Lowthorpe Mill Diversion

Winner of the Wild Trout Trust 2016 Conservation Award for Medium-Scale Habitat Enhancement Scheme


Biffa Award, a multi million pound fund that helps to build communities and transform lives through awarding grants to communities and environmental projects across the UK.



There are records of a water mill on this site in the early 14th century. The mill on this site was refurbished on several occasions and passed through various owners. In 1720 it was purchased from the Pearson family by Sir William St Quintin of Harpham.

The bulk of the Lowthorpe estate still belongs to the Legards of Scampston, descendants of the St Quintins. Following the final modification in about 1770 the mill sluice provided a ‘head’ of 1.8 metres to drive the breast fed water wheel. The mill was demolished in 1959. All structures apart from the sluice were removed.


In the late 1970s and early 1980s the sluice was modified by Yorkshire Water to provide flow gauging as part of a river augmentation project. It was intended that the additional pumped supply would benefit the YW abstraction downstream at Tophill Low WTW.

In recent times the sluice mechanism fell into disrepair and both sluice plates became seized and locked in the open position.






Following an EU Water Framwork Directive issues on constraints to fish passage and sediment transport were raised based on the presence of this structure.

1. The sluice and the head of water was an effective barrier to the migration of fish.

2. The mill pool acted as a sediment sink and required regular dredging operations to maintain open water.

3. Initial plans to install a fish pass within the structure resulted in many and varied issues relating to soundness of the structure and long term plans for the watercourse.

4. Financial constraints for river management led to withdrawal of funding for the required maintenance needed to maintain the mill pool.


Negotiations with Christopher Legard, Land Owner and tenants including the Foston Fishing Club eventually gained approval for a major river diversion. This would primarily follow the old river course then branch out across a meadow to re-join the main river.

The consultants JBA, appointed by NE and a subsequent appraisal of their study by Alconbury Environmental Consultants appointed by East Yorkshire Rivers Trust demonstrated a possible list of possible routes that could be adopted for the new river course around the sluice structure.

The Rivers Trust proposed a longer meandering course that could potentially result in many more pool and riffle sequences that would result in greater flow diversity and habitat creation.

The new river would be over 250 metres longer and the fall in the newly created channel would comply with a typical chalk river (between 1-3 metres per kilometre).

The overall aim is to create a diverse self cleaning channel with very low flood risk to adjacent property that would be aesthetically pleasing and provide good chalk stream habitat, whilst at the same time providing high class angling opportunities.


Ground works started in August 2015 with the new course being excavated across the meadow. This was undertaken in dry conditions. Levels were taken and the decisions on the exact course were based on core samples.






As the section was drawn out it could be seen that 5cm below grass level the substrate was primarily chalk gravel including some larger pebbles and flints.







The course across the field was kept level with no longitudinal fall. This resulted in both the small feeder channel and the bed of the main Mill tail race being equal bed depth.

Varied angled margins and bed levels followed the main excavation.





At the confluence of the new and old channel below the mill the stream was narrowed to create a natural stream width from a wide, shallow, silted pool. Pre-established coir rolls were used to hold the new margin in place.






Following the excavationof new field section, the old original course was widened to accommodate the likely flood flows. Flows measured at the time of construction were gained from the EA flow gauging station 5 miles downstream.

Very low flows were experienced during construction (0.13M³/sec) the impending flood flows needed to be taken into account (2.97M³/sec during December 2012).

The width of the channel was based on the maximum cross section of an old brick double arch bridge below the mill.

Following the connection to the river below the mill was made the original channel was widened to accommodate flood flows.

The ability to remove stop logs, gradually increasing the flow down the new course gave us the opportunity to judge how the new channel would behave in varied flow conditions.





The stop logs were removed at the mill leat allowing the water level in the mill pool to slowly decrease until the total flow was running through the new course. This fall in level was undertaken slowly so to minimise the soft silt being drawn into the new channel and causing possible polluting sediment to be washed downstream,

The loss of this ‘head’ (1.8 mtrs) of water in the former ‘head race’ meant that the old channel slowly became de-watered .

A fish rescue was undertaken and 24 trout between 10 – 35cm were transferred into the new river course. Numerous brook lampreys were also rescued and transferred to a clean section of the river.

A short section was in filled creating a crossing for machines enabling work to take place on either side of the river.

The Mill Pool

The west bank of the former mill pool was narrowed using the ‘Dig & dump methodology developed by Nigel Holmes (Alconbury Environmental Consultants).

This resulted in the pool being narrowed to half its original width resulting in a more self cleaning channel. This also created a wide marginal area where the plants from the old bank could become established.

The river margin was defended by the use of pre-established coir rolls and the soft berm was protected with coir matting which was seeded with a marginal seed mix.

Once the old channel had been de-watered the project site was closed to allow the deep silt to dry sufficiently to enable it to be handled. The site re-opened in later September 2015 when the removal and stock piling of the silt commenced. Due to the vast amount of silt involved the stock pile extended to cover nearly 2 acres of a former grass field.

The channel was back filled using material from the new channel and dried former dredgings.

Further work stopped while the archaeological interest was recorded. This included an old farm bridge that incorporated a stop log system. The eventual recording of the sluice mechanism was undertaken in early April with subsequent demolition a week later.





The sluice structure was not originally an integral part of the project however due to safety issues and dangerous condition of the structure it was agreed that the structure would be reduced to 30cm below ground level and in-filled.

Once the stock pile of dredgings had dried they were spread over the site creating a natural level field.






A topographical survey was undertaken to ascertain the change in field sizes. This was information required by RPA for the tenants farm payment. The effects of the new channel and old channel widening resulted in slight loss of acreage to the farm holding.






Introducing Trees & Aquatic Plants

The marginal areas and banks were sown with a special marginal grass mix. Marginal plants were imported from the main river derived from weed cutting operations.






Ranunculus ( Water Crowfoot) was introduced to the new channel . Locally indigenous trees & shrubs were planted at strategic sites around the river.

The Ranunculus imported during autumn 2015 finally began to form established beds creating a diverse flow pattern through the new stream course.





Some seeding of margins was undertaken during autumn 2015.

This should be completed when conditions improve later in 2016.






Post project Issues.

The river bed was surveyed upstream of the perceived effect of the mill sluice.

The original perception made was that the back water effect would stop around 150 metres upstream of the sluice. During this survey it was found that this effect would continue for a further 200 metres upstream.

It was found that the bed gradient was between 2-3 times that of the typical chalk rivers in the area.

One proposal was to introduce a series of riffles and / or baffles to slow the rapid flow over this 200 metre section.

This proposal was delayed as it was thought that a more informed decision could be made following a winter of high flows over this exposed river bed.

Following sound geomorphological and ecological principles allowing rivers to promote and maintain the desired and appropriate habitats.

As the winter progressed it was agreed to install a deflector in the channel about mid way along this section.

This took the form of an upstream pointing “V”. This raised the water level by about 20cm which had an immediate slowing effect for about 80 metres upstream.

It is believed that the river bed along this section was clay lined. This clay lining is now breaking up into small pads with gravel surrounding.

The “V” will concentrate flow in a downwards and inward direction and accelerate the removal of this clay.

This should improve erosion and deposition of the gravel to create deep pools and riffles below the structure.

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