was confirmed by the flooding reports
  • Construction of the integrated project from Walkley to Riverside drive has started with the Riverside Drive/Bank Street intersection currently under construction. The project now proposes to re-direct the sanitary sewer at the intersection of Bank Street and Alta Vista south to another sanitary collector. The diversion work will include a new sanitary sewer that will greatly improve local sewer hydraulics in the area. This work is slated to start in 2026

Walkley Heron Cluster:

Location and System Characteristics

  • Nine homes reported flooding in this cluster
  • The Walkley Heron area was developed in the early 1960s and is considered a fully separated area, which means that weeping tiles are connected to the storm sewer system
Figure 3 – Walkley/Heron Cluster, August 10 Flooding

Type of Flooding

  • Water mostly entered the basement through the floor drain, which indicated that the sanitary system may have been surcharged
  • On Arizona Avenue there was some basement flooding from water coming from the foundation wall and on Lorraine Avenue there was flooding via a depressed driveway as water entered though both floor drain and driveway
  • There was significant roadway flooding

Previous Flooding and Remedial Measures

  • The high intensity critical events of August 4, 1988, and August 8, 1996 caused approximately five properties to flood in this area 
  • The most recent reported flooding was during the October 20, 2017, event, in which two properties reported flooding 
  • Storm sewer system was deemed to perform within its design level of service with flooding only occurring during critical events

Probable Cause of Flooding

  • Basement flooding occurred due to the surcharge of both the storm and sanitary systems  
  • The lack of a defined overland flow system caused water to spill into depressed driveways or enter via windows 
  • Further investigation will be undertaken in this area to determine if an infrastructure solution is feasible, however given the topographical constraints, options to minimize surcharging of the storm sewer may be limited

Current Investigation and Next Steps

  • Flooded properties on both Arizona Avenue and Lorraine Avenue are located along overland flow routes and are mostly within low point areas that collect upstream surface water
  • Depressed driveways along this route are at risk of flooding as excess surface runoff tries to find its way to an outlet
  • The modelling indicates that the storm system in most of the cluster area was significantly surcharged and showed water surcharging to the surface at some locations
  • The modeling showed that surcharging of the sanitary system should not have occurred however there are reports of water entering via the floor drain
  • Further investigations will be required, but at this time it is suspected that the sanitary system was indirectly impacted by flooded basements, that is that basements that flooded by other means drained back to the sanitary system via the floor drain
  • Investigations will be required to see if stormwater solutions can be implemented to improve the storm system level of service

Sharel Cluster:

Location and System Characteristics

  • 12 homes reported flooding in this cluster. 
  • The Sharel area was developed in the early 1960s and is a combination of both partially separated and fully separated areas, meaning that weeping tiles are connected to the sanitary sewer system in parts of the area and to the storm sewer in others
Figure 4 – Sharel Cluster, August 10 Flooding

Type of Flooding

  • Residents reported flooding from the floor drains, foundation cracks, and around other fixtures. Roadway flooding was also reported. 

Previous Flooding and Remedial Measures

  • A few homes in this area have reported flooding during high intensity critical events of 1986, 1988, and 1996. Flooding may have been caused by an overwhelmed surface drainage system
  • The storm sewer system was deemed to perform within its design level of service with flooding only occurring during critical events

Probable Cause of Flooding

  • Roadway flooding was caused by excess overland flow but could have also been caused by a surcharged storm system that was breaking out to surface within low point areas
  • Most of the area is partially separated, it is suspected that some homes have weeping tiles connected to the storm system and would have been flooded by the surcharged storm sewer system that backed up into weeping tiles
  • Sanitary sewers may have been indirectly impacted due to flooded basements draining back to the sanitary system via floor drains. Further investigation will be undertaken 

Current Investigation and Next Steps:

  • The properties that flooded on Sharel Drive are located near a low point on the roadway, which collects upstream surface water and may lead to excess ponding during rare events
  • Topographic mapping shows that water must pond approximately 0.5 meters on Sharel Drive before spilling to the next downstream segment. If the storm system is at capacity, excess flow would remain on the surface, which explains the reports of excessive depth on Sharel Drive
  • Analysis of the overland flow system will be undertaken, and a review of the storm system will also be undertaken but given the design standard at which the system was built (1960s) 

