Reducing Flood Risk from Flood Plain to Floor Drain Developing a Canadian Standard for Design Standard Adaptation in Existing Communities

Reducing Flood Risk from
 Flood Plain to Floor Drain

Developing a Canadian Standard for Design Standard Adaptation in Existing Communities

Robert J. Muir, M.A.Sc., P.Eng

1.0 Introduction

Flood risks in communities across Canada originate largely from intrinsic design standard limitations related to historical flood hazard management and infrastructure design approaches. Parts of many historical communities have storm drainage and wastewater conveyance systems that overflow or surcharge on a relatively frequent basis, even under moderate storm conditions. In some specific regions of Canada, Environment and Climate Change Canada’s Engineering Climate Datasets also indicate that short duration rainfall intensities affecting infrastructure performance are increasing, suggesting that some existing systems may be even more stressed than at the time of installation. More importantly, significant urbanization and intensification in other regions has added higher demands on existing infrastructure due to greater runoff potential and increased dry and wet weather loadings. These factors contribute to increasing catastrophic losses from flood events across Canada which are a renewed priority for government and insurance industry sectors.

While some infrastructure may be valued for its historical significance[1], vintage infrastructure is more scorned for its low level of service than praised for heritage value as it often contributes to flood risk and damages.

2.0 History of Design Standard Evolution

2.1 Overview
The evolution of infrastructure design standards and risk management practices have evolved considerably over the past 100 years. As a result, levels of service in urbanized areas have increased substantially beginning with improved flood hazard management in some jurisdictions 60[2] years ago, national building code improvements over 40 years ago[3], and regional stormwater master drainage planning 30 years ago[4]. Characterizing these factors affecting flood vulnerability is key to understanding and prioritizing flood risk reduction efforts in existing communities.

Analysis of historical flooding patterns in urban areas as a result of extreme rainfall has revealed order of magnitude difference in risk profile (i.e., flood density) in different established communities. For example, flood reports in Toronto following the May 12, 2000, August 19, 2005 and July 8, 2013 storm demonstrate the highest density of flooding in partially-separated sewersheds, lower flood densities in sewersheds with CSO relief, and lowest densities in newer developments. Similar analysis in the City of Markham revealed during the August 19, 2005 event 1/6th of the flood density in post-1980 service areas as compared to pre-1980 service areas on a normalized basis. Similarly, even newer subdivision exhibited even lower flood risks during a severe July 16, 2017 storm showing eastern Markham subdivisions serviced after 1990 had 1/60th of the reported flood density as pre-1980’s ones. These changes in risk profile reflect the evolution and improvement  in storm drainage system capacity in the late 1970s when dual drainage was adopted (one of the first communities in Canada[5]), and the early 1980’s when master drainage planning was first prescribed[6]. They also reflect the evolution of wastewater system wet weather flow stresses that have been shown to be an order of magnitude higher in pre 1970’s partially-separated areas[7]. These stresses have an accentuated, non-linear impact on surcharge and back-up potential in common gravity-drained wastewater collection systems.

While design standards have evolved differently from region to region and city to city across Canada, broad changes in management and design practices are summarized below for each of the risk categories of riverine, stormwater and wastewater.

2.2 Floodplain Management
Floodplain management to manage riverine flooding risks originated in some provinces in the mid 1900’s, sometimes hundreds of years after initial settlement began in historical communities.  Initial management zones were based on simple estimation of ‘top of bank’ limits using topographic elevation contours superimposed on and aerial photography. Canada's National Flood Damage Reduction (FDR) Program protocols standardized flood mapping methods in 1976-1995[8] under the national program. In some provinces, technical guidelines for flood plain mapping, including both hydrology and hydraulic aspects of the analysis, have been developed and updated since the 1980’s by responsible ministries[9] and regulatory authorities[10].

The extent of flooding defined on flood hazard mapping is typically used to restrict development of any proposed vulnerable land uses (e.g., urban uses) and to identify risk management practices where existing vulnerabilities cannot be reduced, e.g., through removal of the development,  and where damage mitigation is pursued instead[11]. For example, historical settlements in proximity to watercourses for the purpose of power generation/milling, water supply and transportation may have intrinsic risks that can only be managed through flood proofing should removal of the land use not be feasible (e.g., vulnerable development is vital to the community/economy).

Even when robust and effective[12] floodplain and natural hazard management programs are in place in some provinces, the spatial extent of hazard mapping to guide development may only have been estimated in recent years[13], especially where riverine hazards encroached on existing development or where risks have been obscured by numerous enclosures of minor tributaries[14]. In such cases, the minor tributaries with no hazard mapping, sometimes called ‘lost rivers’, may essentially behave as municipal drainage systems serviced by underground infrastructure and residual overland flow paths.  
Communities with riverine flooding risks often have municipal infrastructure servicing limitations as well, as they are often associated with pre-1980’s servicing with less robust storm and wastewater servicing standards and practices.

2.3 Wastewater Collection 
The evolution of urban drainage systems is documented in Adams (1987)[15]. Combined sewers originated in the mid 1800’s following epidemics related to inadequate dry-carriage of “night soil” (human waste) and the subsequent conversion of storm sewers to combined storm and wastewater systems. While effective at addressing human waste locally, adverse receiving water impacts resulted in contaminated water supply resulting the in the addition of interceptor sewers to convey combined loadings to a central treatment facility. The finite capacity of interceptors necessitated the incorporation of combined sewer overflows (CSOs) that relieve the collection system to local receiving water when combined flows exceed the design capacity (typically 2-3 times dry weather flow).

