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0.41

Panshanger

Mimram
Mimram catchment • Tewin • Hertfordshire • ID: 4790TH • Level
(21m ago) • 4 readings/hr • 155 views

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Current Level
0.411 mASD
▬ Steady
24h Max
0.415 mASD
24h Min
0.411 mASD
Typical Range
0.31 - 1.07
mASD
Highest Recorded
1.28 mASD
EA official record
1.28 in our data (since Jan 1982)
Current level is 32% of this
🚽 Sewage overflows nearby

Recent Water Levels

🌍 floodradar.co.uk
1 day

Recent Readings

Falling · -0.2 cm over 5h
10 Oct 13:15 ▬ steady 0.411 mASD
10 Oct 13:00 ▬ steady 0.411 mASD
10 Oct 12:45 ▬ steady 0.411 mASD
10 Oct 12:30 ▬ steady 0.411 mASD
10 Oct 12:15 ▬ steady 0.411 mASD
10 Oct 12:00 ▼ -0.1 cm 0.411 mASD
10 Oct 11:45 ▬ steady 0.412 mASD
10 Oct 11:30 ▬ steady 0.412 mASD
10 Oct 11:15 ▬ steady 0.412 mASD
10 Oct 11:00 ▬ steady 0.412 mASD
10 Oct 10:45 ▼ -0.1 cm 0.412 mASD
10 Oct 10:15 ▬ steady 0.413 mASD
10 Oct 10:00 ▬ steady 0.413 mASD
10 Oct 09:45 ▬ steady 0.413 mASD
10 Oct 09:30 ▲ +0.1 cm 0.413 mASD
10 Oct 09:15 ▼ -0.1 cm 0.412 mASD
10 Oct 09:00 ▲ +0.1 cm 0.413 mASD
10 Oct 08:45 ▬ steady 0.412 mASD
10 Oct 08:30 ▼ -0.1 cm 0.412 mASD
10 Oct 08:00 0.413 mASD

Station Details

  • Monitoring Station: Panshanger
  • Watercourse: River Mimram
  • Nearest Town: Tewin
  • County: Hertfordshire
  • Coordinates: 51°48'12"N 0°8'29"W (51.803418, -0.141267)
  • Open in: Google Maps · Apple Maps (opens your maps app)
  • Date Opened: 1 Jan 1981
  • Status: Active
  • Station Type: River level station
Technical details: references, datum, range, flow archive
  • Station Reference: 4790TH
  • RLOI id: 7336 (the EA's check-for-flooding station id)
  • EA Gauge ID: 4790TH-level-stage-i-15_min-mASD
  • Parameter: Level
  • Unit: mASD
  • Typical rise rate: 1 cm/hr (p95 sustained over 90 days)
  • Typical data delay: ~22 min (measured reading→publication lag)
  • Tidal: No
  • Lock / structure: No
  • Catchment Area: Mimram
  • Typical Range: 0.312 – 1.070 mASD
  • Drainage Area: 134 km² upstream of this gauge
  • 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
  • EA Cross-check: 0.41 mASD (EA at 10 Oct 12:45)
  • Flow Archive: National River Flow Archive ↗

Geographic coordinates may reflect the access point for the gauge, and not the precise location in the watercourse that it is taking readings from.

Nearby Stations

Gauges connected to this river, and others nearby. A distance “by river” follows the river on the map; any other is in a straight line.

Connected upstream

Connected downstream

Same river system, separate branch

Distances by river: OS Open Rivers. Contains OS data © Crown copyright and database rights 2026.

💧 Storm overflows upstream of this gauge

None of the storm overflows FloodRadar holds is traced upstream of this gauge on the mapped river network. That is not the same as none: the map leaves out many small streams and culverts, so an overflow it cannot place may still drain here, and not every company publishes every overflow. Those nearby are listed below.

Nearby, connection not known

Within 6 km in a straight line, but the river map cannot say whether their water passes this gauge.

💧
Thames Water · into Wood Hill Brook · 4.9 km away in a straight line · no mapped watercourse close enough to be sure
0 spills · 0 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 →

Contains OS data © Crown copyright and database rights 2026.

