Watershed-Scale Flood Damage Reduction Using LID BMPs - Does Green Infrastructure for New Development and Redevelopment Significantly Reduce Existing River Flood Risks

River Flood Loss Avoidance (Deferred Damages) with
Green Infrastructure / Low Impact Development BMPs
in New Development and Redevelopment in the US.

A study by Atkins for the U.S. EPA evaluates flood damage reduction across North America using Low Impact Development (LID) Stormwater Best Management Practices (BMPs). The 2015 report "Flood Loss Avoidance Benefits of Green Infrastructure (GI) for Stormwater Management" is available at this link and evaluates benefits of implementing LID BMPs in new development and redevelopment over 20 years.

Flood Losses Avoided in the Year 2040 for Various Zero Damage Thresholds

What is the value of estimated flood damage reduction from 2020 to 2040 by constructing GI / LIDs? Savings range from $63M to $136M per year in 2040, depending on whether river flood damages are assumed to start above 10 year events or more frequently above 5 year events.

Over the 20 year implementation period the deferred flood losses increase from $0 in 2020 to an average of $100 million (2011 dollars) for 5 and 10 year zero damage thresholds.

Deferred Flood Losses with LID BMP Implementation
for Stormwater Management in New Developments

After the first 10 year s of implementation the flood losses avoided averages approximately $50 million. The table to the right indicates the increase in flood reduction benefits over the green infrastructure implementation period.

Key question: is the losses avoidance significant and is there value in implementing green infrastructure to achieve river flood damage reduction?

To explore whether deferred damages are significant, lets compare the average loss reduction over the 20 year implementation with average losses in North America. Munich RE's NatCatService estimates losses in North America for meteorologic events and hydrological events. The chart at right shows that over the past 10 year from 2008 to 2017 the average losses per year we approximately $75 billion in 2017 dollars. (we could net out non-US areas like Canada to make this more apples to apples).

Munich RE Catastrophic and Relevant Event Overall Losses
Inflation Adjusted and Normalized 

The deferred flood losses over the 20 year period with LID implementation are $50 million in 2011 dollars - according to the Bureau of Labor Statistics consumer price index, the dollar experienced an average inflation rate of 1.42% per year. Therefore the annual LID loss reduction amount in 2017 is 8.8% higher than deferred losses in 2011, or $54 million (2017 USD).

Deferred annual flood losses of $54 million represents only 0.07 % out of $75 billion in overall annual losses. This suggests that near-term river flood damage reduction is not a core benefit of green infrastructure implementation.

The cost of expanded green infrastructure implementation is not assessed in the Atkins study as noted here:

"The costs of GI implementation are not included in this document. Nevertheless, new development and redevelopment already require stormwater management expenditures, either on-site or downstream; therefore, GI could be used to meet those requirements fully or partially for little or no
additional cost compared to overall construction costs. This study does not assume retrofitting of existing imperviousness. Retrofitting, in addition to implementation on new development and redevelopment, would be expected to generate more flood loss avoidance benefits but would incur
additional costs."

Given that green infrastructure stormwater controls are assumed to be included in the base cost of development or redevelopment, the micro-sized river flood loss reduction benefit comes at no addition cost, which could indicate good 'value' - however given the almost insignificant percentage of overall flood damages averted, one could question whether river flood risk reduction should be prescribed as a low impact development benefit at all. It would appear that core benefits of green infrastructure are instead the environmental ones related to water quality improvements and erosion risk reduction.

Today it is popular to promote green infrastructure citing its multi-faceted triple-bottom-line (TBL) benefits on many aspects of the environment. It would appear that riverine flood risk reduction is not one of those benefits to consider in the TBL assessment. Many groups and Canadian municipalities have noted impacts of green infrastructure on existing utilities and foundations as a dis-benefit / adverse impact of green infrastructure measures that typically infiltrate runoff into the ground. Many of these negative impacts were recently summarized in the Ontario Society of Professional Engineers' (OSPE) comments on Ontario's draft Watershed Planning Guidance which had promoted the role of green infrastructure for flood control :

https://drive.google.com/open?id=1dNFzxZxlzxUx-g9DzvVHSvwceXhddkCq

The OSPE comments note:

"While green infrastructure has recognized roles in achieving watershed outcomes, including
water balance and water quality management in greenfield developments, the above statement
is inconsistent with numerous studies that discount the flood-control benefits of green
infrastructure. Numerous studies have demonstrated that green infrastructure does not provide
a flood risk reduction benefit."