By the mid 1900’s, combined sewers were no longer constructed and separate wastewater and storm water systems were constructed in new development. Sewer separation in earlier combined service areas has been pursued to reduce CSO impacts, whereby a new storm system is constructed to collect road runoff but groundwater from foundation drains (weeping tiles) remains connected to the wastewater system – hence the term ‘partially separated’ systems. While less prone to surcharge and back up into properties as combined sewers, partially separated sewers are prone to both significant extraneous wet weather flow from a variety of sources including groundwater infiltration in the mainline sewer, service laterals and connected foundation drains, and inflow from maintenance access lid and especially rooftops that are sometimes connected to the foundation drains.

By the mid 1970’s changes in the Canadian Building Code resulted in the prohibition of foundation drain and other direct inflows to the wastewater system. Systems built to this highest standard are deemed fully-separated systems.  They are characterized by extreme weather flow stresses that are a tenth of partially separated systems based on statistical analysis conducted in the City of Ottawa. Consequently, they exhibit the lowest flood risk potential related to wastewater system back-up owing to conveyance system capacity.

2.4 Stormwater Drainage and Management
While some infrastructure may be valued for its historical significance[16], vintage infrastructure is more scorned for the low level of service it provides than it is praised for heritage value. This is due to its inherent design capacity limitations often contribute to flood risk and damages. When storm drainage systems were introduced to relieve combined sewers and the remaining complement partially-separated sewers, they were typically designed to a low level of service to provide convenience from the nuisance accumulation of runoff. It was common for system to be designed to a 2-year return period, i.e., being capable of conveying a storm that has a ½, or 50%, change of occurring each year. Later, 5-year levels of service were introduced resulting in larger conveyance capacity. During infrequent storms that exceed the storm sewer capacity, overland runoff could adversely affect private properties by flowing uncontrolled along the previous ‘lost river’ low-lying drainage path.

By the late 1970’s and 1980’s the concept of dual-drainage design was introduced whereby frequent storms are conveyed in the storm sewer (the minor system) and infrequent storms are conveyed safely to the receiving waters / river along roadways or designed channels (the major system). While dual-drainage design increases storm system capacity, typically up to a 100-year return period, it has the complementary benefit of reducing the potential for uncontrolled inflows to wastewater systems via window wells, reverse slope driveways, and depressed walkouts  that ultimately can enter basement floor drains. Analysis of reported flood claims following the July 8, 2013 storm revealed that the number of basement flooding claims were reported to one insurer were up to 3 times higher in the estimated overland flow zones in the City of Toronto[17] – this demonstrates the interconnection between the storm drainage systems and the wastewater systems.

Stormwater drainage systems have evolved beyond their earliest conveyance function to provide a broader range of management functions intended to reduce downstream flooding and erosion impacts through detention and release of collected runoff. Initially on-line quantity control  storage facilities were constructed within valley corridors, up to the 1980’s in Ontario. These were replaced by off-line facilities and combined water quality and quantity control facilities in the 1990’s in Ontario. Over past decades, distributed low impact development  best management practices (LID BMPs) have been incorporated into stormwater drainage and management system to maintain recharge and baseflows and to better mitigate erosion risks by reducing runoff closer to source, primarily through infiltration to groundwater systems.

3.0 History of Operation and Maintenance Practices

Cities and operating authorities conduct inspections and routine maintenance and rehabilitation of core public infrastructure as part of operational activities. These ongoing activities help to maintain infrastructure’s hydraulic performance including structures that are critical to riverine system performance, as well as wastewater and stormwater infrastructure collection systems. In many cases, municipalities’ duty of care for maintaining infrastructure is prescribed legally in instruments such as certificates of authorization, environment compliance approvals, etc..

Technologies to support the inspection of underground infrastructure have improved over the past 40 years. The City of Etobicoke, Ontario was one of the first municipalities to employ still photography for the purpose of inspection of sewer conditions in the 1970’s[18]. Subsequently, close circuit television (CCTV) inspection technologies were developed however the volume of analogue data (video footage) was a challenge for effective management. Typically, sewers were inspected only after construction and not as part of routine ongoing inspection[19]. Partial standardized codes to the characterization and prioritization of system defects began was introduced with the Water Research Centre (WRc) codes in the UK, and adopted in Canada in the late 1970’s and early 1980’s. NASSCO, the National Association of Sewer Service Companies, was founded in 1976 and its Pipeline Assessment and Certification Program (PACP) standard has now replaced WRc as the North America Standard.

The standard of care for inspection, operation and maintenance activities as defined through programs such as the National Water and Wastewater Benchmarking Initiative can help inform details of operational Best Practices. Maintaining infrastructure capacity through clearing blockages, or rehabilitating system components prone to short-term failure, provides a flood risk reduction benefit as well as a supports long term lifecycle asset management. 

Legal liability for drainage systems, and other municipal responsibilities, is often related to operational activities (e.g., meeting standard of care where a duty of care is owed) or delays in implementing programs (execution of policy), as opposed to negligence related to low, historical design standards.

4.0 History of Flood Mitigation Cost Benefit

Cost benefit analysis is required to justify critical, high-cost flood risk reduction measures. These is very wide spectrum of risk associated with flooding across realms of riverine, storm and wastewater infrastructure systems. Some risks are negligible in some watersheds, river-reaches, trunk sewer systems,  local sewer catchments, sewer segments or building structure. An example would include modern subdivisions constructed with robust floodplain management policies, fully-separated sanitary sewers and dual-drainage stormwater conveyance – flood risk in such systems is negligible and systems are shown to be resilient for even future climate conditions. Some risks are acceptably small but insurable, meaning risk can be readily transferred.  Others risks are higher and widespread in a neighbourhood or catchment and may justify the investment in targeted local flood risk prevention activities that are low-cost, no-regret, activities, e.g., downspout disconnection from wastewater systems and private plumbing isolation from municipal systems with backwater valves, etc. Where risks are moderate or higher based on flood density, and where costs are significant, the benefits of deferred flood damages must be weighted against the cost of implementation.