Saunderson Cluster:

Location and Area Characteristics

  • 12 properties reported flooding in this cluster
  • This area was developed in the 1950s and is considered partially separated, which means that weeping tiles are connected to the sanitary sewers
Figure 5 – Saunderson Cluster, August 10 Flooding

Type of Flooding

  • There was significant flow accumulation on the surface that led to the flooding of homes via openings
  • There were also a few instances of water entering homes via flood drains and foundation cracks/joints 
  • Data indicates that some homes had significant rear and front yard flooding on Raglan Avenue, Saunderson Drive and Hutton Avenue, and that some homes reported basement flooding on Hamlet Road and on Olympia Crescent.  o There was also evidence of excessive overland flow on Hamlet Road coming from the Hillcrest High School area

Previous Flooding and Remedial Measures

  • Properties in this area reported flooding during the 1996, 2009 and 2017 events
  • Previous floods were mostly through floor drains, indicating that the cause was sanitary sewer surcharge.
  • This cluster falls within the greater Elmvale Acres area which has been the subject of various past studies, including in 1992, 1994, and 1995. More recent studies include the 2014 sanitary trunk model, 2016 detailed sanitary model, and 2019 storm and sanitary studies
  • Recommendations from these studies have been implemented over time in the neighbourhood through subsequent design and construction projects
  • Recent and upcoming work relevant to this cluster includes upgrades on Hamlet Road and the replacement and upgrade of sanitary and storm trunk sewers on Saunderson Drive and Valley Drive

Probable Cause of Flooding

  • It is suspected that some homes in this area may have weeping tiles connected to the storm sewer system, thus putting them at risk of flooding from storm sewer surcharge during critical events
  • Some homes flooded via floor drains and basement plumbing due to sanitary sewer surcharge
  • It is suspected that other flooded basements and flooded streets caused an excess of extraneous flow into the sanitary sewer system.
  • Overland flow

Current Investigation and Next Steps

  • Modelling shows that the sanitary sewer system on Saunderson Drive is not surcharged during critical events
  • The sanitary sewers west of Saunderson Drive on Smyth Road and upstream on Haig Drive would be surcharged within typical basement elevation and could cause basement flooding; other portions may have also surcharged. When streets are flooded like they were in this cluster area, water can enter the sanitary system via perforated venting holes on maintenance hole covers. This will be investigated further. 
  • The storm sewer system shows significant surcharging and any homes connected to the storm sewer would be impacted. 
  • Overland flow will require further investigations as significant ponding occurs on both the City Right of Way and in rear yards. 
  • Modelling shows that water will pond in excess of 35 centimeters before spilling on to Smyth Road. 
  • Rear yards can also have ponding depths in the 30 centimeters range. It is unknown at this time if Right of Way water spilled into rear yards. 
  • Overland flow from Hillcrest High School could have also contributed to the excessive depth of flow on Hamlet Road. 
  • The City Currently has a storm sewer renewal project along Valley Drive, extending along Saunderson to the dead-end past Haig Drive. The third phase will benefit the storm drainage in this cluster area by reducing the level of surcharging in the storm sewer system. This work is anticipated to start pending approvals including budget approval.
  • The sanitary sewer model will also be re-evaluated to better understand how the sanitary sewer system could have been impacted in this area and determine if improvements are required and/or feasible. 

Delmar Cluster:

Location and Area Characteristics

  • 24 properties reported flooding in this cluster  
  • The Delmar Drive area was constructed in the mid-1960s and is a fully separated system, which means that the weeping tiles are connected to storm sewers  
Figure 6 – Delmar Cluster, August 10 Flooding

Type of Flooding

  • Resident survey feedback indicated basement flooding within this cluster. These incidents cite various entry points, including floor drains, foundation cracks, walls, and window wells. Residents on Delvin Crescent also reported instances of backyard ponding in addition to basement flooding
  • These incidents cite various entry points, including floor drains, foundation cracks, walls, and window wells 
  • Residents on Delvin Crescent also reported instances of backyard ponding in addition to basement flooding
  • There was also significant roadway flooding which impacted vehicles travelling on Delmar Drive