To support this statement, OSPE cited numerous Master Plans, Master Drainage Plans, Class Environmental Assessment studies, Best Practice documents, local university research, and municipality and water industry comments on the Ontario Ministry of the Environment and Climate Change's draft Low Impact Development guideline.

RJM

Are LIDs Financially Sustainable in Ontario? Philadelphia Green Infrastructure Costs - 1100 Low Impact Development Projects Define Implementation Funding for Long Term CSO & Water Quality Improvement - Comparison with 24 Ontario Projects

Philadelphia Green Stormwater Infrastructure Projects Map - Over 1100
Low Impact Development Projects for CSO Control

See September 2019 Update at Bottom of This Post

Philadelphia has an extensive green infrastructure retrofit program with cost information - recent Ontario low impact development project costs show comparable unit cost for implementation.

***

The City of Philadelphia implements green infrastructure (GI), aka low impact development (LID) best practices (BMPs), to control combined sewer overflows (CSOs).  Having implemented 1100 features in a retrofit setting, Philadelphia has a clear understanding of retrofit implementation costs. The following is a summary of their green infrastructure design construction costs provided by the city program staff:

City of Philadelphia Green Infrastructure / Low Impact Development Best Management Practices - Construction, Design and Planning Budgets Per Total and Impervious Area

Construction Cost
- $175,000 per acre ($432,000 per hectare)

Philadelphia Green Infrastructure Map by SWP / LID Type 

- $270,000 per impervious acre ($667,000 per hectare)

Design Cost
- Design fees typically 20-25% of construction costs

Total Cost (Design & Construction)

Philadelphia Green Infrastructure Map - Spatial Location
of Low Impact Development Measure

- Total costs of $230,000 per acre ($568,000 per hectare)
- Total costs of $350,000 per impervious acre ($865,000 per hectare)

Budgeting
-  $350,000 per impervious acre ($865,000 per hectare) is the overall target/budget cost that is achieved for the program and that does not include contingencies that could be carried for individual projects within the program.
- If estimated costs exceed $400,000 per acre ($988,000 per hectare) based on design estimates and project cannot be re-scoped, it is deemed too expensive and does not go ahead.

In Ontario, green infrastructure has been promoted for stormwater management in new developments since the Ministry of Environment's 1991 Interim Guidelines. Green infrastructure measures were promoted as part of a 'source control' approach and features that promoted infiltration were called Best Management Practices (BMPs). Since then, Ontario cities have developed design targets for achieving specific water resources management goals and have implemented LID BMP measures in appropriate locations. In the City of Markham and York Region, his history was summarized in a National Water and Wastewater Benchmarking Initiative Stormwater Task Force presentation:

Green Infrastructure / Low Impact Development LID Design Tool and Lifecycle Costing NWWBI Stormwater Task Force Robert Muir City of Markham from Robert Muir

The presentation above summarized LID implementation costs for nine (9) recent Ontario projects including bioswales, bioretention, infiltration galleries and permeable pavement. Theses cost are receiving close attention as LID implementation targets in some regions have been increased, e.g., through the Lake Simcoe Protection Act to meet environmental protection / phosphorus reduction goals, and as generic province-wide targets are now being evaluated by the Ministry of Environment and Climate Change.

Additional Ontario LID project implementation costs have been compiled with information shared by Ontario municipalities and also the Lake Simcoe Regional Conservation Authorit. This expands/updates the project costs in slide 17 of the above presentation. These costs include construction, design, administration and in-kind staffing efforts related to implementation of LID projects in the City of Markham (2 projects), City of Brampton (1 project) Town of Whitchurch-Stouffville (1 project), City of Ottawa (2 projects), Town of Ajax (1 project), City of Mississauga (3 projects), Town of Newmarket (2 projects), City of London (7 projects), Town of East Gwillimbury (1 project), Town of Uxbridge (1 project), Town of Aurora (1 project), Town of Innisfil (1 project).

The project costs and unit costs per total catchment are are shown below:

Ontario Green Infrastructure / Low Impact Development Best Management Practice Implementation Costs (No Adjustment for Inflation to 2018 Dollars) - Normalized Unit Costs Per Catchment Area Managed

This is a link to the above compiled Ontario LID costs (let me know if you have projects to add or can suggest edits / updates): Excel - Ontario Low Impact Development BMP / Green Infrastructure Implementation Cost Summary - 24 Projects

The average cost per hectare of $575,000 for these 24 projects is very close to the City of Philadelphia budget cost of $568,000. Cost per impervious hectare treated by the LID BMP would typically be higher (i.e., catchment is less that 100% impervious). Some notes regarding the project costs:

