Flood Risk Assessment in Chichester

A flood risk assessment in Chichester usually comes back to the River Lavant. The chalk stream from the South Downs runs only when winter groundwater is high, and under the city centre it is carried in two long culverts; when they cannot take the flow, the river floods the streets, as it did in January 1994, when the water reached The Hornet and New Park Road. Our consultants prepare flood risk assessments in Chichester for planning, purchase, mortgage and insurance work on sites from Summersdale to the Southern Gateway, along with sequential and exception tests and surface water drainage strategies.

On this page Chichester means the city's built-up area as the Office for National Statistics draws it, all within the PO19 postcode district: the walled centre around the cathedral, Westgate, Parklands and East Broyle to the west, Summersdale, Somerstown and Graylingwell to the north, Portfield to the east, and Whyke, Kingsham and Stockbridge to the south. Fishbourne, Lavant, Westhampnett and Donnington lie just outside the outline, and Bosham further west on the harbour. The same council and much of the same evidence cover them.

Chichester's Flood Zone 3 runs through streets with no river in sight, among them New Park Road, Eastgate Square, The Hornet and Kingsham Road, close to where the Lavant disappears into its culverts.

To talk through a Chichester site, ring our flood risk consultants on 01293 214444 or email enquiries@unda.co.uk.

Where the Lavant goes under Chichester, and what that means for a site

The Lavant rises on the chalk of the South Downs and reaches the city from the north-east, past Westhampnett Mill. It is a winterbourne, dry in most summers and flowing once rain has refilled the chalk. Close to Eastgate it enters a long culvert that follows Market Road and passes under Southgate, and below the city it runs out to Chichester Harbour between Fishbourne and Apuldram.

• The culverts set the limit. In its description of the River Lavant flood alleviation scheme, the Environment Agency says the river is contained in two long culverts beneath the city and that serious flooding can occur when their capacity is exceeded.
• The scheme sends the surplus east. In a flood the Agency first lowers Church Farm Pit and East Pit, east of the city, with sluice gates, then diverts Lavant water into them; once they are full it runs on to outfalls at Pagham Harbour.
• A tenth of the city in Flood Zone 2 or 3. Measured against the outline on this page, the Flood Map for Planning puts about 1 km², roughly a tenth of the built-up area, in Flood Zone 2 or 3. Every part of it is river flood zone; none inside the city comes from the sea.
• Eight metres, piped or open. Policy NE16 keeps new buildings at least 8 m back from a river, including one running in a culvert, so the channel can be reached for repair. Our explainer on what a culvert is covers ownership and consent.

The flood zones are drawn as if the Lavant scheme did not exist, so a site it protects can still sit in Flood Zone 3. An assessment there has to show what happens when the pits are full or a culvert blocks, which is the residual flood risk question.

Check a PO19 postcode against the Lavant flood zones

Type a postcode into this Chichester flood risk map to screen it against Environment Agency data for rivers and the sea, surface water and reservoirs, or use our full flood risk map for anywhere in England. The coral line is the city's built-up area, with Fishbourne, Lavant and Westhampnett just beyond it. In the centre the river flood zones matter most; in Parklands and East Broyle, check the surface water layer as well.

Chichester floods, from the 1994 Lavant flood to the Parklands storm

The district's 2023 flood study names 1974, 1993/94, 2000, 2012 and winter 2013/14 as its notable events, and records of the Lavant flooding Chichester go back to 1713. The dates below run from the 1994 flood to the scheme the county is now preparing for Parklands.

1. Early January 1994. After Sussex's wettest December since 1934, the Lavant burst its banks in the city for the first time in half a century, in what was later called Chichester's worst flood in 130 years. Fire crews across West Sussex took about 500 calls in a few hours and the army handed out 50,000 sandbags, according to a 2019 local press retrospective. The Graylingwell gauge reached 0.92 m on 12 January 1994, still its highest reading.
2. Autumn 2000. With the river rising again, work began on 4 December 2000 on three packages costing £1.3 million, and about 50 pump sets moved Lavant water away towards the sea. The works were carrying floodwater within a fortnight, and the pumping lasted five months.
3. 2003. The district's flood study dates the permanent Lavant alleviation scheme, which diverts excess flow into the Pagham Rife, to 2003.
4. June 2012. On Parklands, 110 mm of rain fell in 28 hours, a fall West Sussex County Council puts at about once in 200 years. The county's report on the storm counted 28 properties affected across west Chichester and Fishbourne.
5. Winter 2013/14. Groundwater flooded the Lavant valley north of the city. The county's Upper Lavant study found sewers inundated across the valley, with tankering or over-pumping needed at eight locations.
6. January 2015 and January 2016. The West Street gauge reached its highest recorded level, 7.66 m, on 8 January 2015, and the Tozer Way gauge its highest, 14.07 m, on 10 January 2016.
7. 2025 to 2026. The county consulted on a West of Chichester flood alleviation scheme for the lower Parklands Estate, with three shortlisted options built around SuDS on green space, rural source control and repairs to the drains.

