River Slea Flood Resilience Project

Closes 21 Jul 2023

Opened 21 Jul 2021


The River Slea arises in the limestone hills to the north east of Grantham, flows in an easterly direction through the town of Sleaford and on towards Cobblers Lock. In the east of the town the river splits to follow the Slea Navigation channel to the north and the original course of the Old River Slea to the south. The navigation follows the contours of the land, dropping the river level from around 13m above sea level in Sleaford, to around 3.5m above sea level via a series of historical locks (some of which are no-longer operational). The Old River Slea follows a more natural course through the Slea valley before joining back with the navigation again at Cobblers Lock.  It then flows on into the Kyme Eau before joining the Lower Witham.

Fig 1. Old Slea upstream of Haverholme Woods

Fig 1. Old Slea upstream of Haverholme Woods

As a river heavily influenced by groundwater flows, the Slea can suffer from low flows at times making abstractions for drinking water and irrigation a challenge. A scheme is also in place to support water levels in the river during dry periods to maintain flow.

Through the town itself, a series of movable structures maintain a water level for aesthetic reasons, although these do interfere with natural river processes, and are a barrier to fish and eel migration and increase flood risk, which is why they have to open during high flows. These structures now require significant investment. Structures along the old navigation channel are also in a state of disrepair.


The watercourse has a complex history of human modification for a range of uses, including navigation, milling and water abstraction.  Consequently there are a large number of historical structures located on the river and river flows have been significantly altered by these interventions.  A number of these structures are deemed flood risk management assets, although their primary function relates to water retention to either provide navigational, milling or amenity water levels.

Flooding to the town occurred in March 1947, when 80 families are reported to have been made homeless, and in February 1977 after significant winter rainfall.

Fig 2. Carre Street Tilting Weir

Fig 2. Carre Street Tilting Weir

Sleaford Town forms a ‘conservation area’ and there is a local nature reserve, Lollycocks Field, adjacent to the Slea to the east of the town.  There are listed buildings close to the Slea, in particular Cogglesford Mill, which is also a museum.

There were a number of instances of prolonged heavy rainfall through 2019 and 2020, resulting in high groundwater levels in the area and increased river flows through Sleaford Town.

A flood warning was issued on the 14 November 2019 for the River Slea and Nine Foot River in Sleaford, when heavy rainfall in the catchment was expected to cause the highest recorded flood level on the Slea.  River levels were already high following several weeks of rain, in excess of levels seen in 2007 when offices were close to flooding, and they were rising steeply. Options for alleviating the levels through management of sluices had already been utilised and exhausted, and residents also called to express their concerns about the high levels.

There were thankfully no flood impacts from this event, and the thresholds have subsequently been reviewed and updated, to inform future flood alerts and warnings.  Recovery works to repair assets damaged by the high levels on the River Slea have included embankments in the vicinity of Cobblers Lock, Anwick and Haverholme.

With government funding to the Environment Agency dependent upon evidenced reductions in flood risk, securing sufficient funding to repair/replace assets with no flood risk benefit is not possible.

This project has been granted accelerated funding to evaluate the project options in2021/22. By working closely with those who have an interest in this river, we hope to develop options to achieve a flood and drought resilient watercourse and restore a more natural channel by removing unnecessary barriers to flows and fish that can secure the required funding.

Timeline plan

Project Objectives

  • Involve and inform stakeholders
  • Sustain and maintain critical banks
  • Make space for water
  • Create a more resilient catchment

Work to date

The project catchment has been divided into compartments. We have gathered our existing data and begun to analyse the current flood risk in each compartment, and potential benefits that the project could provide.  The map below shows the extent of the project area and the individual compartments:

Map showing the extent of the project area and the individual compartments

We have updated our survey data of the watercourses and we now plan to produce an updated computer model of the catchment.  This updated information will inform the next steps of the project and allow options to be tested to see how they might improve the resilience of the catchment going forward.

What’s next…

This is a reasonably long term project and we are still at the early stages, the project is likely to be ongoing over the next 4-6 years.

The Environment Agency are now in contract with our delivery partners ARUP, who will be building the new model for us and planning engagement activities.

Stakeholders and Engagement

From the outset, we plan to provide the opportunity for all stakeholders to express their views on the future plans to manage flood risk on the River Slea. We have ensured that engagement with communities, land owners, businesses and potential partners is a large part of the project brief.

We hope that this project will be the catalyst for a much more collaborative and accessible approach to managing the current and future risks of flooding in this area, including partnership funding solutions. We welcome the input of all parties who have a stake in the sustainability of these watercourses. We feel that there is particular potential to join with those who have interests such as navigation, water supply and the visitor economy.

We hope to invite key stakeholders to be a part of the project board in the future.

If you wish to get in touch with us about the project or be kept up to date on the progress of the project please contact us at the following address:


Regular Watercourse Maintenance

While the River Slea Flood Resilience Project is being developed, the Environment Agency’s operational teams will continue to maintain and manage the flood defence structures (embankments, flood walls, sluices) in the area where resources allow.

These structures all need regular maintenance and each year we deliver a significant programme of works to help ensure they work when they need to. The Environment Agency bids for public funding every year to carry out this maintenance and we use our permissive (discretionary) powers to deliver the works.

Other watercourses (dykes/streams) are still important to local flood risk, but are likely owned by the landowner who will be responsible for its maintenance and conveyance. For more information on the responsibilities of owning a watercourse please see https://www.gov.uk/guidance/owning-a-watercourse

Maintenance is carried out at varying intervals during the year depending on the watercourse. The typical maintenance activities we carry out are grass cutting, in channel vegetation clearance, removing obstructions, bush and tree management and operating sluice gates and pumping stations. For more information on this, please download the accompanying information sheet at the bottom of this page.

Key Terms

Watercourse: A watercourse can be a:

  • river
  • brook
  • beck
  • ditch
  • stream
  • leat
  • goyle
  • rhyne
  • culvert

Riparian: A riparian owner is anyone who owns a property where there is a watercourse within or adjacent to the boundaries of their property.

For more information on the responsibilities of owning a watercourse please see https://www.gov.uk/guidance/owning-a-watercourse

Breach: Where an embankment fails and collapses, allowing water to flow through onto the flood plain.

Compartments: Areas of land within the flood plain that are separated by raised embanked channels or high ground.

Flood Resilience: When flooding happens it causes as little harm as possible.

Storage: Water is allowed to pass onto the flood plain and retained there until the flood subsides.

Weir: A low dam built across a river to raise the level of water upstream or regulate its flow.


  • IDBs
  • Local authorities
  • District and parish councils
  • Environmental bodies
  • Land owners
  • Farming associations
  • Drainage associations
  • RFCCs
  • Elected representatives, including MPs
  • Water companies
  • Members of the public
  • Recreational and commercial river users
  • Community groups
  • Flood action groups


  • Business and industry
  • Flood management
  • Fishing and boating
  • Water resources
  • Water quality
  • Drought
  • Habitats and wildlife