Integration of river, surface and sewer flow models

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Wallingford Software Limited

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““Integration of river, surface and Integration of river, surface and sewer flow models: a novel sewer flow models: a novel

approach to flood risk modelling, approach to flood risk modelling, designed to meet the specific designed to meet the specific

needs of theneeds of the Floods and Water Floods and Water BillBill””

Claire UnderhillClaire Underhill

Legislation

Flooding in 2007Pitt Report 2008 Recommendation 18“Local Surface Water Management Plans, as set out under PPS25 andcoordinated by local authorities, should provide the basis for managingall local flood risk.”

Flood and Water Bill (April 2010)

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SWMPProblems of the future

New DevelopmentsUp to 3 million new homes will be built in England by 2016

Climate ChangeIncrease winter rainfall by 10 – 30% by the 2080s and rainfall intensity could increase by up to 20%.Urban CreepIn London alone, around two thirds of front gardens (equivalent to 22 times the size of Hyde Park) are already partially paved over to provide off-street parking.

(Making Space for WaterUrban flood risk & integrated drainage(HA2)

Types of FloodingSurface Water Runoff (pluvial):Runoff from high intensity rainfall – before reaches underground drainage system or watercourse

Groundwater Flooding;All water below ground surface and in direct contact with ground or subsoil

Sewer Flooding;Capacity is exceeded due to heavy rainfall.Flooding inside and outside buildings

Open Channel and Culverts;Receive most flow from inside urban area also interaction with larger watercourses

Overland Flows entering built up areas from fringe, also from groundwater sources

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Software PackagesTraditionally:

Collection Systems (InfoWorks CS)

River Systems (InfoWorks RS)

•Two separate packages!•Exchange of results through Open MI

Software Packages

InfoWorks CS (Collection Systems)Great for modelling closed pipe systems

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InfoWorks CS

How are river sections modelled?

Prismatic – No change in X sectionBetween upstream and downstream.

InfoWorks RS

InfoWorks RS (River Systems)Good for modelling open watercourses

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InfoWorks RS

How are closed pipes modelled?Manholes are not directly modelled

Not so convenient for pipe shape changes

Modelling 2D Flow Routing

The MeshIn InfoWorks CSIn InfoWorks RS

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The Mesh

IWRSIWCS

Triangles are a horizontal plane with the elevation of the plane derived by averaging the level at each vertex

DTM

1D – 2D connection for IWCS

InfoWorks Collection SystemsMesh

The length of the weir is the circumference of the shaft.

1D / 2D is by a weir or h/q relationship.

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2D Flooding in CS

1D - 2D connection in RS

Bank levels dictate flow to 2D meshElement levels adjusted where > 1D

Z2D

Z1DZsp

2D zone1D Bank Levels

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2D flooding in RS

Integrated modelling

Pitt review

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Models in ICMIncorporates

• River Sections (non-prismatic)

• Underground Pipes

• Culverts

• Bridges

• Controls (orifices,flap valves etc)

•SuDS features

2D Modelling in ICM

2D flooding occurs at nodes

and banks

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ICM

Sewer Flooding;Capacity is exceeded due to heavy rainfall.Flooding inside and outside buildings

Open Channel and Culverts;Receive most flow from inside urban area also interaction with larger watercourses

Direct RainfallSurface Water Runoff (pluvial):Runoff from high intensity rainfall – before reaches underground drainage system or watercourseOverland Flows entering built up areas from fringe, also from groundwater sources

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Other 2D features

Dam Breach

Other 2D Features

Porous BuildingsWalls

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Summary

2007 floods provided a catalyst for Integrated Urban ModellingProvides a more holistic approach suitable for Surface Water Management Plans2D flood routing includes movement between 1D and 2D

Integration of river, surface and sewer flow models

Documents

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