Urban Flood Risk Evaluation to Guide Best Practices and Projects - Tiered Vulnerability Assessment and Risk Mapping for Storm, Wastewater and River Systems from Flood Plain to Floor Drain

A tiered vulnerability assessment framework for existing flood risk in urban systems was developed to support best practices development in Canada as published in this previous post. Risk mapping is critical to defining areas of interest for implementation of no-regrets policies and practically deployed programs that can reduce risk in a cost-effective and technically effective manner. Examples of such include stormwater management peak flow control policies, or construction by-laws, and low-cost programs to reduce stresses on infrastructure systems (e.g., sanitary or combined sewer downspout disconnection) or to isolate flood-prone properties from sewer back-up risk (e.g., plumbing protection through backwater valve installation or foundation drain disconnection/sump pump installation).

A review of vulnerability assessment methods was prepared for the Ontario Urban Flooding Collaborative to share risk mapping approaches being considered as part of an Ontario-wide strategy being developed to reduce existing urban flood risks. The September 13, 2018 webinar presentation is below:

Urban Flood Risk Mapping - Tiered Vulnerability Assessment in Risk Mitigation Frameworks for Existing Communities from Robert Muir

The presentation illustrates examples of tiered vulnerability assessment in areas with existing urban flooding interests and demonstrates how progressively more advanced risk characterization methods (e.g., monitoring, modelling) are considered commensurate with the level of risk. Simple methods including mapping of reported flooding to identify areas of interest for no-regrets initiatives (policies and programs) to more advanced hydrodynamic modelling methods to support economic analysis and design/implementation of viable projects are shown.

An early example of layering of multiple risk factors related to construction practices (e.g., type of drain connections to the municipal sewer network), overland flow (pluvial) flooding risks, and storm sewer surcharge back-up potential is shown, i.e., the presentation author's Stratford City-wide Storm System Master Drainage Plan. The range of simple to advanced risk characterization methods that were combined in the overall system screening and prioritization are illustrated on the following slide:

Urban Flood Risk Mapping - City of Stratford City-wide Storm System Master Plan. Dillon Consulting Limited. 

Several recent examples of multiple risk factor screening are shown in a recent blog post - the following map illustrates how era of construction (design standards inferred from dwelling age), topographic risk factors like catchment slope, overland flow path design (i.e., pluvial flooding risk) and reported historical flooding are related in a north Toronto neighbourhood:

Era of Dwelling Construction, Overland Flow and Catchment Slope, and Flood Report History - Risk Factors Affecting Reported Basement Flooding During Extreme Rainfall Events, City of Toronto Flood Reports.

While there are numerous examples where the risk factors explain the observed flooding, there are equally as many examples of risk factors not explaining the observed flooding. So mapped risk factors can explain overall trends, however there is considerable scatter in the data meaning a high degree on uncertainty when it comes to defining actions required to address priority flood risk reduction measures. As a result, local, detained risk assessments as part of comprehensive studies are required to support and infrastructure investments after areas of interest are screened though high level vulnerability assessment.

A holistic process of tiered flood risk vulnerability assessment to identify no-regrets, low-cost policies and programs (i.e., best practices) and then, commensurate with risks, more advanced assessments to define capital projects is shown in the following slide from the presentation above.

Process for Defining Policies, Programs and Projects for Urban Flood Risk Reduction Including Tiered Vulnerability Assessment (Risk Mapping).

Some 'best practices' can be identified with high level, simple to intermediate risk screening as shown below:

Defining No-regret, Low-Cost, Practically-Deployed Policies and Programs  for Urban Flood Risk Reduction With Simple and Intermediate Vulnerability Assessment (Risk Mapping).

When considering sanitary / wastewater collection systems, this holistic process for assessing risk and defining policies, programs and projects is illustrated below, including example risk factor thresholds that may be used to guide progression to more advanced tiers of assessment, and ultimately design and economic screening.

Sanitary / Wastewater System Risk  Assessment Process to Implement Policies, Programs and Capital Projects - Simple to Advanced Risk Mapping and System Analysis to Prioritize Actions with an Urban Flood Risk Reduction Strategy 

Similarly, storm systems can be assessed in a holistic manner with progressively more and more advanced / detailed risk characterization.

