River Lox Flooding & Flood Risk

The River Lox is a small clay-country stream on the Surrey–West Sussex border, but it floods often enough that the Environment Agency runs a dedicated warning service for the homes along it. It rises in the wooded country around Chiddingfold and Dunsfold, drains a catchment of heavy Weald clay that sheds rain almost as fast as it falls, and runs south through Ifold and Loxwood to join the River Arun at Drungewick. When a wet spell sets in, it rises quickly and spills onto the low ground at Loxwood, Brewhurst and Drungewick. Unda prepares flood risk assessments, drainage strategies and related reports for sites across the River Lox floodplain — call 01293 214444 or email enquiries@unda.co.uk.

On Christmas Eve 2013 the River Lox rose to its highest level on record at Drungewick — 3.45 metres, against a typical winter peak of about 2.25 metres — and flooded homes and roads through Loxwood, Brewhurst and Ifold.

• A flashy clay-catchment stream. The River Lox drains impermeable Low Weald clay, so runoff reaches the channel fast and levels peak sharply within hours of heavy rain.
• An ordinary watercourse — but a warned one. The River Lox is not a designated Main River, yet the Environment Agency still operates a flood alert and a property-level flood warning along it, a measure of how regularly it floods.
• A live Environment Agency gauge at Drungewick. The gauge near the River Arun confluence updates in real time and appears on the map below, alongside the (currently suspended) Brewhurst Mill gauge at Loxwood.
• Two counties, two flood authorities. The river crosses from Surrey into West Sussex, so responsibility for it is split between Surrey County Council and West Sussex County Council as Lead Local Flood Authorities.

Check flood risk along the River Lox

The map below draws the River Lox in coral, with the Environment Agency’s live river gauge shown along it — click the pin to see its latest level, its typical range and its record peak. Enter a postcode near the river to zoom in and screen that location against the Environment Agency’s flood data for rivers and sea, surface water, reservoirs and the flood zones used for planning. It is an indicative screening tool, not a flood risk assessment.

Why does the River Lox flood?

The River Lox floods because of the ground it drains. Its catchment sits almost entirely on Weald clay — the heavy, impermeable mudstone that underlies this stretch of the Low Weald — and clay does not absorb rain, it sheds it. Water runs off the fields, woods and lanes into the channel far quicker than it would over chalk or sand, so the river fills rapidly, peaks sharply and then falls away again once the rain stops. Hydrologists call a river that behaves this way “flashy”, and the Lox is a clear example: it can go from placid to out-of-bank in a matter of hours.

The river gathers in the country around Chiddingfold and Dunsfold in Surrey, where its upper reaches are also known as the Loxwood Stream, then flows broadly south through Ifold and Loxwood before meeting the River Arun at Drungewick, just south of Cranleigh and a little upstream of where the partly restored Wey and Arun Canal rejoins the Arun. For much of its lower course the canal runs close alongside the river, and where the canal is embanked above the surrounding fields it adds its own dimension to local flood risk. The Environment Agency records the river’s named reach as running roughly 14 kilometres from the Surrey hills to the Arun.

• An impermeable catchment. Weald clay across the catchment produces rapid surface runoff and a fast-rising river after prolonged or intense rainfall.
• A network of feeder ditches. The Loxwood Stream and a web of field ditches and minor watercourses concentrate runoff into the main channel, sharpening the peak.
• The Wey and Arun Canal alongside. The canal shadows the lower valley and joins the Arun near Drungewick; embanked lengths sit above the floodplain and interact with how water drains off it.
• A gauged lower reach. The Environment Agency’s Drungewick gauge, open since 1981, records levels close to the Arun confluence — the reach where flooding bites hardest.

Which areas does the River Lox put at risk?

Flooding from the River Lox is concentrated on the low ground of the valley floor, and the Environment Agency runs a formal warning service for the communities most exposed. A flood alert area — “River Lox in West Sussex from Chiddingfold to Drungewick, including the Loxwood Stream” — covers the whole river, and within it a more precise flood warning area can warn individual properties at Dunsfold, Upper Ifold, Ifold, Loxwood, Brewhurst and Drungewick. The table below summarises the main settlements at risk from source to mouth.

If your site sits within one of these areas, the Environment Agency’s flood map for planning is likely to place it in Flood Zone 2 or 3, which triggers the need for a site-specific flood risk assessment. You can screen any address against the live Environment Agency data using the map above, and the towns and districts around the river are covered in more depth on our local pages for Cranleigh, Horsham, Guildford and Godalming.

A history of flooding on the River Lox

The Lox has a long local record of flooding, bound up with the wider history of the Arun and Wey catchments that meet nearby. Catchment-wide flooding is documented in the storms of 1968 and 1990, and again through the exceptionally wet winter of 2013–2014, when watercourses across this corner of the Weald burst their banks repeatedly.

The benchmark modern event on the Lox came on Christmas Eve 2013. The Drungewick gauge reached 3.45 metres at 6:30am on 24 December 2013 — still its highest level on record, and well above the roughly 2.25 metres it reaches in a typical wet winter. Homes, gardens and roads flooded through Loxwood, Brewhurst and Ifold, and private water-control structures at Brewhurst were operated to hold back what they could. The river has been in flood alert or warning many times since, and every recent wet winter has brought minor flooding of fields, rural roads and low-lying gardens along its length. These are the events an assessment for a nearby site has to reckon with.

