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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? |
The pursuit of extreme weather resiliency and climate change adaptation technical tools and planning / management approaches for core public infrastructure requires a broad review of industry practice and commonly held assumptions about adaptation needs that have been held as tenets. Many of the assumptions do not hold up to scrutiny upon review of fundamental economic and technical data. Some assumptions are overly simplistic and do not recognize the diversity of systems and system components in real-world planning and design environment - the diversity is wide, ranging from newer systems with negligible existing or future climate risks due to inherent design safety factors, to older systems with significant existing risks and fundamental physical and economic constraints to adaptation. The review of newer and older systems and their components and their existing and future risks will help focus the identification of knowledge, technical tool and planning / management framework gaps on areas with the highest risk and highest benefits associated with adaptation efforts.
“Do I really look like a guy with a plan? You know what I am? I'm a dog chasing cars. I wouldn't know what to do with one if I caught it! I just do things.” The Joker in The Dark Knight
It is important that engineers don’t ‘just do things’. If they plan to adapt infrastructure systems to any changes in societal requirements, whether environmental or economic, or to modify approaches to planning and design, there should be a sound basis. Unlike Jokers, they don't 'just do things'.
Imagine the car is future climate and weather details, and the engineering and scientific community is the dog. Imagine if future 5 minutes rainfall intensities and temperatures across Canada were now predicted with exact certainty on a fine 10 m grid across Canada out to the year 2100 and all hydrologists, musicians, municipal engineers, and hydrogeologists were all given the complete future data. What would they do with it? What would be the plan with this new data? Would they have a sound basis to adapt their practice to this data? Evaluating what they would do with this data can help us review assumptions about systems and system components and explore other fundamental uncertainties in planning, analysis and design.
The Hydrologist
The hydrologist could do things with the minute-by-minute future weather data. Like quickly screen for major events and use some coarse existing hydrologic and hydraulic tools to prevent damages with exact military precision. He would aggregate future rainfall data on a broad catchment basis for his existing hydrology models, and silently curse the fact that he has to now load different storms for each catchment (because he feels that it is less conservative that hitting all catchments with the same intensity peak all at once).
The hydrologist would do his first modelling for areas upstream of known river flood hazards, e.g., Special Policy Areas in Ontario that have big historical and exiting weather flood risks. He would use his steady state river hydraulic model to predict floods levels to the centimetre and get the GIS department to plot the flood limits (but not until after they debate the difference between the hydraulic model elevation benchmarks and the GIS digital elevation model benchmarks) and he would then coordinate with emergency services, engineers and utilities to reinforce existing infrastructure components in the predicted floodplains, and safely evacuate residents and businesses well in advance of each event. He may communicate future flood levels to all property owners in the flood zones and using this information, some owners may or may not flood-proof their properties, depending on whether their insurance policy will cover damages and depending on the benefit/cost of flood-proofing efforts.
After the first flood event, it will be revealed from crowd-sourced drone video footage that the hydrologist’s models were not perfect - in fact the hydrologist ‘rounded down’ to AMC II conditions in the hydrology model to predict peak flow, underestimating the actual antecedent moisture before the first flood, instead of the wet-antecedent condition AMC III model which he thought was too conservative. The hydrologist also argued that the hydrologic model was actually calibrated with smaller storms so he never really had a hope of matching actual storm flows for a large event exactly anyway. The hydraulic model was also not perfect. It overpredicted levels in some areas an underpredicted levels in others, even once the actual vs. predicted flow discrepancies were factored out. Underpredicted model levels were later attributed to culvert grates clogged with debris during the flood that raised actual levels in some locations. The hydrologist argued that the model hydraulic model should not be blamed for these operational issues in the real world system. Also, several cars, picnic tables, pedestrian park bridges, and large dumpsters washed into some large urban channels and clogged culvert openings, raising actual flood levels above those predicted. In some ‘flat’ river reaches the hydraulic model underpredicted the flood level because the model incorporated ‘ultimate roughness’ values to characterize the overbank flow areas that were much higher than the existing values. Lastly, operation of a couple small dams may not have occurred exactly as predicted in the model. You win some you lose some.
