26th July 2018

Tarring High Street – Flood mitigation with SuDS Tarring Flood Action Group

Overview of the problem

Overview of the problem

Economic impacts of flooding in the UK

• Association of British Insurers (ABI) estimated £1.3 billion cost for 2016• Summer 2007 flooding cost UK insurers £3.2 billion•DEFRA’s 2012 UK Climate Change Risk Assessment estimates average annual cost between £1.6 and £6.8 billion by 2050.

Source: LSE

Tarring site

Study area

• 1 - Rectory Road near Fairoak Triangle• 2 - High Street, including Vine PH Car Park• 3 - Glebe Road• 4 - South Street to St Lawrence Avenue• 5 – Church Road outside St Andrew’s

© Google Maps

Site levels

© OS and EA

Site risk• Environment Agency mapping shows several areas at HIGH RISK

• Entire study area at risk of flooding to some degree

© OS and EA

Site risk1 - Rectory Road

© OS and EA

Flooding in Rectory Road carriageway only. Properties not seemingly at risk.

Risk to High Street when water volumes on Rectory Road overspill

East side of High Street is lower, so water will flow there

Site risk2/3 – High St/ Glebe Rd

© OS and EA

Water flows down High St.Junction levels act as a dam to hold back water.

Gulleys become overburdened. Water builds up and junction floods.

Wash from cars floods properties, especially eastern side.

Site risk4 – South St

© OS and EA

Slight slope southwards means properties close to Tarring Park are more at risk.

Slight fall to western side.

Low kerbs allow water to overflow onto footway easily

Site risk5 – Church Rd

© OS and EA

Ponding occurs at entrances to lychgate side road, particularly around eastern arm

SuDs measures

There are many SUDS options available across the spectrum, but only appropriate ones have been considered, as follows:

•Downpipe disconnection and control at source

•Rain gardens, both in private gardens and in the Public Highway on verges and in the carriageway

•Tree pits with retention volume

•Permeable paving, with suitable visual quality for use in Conservation Area

Cost, efficacy at retaining water volumes and complexity to build are all rated out of 5

Disconnect downpipes

To planter

Cost level: 1/5Volume retained: 1/5Complexity: 1/5

Disconnect downpipes

Rain gardens

Cost level: 2.5/5Volume retained: 3/5Complexity: 3/5

Retention basins

Cost level: 2/5Volume retained: 5/5Complexity: 3/5

SuDS tree pits

Cost level: 3/5Volume retained: 2/5Complexity: 3/5

Permeable paving

© Paving Expert

Cost level: 5/5Volume retained: 4/5Complexity: 5/5

Outline proposals

•These are outline proposals for discussion

•We have been through a process of elimination already and discounted several ideas

•As yet, proposals are not costed

•Works to public and private land entirely at the discretion of the land owner

Proposals1 - Rectory Road

Network of rain gardens / tree pits; up to 5-6 components, including a narrowing of the carriageway

Resurfacing/ installing new gulley at low point

Permeable paving (and potential kerbside rain gardens) to eastern side of High St

Generally: divert downpipes into retention planters, water butts or private rain gardens.

Proposals 2 – Top of High St

Rain gardens and permeable paving to east side.

Gateway rain garden feature at One Way sign.

Generally: divert downpipes into retention planters, water butts or private rain gardens.

NB The Vine PH car park is not viable for retention because it is higher than the street level and we cannot get water to flow into it

Proposals 3 – High St/ Glebe Rd junction

Remodel junction to allow for rain garden permeable paving built into carriageway.

Demolish wall and build ground level rain gardens at existing raised planter outside pub

Permeable paving and geocellular storage / gravel Rain garden with tree pit on southern side by Dukes Coffee Shop

Permeable paving in parking bay outside Tarring Village Store

Generally: divert downpipes into retention planters, water butts or private rain gardens.

Property-level flood protection

Proposals 4 –Glebe Rd

Remodel carriageway channels so that water can reach gullies at low points. NB, Southern side works are all subject to proposals for new footway.

Permeable paving at low point in Parish Hall car park

Generally: divert downpipes into retention planters, water butts or private rain gardens.

Proposals 5 – South Street

Permeable paving and potential footway widening along entire western side, and parking area to east before roundabout

Rain gardens at buildouts at roundabout

Swale and shallow retention basin in Tarring Park

Generally: divert downpipes into retention planters, water butts or private rain gardens.

Property-level flood protection

Proposals 6 – Church Rd

Resurfacing/ installing new gullies or inlet at low points

Rain garden/ detention basin in green area

Dropping kerbs on island at slip road to let water on to grass

Permeable paving to entry points

Next steps

• Feedback from TFAG, WSCC and WBC needed to guide design

• Technical assessment of hydraulic performance of network and SuDS measures

• Check proposed locations against underground utilities, both on paper and by digging trial holes

• Draw up designs and provide cost estimation

• Final report issued late August

• Summary presentation to TFAG 11th September

Thank you!

Q & A session