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Environmental Modelling in Industry StudyGroup

Onno Bokhove

EPSRC-funded UK Network Maths Foresees with Tiffany Hicks & Tom Kent

Turing Gateway to Mathematics, Cambridge, April 3–6, 2017

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1 Welcome

2 Format

3 Challenges

4 Data

5 Inconvenient Truths

6 Control-the-Flow

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1. Welcome

. . . to the Environmental Modelling in Industry StudyGroup.

The second study group organised by the EPSRC networkMaths Foresees (1st: 2015, 2nd: 2017).

Thanks to Network Coordinator Tiffany Hicks and theTuring Gateway to Mathematics: Lissie Hope & ClareMerritt.

Questions: ask Clare Merritt (TGM), Tom Kent (flyingreporter) or me.

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2. Format

The study group recipe is straightforward:

There are 5 challenges, which will be presented shortly bythe challenge holders.

Make a choice in the course of today/Monday and sign-upfor one challenge & group.

Solve the challenge.

Start after today’s tea at 14:45!

Please keep an eye on the composition of the groups.

Final presentations on Thursdayhttp://www.turing-gateway.cam.ac.uk/event/

tgmw41/programme

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2. Format

Interim presentations for feedback: Tuesday 4th April19:00–20:00; 8+3min.

Where needed call in expertise from other groups; discussmatters at lunches, teas & coffees.

Tonight’s dinner at St. John’s College; Tuesday’s Buffet atINI; Wednesday Pizza Supper at INI (optimise).

Expense forms are available at the INI front desk fornon-UoL staff & all PhD’s.

Two room access passes per group.

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3. Challenges

Challenges & break-out rooms:

Seminar Room 1 (INI): A Risk-based Analysis of SmallScale, Distributed “Nature-Based” Flood Risk Measures—Barry Hankin (JBA Trust) [-]

Discussion Room (INI): Modelling Sewer Networks—James Franklin (Sweco) w. [GE & SVC]

Meeting Room 4 (CMS): Estimating Flood ProbabilityUsing Historical Data—Adam Baylis & David Cotterell (EA) [-]

Meeting Room 5 (CMS): Making Decisions UsingUncertain Forecasts—Adam Baylis & David Cotterell [-]

Meeting Room 15 (CMS): Understanding Rainfall Patterns—Adam Baylis [JV]

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4. Data

All challenges concern flood-related problems.

EA challenge on Understanding Rainfall Patterns will besupported by live showcasing of the Wetropolis flooddemonstrator on Wednesday.

I collected some helpful data sources on flooding.

Let me demonstrate use of these data in some examples.

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To mitigate floods, an idea is to avoid flood levels tobecome critical, e.g., by spreading/lowering flood peaks.

E.g., Boxing Day flood; type in: Armley (gauge Leeds) athttp://www.gaugemap.co.uk:

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Estimate the river levels of the mean area/rectangle abovethe Typical Range 2.12m & the mean area/rectangleabove Flooding Possible 3.90m: at arrows 2.8m & 4.5m.

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Estimate the river levels of the mean area/rectangle abovethe Typical Range & the mean area/rectangle aboveFlooding Possible: at arrows 2.8m an 4.5m.

Use the time slider on the same profile to estimate (i)duration of flood above 2.12m (first warnings): from7:00pm 25/12 to 6:00pm on 28/12, soperiod1 = 71 ± 1hrs.

Same procedure to estimate (ii) duration of flood above3.90m (flooding starts at Kirkstall): from 10:15am 26/12to 6:15pm on 27/12, so period2 = 32 ± 1hrs.

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To get the flood volume of water that we need to store orhold, we need the discharge inm3/s = 219gallons/s ≈ 4.38bath tubs/s.

Environment Agency report Hydrology of the December2015 Flood in Yorkshire or The flood of December 2015 inNorthern England (Spencer et al. 2016, EA).Peak flow = 350m3/s with 200+ year return period.

Boxing Day peak is at 5.21m (use slider) and top typicalrange is at 2.12m.

Estimate average flood flow based on the mean height wefound for both periods of (i) 71hrs and (ii) 32hrs.

That is: (i) 2.8m and (ii) 4.5m.

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This gives (i) 2.8/5.21 = 0.52 or 54% so average flow2.8

5.21 350m3/s ≈ 188m3/s and(ii) 4.5/5.21 = 0.86 or 86% so average flow4.5

5.21 350m3/s ≈ 302m3/s.The fractions for flood reduction are estimated as: (i)(flood peak − mean level)/flood level =(5.21 − 2.8)/5.21 = 0.46 & (ii) (5.21 − 4.5)/5.21 = 0.136.Yielding flood storage volumes (i) and (ii):

Flood volume1 =0.46 × Time in s × average peak flow

=0.46 × 71 × 3600 × 188m3

=22.2 × 106m3

Flood volume2 =0.136 × Time in s × average peak flow

=0.136 × 32 × 3600 × 90m3

=4.75 × 106m3

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That is either (i) 22.2 million or (ii) 4.75 million cubicmeters of water, i.e.,(i) 100MBT or (ii) 21MBT million bath tubs

That can be stored in a lake of 1m mean depth of either(i) 4.72km2 or (ii) 2.18km2 (square kilometers).

That can be stored in a lake of 2m mean depth of either(i) 3.33km2 or (ii) 1.54km2 (square kilometers), i.e.,(i) 2mile2 or (ii) 0.93mile2 (square miles)

That is for (ii) an area of ca. 20min walking one way andthen 20min walking at right angles to it with my head at6ft5” under water.