Rainfall & Weather

Loading rainfall and weather data...

How often this river runs high

This gauge rarely reaches its typical high of 1.07 m: 0 days since 2017. This year so far: 0 days.

2026 0 days so far
2025 0 days
2024 0 days
2023 0 days
2022 0 days
2021 0 days
2020 0 days
2019 0 days
2018 0 days
2017 0 days

Counted from each day's highest reading. Days with missing or implausible readings are left out.

Flood history near this gauge

Official Environment Agency warnings issued since 2014 for the 9 flood areas linked to this gauge (nearest 0.8 km away).

3flood warnings 3flood alerts

Most recent flood warning: 18 Jun 2021 — Stevenage Brook at Stevenage

Year by year
YearWarningsAlerts
2025 0 1
2024 0 1
2021 1 0
2015 1 0
2014 1 1

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 Tewin flood history.

Flood areas linked to this gauge

Flood warnings and alerts are issued for whole areas. These are the 9 areas linked to this gauge, nearest first.

Show 1 more

Catchment Character

🌊 Groundwater-fed Slow 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
0.72
groundwater-fed — slow & steady
Avg Annual Rainfall
670 mm/yr
1991–2020 · +5% since 1941–70
Urban Extent
6.5%
partly urbanised
Median Annual Flood
2.02 m³/s
QMED — typical yearly peak flow
Highest Daily Mean Flow
2.43 m³/s
13 Oct 1993 · daily mean, not the instantaneous peak
Flow-Duration Curve
mean 0.5310.9910.4890.2185% (high)% of days exceeded95% (low)
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.
Land Cover (2023)
Woodland 9%Grassland 29%Arable 49%Urban 13%
Arable 56% → 49% since 1990

Flow affected by: groundwater abstraction, industrial / agricultural abstraction.

Photos

Gauging-station photographs from the National River Flow Archive (UKCEH).

Photos © NRFA / UKCEH & the measuring authority — shown at web resolution. Full gallery on the NRFA ↗

About this gauge

Station located in the lower catchment of the River Mimram.

More detail

The catchment

A predominantly permeable catchment (Upper Chalk overlain by glacial deposits near headwaters). Mainly rural but substantial urban growth in the lower valley - the Mimram drains Welwyn Garden City.

The station

Critical-depth flume; 5m wide. All flows are contained.

How it measures flow

One rating applied across period of record. Rating is reasonably accurate, though overestimates flow. Theoretical calibration confirmed by gaugings but computed flows may be slightly overestimated by as much as 10%. The gauge was reviewed in 2014.

Flow regime

Appreciable net export of water. Considerable gw abstraction for industry & agriculture occurs in the headwaters. Very high baseflow component but peak flows increasing due to urbanisation. AMAX is commonly recorded during the summer half-year.

The flow record

Frequent discharges caused by fish farm are eliminated to produce naturalised flows. Full period of record peak flow data reviewed and released in September 2019 (WINFAP Files v8).

Descriptions from the National River Flow Archive (UKCEH). NRFA station record ↗

Gauge Details

How this gauging station is built and how long it has measured (NRFA / UKCEH).

Gauge type
Flume
Operating since
1952
Station datum
47.1 mAOD
Flow record
1952–2024 · 72 yrs · 100% complete
Peak-flow record
since 1952
Hydrometric area
38
Measured by
Environment Agency

Frequently asked questions

Is the River Mimram at Panshanger flooding today?

The current level is 0.41m, which is within the typical range of 0.31 to 1.07m. Flooding is unlikely at this level.

Is the river level rising or falling at Panshanger?

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 Mimram at Panshanger?

The typical range at this station is 0.31m to 1.07m, based on Environment Agency historical data. Levels above 1.07m 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:

Check any UK postcode’s flood risk →

🏠 Buying or renting around here? Get the Property Flood-Risk Report for any English postcode — official risk band, recorded floods, warning history, river behaviour and nearby storm overflows. £19 one-off. Learn more →