action workshop on urban runoff modelling why not do it ...action workshop on urban runoff modelling...

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Action Workshop on Urban Runoff Modelling

Why not do it Properly?

Cropston Wednesday 18th April 2007

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Runoff GroupMost recent research

group• Focus on improved runoff

modelling

This was the third FWR/WaPUG workshop to consider how runoff modelling can be improved. The first reviewed the subject. The second identified strategies for improving modelling. WaPUG reviewed the outcome of workshop 2 and concluded progress will be made by dividing the subject into three task-areas. The purpose of this, the third workshop, was to work on the task-areas.Runoff modelling is the weakest part of sewer modelling.

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modelling

• Annual Workshops each April

• Discuss new research

The runoff models in use today were based on field measurements made 30 years ago, albeit 100 field measurement sites were used. Unavoidably, field measurements of runoff are limited – there is a limited number of surfaces and precipitation events that can be measured. It is time to revisit this field work. The photographs show examples of hard surfaces in urban areas and recent work experimental work looking at runoff. The first rain to fall on a surface might remain trapped in the surface and not runoff; at the same time it is subject to evaporation. Eventually the depressions and roughness fill up, water overflows to the next depression and runoff follows. Runoff can continue for an extended period of time after the end of precipitation as the depression storage drains until each is an isolated store [puddle].

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modelling



• Develop new modelling tools

• Identify research needs

• 2D or not 2D?

Even at the time of the first workshop, computing power was considered to be inadequate to go beyond 1-dimensional modelling, but now 2D is practicable. 1D restricts modelling to defined channels whereas 2D enables models to compute overflow from channels and overland flow.

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modelling



• Develop new modelling tools

• Identify research needs

• 2D or not 2D?

• Disseminate Best Practice

• Produce Guides

WaPUG has decided to continue with the April workshops. They have advanced the subject and, judging by the number of hits on the FWR website, they are satisfying a need for information.

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OBJECTIVE OF DAY - 2007

To launch Working Groups set up from 2006 workshop – 30 delegates across 3 groups

• Determine and consolidate current best practice in runoff modelling

• Think to the future– How can we improve current techniques?– Can we better define & measure impermeable area?– How can software develop – long term– Are new runoff models required – long term– Address the design issues – short term fixes

• Aim to produce definitive industry help– User Notes– Guides

Workshop 2 identified that because of a lack of standardisation, models currently have limited life and limited transferability. This is a significant inefficiency. WaPUG resolved to try to increase the longevity of models and of the calibration data by introducing more standardisation. Three Working Groups have been proposed as the following slides discuss.

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Surface Measurement Group• Standardise surface measurement and applications (and

thus model transferability)• Confirm key measurables for contributing surfaces and their

application to models

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Standard Surfaces Outcomes• Review use of MasterMap to digitise areas

– Big saving to industry in terms of time and cost

The intelligence within digital maps increased enormously when Ordnance Survey released MasterMap. Prior to MasterMap there was no intelligence in the lines, but now the mapping software knows which features are roads (for example) however it still does not know the nature of the surface with respect to runoff.

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• Satellite Imagery to determine contributions

Satellite imagery is now easily available (GoogleEarth, etc.) and enables discrimination between different types of surface – possibly with some ground-truth referencing.

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• Satellite Imagery to determine contributions• Investigate, research and measure typical surface

parameters– Depression storage, slope, roughness– Effect of cracks, puddles etc

• Recommend optimum number of surfaces to use in models– Simple = 3; complex now = 12; future = ???

• Recommend standard approaches to quantifying surface types and the survey of these

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Runoff Processes Group• Improve the field measurements used as basis of runoff

process models – 30 year old data sets in current models• Represent in more detail the characteristics of paved

surfaces (routing, storage, variability across type)• Better represent the connection of paved surfaces to the

sewers – inlets

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Runoff Processes Outcomes• More understanding of roof drainage and entry

– Need to include in models, esp drain pipe capacity– Long term – roof volume and routing models

• More emphasis on detailed modelling of gully restrictions and highway overland flows– Not adequately done, need improved methods– Formal guidance note to be written on current best

practice

Entry of surface water into the drainage network [whether form roofs or highways, etc.] needs better understanding. For example, a significant amount of runoff can flow over or around gullies during high surface flow velocities: i.e. some is admitted and some is passed forward – the proportions depend on the designs of the inlets. We do not model the inlets currently.