Examples of robust cost-benefit analysis for flood risk reduction in Canada include the Manitoba Royal Commission Report of December 1958 recommended the construction of the Red River Floodway. The  $72.5 million projects yielded average annual savings of flood damage and management costs, resulting in a cost benefit ratio of 1:2.73 in construction costs versus flooding costs[20].

Watt (1984)[21] describes economic efficiency criteria and principles associated with river flood risk reduction projects. He notes “It is therefore reasonable to require that all projects that provide or improve flood protection be justified economically before public funds are allocated”. He adds that “contrary to public opinion, the direct and indirect benefits of flood control tend to overshadow the intangible benefits” and therefore “expected benefits should exceed cost by a sufficient margin and the level of protection should not be pushed beyond the point where the additional costs exceed the incremental benefit.” As flood control projects rank high in terms of public welfare, these are often approved even when the benefit/costs is slightly below unity.

The Conservation Ontario Class Environmental Assessment For Remedial Flood and Erosion Control Projects[22], an approved Ontario Environmental Assessment process for flood mitigation projects. The first step includes ‘problem identification’, to determine if the risk to property or human life is sufficient to warrant Conservation Authority involvement. This screening may be considered the application of the ‘risk lens’ to is currently promoted for infrastructure investments in Ontario as part of its Long-Term Infrastructure Program[23] – low risk conditions would not warrant follow-up study. Studies that advance develop and evaluate alternatives to flood remediation including the mandatory ‘no nothing’ alternative that may be selected as preferred when risk are minimal and consequences are low. A range of alternatives are considered escalating from flood-proofing to structural measures (i.e., large capital works) for which alternatives are evaluated according to technical effectiveness (i.e., flood risk reduction) and costs.

Municipal storm drainage projects may undergo economic screen of alternatives to guide remediation efforts on a sewershed-by-sewershed basis, however it is not a common practice. The City of Stratford City-wide Storm System Master Plan[24] by Dillon Consulting Limited is one unique example where average annual damages were estimated by sewershed area and used to establish relative benefit/costs for storm sewer system upgrades. The study demonstrated that the benefit/cost ratio varied by over and order of magnitude in different sewersheds, guiding where risk and potential deferred damages were low and where only plumbing protection or inlet controls were warranted, and, alternatively, where risks were high and deferred damages could warrant the cost on major capital upgrades to the storm sewer system. Where flood densities were less than 0.35 reports per hectare, benefit/costs were 0.06 to 0.34, indicating areas where major capital works would likely not be justified. Where densities were up to 3.38 reports per hectare, benefit/cost ratios were up to 0.77 and major works were justified and the city proceeded to further alternative refinement and implementation.

The City of Toronto applies a construction cost threshold for implementation of capital projects for basement flood risk reduction. After projects are identified in the Municipal Class EA process at a conceptual stage, more advanced construction costs are then estimated based on preliminary design, and the cost per benefiting property are assessed (i.e., based on the number of basements that are no longer at risk of flooding during the 100-year event due to lowering of the hydraulic grade line in the sewer system). A cut-off of $32,000 per benefiting property determines is the project is financially viable and will proceed to construction, or be assigned to a ‘state of good repair’ list for later consideration[25].  Analysis by Muir (2015[26]) indicates that flood densities in Toronto ranged as high as 4 reports per hectare in the highest risk, low slope catchments that are subject to limited major overland flow capacity. Numerous catchments are characterized by less than 0.5 report per hectare, suggesting the priorities for detailed risk assessment and potential capital works remediation would target those areas with greater than 0.5 reports per hectare, to achieve a reasonable degree of flood reduction benefits.

As flood risks are highly variable according to planning and design practices, flood densities vary considerably. Muir (2017[27]) has documented variations in flood density across the City of Markham and the City of Toronto and has related flood risks to infrastructure servicing practices. City of Toronto flooding during the May 8, 2000, August 19, 2005 and July 13, 2005 severe storms resulted in the highest normalized density of flood reports in the partially-separated wastewater system era between 1961 and 1980 – flood densities in those high risk areas were over double the rates in older areas with CSO relief, and an order of magnitude higher than rates in modern construction areas. Similarly, in Markham the partially- separated service areas in east Markham experienced the highest degree of flooding, with 2.4% of properties flooded during a July 16, 2017 storm. In contrast, properties serviced by sewers constructed between 1980 and 1990, reflecting more advanced stormwater dual-drainage design and sanitary inflow risks, reported a lower 0.6% of flooding. Furthermore, those properties developed and serviced after 1990 experienced 0.04% flooding, on a normalized basis.