- complete costs are not available for some projects (e.g., Markham Green Road bioswale vegetation)
- one service area has been adjusted based on different sources (e.g., East Gwillimbury area reflect municipality's project brief and not original TRIECA 2017 presentation value).
- one projects has only tender cost estimate available, not actual construction cost (e.g., Newmarket Forest Glenn Rd)
- one project from LSRCA was not included in the list as it did not proceed to construction, but nonetheless incurred design and administration costs (e.g., City of Barrie, Annadale Recreation Centre, design/administration/geotechnical/in-kind staff cost of over $78,000) - this may reflect go/no go decisions on implementation that the others also consider
- most projects are retrofits, however some are new builds (Markham Green Road, Innisfil Fire Station)
- bioswales/enhanced swales require review given the wide range in unit costs per hectare of $51,000 (Uxbridge) to nearly $1.9M (Newmarket), with obvious sensitivity to the drainage area served

Previous cost estimates cited on this blog considered unit costs of approximately $400,000 per hectare and significant concern regarding the financial viability of any widespread implementation across Ontario's 852,000 urbanized hectares. Considering the expanded project cost review and adjusting for inflation, today's Ontario green infrastructure implementation costs can be estimated to be in the order of $600,000 per hectare. This magnitude of cost is comparable to Philadelphia's budgeting cost, considering over 1100 projects. These costs support the concern related to emerging Ontario policies that have not considered implementation cost impacts or financial viability.

The Ontario Society of Professional Engineers (OSPE) has recently highlighted concerns with the implementation of green infrastructure in Ontario in comments on Ontario's Long-Term Infrastructure Plan (my bold emphasis on the recommendations)

"....OSPE recommends that the Government of Ontario:

i. Critically apply the proposed ‘risk lens’ to infrastructure investments related to extreme
weather adaptation, recognizing variations in observed and predicted trends across the
province.

ii. Evaluate adaptation measures such as green infrastructure for stormwater management,
often cited as key mitigation measure, using the same ‘risk lens’ and consider the cost-
effectiveness of those infrastructure investments.

iii. Recognize that green infrastructure must be viewed through the same lens as
conventional infrastructure, adhering to established asset management principles and
full cost accounting—meaning it must be addressed up-front and directly, considering
system-wide costs."

OSPE has also commented on the limited role of green infrastructure for flood control and life cycle cost concerns in response to Ontario's draft Watershed Planning Guidance.

"Recommendation:

Green infrastructure LID implementation costs should be acknowledged to be potentially higher
than conventional grey infrastructure design, particularly for retrofits, and funding for additional
incremental retrofit costs should be considered in the comprehensive evaluation of alternative
management solutions beside green infrastructure and LIDs, including enhanced conventional
grey infrastructure designs with pollution prevention activities. Higher retrofit costs compared to
greenfield implementation should also be acknowledged.

Consideration for disproportionate costs should be acknowledged as a prohibitive constraint in
general and for linear development retrofits or widespread watershed implementation. A more
strategic approach to green infrastructure implementation, based on local needs and
considering local constraints (infiltration impacts and property flooding) is warranted."

"Recommendation:

The additional lifecycle cost associated with green infrastructure should be acknowledged to
support budgeting for long term operation, maintenance and depreciation.

The cost impacts of green infrastructure in existing communities should also be quantified
including costs in communities that are susceptible to infiltration stresses and sewer back-up
risks, additional treatment costs as infiltrated water is collected in foundation drains and
conveyed to treatment plants and cost of reduced service life of cast iron and ductile iron
watermains due to chloride infiltration in right-of-ways (i.e., accelerated corrosion). Such a
robust and holistic economic analysis can then support more strategic, financially sustainable
implementation policies for green infrastructure."

Let's work toward this sustainable implementation policies for all infrastructure - including green infrastructure - considering costs and strategic goals and specific performance outcomes. Low impact development implementation costs in the order of $600,000 per hectare, as shown through local and other jurisdictions, are simply not sustainable on a broad, system-wide basis.

RJM

***

September 2019 Update

Additional projects have been reviewed in Ontario and a couple have been added from Edmonton, Alberta.  The resulting average cost per hectare (area-weighted) is $581,000.  The following table presents a summary of cost per LID type (porous/permeable pavement, rain garden/bioletention, bioswale and infiltration/exfiltration).

The Ontario/Alberta costs now represent almost 8 hectares of catchment area, close to the EPA BMP database catchment area for projects with costs data (middle column).  Note that the Ontario/Alberta project costs may include several types of LID types in the treatment train.