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⤴Unusual rise — FloodRadar+Top 1% rise rate for this gauge.
Height for "Above a height"
Drag the line on the chart, or type a value:mASD
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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.
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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
Current Level
0.123 mASD
▬ Steady
24h Max
0.133 mASD
24h Min
0.099 mASD
Typical Range
0.11 - 0.56
mASD
Highest Recorded
0.61 mASD
EA official record
0.61 in our data (since Oct 1986)
Current level is 20% of this
🚽Sewage overflows nearby
Recent Water Levels
🌍 floodradar.co.uk
1 day
EA forecast (official)
Prediction V2
Prediction Eris
Nimbus beta
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. The nearest rain gauge has sent no readings in the last day, so Nimbus has no recent measured rain to work from here.
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 8 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.
3 storm overflows are traced upstream of this gauge, the nearest 7.3 km away along the river. 0 report discharging now, 3 report not discharging.
Thames Water · into Alderbourne · 5.0 km away in a straight line · its watercourse is not on the river map
5 spills · 8 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. Explore the sewage map →
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 Denham 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.
🌊 Mixed responseA balance of quick runoff and slower groundwater baseflow.
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
0.63
mixed response
Avg Annual Rainfall
730 mm/yr
1991–2020 · +3% since 1941–70
Urban Extent
12%
partly urbanised
Median Annual Flood
10.35 m³/s
QMED — typical yearly peak flow
Highest Daily Mean Flow
21.70 m³/s
3 Jan 2003 · 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.
One of the major gauging stations on the middle section of the River Colne.
More detail
The catchment
A largely Chalk catchment with Drift cover. Clays in the valleys supplemented by extensive gravel tracts. The Chilterns scarp is largely rural in the headwaters but considerable suburban development characterises the middle and lower reaches. Hydrological and topographical divides do not coincide.
The station
Twin semi-circular broad-crested weirs (one section feeds the Frays River). Overall crest length 30m. Used for both water resource and flood warning/forecasting purposes.
How it measures flow
Power law rating derived using a simplified broad crested weir formula with a discharge coefficient that remains constant with stage. No corrections made for non-modular or drowned flow. Maintenance of weir no longer carried out due to Health and Safety concerns, in channel vegetation can become widespread in growing season. Insensitive to low flows. Some by-passing can occur at extreme stages. Single rating used throughout record. Prior to 2016, gaugings generally within +/- 10% of the rated flow. Between the rebuild in 2016 and installation of the fish pass in 2022, gaugings indicate the rating was overestimating flow by up to 25%. Since installation of the fish pass, gaugings indicate a smaller reverse bias towards underestimation of flows by the rating. However, two gaugings since the installation of the fish pass are close to QMED and fit closely to the rating.
Flow regime
Complex water utilisation within the catchment. Baseflow from the Chalk remains important but considerable groundwater abstraction leads to net reductions in flows. However, increasing effluent contribution (including Maple Lodge STW) makes up a large proportion of low and medium flows. Abstraction is mainly for industry/agriculture.
The flow record
Frays River part of weir sandbagged for downstream channel works between Jan 2008 and 21st April 2008. Levels artificially high. Bypassing of weir observed in winter floods of 2002/03. In mid-2016 the large bridge upstream of the weir collapsed in the channel and it was rebuilt in November 2016. Fish pass installed in September 2022, not accounted for in the rating. No data are rejected as biases in flow arising from rebuild and fish pass are within acceptable limits (see Station Hydrometry). Full period of record peak flow data reviewed and released in August 2021 (WINFAP Files v10).
Timing, not cause. Gauges can move together simply because the same rain fell on both.
Frequently asked questions
Is the River Colne at Denham Colne flooding today?
The current level is 0.12m, which is within the typical range of 0.11 to 0.56m. Flooding is unlikely at this level.
Is the river level rising or falling at Denham Colne?
Based on the most recent readings, the level is currently steady. 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 Colne at Denham Colne?
The typical range at this station is 0.11m to 0.56m, based on Environment Agency historical data. Levels above 0.56m 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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