Sanitary / Wastewater System Risk  Assessment Process to Implement Policies, Programs and Capital Projects - Simple to Advanced Risk Mapping and System Analysis to Prioritize Actions with an Urban Flood Risk Reduction Strategy

For illustrative purposes, the City of Toronto financial screening threshold for basement flood mitigation projects is shown ($32k per benefiting property) to evaluate advanced evaluation projects. A benefit/cost of 2 is also shown, which is based on the eligible Disaster Mitigation Adaptation Fund project Return on Investment (ROI) threshold. Alternative thresholds for benefit/cost ratios (from under unity to 1.3) to support pubic investment in flood mitigation infrastructure are discussed by Watt in Hydrology of Floods in Canada.

A holistic approach to urban flood risk mitigation will focus on high risk areas and deliver risk reduction in a timely and cost-effective manner. Across Canada and Ontario, many communities were designed and constructed under design standards with limited flood resiliency compared to today's modern standards. The proportion of existing residential communities that have resiliency limitations can be estimated according to Statistics Canada data on dwelling construction date ("Dwelling Condition (4), Tenure (4), Period of Construction (12) and Structural Type of Dwelling (10) for Private Households of Canada, Provinces and Territories, Census Divisions and Census Subdivisions, 2016 Census"). Data tables for various geographies (i.e., Canada and Ontario), and for various ground dwelling types (i.e., single detached house, semi-detached house, row house, and other single attached house) have been used to estimate the proportion of residential development within various eras of construction to classify resiliency and risk mitigation needs. The graphs below illustrate the number and proportion of these types of dwelling construction in different construction eras based on Statistics Canada's 2016 Census data.

Ground Dwelling Era of Construction - Ontario and Canada - Design Standards and Flood Resiliency. Dwelling Count and Cumulative Fraction of Dwellings Using Statistics Canada 2016 Census Data.

Ground Dwelling Era of Construction - Ontario - Design Standards and Flood Resiliency. Dwelling Count and Cumulative Fraction of Dwellings Using Statistics Canada 2016 Census Data.

Pre-1990 construction accounts for about 65% of residential ground dwellings in Canada and in Ontario (i.e., excluding apartments). Generally, design standards after 1990 offer high resiliency (very low risk) such that risk mitigation through remediation is not a priority. Lower risks are expected in post-1980's construction where wastewater systems are fully separated (i.e., about 14% of Ontario construction), and moderate to high risks are expected in communities constructed before 1980. Tiered vulnerability assessments will typically begin with the 65% of pre-1990 areas, and progressively refine risks associated with systems within those areas.  To illustrate this, sanitary system upgrades to address flood risks in the City of Markham, determined after advanced risk assessments, may account for less that 2% of the total sanitary sewer length - modelling revealed that only 1.8% of sanitary maintenance holes exhibited surcharge during a 100-year event that would be considered a basement flooding risk.

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More reading:

i) costs and benefits of green and grey infrastructure

An Economic Analysis of Green v. Grey Infrastructure from Robert Muir

ii) technical and financial constraints with green infrastructure / low impact development implementation

Ontario Society of Professional Engineers OSPE Green Infrastructure Roundtable - Green Infrastructure – Cost Effectiveness and Technical Challenges for Flood Mitigation from Robert Muir

iii) Weathering the Storms with Ontario's Environment Plan - Understanding Challenges and Opportunities for Flood Resilience in Ontario

Canadian Flood Underwriter - Can Fire Underwriters Survey History Guide Urban Flood Risk Management Model?

Can the history of the Fire Underwriter Survey provide a roadmap to a future Canadian flood underwriting model?

Fire Underwriters Survey (FUS) is a national organization and was formerly the Insurers’ Advisory Organization (IAO) and Canadian Underwriters Association. As noted on their site, "FUS provides data on public fire protection for fire insurance statistical work and underwriting purposes of subscribing insurance companies. Subscribers of Fire Underwriters Survey represent approximately 85 percent of the private sector property and casualty insurers in Canada."

The history of the FUA and the organizational and technical benefits offered to its members is described in this book:

http://www.fireunderwriters.ca/theunderwriters_e.asp

"The Underwriters, the history of the Insurers' Advisory Organization and its predecessors, the Canadian Fire Underwriters' Association and the Canadian Underwriters' Association," by Christopher L. Hives, 1985.

If "flood is the new fire" as far as Canadian insurance losses go (Fort McMurray 2016 notwithstanding), much can be learned in how the insurance industry developed the Fire Underwriters organization to organize, guide, educate, and support member insurance companies.

How did fire insurance evolve?