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Runoff Processes Outcomes

• Better use of current empirical models– Variable catchment wetness of impermeable surfaces– Use improved runoff volume models from WaND– Short to medium term – best use of current approaches

This was a seminal example/demonstration of depression storage and delayed runoff. Runoff would continue for a long time after the cessation of precipitation as depressions drained down.

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Develop Long Term 2D Runoff Models(that work with catchment wide sewer models)

• Currently use subcatchments and empirical volume models

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BM 55.47m

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UTTOXETER NEW ROAD

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COLLEGE

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Gully

Outfall

Gully

Outfall

The difficulty is modelling at the local level [individual properties].. The large area models [the Drainage Area Plans DAP] are good enough.Scandinavia and NL are much better than the UK at modelling sewer processes; in the UK we generally assume that what goes in comes out even though we know this is not true.

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• Grid Cells not subcatchments• Better inlet modelling

BM 55.47m

WB

68

El

34

24

Sub Sta

11

21

UTTOXETER NEW ROAD

Tank

136

1822

14

8

16

42

COLLEGE

64

1

6362

MEWSGeorgian

House

154

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• Grid Cells not subcatchments• Better inlet modelling• Models true routing based on

surface characteristics, not assumed routing / delay coefficients

• Similar to current 2D overland flow models, but smaller scale and used as flow input

...noff Test>Sims>Car park - Wallingford 1mm>12M-120>Runoff Test>Sims>Car park - Fixed 1mm>12M-120

...ark - Detailed grid model 1mm (all one node)>12M-120...st>Sims>Car park - Detailed grid model 1mm>12M-120...Detailed grid model 1mm (variable dep store)>12M-120

Flow (m3/s)Min

-0.000-0.000-0.000-0.000-0.000

Max0.0040.0050.0050.0020.002

Volume (m3)10.12413.33213.61511.98610.213

Runoff following 1 mm rainfall from a carpark into a gulley versus time for 5 different models. Wallingford shows the most rapid response and a detailed grid model with variable depression storage shows the slowest response. The volume of runoff is the same in these two extreems (10 m3) but the maximum flow rate was 0.004 and 0.002 m3/s respectively, which obviously makes a huge difference in the prediction of the size of pipe required.

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Design Parameters Group• Confirm best practice for design scenarios to address

issues highlighted in industry in last 5 years

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Design Parameter Outcomes• Establish industry best practice with use of antecedent

conditions in design– Questionnaire– Literature Review– Sensitivity of parameters– Many conflicting approaches, often not fully understood

• Produce user guide for 2007 – needed urgently• More investigation of application of creep to design models

– What is annual % increase to patios????

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Future WaPUG Research Topics

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• Continue with Runoff Modelling Research• Best practice for overland flow modelling of flood

flows– Gradually being developed and used but little guidance and

best practice

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• Continue with Runoff Modelling Research• Best practice for overland flow modelling of flood

flows– Gradually being developed and used but little guidance and

best practice• Integrated Catchment Modelling / Planning

– Flood risk assessment becoming more and more integrated– Overland flow– River, sewer, STW models talking to each other?– Transfer of skills across disciplines?– Experience gained in DEFRA Pilots

• 16 pilots across UK to look at integrated catchment planning

• Open Forum at November WaPUG for Members to identify next few years research needs

The following were added during discussion:•Energy demand reduction e.g. by better pumping and by monitoring. A UK water company has reduced kWh electricity used by 7% as a result of comparing kpi for pumping in terms of kWh/m3/m lift – pumps with exceptional kpi were then examined and this has led to identification of some inefficient pumps which have been replaced – the data were available within the company, it was just a matter of doing some critical ratio calculations.•Anaerobic digestion – there are developments in this long-established technology and in addition there are opportunities for co-digestion, however the breathtakingly stupid decision to require PPC licensing for CHP engines burning 3MW biogas has meant that some companies with sites slightly exceeding 3 MW have installed 2.9 MW engines and flare the surplus.•Flood risk management•Treatments to remove priority hazardous substances – their financial and climate change costs•Alternative or enhanced P-removal - Dr John McGrath’s work (Queen’s University, Belfast http://www.qub.ac.uk/bb/people/mcgrath/research.html) was cited. His group has demonstrated that reducing the pH of the bio-P activated sludge to around 6 doubled the P removal.•Real time control – Richard Kellagher is looking at this. Dr. Michael Teufel (NIVUS GmbH www.nivus.de) presented a paper on RTC in Vienna‘s sewers at WaPUG Spring conference.•The EHS-NI has been able to write consents for WwTW in IN since 1st Aprl 2007

action workshop on urban runoff modelling why not do it ...action workshop on urban runoff modelling...

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