Some roadways will wash out during the flood and a provincial inquiry would be held to determine who was responsible. Justice Riviere will conclude that in many cases the flood exceeded the design capacity of the roadway and so wash outs could be expected. He’d struggle with the definition of a ‘dam’ because expert witnesses representing municipalities argue that road embankments are not dams. The railway companies would hire the most expert of experts and argue their embankments are not dams either. In the end, Justice Riviere would recommend mandatory screening of roadway embankments for dam safety based on semi-quantitative risk assessment (like Ontario did for Drinking Water Source Protection) to be developed by a group of provincial ministries and newly conceived Flood Protection Boards. We would wait a long time for the regulations, director rules and guidance documents under the new Ontario “Roads are dams. Yes, it’s a ‘Thing’ “ Act. The hydrologist would retire well before this inquiry was over.
The Musician
The musician would write songs about the drought of 2041-45, rhyming ‘dust’ with ‘rust’, and the great Flood of ‘67, quietly wishing for an earlier flood year, like one with more long vowel sounds to draw out like ‘49 - or a ‘54 flood, “that would be much better alliteration - flood o’ fifty-four” he mused. Hearing about the upcoming droughts, the musician’s brother would open a successful lawn painting business like they have in Las Vegas.
Municipal Engineers
Municipal engineers would talk to their managers about upcoming training in Banff to attend a 1-month symposium to learn about how to download the new future data sets, how to do statistical analysis on it, and how to consider it in updating design standards. Why Banff? Its beautiful and everyone can go on nice hikes after the sessions of course. And that funny musician who sings about future weather events will be there too for entertainment on the ‘ice-breaker’ opening night. They heard his repertoire includes old stuff like When the Levee Breaks, but a nice acoustic version. Why statistical analysis? Because most undergraduates have limited competence in this and many practitioners do not use statistics, but rather apply simple conservative fixed, deterministic design values in their everyday practice. It would be worthless trying to apply the future data without considering the variability.
Municipal Engineers’ Managers
The municipal engineers’ managers would go to Banff, not the engineers. The private sector managers would leave staff behind to work and ‘pay the bills’, and public sector municipal engineers would approve their own training requests. When they returned they would know this new future data represented a dilemma and they would hold a meeting of the secret society of municipal engineering managers, cleverly named the “SWMinatti” during an earlier BEvERage-infused meeting. They said it stands for Storm-Water-Management-Is-Never-A-Truly-Tested-Initiative. They laughed but their wives just shook their heads once this was shared at home. At this special meeting they would discuss how they would ‘come clean’ in the eyes of the public and regulators and dew-eyed engineers-in-training about the ‘real’ state of practice in municipal engineering design and why they had absolutely no appetite for the new, perfect, high resolution, future climate datasets. The future datasets would mean their municipal and stormwater management practice could now be ‘truly tested’.
The municipal engineering managers would meet. They’d initially joke about the “Weather Zoltar” machine that knows all and tells all - and question if it was really predicting accurate temperature and precipitation on a 10 m grid scale across Canada every 5 minutes for the next 84 years? It turns out it was indeed. How? Early on, several GTA conservation authorities got together and made a $20M grant request to confirm the Weather Zoltar predictions and installed high-precision climate stations every 10 metres in a test catchment north of Toronto - the grant request was immediately fulfilled. The total precipitation measurements every five minutes for 2 years of continuous monitoring were within 3 percent of the Weather Zoltar predictions but the extreme rainfall intensities were less accurate given the bias in equipment measurements. So just a minor measurement error. Temperatures were “bang on” to the first decimal except at the stations affected by shading. Weather Zoltar did know all.
