Ouse or Hundred Foot Washes
Water Levels and management

Introduction

The water levels of the two non-tidal river systems on the west side of the Washes (the Counterdrain/Old Bedford, and the Old Bedford/Delph) and water within, or on, the Washes, are controlled (as far as possible) by the Environment Agency (EA) in accordance with a Water Level Management Plan (WLMP) as amended from time to time.

The Plan sets out the objectives - flood defence, nature conservation, agriculture and recreation - and the management needed to try to balance and satisfy the different requirements of those activities. It contains guidelines, target water levels, and the operating rules for some of its water control structures - in particular, Earith Sluice (which controls the flow of water into the Old Bedford/Delph) and Welches Dam Pumping Station (which controls levels in the Counterdrain/Old Bedford) are operated in accordance with very precise water level figures.

Water Level Measurements

Water levels are measured against a reference or datum point known as Ordnance Datum (OD) set by the Ordnance Survey (OS) for measuring heights above "mean" (average) sea level. Levels above that are "AOD" - Above Ordnance Datum (the 'A' or 'Above' is commonly omitted). This is the same datum point used to indicate heights of land on maps.

A point to note when reading old documents is that the OD point changed in 1921 from Liverpool (ODL) which had been used since 1844, to Newlyn (ODN). If the last character is not shown, care must be taken to ascertain which point is referred to. Unfortunately, due to limitations of earlier levelling techniques, the difference between the two varies across the country - there is no single conversion factor. Fortunately, the OS have a useful on-line conversion facility which provides figures for every grid square. Using that facility, the following chart shows the converted levels at locations in the south-west and north-east of the Washes:

location	OS grid square	OD Liverpool (1844-1921)	OS on-line conversion factor	OD Newquay (since 1921)	metric equiv/td>
Earith Sluice	TL 38 74	13.9 ft	minus 1.3 ft	= 12.6 ft	3.84m
Denver Sluice	TF 58 01	13.9 ft	minus 1.6 ft	= 12.3 ft	3.75m

A difference of 1.3 or 1.6 ft would be unimportant in upland areas, but extremely important in the low-lying Washes. Also, the difference in the converted Earith and Denver figures, 0.3ft (3½ inches), may seem small but can be very significent in terms of operating the control structures.

My choice of 13.9 ft for Liverpool was not random - it was the original "summer" drawmark level for opening the gates at Earith sluice as shown in the 1920 Act. That level is now set at 3.77m, so it does seem that the operating level has changed since 1920 despite the oft-quoted statement that it cannot be altered. It may have changed under the terms of the 1930 Act, but so far I have not been able to find any reference.

In the South Level and Middle Level much of the land is below sea level (ordnance datum). To avoid negative values, measurements are shown against 'South Level Datum' (SLD) which is OD plus 100. A reading of  101.0 SLD = 1.0 AOD; and 98.8 SLD = minus 1.2 OD.

Gaugeboards

Simple gauge boards made of plastic or alluminium with painted or embossed markings, affixed to a wooden back-board, can be seen at many places in the washes.

Reading them can be tricky, but with care, readings can be made to the nearest centimetre. The figures relate to top of line below. The figure above each 9 indicates full metres, the other figures tenths of a metre. Top and bottom of short lines indicate hundreths.

These two photos are the same board, in the Delph at Welney; the left view is typical of most boards with the full metre figure difficult to spot - here it is the 4 between the 1 and 9. This board was amended in 2009/2010 and is much easier to read with full metre figures shown in red and moved to the right to distinguish from the tenths.


The main board at Welney (click for larger views)
Left Feb 2009, 3.40m AOD; Right Mar 2010, 3.54m AOD

Note, water level does NOT indicate water depth. Also note that some bridges over navigable waterways have similar looking gauges fitted, but they show headroom under the bridge; again that is not an indication of depth. The only depth gauges I have seen in the Washes are on the verges of the Wash Road (A1101) at Welney, erected by Norfolk County Council. The local community website says they are very inaccurate; my own checks in 2011 revealed they under-read then by about 8" (20cm). They may have been corrected since.

Telemetry Gauging Sites

The EA have some very sophisticated gauges which the public do not have access to (although some figures are available on-line, see below).

Readings are taken by a sensor or logger, often a submersible pressure transducer, and transmitted at regular intervals, perhaps every 15 minutes, via 'telemetry' direct to the EA control centres. (Telemetry is the transmission of electronic signals from one place to another.)

In 1996 the EA had 7 'telemetry gauging sites' monitoring levels in the washes. These are the same in 2025.

On right, the telemetry site in the Delph at Welney, seen looking north from Old Bedford Bridge.
Readings for this site are available on-line at River Level at Welney They are of particular interest to motorists using the A1101 Welney Wash Road where flooding begins at 2.4m AOD. Unlike the original page on the EA website the .gov pages are very clear.