The Environment Agency's warning area for the city, Chichester on the River Lavant, covers the river through the centre, Whyke, the A285 and A286 and Chichester College. At Tozer Way, property flooding is possible above 14.60 m; at West Street, above 8.00 m. Both gauges, with Graylingwell upstream, appear on our live river levels map.

Gravel over clay: groundwater, rain and sewers in the city

Most of central Chichester stands on gravel, sand and silt spread by the Lavant, laid over London Clay, according to the British Geological Survey's 1:50,000 mapping. Head deposits cover the clay at Parklands and the Lambeth Group around Graylingwell, while the chalk that feeds the river lies north of the city under the Downs. So a soakaway that drains well in the gravel near the centre may fail on the clay-rich ground at Parklands, while a basement in the centre has to allow for a water table that rises through the gravel every wet winter.

The Flood Map for Planning has no layer for groundwater at all, so a city assessment has to go looking for it. For schemes that rely on soakaways, West Sussex County Council asks for groundwater monitoring to find the highest level, ideally through the winter, and a metre of clearance below the base of any infiltration feature; our guide to groundwater monitoring for planning explains the timing, and the geology and soakaway map gives a first read of the ground before a trial pit is dug.

Policies NE16 and NE17: what Chichester District Council asks of a city site

Chichester District Council decides applications in the city under the Chichester Local Plan 2021-2039, adopted on 19 August 2025. Land inside the South Downs National Park, which begins north of the city, is planned by the National Park Authority instead. West Sussex County Council, the Lead Local Flood Authority, comments on surface water for major schemes, and the Environment Agency advises on the Lavant. Policy NE16, Flood Risk and Water Management, sets the local tests.

• The sequential test starts from the SFRA. The council's latest flood study, with its own sequential test method, is the starting point; the exception test follows where national policy calls for it.
• Floors 300 mm above the highest datum. For vulnerable development, finished floors sit at least 300 mm above whichever is highest: the average ground level of the site, the road beside the building, or the 1 in 100 river level with climate change. Materials of low permeability go up to the same height.
• No faster runoff. Surface water may not leave a site faster than it does now, and a brownfield site should come down to greenfield rates wherever possible. SuDS are designed into the landscape of every major scheme and of any scheme that needs a flood risk assessment.
• A plan for what remains. Where residual risk is left, a site-specific flood warning and evacuation plan is required, and floodplain storage lost on a site is replaced level for level, ideally on the site itself.

Policy NE17 adds a rule about the sewers. Apuldram Wastewater Treatment Works serves the city and discharges to the head of Chichester Harbour, and so much groundwater leaks into its network in winter that the storm overflow has run for long periods. Inside the settlement boundaries of Chichester, Fishbourne and Stockbridge, a scheme of ten or more homes must show in a drainage impact assessment that flows to Apuldram will not rise at all; a smaller one should aim for the same; and new development outside those boundaries will not drain to Apuldram. NE17 also keeps new surface water out of public foul and combined sewers.

The joint Apuldram position statement from the Environment Agency and Southern Water lists the usual ways to reach no net increase: taking surface water out of combined sewers, retrofitting water efficiency elsewhere in the catchment, and offsetting existing flows. Our article on sewage capacity and planning explains how treatment capacity has come to decide which schemes get permission.

Behind both policies sits the Level 1 SFRA that JBA Consulting prepared for the council in December 2023, with a Level 2 study of the allocated sites and a sequential test method. Nationally, flood risk sits in chapter 18 of the NPPF: policy F4 sets when an assessment is needed, F5 and F6 the sequential and exception tests, and F8 expects all development to follow the 2025 National Standards for sustainable drainage, which the county applies through its SuDS guidance.

Southern Gateway, West of Chichester and the city's allocated land

The Local Plan allocates the city's growth sites by name, and several come with flood and drainage requirements written in. An application on any of them still needs its own assessment, but each one starts from a published position. West of Chichester and the land to the north-east and east sit on the edge of the built-up outline or just beyond it, and the plan treats them as extensions of the city.