Using a napkin, the municipal engineering managers would start a list of the things that they do in planning, evaluation and design that could be shown to be questionable by the Weather Zoltar data (i.e., overdesigned or underdesigned) and the things that would really benefit from the precise future climate and weather datasets. They would start with things they design for new developments and decide on a code for evaluating issues with each. The code “Not a Thing” meaning that the future data would be of little value, and the need for adaptation for the component design was unnecessary. The code “Might be a Thing” meaning some analysis could be pursued to confirm if any adaptation was required:
New Development System and Component
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Will Future Weather Datasets Help? / Why? / How?
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New Storm Systems
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Draft plan lot layouts
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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.
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Stormwater pond sizing
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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.
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Storm sewer sizing
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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.
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Local culverts
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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.
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Storm outfalls
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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.
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Overland drainage sizing (on roadways)
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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.
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Storm pumping stations
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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).
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New Sanitary Systems
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Local sanitary sewers
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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.
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Sanitary pumping station
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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.
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Sanitary trunk sewer
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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.
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New Water Systems
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Local watermain distribution system
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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.
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So the overall assessment of new development servicing is that storm systems are full of resiliency now and would not require adaptation for future. The municipal engineering manages raised a glass. They decided that system components could be checked with future IDF values, but may not require upsizing if existing safety factors, such as HGL freeboard in storm sewers are adequate and overland capacity remains excessively conservative - someone should get federal funding and do a detailed model of a new subdivision to show this with the future climate data they all agreed. The acknowledged that some components such as pumping stations and ponds designed using hydrograph methods would benefit from a review of design storm distributions to ensure conservative design.
Their overall assessment of new development sanitary systems suggested that design approaches for considering inflow and infiltration should be reviewed to account for existing extreme weather stresses as well as future ones. But in new developments this seems to be a low risk area - new builds do not have infiltration inputs like old ones, nor the inflow ‘pathways’, like downspouts to foundation drains or unmanaged overland inflows. Again, they agreed someone should apply for federal funding to analyze a new subdivision to confirm this so they could put the adaptation question to bed.
All of a sudden, a giant asian carp leaped out of the channel - they were meeting at the Keating Channel Pub & Grill - and ‘took’ out the littlest manager. BAM! Bonked him right in the head. Since he was from a city with mostly new development it didn’t matter that he was now out cold on the patio for the rest of the discussion because his systems seem to be in good shape with a bit of review of safety factors in existing design approaches - it was noted that the University of Waterloo’s Intact Centre for Climate Adaptation was developing a Flood Resilient Community Design Guideline to identify high level master planning requirements and local storm, overland and sanitary design objectives to limit flooding - engineers could follow a simple checklist to see if they are following this good standard practice approach in their planning requirements in their Official Plans and engineering design standards. If they do this, there is little need to focus further on climate adaptation in new developments.
So the municipal engineering managers would feel pretty good, except for one. He worked in a city with little new development but a lot of old pre-1970’s development and infrastructure built to early limited design standards. His systems included many storm drainage systems built with no overland drainage system, and many combined and partially separated sanitary sewer systems. The managers all agreed that they spend most of their time and effort on these old limited standard systems - these are the ones where there is ongoing litigation or claims regarding system performance and damages. The ‘old development city’ manager said his city was undertaking basement flood management studies in all these old areas, completing remediation projects to upgrade service levels, and undertake billion-dollar strategies for CSO management and operational improvements. He said he saw a great blog that analyzed the historical floods in 2000, 2005 and 2013 and correlated the flood density to the era of construction - so these is a lot of variability within the subset of older systems, with combined CSO systems generally having lower flood risk due to the surcharge relief while partially separated systems have the highest flood density. The manager with a balance of new and old development echoed this observation on diversity, saying he has litigation ongoing for flooding in one old area -never new areas - and all his ongoing storm flood remediation projects are in pre-1960’s areas. All the sanitary I&I reduction efforts focus on the high extraneous flow old areas too - nothing is done in the new developments because when we get 25-year storm, we don’t get calls from new areas. Climate adaptation in new areas is really ‘Not a Thing’. Bottoms up!
The SWMinatti found another napkin on the next table and started to evaluate the infrastructure components in old, existing developments to see how many things they could find to adapt given the perfect Weather Zoltar data now in hand:
Old Development System and Component
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Will Future Weather Datasets Help? / Why? / How?