Sites in or around the Ouse Washes

Station name	River	EA grid ref	notes
Salters Lode	WC	TF 587 017
Earith	GOR (BO)/OBR	TL 389 749	details on-line - see below
Sutton Gault	OBR	TL 428 797	details on-line - see below
Welches Dam	CD/OBR & OBR/DR	TL 471 859	details on-line - see below
Welney causeway	OB/DR	TL 529 939	details on-line - see below
Welmore Lake Sluice	Delph & Tidal River	TL 572 987
Old Bedford Sluice	CD/OBR	TL 585 015

Source: NRA OW WLMP, March 1996

Telemetry levels available on-line

Many site figures are on-line, updated frequently and very useful. Those affecting the Ouse Washes including upstream sites on the Great Ouse are shown below. Click place name/link to view the page.

Note. measurements are usually relative to a local site datum, not to Ordnance Datum (OD). Site datum added to the readings gave AOD.

Earlier pages (pre-2015?) showed the datum figure, current pages do not. Also note the times are GMT.
See map at Map of flooding and site locations (expand map to view area) Clicking a site icon will bring up the level data.

river, place & EA weblink EA site ID no.	location details	site datum AOD	normal levels	recent highs (R=record) as per EA at Jan 2014	record high	Remarks
Upper Grt Ouse Offord(Cluny)1 6078		11m	0.00-0.42	0.92, 08/01/08 1.20, 25/12/12	1.48
"Great Ouse" (OBR ?) Earith 6180		1.89m	0.07-2.06	2.59 (4.48 AOD),16/08/09 3.04 (4.93 AOD),20/04/12	2.66? 3.15?	sluice opens, AOD 3.77 Apr-Oct 3.17 Nov-Mar
"Great Ouse" (OBR !) Sutton Gault 6252		0m	0.41-3.05	3.89,22/01/08 4.01, 28/12/12 (R)	4.01 (was 3.97)
Counter Drain Welches Dam 6261		0m	0.69-1.14 0.75-1.09	1.49, 04/03/07 1.55, 30/04/12 (R)	1.55 (1.70 4)	PS starts 1.10
"Great Ouse" (ie Delph River) Welney causeway 2 6245	near west bank of R.Delph, 100 yds north of bridge.	0m	0.00-2.00 4 0.46-2.40	3.58, 04/03/10 3.88, 29/12/12	4.13 07/01/03 (4.17 4)	Wash Rd floods at 2.40 AOD
Old Bedford Salters Lode 5 E21381	at Old Bedford Sluice		1.08-1.51 5
Ely Ouse Ely 6254		1m 3	1.44-1.67 4 0.43-0.90	0.82 (1.82 AOD),30/12/09	1.39 (2.39 AOD)
Delph Welmore Lake 5 E22095			1.64-1.97 5

Notes:

1	Although a long way from the start of the washes, the flow here can affect the operation of Denver Sluice, (and maybe Earith Sluice?). High river levels may suggest high flows, but I don't know of any way of relating these accurately.
2	The EA site name is confusing; the telemetry site location is as I've noted; the name really ought to apply only to the visual gauge boards immediately south of the the Delph Bridge, one of which shows when the "causeway" i.e the A1101 Welney Wash Road, will start to flood. From my observations, the gauge board and telemetry readings correspond.
3	site datum shown on EA website in 2011 was 0m . Don't know date & reason for change
4	figures(s) shown on EA website in 2011.
5	location details not shown on EA map and webpages. Info here from a private site, www.riverlevels.uk

Jan 2014 update. A private website, www.riverlevels.uk, shows all the EA's country-wide river level information. Welney Wash Road (which the EA calls Welney Causeway) can be found at https://www.riverlevels.uk/river-ouse-welney-welney-causeway . Do try it.

Target water levels: metres, AOD

Land drainage

river¹	location	dates	min	target	max	notes
CD/OBR				0.91	1.15²
DR	WD	Apr 7		0.80		gradual lowering of levels by pumping at Welmore Lake
DR	WD	Apr 14		0.70
DR	WD	Apr 21		0.60
DR	WD	Apr 28		0.55
DR	WD	May-Oct		0.50

Nature conservation

river¹	location	dates	min	target	max	notes
	washes	winter	1.00		1.50
DR		May-Oct		0.50
DR		Nov-Apr	1.00			for overwintering birds
CD/OBR		summer	0.75	0.91

Grazing

river¹	location	dates	min	target	max	notes
OB/DR		summer	0.50
CD/OBR		summer	0.65

Navigation

river¹	location	dates	min	target	max	notes
BO				2.13
CD/OBR	WD		0.75	0.91		nth of 40 Ft lock

Fishing

river¹	location	dates	min	target	max	notes
CD/OBR			0.50

Notes and sources

source	NRA OW WLMP, March 1996
1	OBR=Old Bedford River; NBR=New Bedford River (100 Ft River); DR= Delph River; CD=Counterdrain; WC=Well Creek; RGO=River Great Ouse
2	achieved by gravity discharge through Old Bedford Lock at Salters Lode when tide permits, otherwise via spillway at Salters Lode into Well Creek. At 1.15 Welney Gate closes and WD PS starts pumping into DR

Flood Alerts and Warnings

For details of predicted or actual flooding of the roads (causeways) crossing the Washes at Earith, Sutton Gault and Welney, go to the EA page: Hundred Foot /Ouse Washes

For more road news around the Washes, see BBC Cambridgeshire Travel

Gauge Board Sites and Readings

Below are just a few of the many gauge boards in the Washes; I will add new sites in due course. I will also try to regularly record and display readings which influence the operation of sluices etc.

