|What if a "Weather Zoltar" machine answered|
all our questions on future climate change
conditions - would we know what to do with
that precise detailed data?
Are our current decision making processes even
sophisticated enough to make use of it?
New Development System and Component
Will Future Weather Datasets Help? / Why? / How?
New Storm Systems
|Draft plan lot layouts|
No, lots are far beyond river floodplains (no events above Hurricane Hazel freeboard before 2100). Seems reasonable as Pielke has shown decreasing tropical storm frequency and intensity in the US.
Adapting to larger floodplains affecting new development limits - Not a Thing.
|Stormwater pond sizing|
No, so many uncertainties in the subdivision design that pond blocks are oversized in the draft plan. Plus ponds have spillways with freeboards to handle flows well in excess of current 100-year design.
Adapting new pond sizes for quantity control - Not a Thing.
What might be a Thing? Review design hyetographs for existing weather - if conservative for existing, adaptation to future weather not expected to be a Thing.
|Storm sewer sizing|
No, pipes flow partially full with today’s 100-year and predicted higher intensities and peak flows will be throttled by inlet control devices. If some enter the storm sewer system (exceed today’s 100 year design flow) it will be accommodated in the freeboard to the basement elevation (basement slab’s 1 m above HGL).
Adapting new storm sewer sizing for basement flood reduction - Not a Thing.
No, they are sized for 10 year events so they will overtop 6 times in their 40 year design life vs 4 times in the old climate. But it is sort of an arbitrary “even number” design return period anyway (as humans evolved with 10 fingers and toes probably and gave us this base 10 number system). If culvert was something critical, with consequences of failure, it would be sized to a higher design standard.
Adapting new small culvert sizing to manage overtopping - Not a Thing.
No, they are susceptible to erosion wash-out by the receiving watercourse. Ideally they are set back from the meander belt-width with local connecting channels to limit risk of wash-out. They are often ‘fail-safe’, meaning some headwalls can fall into the creek with little consequence. Knowing future weather could be used to assess different future shear stresses in the creek but there is so much uncertainty in selecting critical shear stresses for reaches, etc. that no different design action beyond common sense set-backs would be followed with the perfect future climate data, imperfect derived flow data, and highly uncertain derived stresses and resulting vertical or lateral migration rates of the watercourse.
Adapting new outfall design to manage wash-out risks with future weather erosion stresses - Not a Thing.
Add changing freeze-thaw cycles to above … even less of a Thing.
|Overland drainage sizing (on roadways)|
No, these are often very overdesigned for yesterday’s weather. In one example, the ‘Rouge 4A’ subdivision, there were 2 critical overland flow evaluations points in design. At “LP#1” the overland capacity was 3.70 cms, 276% of the 100-year design flow of 1.337 cms. And at “LP#2”, the overland capacity was 1.85 cms, 791% of the 0.234 cms design flow. There is plenty of spare capacity.
Adapting new overland drainage systems to prevent spilling / flooding - Not a Thing.
The engineers agreed that ‘overland flow climate adaptation’ was “not a thing” to worry about due to existing overdesign in the GTA. But agreed that some considerations should be made in SW Ontario where a saw-tooth road grading pattern keeps all the runoff on the road - some sensitivity analysis toward storage in those systems would be worthwhile to see if freeboards are adequate to store more runoff from higher Weather Zoltar events.
What might be a Thing? Check and modify freeboard on-road storage design standards to accommodate future weather.
|Storm pumping stations|
No, these are not common in the GTA except in SW Ontario they are used to empty ponds or drains when receiving water levels are high. The pump stations operate only under certain conditions. If lake levels or watercourse/municipal drain levels increase, pumps will operate more frequently.
Adaptation of new storm pumping station capacity to future weather - Not a Thing.
What might be a Thing? Review design hyetographs used for pump storage - currently conservative 6-24 hour Chicago events evaluated. Would a future time series of more extreme weather, presuming lake and watercourse levels could be predicted, such that there is a need to change the size of pumps? Or would longer upstream roadway flooding be acceptable (existing 36 hour drawdown period is used for design).
What Is a Thing? Design standards for resilient power supply and back-up capacity should be reviewed, updated as required considering critical features such as some transportation routes, etc (e.g., served by pumping station pumping underpasses).