Is the River Lox a Main River or an ordinary watercourse — and what that means for your site

The River Lox is an ordinary watercourse, not a designated Main River. That distinction matters if you are developing near it. On an ordinary watercourse the regulator is not the Environment Agency but the Lead Local Flood Authority — here Surrey County Council in the upper catchment and West Sussex County Council lower down — together with the riparian owners whose land the channel crosses. Work that would obstruct or alter the flow, such as a culvert, headwall or bridge, needs Ordinary Watercourse Consent from the LLFA under the Land Drainage Act 1991, rather than a Flood Risk Activity Permit from the Environment Agency. The difference between the two regimes is set out in our guide to Main Rivers and ordinary watercourses.

Being an ordinary watercourse does not make the Lox any less of a flood risk — the Environment Agency’s decision to run a flood warning service here shows that plainly. A site in the river’s floodplain will still, in almost all cases, need a site-specific flood risk assessment to support a planning application, and the responsibilities that come with riparian ownership of a bank or ditch are a live issue for many sites along the valley.

• Consent from the council, not the Environment Agency. Works affecting flow in the River Lox generally need Ordinary Watercourse Consent from the Lead Local Flood Authority, sought alongside — not instead of — planning permission.
• Flood zones drive the assessment. A site in Flood Zone 2 or 3, or a larger site in Flood Zone 1, needs a flood risk assessment for planning.
• Know which watercourse you are on. The Lox is an ordinary watercourse under the county councils; a site may also adjoin ditches with their own riparian responsibilities. We confirm the classification for every site.

Managing flood risk on the River Lox: policy and authorities

Several bodies share responsibility for flood risk on the River Lox, and it is worth knowing who does what. The river sits within the Arun and Western Streams catchment, and because it straddles the county boundary it falls to two Lead Local Flood Authorities: Surrey County Council around Chiddingfold and Dunsfold, and West Sussex County Council through Loxwood and Drungewick. Planning applications along the river are decided by Waverley Borough Council in Surrey and Chichester District Council in West Sussex, each with its own strategic flood risk assessment. The Environment Agency publishes the flood map for planning, runs the gauges and issues the flood warnings, even though the Lox is not a Main River.

One further constraint shapes almost every scheme in this area. Loxwood and the surrounding catchment lie within the Sussex North Water Supply Zone, where development has had to demonstrate water neutrality to protect the internationally important Arun Valley wetlands — a requirement that stalled thousands of homes before its late-2025 withdrawal. Drainage design in the district has tightened too, with Arun and neighbouring authorities raising the bar on the infiltration evidence and SuDS detail expected from the outset.

Flood risk and drainage services for sites near the River Lox

A development near the River Lox can call for several different reports, and it helps to be clear that they answer different questions. A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a planning submission, but they address separate things: whether the site is safe from flooding, whether the development should be located here, and where the surface water goes. Unda prepares each of them for sites across the River Lox catchment.

• Flood risk assessments for planning. Site-specific assessments dealing directly with the Environment Agency’s and the council’s requirements for development in the river’s flood zones — see our flood risk assessment for planning service.
• Assessments for property purchase and insurance. Independent reports for buyers, owners and lenders through our flood risk survey for property purchase and flood risk assessment for insurance.
• Drainage strategies and SuDS. Surface-water designs that manage runoff on heavy clay and meet the discharge limits set by the Lead Local Flood Authority — see our sustainable drainage strategy service, with detail followed through to discharge of drainage conditions.
• Sequential and exception tests. Locational justification where policy requires it, through our sequential and exception test reports.
• BREEAM and groundwater. A BREEAM flood risk assessment for the Pol 03 credit, and a groundwater flood risk assessment where a high winter water table on the clay is in play.

Where national mapping is not enough — a common situation for a site right beside the river — we can bring in hydraulic flood modelling to derive accurate flood levels and extents, and prepare preliminary drainage design so infiltration and runoff are settled before they affect the site layout. Everything we do is framed by the NPPF and its planning practice guidance, and you can read how a flood risk assessment is put together and what a flood risk assessment costs in our guides.

How Unda helps with flood risk on the River Lox

Unda understand how a clay-catchment stream like the River Lox behaves in flood, and what the planning system, the council and the Environment Agency expect from the reports that follow. We know how quickly this river responds to rain, where its floodplain bites hardest through Loxwood, Brewhurst and Drungewick, and what a robust, compliance-led flood risk assessment has to demonstrate to carry a development through planning. We prepare assessments and drainage strategies for developers, planning consultants, architects, agents and homeowners with sites the length of the valley.

Every assessment rests on the same evidence the regulators use: the Environment Agency’s flood mapping, the river’s gauged levels, the local strategic flood risk assessments and the planning policy that applies to the site. If you are working on a site near the River Lox, talk to one of our experienced flood risk consultants about what your application will need, or read more about our flood risk assessment service.

Live levels and emergency contacts for the River Lox

The River Lox rises and falls quickly, so its live gauge is worth watching in a wet spell. The links below cover the live level, the Environment Agency’s warning service and who to contact in a flood.

• Live river level. Check the River Lox at Drungewick gauge on the Environment Agency service, or use our own live river levels map.
• Flood warnings. See the current status of the River Lox flood alert area and the Loxwood, Brewhurst and Drungewick flood warning area, and sign up for Environment Agency flood warnings.
• Screen a location. Try our free flood risk map and, for drainage on clay, the drainage calculators, the BRE 365 infiltration calculator and the ground conditions and soakaway map.
• Floodline. Call the Environment Agency’s Floodline on 0345 988 1188, open 24 hours a day.
• In a flood emergency. Call 999 if life is in danger, and 105 for power cuts.

River Lox flood risk: your questions answered