Arun and Western Streams catchment
• Princes Marsh • Hampshire • ID: E10368 • Level
(23m ago) • 4 readings/hr • 183 views
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⤴Unusual rise — FloodRadar+Top 1% rise rate for this gauge.
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You'll be notified when this gauge is rising more than 0.10 m/hr — a sign of rapidly increasing water levels.
You'll be notified when a new storm-overflow (sewage) discharge starts within ~3 km of this gauge, based on the water companies' near-real-time feeds.
Get notified when recent rainfall near this gauge crosses its learnt rise trigger — an early "watch"
signal, typically hours before a rise. Experimental; not an official flood warning.
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Not an emergency service — if in danger call 999. Alerts rely on
EA/SEPA/NRW data and are best-efforts. Terms
Experimental model fusing soil moisture, river flow, groundwater and catchment
character. The shaded band is its 10–90% range, widened so that about 80% of recent outcomes fall inside it.
Under evaluation — not yet promoted, so treat as a second opinion.
River Flow
90 days
Daily mean discharge (m³/s) with the daily min–max band, from the EA Hydrology API. Flow is the volume of water passing the gauge — often a more direct flood signal than level.
Flow Data: Daily mean flow (m³/s) to 23 Oct (2 days behind — the EA publishes each day's mean a day or two after it ends; unchecked, provisional)via EA Hydrology
Storm overflows whose water reaches this gauge on the mapped river network, nearest first by distance along the river. The status is each water company's monitor: it says whether an overflow is discharging, not how much or what it contains.
1 storm overflow is traced upstream of this gauge, the nearest 1.1 km away along the river. 0 report discharging now, 1 reports not discharging.
Southern Water · into Unnamed Strm To Tilmore Brook · 4.5 km away in a straight line · its recorded watercourse is not the one mapped beside it
5 spills · 11 hours in 2025
Not discharging now · last
2 other overflows within 6 km are downstream of this gauge or on another branch of the river network, so they are not listed.
These are the water companies' monitor statuses; a spill does not by itself explain a change in the gauge level. River connections and distances are traced on OS Open Rivers (edition 2026-04), which leaves out many small channels. Sewage & storm overflows →
In a typical year this gauge reaches its typical high of 0.90 m
on about 6 days.
This year so far: 4 days.
20264 days, 4 of them high · 4 highso far
20256 days, 6 of them high · 6 high
20248 days, 7 of them high · 7 high
20238 days, 6 of them high · 6 high
20225 days, 4 of them high · 4 high
202111 days, 11 of them high · 11 high
20209 days, 6 of them high · 6 high
20194 days, 4 of them high · 4 high
20182 days, 1 of them high · 1 high
20170 days
Counted from each day's highest reading. Days with missing or implausible readings are left out.
The darker part is days above 0.97 m, the level this gauge tops only a few days a year.
Flood history near this gauge
Official Environment Agency warnings issued since 2013 for the 6 flood
areas linked to this gauge (nearest 1.2 km away).
Warnings apply to a whole flood area, not necessarily this exact spot. Years before 2006 aren't covered by the EA's historic record.
See also the Princes Marsh flood history.
Flood areas linked to this gauge
Flood warnings and alerts are issued for whole areas. These are the 6 areas linked to this gauge, nearest first.
🌊 Groundwater-fedSlow and steady — fed largely by groundwater, so levels change gradually, not in sudden spikes.
Your catchment is all the land that drains rainfall into the river above this gauge. Its character — how
steep, wet, wooded, urban or chalky that land is — decides how fast rain here turns into a rising river. A steep, bare or clay
catchment is “flashy” (rises and falls quickly, floods easily); a flat, chalk or well-wooded one is
slow and steady. The tiles below put numbers to that; the flow-duration curve reads left-to-right
from the river’s typical high flows (Q5) down to its low flows (Q95) — a steep curve means a flashy river.
The physical character of the land that drains to this gauge, and how it shapes its flood response — from the National River Flow Archive (UKCEH).
Baseflow Index
0.66
groundwater-fed — slow & steady
Avg Annual Rainfall
1,003 mm/yr
1991–2020 · +8% since 1941–70
Urban Extent
3.1%
partly urbanised
Highest Daily Mean Flow
21.00 m³/s
23 Dec 2013 · daily mean, not the instantaneous peak
Flow-Duration Curve
Daily flow (m³/s) exceeded each % of the time — a steep curve is flashy, a flat one is steady. Q5 high · Q50 median · Q95 low.
Crump profile weir draining a predominantly Chalk catchment in the headwaters. Regime is responsive but dominated by baseflow.
More detail
The catchment
Geology is mixed, Chalk predominates in the headwaters. Upper Greensand, Gault Clay, Folkestone Beds, Sandgate Beds & Hythe Beds also present. Half of the catchment naturally impervious, half pervious. Land use predominantly rural with large woodland tracts and significant urban development in the lower catchment.
The station
Crump profile weir, crest 5m broad. Removed from peak flows dataset in September 2019 (WINFAP Files v8).
How it measures flow
Large capacity structure, but modular limit is ~0.7m. Problem of drowning illustrated by spot flow data, 2003 rating review suggests due to road bridge 0.27 km downstream. This is thought to act as the hydraulic control at high flows. Downstream silt deposition during floods can occasionally cause temporary drowning also, however is soon removed by re-suspension under normal flows. Crest tapping present but not currently used. Bridge across centre of weir, not good for gaugings but good for maintenance. Hysteresis problems experienced at the site. Downstream head recorder installed, used to correct data for backwater effects. One peak flow rating applied across period of record. Rating derived from hydraulic modelling, mid-range gaugings suggest that the rating is seriously overestimating flows, but also some gaugings underestimate flows.
Flow regime
Significant baseflow but responsive regime. Abstractions and discharges have a minor impact on flows - small net loss. Runoff is increased by effluent returns; station is adjacent to sewage works at Petersfield UDC.
Timing, not cause. Gauges can move together simply because the same rain fell on both.
Frequently asked questions
Is the River Rother at Princes Marsh flooding today?
The current level is 0.13m, which is within the typical range of 0.08 to 0.90m. Flooding is unlikely at this level.
Is the river level rising or falling at Princes Marsh?
Based on the most recent readings, the level is currently falling slightly. The chart above shows the last 12 hours of measurements by default (up to 7 days), updated roughly every 15 minutes.
What is a normal level for the River Rother at Princes Marsh?
The typical range at this station is 0.08m to 0.90m, based on Environment Agency historical data. Levels above 0.90m are higher than usually seen and may indicate a flood risk.
How often is this river level data updated?
Readings are supplied by the Environment Agency gauge. FloodRadar checks for updates roughly every 15 minutes; the timestamp above shows how recent the latest available reading is.
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📮 Flood risk by postcode near this gauge
Postcodes within 5 km with properties in the Environment Agency’s rivers-and-sea flood-risk bands:
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