5.0 Draft Best Practices

The following draft best practices for mitigating flood risk in existing communities are organized in the following categories:

Category 1 – Vulnerability Assessment:  practices are identified for riverine, wastewater and stormwater drainage systems including a range of vulnerability assessment methods.  It is expected that as simple vulnerability assessments are undertaken, some best practices may be advanced in low and moderate risk areas (see Section 4 for discussion on flood density and benefit/cost considerations). Where risks are moderate and widespread capital works are expected, more advanced vulnerability assessments are required to refine the geographic extent of flood risks and to quantify system characteristics that will guide the selection of more advanced best practices. For example, a “Simple” screening of flood density during a major storm (VA2) may reveal a flood density of less than 0.5 properties per hectare warranting only PC2 Minor Capital downspout disconnection and Planning and Operational best practices (PO). A flood density of 1.5 or greater properties per hectare in a catchment would warrant more detailed vulnerability assessment such as VA2 ‘Intermediate’ flow monitoring to characterize sewer system extraneous flow stresses. Alternatively a flood density of over 3 properties per hectare, or evidence of repeated flooding (e.g., 2 events in less than 5 years) that could affect the availability of insurance, would warrant more advanced vulnerability assessment and likely require major capital works, defined through a comprehensive alternative development and evaluation process that considers technical performance (e.g., flood risk reduction), environmental benefits or impacts, social impacts and benefit/cost (e.g., Ontario Class EA process).

CATEGORY 1 – VULNERABILITY ASSESSMENT (VA)

-          VA1 Riverine Flood Vulnerability  – Municipalities and watershed management agencies should map jurisdiction-wide vulnerability for riverine flood hazards using best available technology, and extend and update floodplain mapping through existing communities established prior to floodplain management policy implementation (up to catchment size of minimum 75 hectares). Methods/technologies for establishing flood hazard limits range in sophistication and may include:
o   Simple - Mapping “top of bank” using topographic mapping and GIS-based screening tools, or historical high level markings (only for long periods of record and limited changes in watershed characteristics).
o   Intermediate - Floodline estimation mapping (e.g., regression based hydrology coupled with HEC-GeoRAS modelling, excluding hydraulic structures) – moderate costs and conservative limit estimates
o   Intermediate-advanced - Floodline mapping meeting FDRP standards (calibrated hydrology, detailed hydraulic structure surveys) considering regulatory design event or minimum 100-year event.
o   Advanced – Floodline mapping as above, expanded for lower return period events e.g., 5-, 10-, 25-, 50-year events, flood inundation mapping for roadways and building structures and sensitivity analysis for operational factors (ice blockage, debris bloackage, etc.).
§  OUTCOME Jurisdiction-wide mapping of riverine flooding vulnerability. Identifies zones, sorted by severity, where various Category 2 Best Practices (planning, major and/or minor works) may be evaluated and adopted.

-          VA2 Wastewater System Surcharge Vulnerability – Municipalities should map jurisdiction-wide risk factors related to wastewater conveyance system vulnerability due to wet weather extremes. Infrastructure configurations should be classified in terms of general configuration based on age of construction and extraneous flow characteristics where available wet weather flow monitoring records. Methods/technologies for establishing wastewater system configuration and risk range in sophistication and may include:
o   Simple: Map location of reported basement flooding reports / customer service calls, classified by cause (e.g., operational cause, associated rainfall conditions), damage claims, insurance company risk and/or claim profiles.
o   Simple – estimate infrastructure configuration through estimated date of installation using in order of accuracy i) historical air photos  to track development dates, ii) registration date of subdivisions, iii) installation date of individual sewer assets indicated on as-built or design drawings, or as attribute in GIS/asset management systems. Systems should be classified as combined storm, partially-separated and fully-separated sanitary sewer collection systems. Typically, the transition from combined to partially separated sewer systems occurred in the 1940’s-1950’s, while the subsequent transition to fully-separate systems occurred around 1974 based on changes to the Canadian building code[28]. Risk ranking is as follows (highest-partially separated, moderate-combined, lowest-fully separated). In Toronto, the last combined sewers were installed in the mid 1950’s[29].
o   Intermediate: identify evidence of sewer surcharge through inspection of maintenance hole high water marks and debris levels (e.g., paper on access rungs) following extreme event.
o   Intermediate – short-term flow and rainfall monitoring to rank sewersheds by relative wet weather flow response (high, medium, low) normalized by recorded rain event characteristics (intensity, volume).
o   Intermediate-advanced - long-term continuous flow monitoring of system-wide catchments to support advanced characterization of wet weather flow response and return period analysis of peak wet weather flows and volumetric response – ranking of inflow and infiltration per InfraGuide[30] metrics (litre/centimetre of diameter/kilometre of length/day (l/cm/km/d); litre/metre of length/day (l/m/d); litre/capita/day (l/cap/d); and. litre/hectare/day (l/ha/d)).
o   Advanced – Calibrated hydrodynamic modelling of compete wastewater network to establish surcharge potential at all maintenance holes to indicate basement bask up potential (typically 1.8-2m freeboard to ground is adequate for 100-year events). Model development including documentation and criteria should follow a consistent process (e.g., City of Toronto[31]).
§  OUTCOME Jurisdiction-wide mapping of wastewater system back-up vulnerability to guide selection of Category 2 BPs (planning and capital works for flood risk / damage reduction).

