The Welney Website

"Welmore Lake Sluice is the only means of evacuating flood water from the Ouse Washes into the tidal Hundred Foot River. The first sluice known to have been built on the site was constructed in 1825 and consisted of four sluiceways spanned by masonry arches. Discharge through the sluice was controlled by timber pointing doors, which closed automatically on high tides to prevent the ingress of saline water into the Washes. The original sluice was replaced in 1933 by a larger structure constructed from reinforced concrete and with steel sheet piling for the side walls. There were only two waterway openings through this sluice, but these were bigger and more efficient than the four openings of the original sluice.

The sluice gates themselves were made of steel, with vertical lift gates controlling the water level in the River Delph on the Washes side, and large counter-balanced flap gates on the tidal side.

To avoid the threat from tidal flooding during the building of the 1933 sluice, the structure was positioned on the Washes side (i.e. upstream) of the original sluice. Although this helped the construction work, it had the adverse affect of moving the sluice further away from its outfall into the tidal river. The 1933 sluice has served the Environment Agency and its predecessors very well, but a continuing major problem has been the build up of silt immediately in front of the tidal flap gates. This occurred whenever the Washes were dry with no flood water being discharged through the sluice.

ln 1996 the then National Rivers Authority made the decision to replace the 1933 sluice with a larger, modern structure, which was to be located as close as possible to the Hundred Foot River in order to minimise the problem of silt build up in front of the tidal doors. At the same time, the sluice's discharge capacity was increased by 50% to reduce the length of time that flood water remained on the Washes. This was achieved by providing three waterway openings instead of the two previously provided. Construction work started on site in July 1997.

Like its 1933 predecessor, the new sluice uses steel vertical lift gates to control the water level in the River Delph. However, this time tidal ingress of saline water will be prevented by the action of large timber pointing doors, similar in principle to those used in the original 1825 sluice.

It is realised that siltation in front of the tidal doors will continue to be a problem, despite the benefits of positioning the new sluice much closer to the tidal river. To combat this problem and to ensure that the tidal doors can always open whenever flood water inside the Washes has to be evacuated, a purpose built system of high-pressure silt jetting nozzles has been incorporated onto each of the tidal pointing doors. This silt jetting equipment will be operated on a regular basis throughout periods when the sluice is not discharging, so avoiding the build up of silt in front of the pointing doors which has been such a problem with the earlier structures.

In addition to the silt jetting, the new sluice incorporates two separate land drainage pumps, to be used for evacuating the last remaining volume of flood water which cannot be discharged by gravity into the tidal Hundred Foot River. This will enable environmentally beneficial target water levels in the River Delph to be achieved and maintained over the spring and summer seasons, providing there are no high flood flows in the Great Ouse during this period that would cause the flood control sluices at Earith to operate.

The 1933 sluice was demolished during August 1999 and the public footpath over it was officially re-routed across the access bridge over the new sluice. This bridge will be strong enough to carry any size of any heavy duty plant or equipment which may be needed to undertake future maintenance work either in the Ouse Washes or to the structure itself.

The reconstruction of Welmore Lake Sluice was substantially completed in early September 1999 and an official opening ceremony is to take place in April 2000.

P Cowie, Project Manager."