Previous Flooding and Remedial Measures

  • There are over 60 reports of flooding in this Cluster area, the majority from events in 1988, 1996, 2009
  • These were high intensity critical events which produced a significant amount of runoff in a short period of time, impacting mostly the storm sewer system and the overland flow system
  • The City created a dual drainage model of this neighbourhood in 2015 to support the replacement of the Valley Drive storm trunk, and in 2020 and engineering firm leveraged this model to complete the Halifax/Valley Drive Dual Drainage Study which confirmed the existing level of service and investigated remedial solutions
  •  The City has since completed additional analysis on Delmar Drive. The low point on Delmar Drive is one of the problem areas as it was found that water depth became significant before it spilled eastward via private property
  • This greatly limited solutions of reducing surcharge in the storm sewer system using inlet control devices since such solutions would have worsened the surface flooding situation. Upsizing the entire local storm sewer was not feasible since the storm sewer capacity is limited by the capacity in the existing downstream system
  • Upsizing the entire local storm sewer was not feasible since the storm sewer capacity is limited by the capacity in the existing downstream system
  • The storm sewers that connect Delmar Drive to the Kilborn  Allotment Garden run through private property and construction would impact adjacent homes. As such, only limited improvements were recommended until the downstream system is upgraded
  • The existing sanitary sewers on Delmar Drive from Beattie Avenue to Playfair Drive are also recommended to be upgraded in conjunction with the proposed storm sewer upgrades to improve the local capacity

Probable Cause of Flooding

  • Flooding in this cluster area is likely caused by a combination of storm sewer surcharge, sanitary sewer surcharge and overland flooding
  •  When basements flood due to overland flow or storm sewer surcharge, the water returns to the sanitary sewer via the flood drain and can cause surcharging of the sanitary sewer system. Further investigation is ongoing to find a long-term solution

Current Investigation and Next Steps

  • Short term storm drainage improvements are scheduled for the near future, but this will only help during more frequent and less severe events
  • Solutions such as storm water facilities in the allotment garden area will be studied but implementing them will take time and require environmental assessments  

Sandra Cluster:

Location and Area Characteristics

  • Seven properties reported flooding in this cluster
  • The Sandra Avenue sewer system was constructed in the early 1960s and is a partially separated system, meaning that weeping tiles are connected to the sanitary sewer system 
Figure 7 – Sandra Cluster, August 10 Flooding

Type of Flooding

  • Residents reported property flooding as well as basement flooding
  • The majority of the flooding was due to an overwhelmed drainage system at the rear of the properties in the Allotment Garden areas, although some properties may have experienced sanitary backup as well

Previous Flooding and Remedial Measures

  • There are five reports of historical flooding this area, one in 2005, one in 2006, two in 1996 and one in 2014.   
  • Due to the sporadic nature of the previous flooding reports, no investigation was previously undertaken at this specific location.  
  • A study of the entire Elmvale Acres area was undertaken following the 2017 event, however the main focus of the study was the sanitary sewer system, and it did not identify this specific location as being a concern for flooding.

Probable Cause of Flooding

  • The flooding reports in this cluster point to surface draining issues,  o The area of concern is the Allotment Gardens behind Sandra Avenue
  • There may have been sanitary surcharge due to additional inflow which will require further investigation

Current Investigation and Next Steps

  • Survey results from residents on Sandra Avenue noted that runoff in the Allotment Garden behind the homes on Sandra Avenue overwhelmed the ditch and culvert system. The Allotment Garden area will also be looked at in greater detail to see both short term and long-term solutions can be implemented  
  • Modelling analysis of the storm sewer system showed significant surcharge in the storm trunk through the Allotment Garden, which could have hindered the ability of the system to capture surface runoff and could have also led to surface breakout near Haig Drive 
  • The computer simulation of the sanitary system indicates that the sanitary sewers should not have surcharged, but flooding from other causes draining to the floor drain may have led to the sanitary sewer being impacted 
  • Remedial measures for this overland flow system are currently being investigated 
  • The sanitary sewer model for this area will be re-visited to see if modifications to the sanitary infrastructure to improve the level of service are feasible

Arch Cluster:

Location and Area Characteristics

  • 33 properties reported flooding in this cluster, with the most severely affected properties located along Adams Avenue 
  • The sewer system in this area is partially separated, meaning that weeping tiles are connected to the sanitary sewers
Figure 8 – Arch Cluster, August 10 Flooding