-          VA3 – Storm Drainage System Exceedence Vulnerability– Municipalities should map jurisdiction-wide risk factors related to stormwater collection systems vulnerability due to wet weather extremes. For the minor system, eras of design standard evolution should be used to characterize typical design return period of storm sewers (e.g., 2-year, 5-year, 10-year, etc.) and the inclusion of dual-drainage design methods for overland / major system flow and the inclusion of catchbasin inlet controls in advanced stormwater drainage design. Methods/technologies for establishing stormwater collection system configuration and risk range in sophistication and may include:
o   Simple: map location of reported basement flooding reports / customer service calls, classified by cause (e.g., operational cause, associated rainfall conditions), damage claims, insurance company risk and/or claim profiles.
o   Simple-Intermediate – estimating infrastructure design level of service through estimated date of installation using in order of accuracy i) historical air photos  to track development dates, ii) registration date of subdivisions, iii) installation date of individual sewer assets indicated on as-built or design drawings, or as attribute in GIS/asset management systems. Systems should be classified according to minor system capacity, inclusion of dual-drainage design, and inclusion of inlet control devices if used.
o   Intermediate: identify evidence of sewer surcharge through inspection of maintenance hole high water marks and channel/overland flow path debris levels (e.g., on riparian vegetation, structures, etc.) following extreme event.
o   Intermediate – estimate major drainage catchments, overland flow paths and poorly-drained low-lying areas using typical GIS-based ArcHydro or similar Spatial Analyst hydrology tools. Compare major drainage catchments to minor system catchments to identify areas where major drainage during extreme events may overwhelm the minor system capacity (i.e., additional flow contribution area not considered in design). Assess  overland flow risk using commercially available products to assess building proximity to overland flow spread (DMTI spatial JBA Risk overland flow risk products) or using standard hydrology and hydraulic relationships to generate overland flow spread surrounding ArcHydro flow paths (centreline)(e.g., up to 3-5 hectare catchment threshold and 100 year flow spread). Complete spatial analysis to identify number of building in proximity to flow path. Rank major drainage catchments by the count of vulnerable buildings and classify as high, medium and low[32]
o   Advanced – Calibrated hydrodynamic modelling of compete dual drainage stormwater network to establish surcharge potential at all maintenance holes to indicate basement bask up potential (typically 1.8-2m freeboard to ground is adequate for 100-year events), and to establish depth of flooding in open ditch systems, roadways and other major drainage flow paths.
§  OUTCOME Jurisdiction-wide mapping of stormwater system flood vulnerability (minor system design capacity/level of service, and major overland flow system design capacity/level of service – accuracy depends on methods). Vulnerability assessment will guide the selection of any planning and capital works Best Practices for remediation (Category 2 BPs).

-          VA4 – Historical Flood Vulnerability – the most effective means of identifying flood risk reduction opportunities is to compile and analyze past events to identify high risk clusters, including areas with repeated flood reports.
o   Simple – interviews with long-term staff to characterize neighbourhoods or individual streets with repeated flood issues
o   Intermediate – maintain a customer complain system that classifies the nature of flood reports, that integrates with a work order management program for routine maintenance and that is reviewed as part of broad flood reduction program development and capital project refinement[33]. Records may also include written complaints and claims submitted to clerks departments by residents or their representative insurance companies, etc.
o   Advanced – compiled claim data by individual insurance companies (previously embedded in IBC MRAT Tool) aggregated to local scale, or regional scale[34]. Risk profiles or claim data from the individual municipality’s insurance provider.

CATEGORY 2 – PLANNING, MINOR AND MAJOR CAPITAL BEST PRACTICES (PC)

PC1 – Planning and Capital Works for Riverine Flood Risk Reduction
o   Planning:
§  Remove / replace vulnerable land use (highest risk areas, e.g., buildings within 5 year floodplain), i.e, land acquisition.
§  Require flood proofing of existing buildings up to regulatory flood event (e.g., 350 year floodplain). 
§  Designate special policy area to minimize existing flood risks in existing communities where vulnerability cannot be reduced but where damages can be mitigated.
§  Develop and implement a flood warning and emergency response plan.
o   Minor Capital
§  Flood-proofing of buildings (active, passive).
§  Backwater valves, sump pumps if floodplain hydraulically connected to storm sewer system and affects local systems (buildings with basement elevations below 100-year flood level).
·       Note: requires confirmation of foundation drain arrangement to avoid aggravating flood risk[35].
§  Culvert replacement / capacity upgrades (where classification of roadway and overtopping do not meet local criteria, e.g., Ontario Ministry of Transportation Directive B-100, etc.).
o    Major Capital
§  Evaluate alternatives following accepted planning and consultation process for flood control works (e.g., Ontario Municipal Engineers Association’s  (MEA’s) Municipal Class Environmental Assessment (MCEA) process[36], or Conservation Ontario’s (CO’s) Class EA for Remedial  Flood and Erosion Control Projects[37]). Best Practices may include ‘do nothing’ where the evaluation of natural environment, social, financial and economic impact does not identify suitable remedial actions, or municipal linear paved facility (roadway) upgrades that may include one or more of the following facilities (MCEA):
·       new culvert
·       upgraded culvert
§  Projects under the CO Class EA process to address riverine flooding may include:
·       Prevent Entry of Floodwater
·       Modify River Ice Formation and/or Break-up Process
·       Increase Hydraulic Capacity of Waterway
·       Divert Water From Area
·       Increase Upstream Storage
·       Do Nothing
·       Dam Decomissioning
§  Projects under the CO Class EA process to address shoreline flooding may include:
·       Prevent Entry of Floodwaters
·       Reduce Wave Energy
·       Do Nothing
o   Note: Like MCEA projects, CO projects also must consider the ‘do nothing’ alternative given the provided rationale: “The Authority may decide that the "do-nothing" option is the best approach at this time. This would be the case in situations where risk to existing development or public safety is determined as minimal, or where the consequences of flooding or erosion are not of the magnitude that require Conservation Authority involvement.”
·       Note: Major capital projects will sometimes undergo a benefit/cost analysis to support the evaluation and comparison of alternative solutions and to guide the selection of a preferred alternative than may include major capital works.