New Sanitary Systems
|Local sanitary sewers|
No, sewers are over designed with excessive dry weather peak flow rates and peaking factors and sewers are designed to flow partially full. Limitations with current design include deterministic infiltration and inflow allowances that do not account for extremes. But because extraneous flow stresses in new fully-separated sanitary sewers are limited (100 year I&I rates an order of magnitude below partially-separated system rates) systems have an intrinsic buffer against surcharging and back-up. Also, many municipalities require backwater valves on the sanitary lateral, such that in a rare event,
Adapting sanitary sewer capacity for future weather - Not a Thing.
What might be a Thing? Thorough review of I&I allowances in design. A doubling of current I&I rates may be in order, at least though a check storm? Some case study subdivisions should be evaluated to confirm if this potentially “Is a Thing”. This is required regardless of the future climate data trends.
|Sanitary pumping station|
Yes, we found a thing foreshadowing even bigger things in existing systems! Pumping stations are designed for dry and wet weather conditions. Like local sanitary sewers, pumping stations are designed with infiltration and inflow allowances that may not reflect today or future weather’s extraneous flows. The consequences of failure are significant in terms of back-ups / flooding or environmental impacts due to overflows/by-passes.
Adapting new sanitary pumping capacity to today’s and future weather - It’s a thing.
|Sanitary trunk sewer|
No, these are typically deep with no property connections such that existing or future weather extremes do not have consequences in terms of flood or environmental impacts. Dry weather flow rates and peaking factors accumulate in trunk design, resulting in excess capacity compared to conservative design values.
Adapting new sanitary trunk capacity for future weather - Not a Thing.
|New Water Systems|
|Local watermain distribution system|
No, fire flow scenarios governs watermain size. While future higher temperatures may increase irrigation requirements and peak hour demands, these do not govern design. If governing demands were to increase as a result of irrigation, demand management would be more cost effective than system upsizing especially given the water quality / public safety issues of oversizing systems and reduced chlorine residuals.
Adapting new local watermain sizing for future weather and irrigation demands - Not a Thing.
Old Development System and Component
Will Future Weather Datasets Help? / Why? / How?
Old Storm Systems
|Storm sewer system|
No, systems may be built to 2 year storm capacity, so there are predominantly exiting weather risks. Upgrades to today’s conservative 100-year storm are often ‘maxed-out’ within right of ways meaning bigger upgrades at not always feasible. Some system upgrades are not cost-effective and do not meet the Council approved threshold for implementation funding. Larger upgrades would introduce more utility constraints and expensive relocations, deeper systems with higher marginal costs due to dewatering requirements or more more costly unconventional construction methods. Small marginal incremental benefits of larger upgrades for future weather would have to be measured against high marginal incremental cost, and low benefit/cost ratios. This cost/benefit analysis should be completed against the backdrop that normalized catastrophic losses are not increasing in Canada considering net written premium growth.
Adapting old storm sewer capacity to prevent basement flooding - Not a Thing. Why? Because it’s already a big expensive, constrained thing under existing weather (i.e., when cities upgrade to 100 year level of service for today’s weather).
A spike in catastrophic losses - Not a Thing when GDP growth or premium growth are factored in, suggesting no economic driver to address damages beyond those associated with existing extremes.
What might be Thing? Review design hyetographs for existing weather - if conservative for existing, adaptation to future weather not expected to be a Thing. If not conservative, further upgrades may be revealed to be constrained physically, financially, or from an incremental benefit/cost sense.
No, see outfalls under new development. Old outfall siting intrinsically more susceptible to wash-out under either existing or future weather. Rehabilitation / protection required to address existing risk.
Adapting old storm outfalls to future erosion stresses - Not a Thing. Systems are intrinsically highly vulnerable under existing weather due to siting.
|Overland drainage sizing (on roadways)|
No, see storm sewers above.
What might be Thing? Mapping and managing overland flow paths through existing urban areas to guide infill development risk management. Use JBA Risk 2D overland mapping (GRID format) or readily available provincial conditioned DEM overland drainage features (vector format).
Old Sanitary Systems
|Local sanitary sewers|
No, see old development storm sewers. Sanitary systems are constrained like storm. Upgrades consider a 25-50 year historical storm design standard. Future weather will not change the historical standard.