Type of Flooding

  • Residents reported basement flooding via various entry points, with the majority attributing the flooding to floor drains
  • There were reports of basement flooding caused by foundation cracks in two properties and window well issues in one property
  • Residents also reported roadway flooding and provided a video showing the storm sewer system surcharging to surface

Previous Flooding and Remedial Measures

  • This cluster area has a history of flooding, with over 60 reported cases from various year, with the majority being in 1996, 2004 and 2017
  • In 1993, a study of the drainage area and found that the sanitary sewer system had limited capacity and that a significant amount of rainfall runoff was being introduced via foundation drains and depressed driveway connections.
  • Recommendations were made to disconnect depressed driveways and upgrade some sewers.
  • Following the 1996 event where 204 properties flooded, the City upgraded sanitary sewers on Saunderson Drive, Wingate Drive and Arch Street. As a result of the September 2004 event where 47 properties flooded, the City upgraded sewers on Pleasant Park Road, Dickens Avenue and Holt Crescent. 
  • Following the 2017 event, an additional study was done that identified flooding in the Adams Avenue – Holt Crescent area to be caused by surface flooding and overland drainage issues. The storm sewer system was over capacity, however since most homes do not have weeping tiles connected to the storm sewer system, storm sewer surcharge was not the greater source of basement flooding.  
  • The study recommended remedial work along Arch Street and Canterbury Road. The improvements are proposed to alleviate basement flooding issues and include sanitary sewer upsizing, replacement of sewers, and elimination of existing easements between residential properties. Construction is scheduled to start in 2024. 
  • Following the 2024 work, the next phase (in yellow below) consists of upsizing sewers on Haig Drive and Fleming Avenue, which will allow us to divert sanitary flow away from Adams Avenue, 
Figure 9 – Arch Cluster, Sanitary Sewer Upgrades

Cause of Flooding

  • Basement flooding in this area was caused by sanitary sewer surcharging due to the partially separated nature of the sewershed 
  • In addition, the flat nature of many driveways would have cause roadway flooding to make it way back towards houses
  • There are current construction projects in the area to reduce the risk of flooding

Current Investigation and Next Steps

  • Modelling of the sewer system for the August 10, 2023, event was undertaken by city staff, which confirmed surcharging of the sanitary system.  
  • The Arch-Canterbury is scheduled  to start in 2024 and the Haig-Fleming works will start in the following years pending approvals. Additional downstream upgrades are being considered.

Weston Cluster

Location and Area Characteristics  

  • Five properties reported flooding in this small cluster located near the western end of Weston Drive. 
  • The sewer system in this area is partially separated, meaning that weeping tiles are connected to the sanitary sewers.
Figure 10 – Weston Cluster, August 10 Flooding

Type of Flooding

  • Survey reports from residents pointed to water entering via the floor drain

Previous Flooding and Remedial Measures

  • This cluster area has a history of flooding, with over 25 reported cases from various year, with many of them being in 2017
  • A study of the entire Elmvale Acres area was undertaken following the 2017 event

Cause of Flooding

  • Basement flooding in this area was caused by sanitary sewer surcharging due to the partially separated nature of the sewershed. 

Current Investigation and Next Steps

  • Modelling of the sewer system was undertaken by the City, which confirmed surcharging of the sanitary system. The sanitary system surcharges due to excess wet weather inflow from weeping tiles
  • Recommending installing backwater valves on sanitary sewer lateral pipes would be the most feasible interim solution until sanitary sewers can be upgrade as part of infrastructure renewal work

Valley Drive Cluster: 

Location and Area Characteristics   

  • Nine properties reported flooding in this cluster located near Valley Drive and on Plesser Street. 
  • The sewer system in this area is partially separated, meaning that weeping tiles are connected to the sanitary sewers. However, some homes on Valley Drive have connections to the storm sewers.
Figure 11 – Valley Drive Cluster, August 10 Flooding

Type of Flooding

  • Survey reports from residents pointed to excess surface water on Plesser Street and Gill Avenue as well as water entering via the floor drains

Previous Flooding and Remedial Measures

  • This cluster area has a history of flooding, with over 60 reported cases from various years, most of them occurring in 1988, 1996, 1004 and 2017.
  • A study of the entire Elmvale Acres area was undertaken following the 2017 event.
  • The City studied the Valley Drive storm trunk in 2015 to support its replacement, which to date has been constructed from Walkley Road to Weston Park. The next phase of the storm trunk renewal is pending approvals including budget approval and will extend north along Saunderson Drive to the dead end north of Haig Drive. 
  • The upgraded storm trunk has improved the level of service in this cluster, the event of August 10, 2023, was greater than the level of protection for this system. 