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Old Storm Systems
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Storm sewer system
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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.
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Storm outfalls
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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.
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Overland drainage sizing (on roadways)
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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).
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Old Sanitary Systems
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Local sanitary sewers
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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.
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Sanitary pumping station
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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.
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Sanitary trunk sewers
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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.
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Regulator weirs
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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.
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Real time CSO controls
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See above.
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CSO management strategy
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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.
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Wastewater treatment plant
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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.
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The municipal engineering managers put the old development napkin notes down and scooped up the last nachos. The new development city engineer on the patio was still breathing so that was good - they wondered if they may have to cover his part of the bill - not good.
They would sum up the old system adaptation needs observing that old systems have existing capacity limitations intrinsic in their design. They can have very low levels of service - CSOs can occur many times a year, sewer back-ups in most chronic areas can happen for small return periods, never mind extreme events. Fortunately there are large scale programs and projects aimed aimed at remediating existing issues and improving level of service. Unfortunately these improvements also have physical, financial and environmental constraints. As a result the Weather Zoltar future climate details will not change how these existing issues are managed. Low cost measures like inflow reduction through cost effective downspout disconnection will continue whether future rainfall is more or less extreme. High cost measures, like upgrading storm sewers to convey 100 year events will continue regardless of future weather, and these upgrades will be constrained physically and financially. The CSO management strategy that will virtually eliminate CSOs will continue whether future seasonal rainfall patterns are more or less variable, or have a few more extreme in some years - it is needed for operational purposes as well. Erosion protection for intrinsically vulnerable features like sanitary systems in valleys will continue as well - design is based on conservative practices like taking the recommended armouring size and doubling it due to inherent uncertainties in current design practice and past experience with wash-outs.
The municipal engineering managers agreed that the fundamental drivers for climate adaptation should be reviewed. They questioned the common belief from their Environment Office staff that storms are becoming more intense or occurring more frequently - Environment Canada’s own Engineering Climate Dataset version 2.3 and their regional analysis of short duration rainfall shows no detectable trends and in some regions the statistically significant trends are downward. There seems to be an ‘availability bias’ in the media and among those with limited scientific background to list a few extreme events and cite this as statistically relevant information to act upon - the engineers agreed that the plural of anecdote was not data and that data-driven, evidence based policies are needed. To test this our they asked the bus boy if he thought storms and flooding were getting worse - he said that he worked at this Keating Channel pub for 4 years and there are a lot of floods on the local roads so yes, it rain must be getting worse - and look at the flood they just had in Windsor. One of the engineers joked that flooding has been happening since the 70’s .. the 1870’s based on the flood inquiry report for the system - the bus boy didn’t get it. They would have to tip well to make up for harassing him. They agreed that someone should get some federal funding to communicate the historical and regional trends data so engineers know if they are in a higher change zone or if their raw weather data needs any safety factors applied to account for intrinsic biases (short uncertain records with sample bias, raw data not corrected/adjusted for daily measurements). That would support engineers in deciding if they need to update IDF curves. One engineer suggested that this could be a reality check for some Environment Office staff who keep citing now-discredited insurance industry rain trend claims - that storms that happened every 40 years are happening every 6 years - that has been shown to be a theoretical shift in a bell curve and not real Environment Canada data as cited.
The municipal engineering managers agreed that the future climate Weather Zoltar data took away one important aspect of uncertainty in infrastructure planning, analysis and design. What it exposed was all the other sometimes more significant uncertainties that go into infrastructure planning, analysis and design like transforming rainfall to runoff given variable antecedent conditions, or transforming rainfall into sanitary inflows or moderate or slow-response groundwater infiltration responses, or water levels in infrastructure and the routing and storage of peaks. Precise exact future climate data allows engineers to put a sharp point on one part a big, blunt instrument called hydrologic and hydraulic modelling. Maybe someone should get some federal funding and demonstrate these uncertainty factors and how they all work together and show that climate uncertainty should be considered along with all the other uncertainties - for what system components is climate important and how can it be readily addressed. After all we only have exact future climate data available to 2100 and after that we have to make some assumptions about how to handle later uncertainties.
