Storm Warts, The Floods Awaken, A New Hope for Cost-Effective Investment in Flood Management Infrastructure, #NWWC2018 Robert Muir

Storm Warts
Storm Warts are the blemishes in our infrastructure system
capacity that reduce resiliency and contribute to flood losses.

My presentation "Storm Warts, The Floods Awaken" at The National Conference of the Canadian Water and Wastewater Association, Montréal, Canada, on November 5, 2018 will have a light show, light saber show that is.

Click below for the print version of the slides (unfortunately without all the fancy animation and sounds):

The presentation identifies benefit cost analysis as a "New Hope" for guiding infrastructure investment, so that they deliver a high return on investment by focusing on the blemishes in storm and waterwater collection systems, aka, "Storm Warts".

The presentation reviews the statement in the media, put forth by the insurance industry and affiliated researchers, that water damages are increasing and are a key driver for increasing catastrophic losses. The presentation shares data that suggests floods have not "awakened", and are in fact becoming a smaller percentage of total catastrophic losses, as explored in a recent post.

The presentation also reviews case studies of benefit cost and economic analysis related to grey and green infrastructure, including natural infrastructure (green infrastructure, low impact development measures including wetlands and other features). This includes case studies from the recent Insurance Bureau of Canada report reviewed in another recent post. It is suggested that cost benefit studies require certain elements to be robust, reliable, and evidence-based, and that some case studies are lacking in these core requirements, representing "number stretching and concept massaging" as suggested in the Financial Post.

A comparison of return on investment, benefit cost ratios, for Markham's complete flood control program is made, including a group of low-cost, no-regrets best practices (i.e., policies and programs such as sanitary downspout disconnection, and backwater value and sump pump incentives), and city-wide grey infrastructure capital works resulting from a decade of master plans and Municipal Class EA studies.. The ROI of green infrastructure is also explored as part of a city-wide assessment, including an evaluation of potential flood mitigation benefits, as well as erosion mitigation and water quality improvements.

The need for comprehensive engineering analysis is suggested, showing that case studies that relied only on "meta-analysis", or high level estimation techniques, may not be able to provide reliable, meaningful ROI estimates sufficient to guide public infrastructure spending. Wetland, natural infrastructure benefit-cost ratio's are shown to be highly variable and potentially unreliable, as reviewed in an earlier post that incorporates some of the Storm Warts presentation (i.e., Pelly's Lake, Manitoba) and reviews other sources on natural infrastructure flood reduction potential and constraints.

Do Baseflow Impacts of Urbanization Warrant Green Infrastructure Retrofits to Restore Water Balance?

Green infrastructure, low impact development practices (LIDs), also called stormwater management best management practices (SWM BMPs), are often proposed to restore water balance functions and mitigate impacts or urbanization on runoff and recharge. One argument is that baseflows are lowered due to reduced infiltration and discharges to watercourses. It is a simple textbook theory.

What does the data show on baseflow impacts? The following slide presentation was prepared to respond to the Ontario draft LID guidance manual in early 2017 since water balance impacts have been cited as justification for green infrastructure LIDs.

Local studies show that baseflows have increased over decades of urbanization, calling into question the need for such measures considering that potential impact has not materialized. As noted in TRCA's Approved Updated Assessment Report under the Clean Water Act, at most gauges there was an upward trend in baseflows which prompted this statement: "These overall increases to baseflow volumes are contrary to the common thought that increased impervious cover leads to reduced baseflow" - so for those keeping score, data - one, common thought - zero. (see page 3-40 at link to full report - disregard old link in the slide deck thx!).

TMIG also analyzed baseflows in the GTA and noted “The seven-day average consecutive low flow data provides an indication of the observed baseflows within a watercourse, and hence is a suitable measure for determining whether baseflow trends exist in an urbanizing area. The trend analysis identified noticeable baseflow trends in 13 of the 24 recording stations. Of these eight urban and two rural stations exhibited an upward trend, suggesting increasing baseflow.” (link to full report).

It would appear that baseflow stresses due to urbanization, i.e., development within the GTA, do not support the need for green infrastructure implementation to restore water balance functions.