Cause of Flooding

  • Basement flooding in this area was mostly caused by sanitary sewer surcharging due to the partially separated nature of the sewershed
  • Excess surface runoff may have also cause flooding of a depressed driveway on Plesser Street as well as a yard on Gill Avenue. Basement flooding on Valley Drive may have been caused by storm sewer surcharging in conjunction with faulty or missing backwater valves

Cuurent Investigation and Next Steps

  • Modelling of the sewer system was undertaken by the City, which confirmed surcharging of the sanitary system. The sanitary system surcharges due to excess wet weather inflow from weeping tiles.  o Adding a berm in the park behind Plesser Street is currently being studied. This berm would prevent overland flow from the park from spilling onto Plesser Street.
  • Recommending installing backwater valves on sanitary sewer lateral pipes would be the most feasible interim solution until sanitary sewers can be upgrade as part of infrastructure renewal work 

Flooding in Non-Cluster Groups

  • Approximately 182 reports in Ward 18 were submitted to the City regarding basement flooding. 
  • 137 of those are within cluster groups while the remaining 45 are assumed being due to property issues. 
  • Based on the investigation, many areas in Ward 18 flooded due to a private property issue such as tree roots in the sewer lateral, eavestrough downspout connected to the foundation drain or damage to the sewer lateral pipe. This does not mean however, that the sanitary did system did not surcharge since neighbours may have simply not reported flooding or they may have had installed a backwater valve.  

Roadway Flooding

It is normal for water to pool around a catch basin in wet weather. Roads are designed to drain based on the sewer capacity. Roadside ditches are cleared at the outlet end of the ditch system to provide drainage for the spring melt. More information can be found on Ottawa.ca.  

What Can Residents do?

Understanding flooding events can be overwhelming and stressful, we are committed to working with Council, residents to improve our City’s infrastructure. 

Next steps include updating this community on: 

  • The benefits of installing backwater vales and other floodproofing alternatives that would benefit their properties.
  • City staff have met with some residents and will continue to meet with residents to look at ways of protecting their properties from overland flow.
  • The benefit of homes having their sewer lateral inspected or that they apply to the Residential Protective Plumbing Program since the inspection will identify issues on the property.  Should there be no issues with the private connection, the City will then look at the individual location in greater detail. 

The City remains committed to its proactive communications approach and we always welcome feedback.  

Residential Protective Plumbing Program

  • The Residential Protective Plumbing Program (RPPP) provides financial assistance to qualified City of Ottawa property owners for the installation of protective plumbing devices, such as sump pumps and storm and sanitary backwater valves to prevent water and sewage from flooding homes as a result of increased water level (surcharging) in the City’s sewer system.

Residential Grants for Sewer Backups

  • Residents affected by flooding three or more times could be eligible for a grant of up to $1,000 under the Residential Compassionate Grant policy for sewer backups.

Feedback and 311  

Feedback and data from the community are valuable to us, and we have been proactively reaching out to Councillors in the most impacted areas. 

We encourage residents and Councillors to reach out to us at any time to share flooding locations, impacts and other concerns.

Any observed conditions can be reported to 3-1-1.

Next Steps 

The next steps will consist of further simulating the actual flooding event to determine if additional causes to the ones described above were responsible for the flooding and determine if infrastructure improvements are warranted and feasible to reduce the risk of future flooding.  

On October 25, 2023, Council passed  Councillor Carr’s motion for staff to better respond to an emergency flooding event. Infrastructure and Water Services will be reporting back to Council in 2024. 

The City is also in the process of reviewing the Residential Protective Plumbing Program and the Residential Compassionate Grant policy. There will be public consultation in the coming months and the proposed changes will be going to Environment and Climate Change Committee in 2024.