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Brandhall Brook An urban application of ISIS-ESTRY- TUFLOW

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Brandhall Brook

An urban application of ISIS-ESTRY-

TUFLOW

Brandhall Brook Catchment

Brandhall

Oldbury

Sandwell

West of Birmingham

Brandhall Brook Catchment

• Tributary of the River Tame

• Includes the York Brook

sub-catchment

• catchment area 8.4km2

• high to medium density

residential areas

• Small industrial estates

• URBEXT 0.833

Brandhall Brook Catchment

• Hydrology dominated

sewers

• Significant lengths of

culverted watercourse

• Open reaches

canalised/engineered

• Urban debris

Brandhall Brook Catchment

Brandhall Brook Catchment

Brandhall Brook Catchment

Brandhall Brook Catchment

Brandhall Brook Flood History

Study Site

• 2.4ha former college

campus

• Downstream of the flood

alleviation works

• Planning permission for

residential re-

development

• New SFRM model altered

perception of flood risk

SFRM Model

• ISIS-TUFLOW 1D-2D model

• Hydrology derived from

Severn Trent Water sewer

modelling

• 3.9km of watercourse

• 2.6km of culverts

• Strategic scale

Study Site

• Development within FZ 3a/3b

• Site access at significant risk

Aim:

Address flooding issues on the

site facilitating the delivery of

the entire development.

SFRM Model Review

SFRM suitable for strategic overview of flood risk, but:

• Numerous negative depths (>8000)

• High Mass Error (>5%)

• ‘Noisy’ ISIS convergence plots

• ‘Saw-tooth’ water profiles

• Unrealistic flow patterns (Qi vs Qo)

SFRM Model Review

ISIS culvert reaches reviewed:

• No manhole representation

• Pipe size & geometry inconsistent

• Schematisation issues

• Very sensitive

Culverts converted to ESTRY:

• Manholes added to better represent

system losses:

Expansion/contraction

Change in direction

Change in height

• Automatic generation of manhole

type

• Engelhund Manhole loss approach

• Inflows extracted from ISIS and added

to BC DBASE

Alterations – 1D ESTRY Environment

• Truncated ISIS domain just includes open

reaches

• Open channel easier to stabilise

• Prepared for linking with ESTRY:

Orifice units used to represent inlet to

culverts

Dummy QT and HT boundaries

Alterations – 1D ISIS Environment

ISIS - ESTRY Link:

• 1DXH : Water levels passed between domains – default

• 1DXQ : Flows passed between domains – used at inlet

‘Base flow’ simulation undertaken to allow ISIS-ESTRY to synchronise:

1. Dummy QTs given nominal flow

2. Deactivated when all flows have culminated at D/S boundary

3. Unnecessary flows allowed to leave model

4. Restart file and IIC generated once ISIS and ESTRY are in equilibrium

Alterations – 1D ISIS-ESTRY integration

1

2 3

4

• ‘Fixed’ zpt layer replaced with ASCII DEM

• Grid size & orientation optimised

• FLC applied to ISIS HX boundary

• Buildings modelled at ground level with

elevated roughness (0.5)

Alterations – 2D TUFLOW domain

Performance of re-built model

• Negative depths reduced from >8000 to 0

• CE reduced from >5% to 0%

• Improved ISIS-TUFLOW interface (Qi/Qo)

Before After

Performance of re-built model

More stable ISIS domain

Performance of re-built model

Impact of re-built model

York Brook

• Increase in surface flooding

• Reduced culvert conveyance

• Influence of manholes

Brandhall Brook – Upstream

• Floodplain rearranged on

golf course

• schematisation and stability

corrections

Impact of re-built model

Brandhall Brook – Midstream

• Floodplain extents generally

increased

• Reduced within the site

• Study site outside of Flood Zone

3b

• Flood hazard at access re-

defined as ‘Low’

Impact of re-built model

Brandhall Brook – Downstream

• No significant change

• In-channel and floodplain flows

recombined downstream of

embankments

• No manholes

Impact of re-built model

Phase 1 – temporary solution

• Model suitable for detailed

assessment

• Used to design formal flow

route

• Allowed initial phase to be

constructed

• EA FZ updated giving buyers

confidence

• Tested in April/May 2012

Phase 1 – temporary solution

Phase 2 – Future Flood Alleviation

• ESTRY offers a stable environment to model long culverted

reaches and manholes – no work around required

• ESTRY potentially offer a more accurate representation

• ESTRY-ISIS link simple to setup

• Removing culverts allowed ISIS open reaches to be stabilised

• Consideration was needed over initial conditions and isolated

ISIS reaches

• ISIS-ESTRY-TUFLOW offers a good modelling approach for UK

urban watercourses

Conclusions

Thank you

Conclusions