PC2 – Planning and Capital Work for Wastewater System Flood Risk Reduction
o   Planning:
§  Develop and maintain a system wide hydraulic model of, calibrated with dry weather and wet weather flow performance to guide operational activities, long term growth capacity assessment (intensification and expansion) and to assess effectiveness of other BPs (downspout disconnection program, other I&I reduction activities, water conservation, etc.).
o   Minor Capital (service catchments with high I&I or basement flood history)
§  Sanitary downspout disconnection (locations confirmed through smoke, dye and/or water testing of individual downspouts).
§  Sanitary maintenance hole sealing (primary locations may be determine through intermediate ArcHydro analysis under VA3)
§  Mainline lining (high I&I joints, cracks, and connections per National Association of Sewer service Companies’ (NASSCO)  PACP (Pipeline Assessment Certification Program)[38] ratings, determined through CCTV inspection).
·       Note: comprehensive I&I management programs may be developed considering industry resources including national and region guides and best practices reports[39] [40] [41] and may be integrated into broader wet weather flow management strategies to achieve multiple objectives beyond flood risk reduction, such as overflow reduction / water quality improvement.
o   Major Capital
§  Evaluate alternatives following accepted planning and consultation process for flood control works (e.g., Ontario Municipal Engineers Association’s  Municipal Class Environmental Assessment (MCEA) process[42]). Best Practices may include ‘do nothing’ where the evaluation of natural environment, social, financial and economic impact does not identify suitable remedial actions, or wastewater upgrades that may include one or more of the following facilities (per MCEA):
§  sewers (gravity sewer, vacuum line, forcemain)
§  pumping stations
§  sewage treatment plants  (e.g., components that could affect upstream wastewater system hydraulics)
§  flow equalization facility
§  storage (e.g. for combined sewage overflow) installation or replacement of standby-power equipment
§  installation or replacement of standby-power equipment
§  combined sewer separation
·       Note: comprehensive wastewater system management programs may be developed considering multi-objective targets for not only flood risk reduction but also environmental protection (e.g., Ontario F-5-5 compliance for overflows) and broad social values. Often major works also provide an operational benefit to support long term asset management and in many cases provide a significant future climate adaptation co-benefit.  Major capital works cannot be considered in isolation but rather should be coordinated through a comprehensive Master Planning process that integrates multiple programs (e.g., I&I reduction for overflow control and pumping cost savings) and achieves multiple benefits, and that has a sustainable funding source to support implementation. Examples include Toronto Wet Weather Flow Management Program and Master Plans under MEA’s MCEA process.

PC3 – Planning and Capital Work for Stormwater System Flood Risk Reduction
o   Planning:
§  Participate in and conduct comprehensive watershed, subwatershed, master environmental servicing studies to identify policies, programs and capital works required to address existing flood risk and broader environmental and servicing goals.
o   Minor Capital
§  Install inlet control devices where major drainage system has a safe outlet and excessive /unsafe ponding will not occur.
o   Major Capital
§  Evaluate alternatives following accepted planning and consultation process for flood control works (e.g., Ontario Municipal Engineers Association’s  Municipal Class Environmental Assessment (MCEA) process[43]). Best Practices may include ‘do nothing’ where the evaluation of natural environment, social, financial and economic impact does not identify suitable remedial actions, or stormwater upgrades including one or more of the following (per MCEA)
·       extension/expansion of collection system
·       pumping stations
·       stormwater channel improvements
·       stormwater management/treatment facilities
·       facilities for the disposal or utilization of solids/wastes
·       storage (retention/detention)
·       addition of control works such as weirs, dams, hydraulic brakes and other flow-limiting devices
·       installation or replacement of standby-power equipment
·       combined sewer separation
o    Note: comprehensive stormwater system management programs may be developed considering multi-objective targets for not only flood risk reduction but also environmental protection (water balance, erosion stress reduction, water quality improvement, drinking source water protection) and broad social values. Often major works also provide an operational benefit to support long term asset management and in many cases provide a significant future climate adaptation co-benefit.  Major capital works cannot be considered in isolation but rather should be coordinated through a comprehensive Master Planning process that integrates multiple programs and achieves multiple benefits, and that has a sustainable funding source to support implementation. Examples include Toronto Wet Weather Flow Management Program and Master Plans under MEA’s MCEA process, as watershed/subwatershed scale studies. Flood control MCEA’s Master Plans have been completed in cities such as Stratford Ontario to assess high level priorities and to guide subsequent Class EA to identify preferred alternatives for local capital works. The City of Markham has a long term Flood Control Program to address storm system flood risks and has established a dedicated funding source (Stormwater Fee) for this storm system flood risk reduction.

CATEGORY 2 – PLANNING, POLICY AND OPERATIONAL BEST PRACTICES (PO) DRAFT

-          PO1 Wastewater Operations,  Maintenance and Monitoring
o   CCTV/zoom camera inspection, cleaning of critical locations (e.g., siphons affected by FOG or sediment, calcite build-up, roots, etc.), identify the need to routine inspection.
o   Coding of defect severity using standard methods (WRc, PACP), data management systems to manage and prioritise defects for rehabilitation / preventative maintenance and to support capital planning.
§  Note: PO1 activities may be guided by VC4 findings
o   Monitoring may include real-time surcharge monitoring (SCADA or other remote monitoring) with alarms (may include alarms from rain gauges based on thresholds) including pumping station alarms.