The first fire policy was written by the Phoenix Company in 1782 policy in Sr. John's, Newfoundland and the first Canadian company to offer fire insurance was the Nova Scotia Fire Insurance Association, founded in 1809 in Halifax. More players joined and by the mid 1800's it was apparent there was a need for standardization and organization - so in 1857 "in order to better serve the interests of the community and the participating companies, a joint body or association called the Halifax Insurance Board (was) formed".

Following a 1859 severe fire in downtown Halifax with payouts of £128,075 the board commented on causes and identified "the want of sufficient supply of water at the commencement and to a general want of management". It made recommendations for an improved city water supply for the city, more firemen, and water supply infrastructure along Barrack Street with branch lines exclusively for fires. Without these risk reduction measures, the board would increase tariffs (i.e., premiums).

The early Halifax example illustrates the partnership between government and insurance industry whereby standards for municipal services consider insurance industry needs, which it could be argued, mirror the financial needs of the economy, and the government's need to promote safety and security in the community as a whole.

Over the next century or so, a national organization was formed, evolved and grew (Canadian Underwriter's Association (CUA) founded in the late 1880's, and Insurer's Advisory Organization (IAO) in the 1970's incorporating CUA and independent members). In the late 1970s, lAO developed one of its first computer applications to determine whether a sprinkler system would function properly and if the water supply was sufficient. This replaced inefficient manual calculations.

One could draw parallels between the IAO's analysis of sprinkler fire suppression systems and the assessed benefits of flood prevention systems. In the case of large watersheds in the Toronto area, prevention features would include infrastructure such as the Lower Donlands Landform Berm, Black Creek Channel, and TRCA dams - all incorporated in JBA's flood defense layers. At the local municipal level, flood prevention features would include drainage and municipal infrastructure standards incorporated in new resilient communities, or upgrades for flood risk mitigation in communities build with lower standards (e.g., pre-1980's subdivisions with limited overland drainage design, and partially-separated wastewater systems).

Currently CGI Risk Management Services conducts  Fire Underwriters Survey (FUS) services for the Canadian insurance industry, including assessment of municipal water supply systems including adequacy of available flow rates for structures in the community, and distribution system adequacy and reliability. This information helps guide community improvements and to establish "municipal gradings for insurance purposes", according to CGI.  

The parallel in the context of urban flood risk assessment would be i) assessment of wastewater systems to safety convey extraneous flows during extreme wet weather events, without surcharging and causing floor drain sewer back-up, and ii) assessment of overland drainage systems to safely convey overland runoff ('major drainage system flows) to an adequate outlet like a channel or valley, without surrounding and entering buildings. Since the 1970's, computer assessments of wastewater system capacity has been pursued using the SWMM model, typically in the context of flood remediation or CSO reduction studies. Today, such models are more widely available, but even in jurisdictions like Toronto, they are only now being developed to cover the entire municipality and to be developed with robust standards. Over time, the risk characterization from such models could be used to establish a municipal grading for insurance purposes, likely at a block face level of detail. Overland flood risk models are only now becoming commonplace, including JBA's riverine and surface (pluvial) flood risk models based on 2D overland flow modelling. 

The difference between CGI's fire risk assessments and flood risk assessments is that no flood risk assessments are tied to 'municipal gradings'. Municipal wastewater system assessments can result in infrastructure improvements, or when not cost effective, deferred projects. But neither condition is communicated to an insurance risk body, and the insurance industry is not known to participate as a stakeholder in the municipal environmental assessment studies that guide the improvement strategies. Similarly, the overland risk assessment available to those writing individual policies are not shared with municipalities to guide macro-scale, neighbourhood-level improvements to infrastructure that could mitigate risks and premiums. IBC's Municipal Risk Assessment Tool (MRAT) estimates municipal wastewater back-up risks but these are not used to set premium rates or identify specific municipal infrastructure improvements (i.e., MRAT provides generalized, regression-based "high-low" risk mapping for one type of flood risk but does not incorporate system hydraulics to assess upgrades, nor does it assess neighbourhood overland flood risks or remediations).

Given that fire insurance and underwriting support evolved over more than 200 years, and that technical assessments of some risk factors like fire suppression sprinklers emerged only 40 years ago, flood risk underwriting likely has decades to go before an effective partnership can develop between the insurance industry and municipalities and other levels of government.

