CSA W210:21

Preface This is the first edition of CSA W210, Prioritization of flood risk in existing communities . The purpose of this Standard is to provide voluntary guidance on a flood hazard and vulnerability screening framework. The purpose of the screening is to support the process of prioritizing flood risk areas within an existing (previously developed) community comprised of residential and mixed uses. This Standard provides a transparent, evidence-based, and defensible framework that supports resource allocation decisions regarding flood risk-reduction at the community level. Users of this Standard are reminded that additional and site-specific requirements could be specified by federal, provincial/territorial, municipal, or other authorities, or by a project owner. This Standard should not be considered a replacement for the requirements contained in any: a) applicable federal/territorial, or provincial statute; b) regulation, license, or permit issued pursuant to an applicable statute; or c) contract that an owner has with a contractor. CSA Group gratefully acknowledges the generous support of the StandardDetails Council of Canada in helping make the development of this Standard possible. This Standard has been developed in compliance with StandardDetails Council of Canada requirements for National StandardDetails of Canada. It has been published as a National Standard of Canada by CSA Group. Scope 1.1 General This Standard outlines voluntary guidance associated with a flood hazard and vulnerability screening framework. The purpose of the screening framework is to aid in the process of prioritizing flood risk-reduction work within existing communities. This Standard provides a) a guide to users; b) references to related publications; c) definitions for use in the Standard; d) a description of flood mechanisms; e) context of climate change considerations; f) approaches to prioritizing flood resilience works; and g) an overview of possible best practices. 1.2 Guiding principles and criteria This Standard for existing communities (as opposed to new or recently planned communities) is guided by a number of principles and criteria which are intended to support the development and application of this Standard in various jurisdictions across Canada. This Standard is intended to support unbiased and transparent decision-making related to those locations within a municipality which are deemed to be most vulnerable to flooding. Once identified, these areas would be the priority for more advanced flood risk analysis, development and design of solutions, and/or flood mitigation investment. The principles include a) the consideration of the full range of flood mechanisms present in a community; b) the consideration of interdependency between various flood mechanisms in establishing flood risks; c) the consideration of site-specific conditions, as well as existing community planning policies and principles, in the determination of flood risk; and d) the consideration of flood-exacerbating factors such as climate change (future frequency and severity of precipitation), urban intensification, and changes in upstream land uses that affect long-term resilience. This Standard is not intended to replace local, provincial, federal, or territorial directives related to infrastructure planning and design. It is to be viewed as a complement to existing CSA StandardDetails and those guidance initiatives. Common requirements in some jurisdictions are referred to in Annex D. Note: While increases in runoff due to climate change have received more attention, the impacts of uncontrolled intensification might actually be more severe if left unchecked. For instance, climate science suggests that rainfall intensities could increase by 30% to 40% by 2100 in some areas, while in some others decreases in local intensities are projected. In comparison, doubling the imperviousness from 30% to 60% might increase the runoff by more than 100%. This highlights the need for appropriate stormwater controls as part of integrated land use policies in communities subject to not only climate change, but intensification as well. 1.3 Topics in and out of scope The following summarizes those topics within and outside of the scope of this Standard. Geography - In scope:  Canadian communities located below the 60th parallel north (i.e., southern communities) Out of scope: Communities north of the 60th parallel, including permafrost communities  Flood hazards - In scope:  Riverine (fluvial) Overland (pluvial) Storm and sanitary sewer black-up infiltration (see page) High lake levels Out of scope:  Tidal/coastal Storm surge, and sea level rise Unique flood hazards (e.g., dam failures, tsunami, etc.) Ice jams Development type - In scope:  Urban and suburban residential developments Mixed-use development/neighbourhoods (e.g., residential and commercial/employment and institutional) Out of scope:  Stand-alone non-residential developments (e.g., solely industrial, commercial and institutional land, agricultural land, and major transportation routes) Note: In the absence of coastal-specific guidance, the prioritization framework described in this Standard might also be applied to efforts to identify and prioritize areas where flood mitigation action might be needed in communities impacted by coastal processes. 1.4 Users This Standard is intended for use primarily by municipalities and other authorities having jurisdiction across the different regions of Canada. Municipalities are typically the owners and operators of (public) storm infrastructure and related amenities; hence, are usually on the "front-line" during the planning and budgeting phases, which this Standard will support. Given that the factors that affect the nature and extent of flooding extend beyond municipal boundaries, other levels of government and flood stakeholders are also involved to varying degrees and roles. Users of this Standard could include a) municipalities and regional government agencies; b) watershed managers and conservation authorities; c) federal, provincial, and territorial governments; d) Indigenous communities; e) senior municipal administrators; f) water and wastewater utilities; g) elected officials; and h) the business and development communities. 1.5 Application The guidance provided in this Standard applies to municipalities and other authorities having jurisdiction who are responsible for establishing budgets and programs to assess and manage flood risks within residential and mixed-use areas within their watersheds. Through the application of the provisions in this Standard, municipalities will be better informed as to where the locations of highest flood risk are within their limits and then to plan for logical and systematic investment, premised on a consistent and transparent protocol. 1.6 Terminology In this Standard, "shall" is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the Standard; "should" is used to express a recommendation or that which is advised but not required; and "may" is used to express an option or that which is permissible within the limits of the Standard.