-          PO2 Riverine Operations, Maintenance and Monitoring
o   Environment and Climate Change Canada, TRCA, Halton Conservation storm warning / flood forecasting systems (in development)
o   Maintenance of critical culvert grates and inlets (proactive cleaning including prior to major storm events)
§  Note: PO1 activities may be guided by VC4 findings
o   Monitoring may include real-time surcharge monitoring (SCADA or other remote monitoring) with alarms (may include alarms from rain gauges based on thresholds)[44] 

-          PO3 Riverine and Stormwater Operational Maintenance and Monitoring       
o   Maintenance of critical culvert and sewer outlet grates and major system inlets (proactive cleaning including prior to major storm events)
o   Monitoring may include real-time surcharge monitoring (SCADA or other remote monitoring) with alarms (may include alarms from rain gauges based on thresholds)
§  Note: PO1 activities may be guided by VC4 findings
o   Channel maintenance – vegetation removal and dredging (may require environmental permits), debris removal.
o   CCTV / Zoom Camera, BPs could be provided related to CCTV inspection, cleaning of critical locations (e.g., siphons affected by FOG or sediment, calcite build-up, roots, etc.), identify the need to routine inspection.
o   Coding of defect severity using standard methods (WRc, PACP), data management systems to manage and prioritise defects for rehabilitation / preventative maintenance and to support capital planning.
o   Inspections of culverts and bridges per local Bridge Code, etc.
o   Cleaning/flushing of storm sewers at critical locations (sediment buildup), street sweeping and CB cleaning can reduce sediment loadings to storm sewers
o   Inspect and repair inlet control devices

-          PO4 – Compliance with Sewer Use Bylaws

o   Enforce existing sewer use by-laws and policies (e.g., downspout disconnection), allowable discharges, etc.

-          PO54 – Planning

o   Prohibit basement underpinning (lower) in high surcharge areas unless backwater valve or sewage ejector pump, and sump pump are installed to isolate property from municipal system.

o   Require new separate laterals (storm and sanitary) as part of infills to reduce I&I

o   Stormwater quantity overcontrols (100-year post development to 2-year predevelopment rates) as part of site redevelopment in areas with limited design standards (no overland flow path, low minor system capacity, etc.).