Lastly, the managers agreed that what is really needed is a review of the economic drivers for climate adaptation. Since US data shows tropical storms are less severe and frequent and there is local data on decreasing intensity trends, like from convective storms, there must be other drivers for increasing catastrophic losses. The growth and intensification of urban areas could be reviewed - one engineer suggested his initial GIS analysis showed watershed urbanization increasing 100% a decade compared to research showing peak rain intensities increasing 1-2% per decade. Those drivers have to put into perspective so that remediation actions can be prioritized. Analysis in the US showed flood losses normalized for GDP growth were decreasing - increases could be explained by growth and more insurance market penetration. This means the issues of flooding is still significant, but it is not ballooning out of control such that the investment in existing flood mitigation or future flood adaptation should baloon as well. One engineer shared that he normalized the Canadian catastrophic loss trends from 1990 to 2015 using person property premium totals and there is no normalized upward trend. The economic drivers could be considered as part of comprehensive cost-benefit analysis for infrastructure planning and could help refine budget thresholds currently being placed on rehabilitation projects.
The Hydrogeologists
The hydrogeologist (just one - they don’t have friends to hang with) looked at the infographic that came with the future weather datasets and laughed. “What am I going to do with this? So what if I have the rainfall and temperature data. Yes I want to refine my recharge estimates that drive my groundwater model, but the biggest part of the water balance, the evapotranspiration, is still a great big hairy unknown. My empirical equations are really really rough as it is now. Anyway, before Weather Zoltar, we did a sensitivity analysis on future climate for a really stressed groundwater water supply system. We found that most scenarios gave us more recharge because of more precipitation and less frozen soil and that resulted in increasing groundwater levels at the municipal well. The assumption that climate change would automatically decrease groundwater levels, starve baseflows and necessitate costly infiltration BMPs is really unfounded. The Weather Zoltar data confirms it. I’m always amazed at these municipal engineers - they have these cartoonish representations of water budgets for cities and claimed in the past that urbanization would decrease baseflows - what do we see in our watersheds? - increasing baseflows. The same was predicted for baseflows with climate change early on and now we show that is unfounded. If groundwater levels are going to drop - and I don’t know if they will, I don’t have an evapotranspiration Zoltar, or a perfect representation of the groundwater systems - then just monitor the situation and drill a deeper well if you ever need to. It would be way too expensive to change what we are doing now based on uncertain impacts, even with this perfect Weather Zoltar data. Done.
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So what do the hydrologists, municipal engineers, and hydrogeologists do when they ‘catch the car’? When they have perfect future climate data to use? They find that they have significant design safety factors in new systems and take the opportunity to look at weather closely and test assumptions on design storms. Some further study is required to confirm these safety factors. They check if their current local or regional IDF data has been trending higher and needs updating. And they realise they could do these things even without the Weather Zoltar data. The also realise they have a lot of other outstanding uncertainties in any planning, analysis and design. Even perfect future climate data does not help address uncertainties in processes resulting from climate data (e.g., water balance losses, runoff and infrastructure flows). In old systems there are significant physical and financial constraints under existing conditions such that future weather may not change their strategies significantly. Robust cost-benefit analysis as part of multi-objective risk-based decision making is therefore required to guide any adaptation measures that would increase infrastructure investment considering climate impacts. This analysis should consider some decreasing regional trends in extreme rainfall and relatively ‘flat’ trends in losses relative to economic growth and insurance premium growth.
(c) R.J.Muir, Toronto - 2017
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).
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Make a wish. All future rainfall details .... if your wish is granted then you'll need a few more arcade machines to predict
how the rain becomes runoff, how runoff becomes infrastructure flow, how flow becomes flood depths, how flood depths
becomes losses, and how to determine the appropriate economic investments in infrastructure to address the issues ... oh,
and another machine to predict future interest rates to support the discount rate in the economic analysis. |