"...our industry will undergo fundamental and radical changes which will severely test the mettle of all the players in the league. 'To be sure, the 'good old days' are gone forever. Today's conditions, regarded by many as 'abnormal' are, in reality, 'but a mild rain shower compared to the storms of the future ...obviously, the future is no place for the faintheaded, the rigid traditionalists and the seekers of the status quo. The survivors will be the courageous, the alert, the flexible, the imaginative,

the planners and the managers of change. With the continued support of its Members, lAO would like to be counted among the latter."

Ted Belton's comments on the status ofthe industry at the end of 1980, following all time high 1980/1981 loss ratios.

Given current flood loss trends, Mr. Belton could have been looking out 35 years to today when investment earnings are low (again) in this low interest environment, and when extreme rainfall losses are on the rise. Imaginative change is again needed to develop a flood underwriting strategy.

Drought to Deluge - Toward Holistic Flood Risk Management

An online article in Canadian Underwriters describes the new flood risk models developed to assess hazards, price flood endorsements and assess portfolio risk in canadianunderwriters.ca.  In the comment below, we look beyond the short term insurance risk data needs and toward to holistic approach risk management.

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The journey toward a Canada-wide flood risk model shows one thing - a paradigm shift is needed in how the insurance industry, regulatory agencies and municipalities share data on flood risks. Only then will there be data to support fair and accurate insurance products based on risk, data that society can access and use to make important risk management decisions, and data that municipalities/regulatory agencies/ministries can use to set risk avoidance, reduction and remediation policies. The discussion today is just the first step toward that. While a robust 10 m fine grid flood risk screening tool could satisfy the immediate need for price local insurance products and assess portfolio risk, the long term goal has to be a comprehensive risk management strategy built on this type of data. How? Well if "flood is the new fire", consider the fire model where fire underwriters, municipal fire services their consultants, and property owners participate in a system that quantifies and shares risk data and where risk management decisions are made in a coordinated manner. 

With immediate product needs, the insurance industry requires a consistent risk model across the country and so has to resort to coarse 30 m topography cell screening to at best identify riverine risks - but can not account for the local factors such as hydraulic relief structures that are important for the higher frequency events (i.e., bridges, culverts and embankment underpasses that are 'under' the 30 m topography model), or the underworkings of sewer infrastructure or surface constraints (building flow obstructions) critical in urban flash flooding beyond river valley systems. Meanwhile, some municipalities are sitting on InfoWorks and EPA SWMM dual-drainage models that predict hydraulic flood levels pipe-by-pipe that characterizes basement flood risk, and predict block by block overland ponding for all storm return periods. Similarly, conservation authorities in Ontario have return period riverine flood levels derived from survey-grade topography and hydraulic structure surveys, considering calibrated flow hydrology. Flood risk data is not new - Toronto East York SWMM models were first developed in the 1970's on punch cards, Toronto North York models in the 1980's on 20MHz 386's - no need for GPU processing really. Today Toronto is covered in InfoWorks models, Hamilton has Mike Urban, Calgary XPSWMM ... and on.

But all this existing data is in silos, each with a single regulatory or management purpose, and never rolled-up, parsed, or aggregated to provide a baseline for insurance risk purposes. You can understand why Carpenter pursues a Canada-wide 30 m grid model for surface flooding or IBC develops MRAT for sanitary back-up risk characterization - its because it is easier to start from scratch with coarse risk assessment than to get down in the weeds of pipe-by-pipe municipal infrastructure flood models (that do vary by neighbourhood to neighbourhood, consultant by consultant, model platform by model platform), or creek-by-creek conservation authority (or other provincial agency) floodplain models (that do vary as well in terms of vintage, accuracy, consistency in hyetographs/design storm drivers).  So there has been a deluge of data building for a half century on riverine flood risk, and over decades on urban flood risks - but it has never been approached in a way that it can be leveraged for holistic flood risk management.

Under a new paradigm, with a more holistic risk management end goal in mind, flood risk data can be collected, developed and applied through a partnership approach, without the need to reinvent or duplicate riverine flood risk mapping. Consistent, shared risk data would support alignment between the regulatory aspects of flood risk management, the business decisions related to development, and municipal and government decisions on infrastructure investment and risk reduction programs (flood proofing, emergency preparedness, education).  The constraints to getting to there is not GPU computing power for 1 metre-cell 2D urban dual drainage models, but rather it is more fundamental and more challenging, relating to how various private and public organizations cooperatively manage issues of common interest.