an introduction to bwb land
TRANSCRIPT
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
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)
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
• 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