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,
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
years ago, national building code improvements over 40 years ago,
and regional stormwater master drainage planning 30 years ago.
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),
and the early 1980’s when master drainage planning was first prescribed.
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.
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
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
and regulatory authorities.
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.
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
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,
especially where riverine hazards encroached on existing development or where
risks have been obscured by numerous enclosures of minor tributaries.
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).
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,
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
– 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.
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.
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.
Watt (1984)
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,
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
– 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
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. Analysis by Muir (2015)
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)
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.
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.
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
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).
§ 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.
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.
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.
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.
§ 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,
or Conservation Ontario’s (CO’s) Class EA for Remedial Flood and Erosion Control Projects).
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)
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
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).
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).
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)
-
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