© R.Muir (CityFloodMap.Com) v2 February 25, 2018




[1] http://www.cbc.ca/news/canada/toronto/st-lawrence-market-costs-1.4298986
[2] Ontario – Hurricane Hazel 1954
[3] Foundation drain and direct inflow connections to wastewater collection system prohibited in National Building Code in 1973.
[4] The Implementation of Storm Water Management Program : Urban Drainage Modelling Procedures, Paul Wisner
Publisher, University of Ottawa, Department of Civil Engineering, 1982  https://books.google.ca/books/about/IMPSWM.html?id=3T-foAEACAAJ&redir_esc=y
[5] (former) Town of Markham Design Standards, 1978
[6] (former) Town of Markham Stormwater Management Design Standards
[7] SANITARY SEWER EXTRANEOUS FLOW ANALYSIS, Memorandum, City of Ottawa – Eric Tousignant, 2008, https://drive.google.com/open?id=0B9bXiDM6h5VianROT1EtV2c5UFU
[8] THE NATIONAL FLOOD DAMAGE REDUCTION PROGRAM: 1976 – 1995, W. Edgar Watt, Canadian Water Resources Journal, http://www.tandfonline.com/doi/pdf/10.4296/cwrj2004237
[9]Example, Ontario: Flood Plain Management in Ontario, Technical Guideline (1986). Provincial Flood Plain Planning Policy Statement Implementation Guidelines, M.M.Dillon Limited for OMNR (1988), The Technical Guide, River and Stream Systems; Flooding Hazard Limit, Dillon Consulting Limited (2002), http://www.renaud.ca/public/Environmental-Regulations/MNR%20Technical%20Guide%20Flooding%20Hazard%20Limit.pdf
[10] TECHNICAL GUIDELINES FOR FLOOD HAZARD MAPPING, Central Lake Ontario Conservation Credit Valley Conservation, Grand River Conservation Authority Ganaraska Conservation, Toronto and Region Conservation Authority Nottawasaga Valley Conservation Authority Environmental Water Resources Group Ltd., by Dr. B. Adams & D. Haley (2017)
[11] See section 3.1.4, Ontario 2014 Provincial Policy Statement Under the Planning Act http://www.mah.gov.on.ca/AssetFactory.aspx?did=10463
[12] https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjWqq2JnMjXAhWIYiYKHdVzB7kQFggtMAA&url=http%3A%2F%2Fwww.creditvalleyca.ca%2Fwp-content%2Fuploads%2F2013%2F01%2FMichiganOntarioFlooding.pdf&usg=AOvVaw1K5vyLsTlFctM-mSBCGA8O
[13] TRCA Generic Regulation HEC-GeoRAS Flood Estimation Mapping, Dillon Consulting Limited, 2006, Don Mills Channel Regulatory Mapping (COLE, 2011).
[14] Examples include i) Don Mills Channel, Markham Ontario, ii) Spencer Creek culvert, Dundas/Hamilton, Ontario, iii) Lorne Avenue Diversion, Stratford, Ontario, iv)  Don River Tributary (Henderson Avenue Enclosure), Markham, Ontario
[15] Adams, B.J.: Implementation of Analytical Models for Continuous Probabilistic Analysis of Urban Drainage Systems," Technical Report, NSERC Cooperative Research and Development Grant P-83 12, 1 987. and Urban Stormwater Management Planning with Analytical Probabilistic Models, Barry J. Adams, Fabian Papa ISBN: 978-0-471-33217-6, http://ca.wiley.com/WileyCDA/WileyTitle/productCd-0471332178.html
[16] http://www.cbc.ca/news/canada/toronto/st-lawrence-market-costs-1.4298986
[17] R. Muir. Urban Flood Risk from Flood Plains to Floor Drains, CORRELATION OF BASEMENT FLOODING WITH OVERLAND DRAINAGE & TOPOGRAPHIC RISK FACTORS  - https://www.slideshare.net/RobertMuir3/urban-flood-risk-from-flood-plains-to-floor-drains
[18] Swann, W.N.: "A Municipal Engineer's View of Urban Drainage," in Modern Concepts in Urban Drainage, Conference Roceedings No. 5, COA, Environment Canada, Ottawa, 1978
[19] NASSCO’s Pipeline Assessment and Certification Program (PACP) Overview, Rod Thornhill, PE White Rock Consultants, 2009, https://www.mi-wea.org/docs/Rod%20Thornhill%20-%20MWEA_PACP_Review.pdf
[20] Manitoba History: “Duff’s Ditch”: The Origins, Construction, and Impact of the Red River Floodway http://www.mhs.mb.ca/docs/mb_history/42/duffsditch.shtml
Bumstead, J.M. 2002. “The Manitoba Royal Commission on Flood Cost Benefit and the Origins of Cost-Benefit
Analysis in Canada.” American Review Of Canadian Studies Vol. 32 , Iss. 1.
[21] Watt Hydrology of Floods in Canada http://nparc.nrc-cnrc.gc.ca/eng/view/accepted/?id=7b18d8c9-6c5f-425f-8338-ac4a24f8170b
[23] https://www.ontario.ca/document/building-better-lives-ontarios-long-term-infrastructure-plan-2017
[24] https://drive.google.com/open?id=1n7_s117YD9npoEhyyEVkB4UJRDi-eiqK
[25] 2017 Wet Weather Flow Master Plan Implementation Status Update, April 24, 2017 https://www.toronto.ca/legdocs/mmis/2017/pw/bgrd/backgroundfile-103216.pdf
[26] Urban Flood Risk from Flood Plains to Floor Drains
https://www.slideshare.net/RobertMuir3/urban-flood-risk-from-flood-plains-to-floor-drains
[27] Thinking Fast and Slow About Extreme Weather and Climate Change http://www.cityfloodmap.com/2015/11/thinking-fast-and-slow-about-extreme.html
[28] Ontario Building Code precluded foundation drain connections to the sanitary sewer system in 1972.
[29] T. Dole, Toronto Water. Personal Communication.
[30] National Guide to Sustainable Municipal Infrastructure. Infiltration/Inflow Control/Reduction for Wastewater Collection Systems, https://www.grandriver.ca/en/our-watershed/resources/Documents/Water_Wastewater_Optimization_InfraguideInflow.pdf
[31] City of Toronto InfoWorks CS Basement Flooding Model Studies Guideline, October 2014
https://drive.google.com/open?id=11jYgrwynKC2vogpsopBs3i850_wSEVeZ
[32] City of Markham, major drainage assessment (Geographis). R. Muir. Southern Ontario major drainage assessment, https://www.slideshare.net/RobertMuir3/urban-flood-risk-from-flood-plains-to-floor-drains. Ontario major drainage assessment, http://www.cityfloodmap.com/2016/06/ontario-overland-flood-risk-mapping.html
[33] Example: City of Markham Customer Service Request database (2002-2015 flood call classification), ongoing Hansen Work Order Maintenance / Asset Database, yearly National Water and Wastewater Benchmarking Initiative complain classification by cause, Flood Control Program remediation area prioritization (Markham Village/ Unionville) - ongoing.
[34] CatIQ, https://www.catiq.com/
[35] CATtales, Basement flooding and backwater valves Are insurers giving bad advice? By Glenn McGillivray, Managing Director, ICLR, September/October 2014, https://www.iclr.org/images/Cat_Tales_Sept_Oct_2014.pdf
[36] Municipal Engineers Association Municipal Class EA, http://www.municipalclassea.ca/
[37] Conservation Ontario Class EA For Remedial Flood and Erosion Control Projects, http://conservationontario.ca/fileadmin/pdf/conservation_authorities_section_planning___regulations/Class_EA_for_Remedial_Flood_and_Erosion_Control_ProjectsCA.pdf
[38] https://www.nassco.org/content/pipeline-assessment-pacp
[39] INFILTRATION/INFLOW CONTROL/REDUCTION FOR WASTEWATER COLLECTION SYSTEMS A BEST PRACTICE BY THE NATIONAL GUIDE TO SUSTAINABLE MUNICIPAL INFRASTRUCTURE, https://www.grandriver.ca/en/our-watershed/resources/Documents/Water_Wastewater_Optimization_InfraguideInflow.pdf
[40] ONTARIO CENTRE FOR MUNICIPAL BEST PRACTICES – BEST PRACTCES SUMMARY REPORT Water and Wastewater, http://www.omkn.ca/OMKN-Docs/Best-Practices/Water-and-Wastewater/2008/OMBI-Project-Approach-Best-Practice_Feb2008_Final.aspx
[41] ONTARIO CENTRE FOR MUNICIPAL BEST PRACTICES – INFLOW AND INFILTRATION – INCREASING SYSTEM KNOWLEDGE THROUGH FLOW MONITORING, http://www.omkn.ca/OMKN-Docs/Best-Practices/Water-and-Wastewater/2008/Peel_York_Niagara_II_FlowMonitoring_Feb2008_Final2.aspx
[42] http://www.municipalclassea.ca/
[43] http://www.municipalclassea.ca/
[44] TRCA/Markham Fonthill Creek Flood hazard area

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