Lower Idle Asset Management Scheme (LIAMS)

Overview

Lower Idle Asset Management Scheme (LIAMS)

West Stockwith Pumping Station (WSPS)

The Lower Idle Asset Management Scheme (LIAMS) aims to provide a catchment-based approach to managing flood risk in the Lower Idle through interventions at West Stockwith Pumping Station (WSPS) and complementary risk management solutions.

The LIAMS project focusses on the flood risk management of all flood risk assets in the Lower Idle. The Project area covers the whole of the Lower Idle catchment, beginning at Bawtry Bridge and following the river until WSPS where it discharges into the River Trent. WSPS is due for replacement or refurbishment as it is beyond the end of its economic life expectancy.  It is expensive to operate, difficult to maintain and it is not compliant with the Eel Regulations 2009.  It is also a high carbon emitter and energy intensive and is very inefficient.  Following on from the recent refurbishment at Keadby Pumping Station, there is scope to bring this Station up-to-date.

Key sites we will  be examining within the catchment include the 4 SSSI (Sites of Special Scientific Interest) units and the Misson East and Misson West flood storage reservoirs. The Project aims to maximise wider environmental benefits and potential opportunities to do that include improving flood storage within the catchment, floodplain restoration and improving rural land management practices.  We also plan on opening up the River Idle to fish and eel passage and to reduce the carbon footprint of both the construction and whole life  cost of the various Flood and Coastal Risk Management assets.

This work is part of the Isle of Axholme Strategy. The Defra approved ‘Isle of Axholme Strategy 2013’ and subsequent ‘Implementation Report’ from 2015 which provides the basis for a flood risk management strategy concentrating on managing flood risk from the Rivers Torne and Idle, where they flow across this low-lying area.The Strategy ensures that both WSPS and Keadby PS’s are maintained as terminal outfalls offering a 1.33% (1 in 75 year) standard of protection.  

Misson West spillway

The LIAMS project cost will total around £20m with around £12m Flood Defence Grant in Aid (FDGiA) funding, £3m asset replacement allowance and £415k of Local Levy already secured*.

*Note that our capital schemes are subject to government funding rules which require projects to demonstrate that economic benefits are greater than costs in order for it to be classed as an economically viable project and proceed with FDGiA funding. Many schemes also require partnership funding, wherein to proceed, additional external funding must be secured to make a scheme financially viable. Presently, the LIAMS Scheme has a partnership funding gap and we will be exploring funding opportunities with our professional partners and communities.

Current situation

We are currently working on the Outline Business Case (OBC) and this period of work will continue until winter 2025/26.

The recent storms have brought record rainfall to many parts of the East Midlands, we have seen record river levels in our watercourses and the impact on homes and business has been devastating, as we are aware has been the case in the Lower Idle catchment.

Following the scale and extent of the recent flooding and the record levels on the River Idle, our current focus is to use data from Storm Babet to calibrate both the hydrology and hydraulic modelling e.g. use of latest gauge data. This will ensure we are using the most recent data to provide the best representation of the Lower Idle catchment in the model. We will then begin baseline modelling and options development, leading on to an outline design for our preferred option.

We are also undertaking stakeholder mapping exercises to identify relevant communities/landowners and professional partners that may be impacted by the project. External engagement will begin in late 2024/ early 2025. 

Frequently asked questions

1. Why don’t we dredge the river?

Dredging means different things to different people. Within the Environment Agency we mean removing accumulated material in the river to maintain the conveyance of the channel. This includes material like gravel or soil – often referred to as silt - that has been washed into rivers from somewhere else, as well as rocks and plant life. Other maintenance activities such as in-channel weed clearance, blockage removal and vegetation management are also important to maintain the conveyance of channels.  

The Environment Agency prioritises those activities which achieve the greatest benefit in terms of better protecting people and property from flooding. Dredging and clearing channels are important parts of the Environment Agency’s maintenance regime, when they improve the channel’s ability to carry increased river flows and manage flood risk.  

Dredging can, and does, contribute to reducing flooding in some locations and each situation is individually assessed. Where there is evidence that dredging will reduce flood risk to local properties without increasing flooding downstream, it meets government criteria, and is cost effective, we will do it.  In some locations and circumstances, dredging would not be an efficient or effective way to manage flood risk. Therefore, it is not the best long term or economic solution compared with other flood risk measures such as building walls or providing storage upstream. Any structures in the river such as bridges and natural features need to be considered, as these pinch points can make dredging ineffective.  

Dredging may increase a river’s ability to convey water and water levels may be lower during low flows. However, the reduction will be less noticeable for higher flows when the water is deeper, and the channel is nearly or completely full. Deepening of a river channel makes little difference to water levels in flood flow when the amount of water trying to enter the channel far exceeds the small additional capacity dredging would provide. The natural processes in many rivers can cause the silt to return and accumulate in the same places very quickly. The ongoing disposal cost of this material often makes dredging less sustainable than other measures. We also know from historic records and modelling that dredging in some locations can increase erosion and flood risk for communities downstream and alter the ecosystem for wildlife. 

Whilst dredging is part of the solution in some locations, it is not a universal solution to what is a complex issue. 

1. How is dredging different from de-silting and what are the alternatives?

Desilting is usually undertaken more frequently to remove recent deposits of silt to the bed level of a river. We use dredging to describe removing a range of materials or for making the channel larger by removing the bed and channel side material. It is undertaken less frequently and is a bigger exercise.

In many cases we will look to enhance or adapt natural processes as an alternative to engineering solutions. Often, a build-up of silt in river channels occurs as a result of the river lacking the energy to continue to move sediment downstream. This is very common in our modified waterways, which have often been over-widened. To combat this, where possible, we look to design in-channel features to mimic natural flows, such as flow deflectors, or design two-stage channels where the river is concentrated enough to move fine silt at low flows, but still retains its capacity to convey high flows. These interventions allow us to both enhance the biodiversity potential for our waterways, through mimicking natural habitats, whilst reducing our maintenance costs, and not compromising on flood risk. 

Another key component to better maintaining our waterways is through encouraging more sustainable land practices. Agriculture is estimated to account for 75% of the sediment lost to the water environment.  Some measures that can tackle soil erosion include:

• change land use to less intensives uses (for example woodland or unimproved grassland) to manage risk.
• restrict certain cultivation operations at high-risk times and/or locations (for example to avoid compaction and exposure to high rainfall)
• restrict use of feeding stations at high-risk times/locations
• improve farmyard drainage infrastructure.
• soil management planning: leaving a rough seedbed post-harvest; encourage the use of low ground pressure tyres on machinery and trailers; restricting livestock access to riverbanks and channels.

Whilst other measures can be used to stop silt from reaching waterways, examples of this include:

• restoring the riparian zone – for example establish/improve riparian woodland and buffer strips.
• fit/improve existing urban/rural sustainable drainage systems.
• create/improve wetlands.
• new or improved farm infrastructure (for example tracks, gateways, drainage); improve field drain management; break compaction on tram lines and in grass fields.
• fit interceptor traps/gully pots to capture sediments (and contaminants) in drainage water; improve maintenance of interceptor traps/gully pots.
• reduce slope length, consider planting hedges and woodland buffer cross slope strips and beetle banks.

For more information please see here.

More Information

For more information on the River Idle, please visit the River Idle page.