What might be a Thing? Review historical design hyetographs for existing weather. Complete cost-benefit analysis to determine if alternative design standard can be justified for more extreme existing weather or future weather.
|Sanitary pumping station|
No, see local sanitary sewers above.
Standard practice for sanitary pumping station design in an old development with high extraneous flows would include the evaluation of overflow / by-pass devices, and I&I reduction. Peak flows under existing or future weather would not necessarily be accommodated in the pumping station.
Adapting old pump station capacity in a high extraneous flow system - Not a Thing.
|Sanitary trunk sewers|
No, old development trunk sewers in valleys are often highly susceptible to natural erosion processes, downcutting and lateral migration of watercourses. Significant investments in remediation and protection are ongoing. Key existing challenges are access for ongoing operation and maintenance and lifecycle replacement of features in constrained valleys (property constraints, topography constraints, environmental constraints).
Adapting old sanitary trunk sewers for future watercourse erosion stresses - Not a Thing.
Yes, the operation of regulator weirs could be greatly optimized to minimize CSO’s and/or limiting basement flooding with minute by minute weather predictions.
Well not quite. The city’s hydrologic models even with perfect rainfall inputs, predict peak flows within a range of -10% to +25%, so CSOs could be better managed but perhaps not optimized. Trade-offs between environmental impacts (aquatic habitat, beach closings) and flooding impacts would have to be made, with one objective satisfied at the expense of the other. And some regulators would not be adjustable remotely or in real time.
Adapting sanitary system operation to minimize CSO’s, and/or limit basement flooding could optimized for some components having real time control capabilities is a Thing. Don’t forget though that Weather Zoltar with minute by minute rain predictions is not a Thing, this is fiction.
|Real time CSO controls|
|CSO management strategy|
No, the city’s strategy is already build on a historical continuous period rainfall record that virtually eliminates CSO’s. Modifying the strategy to account for some other future extreme years, seasons or weeks would add considerable expense with marginal benefit compared to baseline CSO elimination with existing weather.
Adapting a CSO strategy that already eliminates CSO’s to future weather - Not a Thing.
|Wastewater treatment plant|
Yes, perhaps. Presumably, the future gridded 5 minute rainfall could be put in a calibrated model to transform it into precise wet weather flow at the plant to support optimized operations to maximize treatment efficiency and minimize by-passes. But then again, perfect rain data will not yield perfect flow data at the plant anyway - there is so much scatter in the long term GWI flow response to precipitation, and the short term RDII flow response, plus uncertainty with the macro-scale groundwater systems and foundation drainage (aka mysterious “urban karst”) and surface drainage/wastewater system hydraulic interaction driving inflows during extreme weather, or micro scale interactions between surcharged foundation drains, leaky floor slabs and sanitary floor drains.
WWTP management could be marginally improved with perfect precipitation data, but that perfect data will then reveal the uncertainties in the other complex processes (precipitation-extraneous flow transformations and processes that we don’t even have terminology to describe.
PS - today there is a considerable amount of effort prognosticating about future intensity-duration-frequency curves - what will they be? Unfortunately this is not converging. The questions we should be asking is what if you knew what they would be exactly ... or better yet what all future rain patterns would be? The possible answers in the Weather Zoltar story show us that once you know the exact future rain, you would have to face the reality that you have wide uncertainty on the next steps in applying rainfall data, whether in deriving a synthetic 'design' storm from that IDF data (rain statistics become simulated storm), or a hydrology transformation (simulated rain storm becomes runoff) or a hydraulic simulation (simulated runoff becomes infrastructure flow), and that a fulsome economic framework does not exist for decision making related to infrastructure investments as a function of system performance (e.g., flood damage losses, environmental issues, etc.... i.e., simulated flow becomes flood depths and potential damages/losses) what is the benefit/cost, what is the ROI, whose benefit? whose cost?. The good news is that most municipalities have a couple decades of obvious remediation work to do based on what we clearly know already about today's rainfall - they should get on with it - the needs are largely in pre-1980's subdivisions with design limitations related to riverine flood risk management (encroachment/enclosure of large channel/watercourses), wastewater system design (high extraneous wet weather flow stresses from foundation drains etc), and storm drainage system design (no explicit major overland flow design, limited minor system / sewer capacity).