C O M P U T A T I O N A L H Y D R A U L I C S I N T E R N A T I O N A L discussion topic Models that...

C O M P U T A T I O N A L H Y D R A U L I C S I N T E R N A T I O N A L

discussion topic

Models that are eco-sensitive ought to be encouraged, over

those that aren’t.


A model is a concept. Concepts are used in engn’rg design and are improved by experience. We do not necessarily require the model that most approaches perfection, rather we seek the model that provides an acceptably accurate explanation. Simple models are often said to be “better” than complex models. Optimal model complexity depends on the questions to be resolved and the resources available.


1. We develop an obvious case for eco-ethical engineering,

2. which clearly implies more “complex” design-analysis models,

3. and supports another old philosophy: period-of-record (continuous) design models

In this presentation “there is nothing new under the sun, Horatio”


Starting suppositions:

World's #1 long-term problem is Loss of habitat and bio-diversity, apparently irreversible. Environmental problems are caused by humans, mainly by their population pressure, and can be solved by modifying their behavior.On the other hand, we generally replace acute by chronic problems, at a price: vigilance.


And a startling position:

Often, simplistic methods are associated with poor drainage design, which is in turn associated with tough living conditions, whereas complex methods are associated with desirable conditions. There may be cogent reasons for this relationship, related to society knowledge and eco-sensitivity.Reversal of environmental degradation has been shown in East Africa to lead directly to real improvements in living conditions, including employment opportunities.


PERIOD MYTHOLOGY IMPLEMENTS1. "ante‑diluvian” "rational" formula, slide rule,from c1892 I‑D‑F curves adding m/c, no data.

2. “ancient" event hydrology: batch mainframes,from c1932 unit hydrographs, pocket calculator.

design storms. c1970

3. "modern" continuous modeling; 16‑bit pc’s, from c1962 time series management minis c1980

4. “new” more than engineering. 32‑bit work stations, from c1993 networks

An archeology of stormwater design

These four periods correspond to use of a: 1. technique, 2. methodology, 3. philosophy & 4. value system


“Things should be made as simple as possible, but not any simpler."

- Albert Einstein

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Traditional design methods use:

1. Few parameters, that subsume great complexity;

2. Empirical equations, based on curve fitting;e.g. linear unit response functions, anddesign storms based on IDF analysis.

Reasons for Use:1. Tradition, 2. thought to produce conservative results, 3. thought to be inexpensive and easy to use.

Real reason: circumvents the need for thought, eliminates complicated, modern issues.


For permeable surfaces, vertical occurs at capacity of

upper layer

From Pecher’s doctoral study, Germany ca. 1970


Event vs continuous hydrology

Event hydrology accounts for wet event processes only. Continuous hydrology on the other hand includes all dry weather processes.Why do some agencies choose to ignore half the processes (the model is provided free, a generous gift of the US Govt)?

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Event vs continuous hydrology

Event hydrology is mistakenly thought to be a cheap design method; it does however produce “cheap” (inadequate) designs. E.g., unit hydrograph and design storm methods cannot account for ecosystem concerns. Continuous hydrology on the other hand allows consideration of aquatic ecosystem (and many other) issues.

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Event models generally….

Do not simulate water quality build-up and wash-offDo not simulate erosion and fluviologyDo not simulate important aquatic bio-system parametersDo not simulate long-term performanceDo not account for the large number of light rainfallsDo not account for sequences of high flowsDo not account for sequences of low flowsDo not account for seasonality Require start-up conditions that are inconsistent, highly uncertain and criticalDeny consideration of ecosystem issuesAssume everything is stationaryEtc.


An overiding issue is the so-called “first flush”

Event models cannot predict first flush effectFirst flush (>50% TSS in rising limb of the hydrograph) probably exists wherever we have efficient drainageManufactured treatment devices and other BMPs are excellent for capturing the first flushWe obviously need to concentrate MTDs wherever a first flush may be experiencedTheir long-term costs/benefits should be computedWe therefore need a continuous model that correctly predicts first flush.


We do not need to immediately and peremptorily replace established

event models

What I am suggesting is: don’t replace your traditional methods; simply encourage addition of the (say) 50-years design storm to your current slate of design storm computations.


Why SWMM?

Most widely used general stormwater programUsed extensively for urban watershed planning, design, development, management, and regulation.Vast archive of applications, users etcPCSWMM for Stormceptor integrates and dovetails with these area-wide models.


How does this concern us?

Urbanization is by definition involved in habitat and biodiversity (H&B) degradation (medicine is the complement)

Globally, we are told, H&B problems are serious and getting worse

Long-term sustainable civilization, we are also told, is dependent on restored H&B


Some humble suggestions

Develop in officials a deep eco-ethos to restore bio-diversity

Develop in the landscape intervention community a new spirit that restores ecosystem diversity.


Design should follow a “sacred ecology” of focussing on less-unsustainable ecosystems

biological equity must determine design, design must reflect bio-regionality, projects should use renewable energy systems, the living world should be the matrix for all design, which should integrate living systems, and follow the laws of life, andprojects should “heal the planet”


Good design:

examines very long-term changes and impacts (>100y)

accepts the limits of our discipline;

corrects the human behavior that caused the problem to the ecosystem;

improves & restores the natural balances and bio-diversity, imitates the structure of the natural, native or indigenous system, and is good for all parts of the natural system;

does not enrich one individual or group to the distress or impoverishment of another;

is in harmony with good character, cultural value, and moral law.

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Simplistic short-term models have trapped us in a rut of producing only politically-correct solutions that fit single-minded ideas of economic growth (e.g. what is the minimum-cost unit?)

Complex, long-term and meaningful models open up a greater variety of options (e.g. what animals are affected by installing the unit?)

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On simplistic vs meaningful models


Prohibit uninformed use of incomprehensible models

More intelligent use of more credible models is what we seek. Training is important.


Models are used to help select the best among competing proposals. It is fundamentally irresponsible and unethical for modelers not to interpret their inherent uncertainty.

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As a rule


The implicit problem in engineering design is to find the optimum cost-effective array of best practices. A solution may be stated: if the 75-year rainfall time series that occurred at the International Airport, had in fact occurred at Foxran Estates, then plan 126 would have been the most cost-effective of the 329 plans examined - had they, of course, all existed over this time.


- model complexity is related to the total number of uncertain input parameters.

Models inevitably become more complex


For design follow a personal or sacred ecology (biological equity, design to restore bio-diversity, very long-term modelling). For design and analysis, eschew simplistic models that do not help to restore the planet.In development, consider the N American idea of a great spirit based on long-term ecosystem health and diversity.

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Summary


The end

www.computationalhydraulics.com [email protected]@uoguelph.ca

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