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Comparing hydrographs Aire River, i.e. 2000 & 2015:

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I visited Slow-the-Flow-Calderdale citizen flood action group inMytholmroyd (March 2017):

In the train (iphone), I made similar volume estimates forthe Calder River at Mytholmroyd.

Peak Boxing Day flood from EA-report: 276m3/s.

Flood level at 4.85m and peak level at 5.65m.

Water above the flood level 4.85m from 26/12 9:30am to26/12 4pm so ca. 7.5hrs (use slider).

Estimate the mean flood flux as ca.(0.5 × (5.65 + 4.85)/5.65) × 276m3/s ≈ 256m3/s.

The fraction with which we wish to reduce the flood is ca.(5.65 − 4.85)/5.65 ≈ 0.146, i.e. 14.6%.

The flood storage volume needed is thus ca.:0.146 × 7.5 × 3600 × 256m2 = 0.98 × 106m3 = 4.3MBT.

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Slow the flow Calderdale slowtheflow.net/ reports thatit will use Natural Flood Management to store7000m3 = 31500BT of water.

Assuming that storage volume is not filled, by previousrainfall and fully available, then this is7000/(1 × 106) × 100 = 0.7% of the Boxing Day excessflood volume required. So?

Again, a temporary lake of 1m depth and 0.99km2

(0.6mile2) created by an adjustable weir would do the job.

In comparison, a similar flood plain for excess Rhine Riverflood water would be ca. 7mile2 by 2 metres deep (over32hrs).

In comparison, a similar flood plain for excess ThamesRiver flood water would be ca. 1.5mile2 by 2 metres deep(over 32hrs).

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What about the so-called “Natural” Flood Managementscheme in Pickering?

Only 10% of this scheme is natural, by leaky woodendams: the remaining 90% is a cement bund.

This protects against 1 : 25 year return period floods.

Information presented by the Pickering Flood ActionGroup presentation at the Churchtown Flood Actionconference 2017.

In contrast to media reports, the scheme in Pickering hasnot faced such extreme floods like in 2007/2012 onBoxing Day 2015 (info from EA report).

The Pickering scheme is hybrid & 10% NFM.

Conclusion: the use of NFM should be estimatedcase-by-case (cf. Ahilan et al. 2014/2016).

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Biggest benefit of NFM is public awareness andengagement:

No problem but . . .

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From EA-report Hydrology of the December 2015 Flood InYorkshire, Kildwick 28km upstream had 163m3/s peakflow against the 350m3/s at Armley.

Over 4,000 homes and almost 2,000 businesses wereflooded with the economic cost to the [Leeds] City Regionbeing over half a billion pounds . . . ?

Hypothesis: 4 controllable weirs in the Aire River cancontrol the required water volume in real time.

Leeds Flood Alleviation Phase 1 with an adjustable weir atCrownpoint costs circa GBP50M? 4 weirs cost GBP200M?

Less or no flooding saves money and lessens the distresscaused by floods —important social aspect.

Nature-based-solutions: 2 weirs upsteam of Kildwick inthe wider Aire valley and 2 downstream at natural spots:e.g., upstream of Saltaire, Horsforth, Rodley?

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Please check the above. In conclusion:

Use, share and interpret data to get gross estimates.

Natural Flood Management plans & research should bebacked up by gross & detailed estimates.

Sometimes NFM works, often NFM cannot work, cf.Sheffield CC’s approach to use NFM to offset climatechange increase of flood risk.

“Some people seem to see it [NFM] as the only solutionand this is based on aesthetics rather than science”.

A hybrid range of mitigation techniques is required, tocontrol-the-flow, not slow-the-flow.

These can include nature-based-flood-solutions, e.g.,choose/make “natural” flood plains.

Could the Leeds floods have been alleviated withsuitably controlled reservoirs?

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Oude IJssel low & high T100: 118m3/s

Research on flooding needs you: maths-oriented scientists.

Enjoy the study group and good luck with solving yourchallenges!

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References

Missing: Digital Terrain Model (DTM) data . . .

Missing: digital river gauge data . . .

Gaugemap river levels UK: http://www.gaugemap.co.uk

UK government river levels:https://flood-warning-information.service.gov.uk/river-and-sea-levels

Government river levels:https://flood-warning-information.service.gov.uk/river-and-sea-levels

Leeds Flood Alleviation scheme:http://www.leeds.gov.uk/residents/Pages/Leeds-Flood-Alleviation-Scheme-Phase-1.aspx

Slow-the-Flow-Calderdale NFM plans, full link (page 7, point 10.6):http://slowtheflow.net/wp-content/uploads/2016/11/

StFC-Pilot-Project-Grant-Application-Report-Rev.B.-12.11.162.pdf

Damage estimates Leeds City: http://www.westyorks-ca.gov.uk/

Slow-the-Flow-Calderdale: slowtheflow.net/

NFM?http://www.itv.com/news/calendar/2017-02-15/floods-minister-visits-mytholmroyd/

Dr Ahilan reported two case studies for NFM: one in the Aire River that helps for floods with 15 yearreturn periods only and one in Portland, Oregon, which works well, and is effective up to 500-yearflow events. see: Ahilan er al. J. Flood Risk Managment 2016, Ahilan et al. 11th Int. conf.Hydroinformatics, New York, HIC 2014.

Pickering scheme: http:

//www.welcometopickering.co.uk/about-pickering/about-the-town/slowing-the-flow/

Example creating space-for-water IJssel River Netherlands (peak ca. 2000m/s):https://www.nemokennislink.nl/publicaties/ijssel-afgetapt-bij-zeer-hoog-water