Phase two of the Westhampnett allocation, between Summersdale and the Lavant, already has outline permission for up to 200 homes with reserved matters agreed in 2021. On the western side, the plan asks West of Chichester to attenuate its runoff to reflect greenfield rates, and the county's options for Parklands include source control on the rural land north of the estate. Our note on why LLFAs object to drainage strategies covers what lead local flood authorities look for when they review that kind of requirement.

When a flood risk assessment in Chichester is needed

The Local Plan follows national policy on the triggers: any site in Flood Zone 2 or 3, sites of a hectare or more in Flood Zone 1, land with critical drainage problems or at increased risk in future, and more vulnerable uses on land at risk from other sources. In Chichester the other sources are usually groundwater and surface water, so the table runs through schemes typical of the city.

A householder plot outside every flood zone may need nothing more than drainage details. If you are unsure, send us the address and one of our consultants will say what the council is likely to want; our guide to Flood Zones 1, 2 and 3 explains how the zones are drawn.

Reports our consultants prepare for the culvert streets, the allocations and Parklands

A buyer on Velyn Avenue, the developer of a Southern Gateway site and a café owner on The Hornet each need a different report, and Parklands raises drainage questions that the centre does not. Each Chichester report goes out only after a senior consultant has signed it off; our consultants are chartered, and Unda is a CIWEM Business Partner.

• River, ground and rain together. A flood risk assessment for a city site weighs the culverted Lavant against winter groundwater in the gravels, surface water and the sewers that back up once groundwater gets in.
• Applications inside the outline. Schemes in the Lavant's Flood Zone 2 or 3, sites of a hectare or more and more vulnerable uses on land at risk from other sources need a flood risk assessment for planning that answers policy NE16.
• Before exchange on a city house. Buyers on Flood Zone 3 streets such as New Park Road or Velyn Avenue can commission a flood risk survey for property purchase that looks at the building itself, its floor levels and any cellar, as well as the postcode.
• Homes in the Lavant flood zones. Windfall housing in Flood Zone 2 or 3 starts from the council's sequential test method, and a sequential and exception test report sets out the search area and why each alternative site was ruled out.
• Every major scheme. NE16 asks for SuDS designed into the landscape of every major development, so even a modest Chichester block needs drainage strategy evidence from the start.
• Clay at Parklands, gravel in the centre. A surface water drainage strategy tests whether infiltration will work on the site, holds runoff to the existing rate or lower and, on brownfield land, works towards greenfield rates.
• Conditions after approval. When a Chichester permission arrives with a drainage condition, discharge of drainage conditions supplies the detail and the maintenance arrangements the council and the county ask for.
• No net increase at Apuldram. Ten or more homes inside the settlement boundary need a foul drainage strategy showing how new flows to the Apuldram works are offset, as part 4 of NE17 requires.
• Winter water in the gravels. Where a cellar under the walled city or a soakaway in the Portfield gravels is planned, a groundwater flood risk assessment sets a design water level from winter readings rather than a single summer visit.
• Depths where the culverts surcharge. National mapping cannot say how deep water gets when a culvert is overwhelmed, so a site on the culvert route or at the Police Field may need flood modelling to fix floor levels and floodplain storage.
• Warning and a way out. NE16 requires a site-specific flood warning and evacuation plan wherever residual risk remains, and the city centre already has its own Environment Agency warning area for the Lavant.
• Premiums on streets that flooded in 1994. Owners around The Hornet and New Park Road can use a flood risk assessment for insurance to set out the risk to their own building for a broker or underwriter.
• Shops and pubs over the culvert. Businesses around Eastgate Square and The Hornet, in Flood Zone 3, can plan for closure and recovery with a business continuity flood risk assessment.
• Land the plan has yet to allocate. Promoters testing sites for the 270 homes the plan leaves to a Site Allocation DPD can use a feasibility study to read flood risk and drainage before an option or a bid.

Who to call about a flood in Chichester

If floodwater in Chichester puts anyone in danger, call 999; for a power cut, call 105. Everything else goes to one of the organisations below.

Along the coast, Selsey sits behind the Medmerry realignment and Pagham beside its harbour, while Arundel, on the tidal Arun, and Portsmouth, across the county boundary, have pages of their own. Bosham, the Witterings and the rest of the county are covered on our West Sussex page.

Questions about Chichester flooding, cellars and planning

Unda Consulting Limited prepares flood risk assessments, sequential and exception tests and drainage strategies for sites across Chichester, from cellar conversions inside the city walls to the new neighbourhoods at its edge. To discuss a site in Chichester, Summersdale, Parklands or Whyke, call 01293 214444 or email enquiries@unda.co.uk.