A problem for the public trying to understand the workings of structures, or monitor the EA's operation of them, is the difficulty reading some water level gauge boards.

Gauge board at Earith Sluice on the upstream side (Bedford Ouse).

Viewing involves trespass and fence-climbing.

Lowest reading marked is 3.9m AOD.

Operating levels of the sluice are 3.77 (summer) and 3.17 (winter)



Welmore Lake Sluice downstream (Hundred Foot River) side, seen here from the Sth Level Barrier Bank. Unreadable even with long camera zoom lens.

Whereas EA staff can see telemetric information from all around the area on their computers, we public may have to walk miles then sometimes find boards are illegible, broken, overgown or positioned out of the water so unable to judge whether structures are working (or soon likely to be) in accordance with the rules.

(Update, Aug 2013. EA staff told me broken boards were a problem for them too, as they could not always rely on telemetry, and a program of repairs is to be undertaken.)

See comments about datum points in page introduction.

Location	river¹	bank	more detail	grid ref	board range	date visited	read ing²
Earith sluice	BO		south-west u/s side
Earith	OBR	W	north of sluice
Mepal   Engine Bank	OBR	W	site of demolished 1930 br	TL 437  814	2.00	16/05/11
Mepal   Engine Bank	CD	W	2 boards	TL 437  814	2.00 3.00	16/05/11
Welney  Wash Rd	DR	W	Sth side of rd	TL 529  936	1.?-2.0 1.8-4.6	21/04/11 21/04/11	lbg lbg
Sutton Gault   on bridge	NBR	E	under sth side		3.0-5.0	26/04/11	lbg
Sutton Gault   on bridge	OBR	W	on sth side		1.0-4.2	26/04/11
Sutton Gault   Anchor pub	NBR	E	3 boards ?			26/04/11
Welney   Gate Sluice	OBR	W	upstream side of gate	TL 5293 9384	?-2.54	21/04/11	0.9 ?
Welney   Gate Sluice	OBR	W	downstream  side of gate	TL 5293 9384	?-2.54	21/04/11	0.9 ?
Welches Dam	DR	W	nth west side of Bailey Br			26/04/11	0.54
Welches Dam	CD	W	seen from 40 Ft lock		broken	26/04/11

Notes:

1	OBR=Old Bedford River; NBR=New Bedford River (100 Ft River); DR=Delph River; CD=Counterdrain; WC=Well Creek; RGO=River Great Ouse.
2	n/l = not legible; lbg = level below gauge; n/v = not visible (e.g hidden by vegetation)

I have stopped adding readings and some items below until I design a better display format

Earith

Mepal

Photo: Eddy Edwards, May 2011

Salter's Lode

Suspension Bridge

Sutton Gault

Sources: .

Welches Dam

Welmore Lake

Welney

There are two boards in the west bank of the Delph River that can be read looking over the south side of the Delph Bridge.  The main board is very tall, reading from 1.6 to 4.5m AOD, and can be seen at all times. A shorter one to the left reads up to 2m at which point it becomes submerged. Neither has any relevance to operation of control structures, but the taller one does indicate to those who know about it whether the A1101 Welney Wash Road is flooded, and if so, by how much.

At some time in 2009 or early 2010 the EA improved the  main board making it easier to read (as described above). A red line was also added at 2.40m to indicate the level when floodwater begins to flow over the road, although there's no sign to say that, and the boards are not visible from the road anyway.

However, it does enable those who know about this to calculate road flood depth by deducting that figure (2.40) from any higher indicated level. It's a shame the EA do not mention this on their otherwise helpful web-page showing regularly updated Welney causeway telemetric levels readings.

When the road is flooded, even by only an inch, barrier gates are put across the road (well, across half the road) at each end (ie, Welney village and Suspension Bridge). Many believe it should be left to individuals to judge whether it is safe to cross, and not to apply a blanket rule to all whether driving a low slung car or a high clearance tractor.

King's Lynn tides TODAY

Tidal influence

The Great Ouse (including sections known by other names, i.e. Tidal River, New Bedford River or Hundred Foot River/Drain and Bedford Ouse) is tidal up to Brownshill Staunch. High tides flowing upriver can act as a "dam" blocking fluvial flows (water from upstream). A combination of high Spring tides or wind driven ones meeting unusually high flows (from heavy rain or melting snow) coming down can lead to flooding of the Washes, either as a result of Earith Sluice opening or the western bank (the 'cradge' bank) of the New Bedford River being "over-topped".

The tide tables for Kings Lynn are available on-line (click 'Kings Lynn Tide Times' in grey box on left), but only for about 7 days. Beware, the datum points are different to Ordnance Datum for land elevation.