Revitalising the River Ivel

The options appraisal identified that the most environmentally effective option would be a combination of river support from a groundwater borehole and river restoration. This proposal is endorsed by the Environment Agency and Affinity Water are working to:

• Implement a river support (augmentation) scheme where groundwater is pumped into the River Ivel.
• Enhance a seasonal wetland, fed by surface water runoff, to regulate the surface water runoff entering the Ivel headwaters and improve the local habitat.
• Carry out river restoration work which could include re-meandering the river channel and the modification of structures to create a more characteristic chalk stream.
• Change our local groundwater abstraction license to reduce the amount by approximately 228 million litres per year from 2025.

For more information about this project, please contact river.restoration@affinitywater.co.uk.

We completed the river restoration construction at Ivel Springs Nature Reserve in January 2024. During the construction phase we have completed the following to enhance the River Ivel’s chalk stream characteristics:

• Re-graded the riverbed and banks.
• Introduced woody deflectors for flow variation.
• Augmented the channel with gravel, creating riffles.
• Constructed brush-wood berms to narrow the channel, creating flow diversity and a meandering channel.

We also enhanced habitat in Areas 1 and 2 by making improvements to existing pond-like features, both online and offline (connected and disconnected from the channel, respectively).

Please note, we will be back at Ivel Springs Nature Reserve in Spring 2024 to hydroseed and plant the river restoration sections. We decided to delay this to ensure that the vegetation has the best chance of survival.

Prior to the construction, our detailed design phase consisted of:

• Numerous site visits with our consultants to assess site conditions.
• Collection and analysis of soil samples to make sure the soils are suitable for reuse on site.
• Topographic and ecological surveys.
• Refining of the outline designs to include more detail (sizes of in-channel features, measurements for channel and bank regrading, determining the extent of tree works) to produce the detailed designs.
• Stakeholder meetings on site to discuss possible opportunities, constraints, and gather local knowledge.
• Hydraulic modelling to ensure the proposed detailed design is not increasing local flood risk.
• A stakeholder workshop to present the detailed designs and gather feedback.
• Applications for the required permits and permissions to allow for the construction of the detailed design.

View our design maps below:

• Design Overview Map
• Detailed Design Reach 1
• Detailed Design Reach 2
• Detailed Design Reach 3
• Detailed Design Reach 4
• River Restoration Cross Sections
• Pre- and Post-Construction Photographs

Due to circumstances out of our control, the seasonal wetland finalisation has been delayed until at least Spring 2024. However, we were able to make considerable progress in December 2023; the area was cleared of scrub and the wetland cells were dug.

Prior to the construction, our detailed design phase consisted of:

• Numerous site visits with our consultants to assess site conditions.
• Collection and analysis soil samples to make sure the soils are suitable for reuse on site.
• Calculating how much time the seasonal wetland could be wet or dry (known as water balance calculations).
• Undertaking topographic and ecological surveys.
• Refining the outline designs to include more detail (width and depth of pools, marginal planting) to produce the detailed designs.
• Meeting with stakeholders on site to discuss possible opportunities, constraints, and gather local knowledge.
• Hydraulic modelling to ensure the proposed detailed design is not increasing local flood risk.
• A stakeholder workshop to present the detailed designs and gather feedback.
• Applying for and obtaining the required permits and permissions to allow for the construction of the detailed design.

The existing surface water outfall and the pond it flows into will remain in place. This pond will feed into a sedimentation pool, the purpose of this pool is to hold surface water which will allow any material to drop to the bottom therefore, the water entering the next pool will be of better water quality. There are two more pools which the water will flow into; filtering the water before it enters the River Ivel. The pools will be planted with marginal plants (plants that grow around pond edges) and reeds. The seasonal wetland pools will be surrounded by the existing wet woodland areas which is a rare and valuable habitat.

View our design and stakeholder feedback below:

• Seasonal Wetland Detailed Design
• Seasonal Wetland Cross Sections
• Stakeholder Feedback

We are currently working to on the second phase of the river support (augmentation) scheme which includes the installation of the infrastructure. In the first phase, we have:

• Completed numerous site visits with our consultants to assess site conditions.
• Reviewed all existing information including where local utilities are located.
• Agreed the required works for the upgrade of the site power supply for the river support (augmentation) borehole.
• Undertaken ground investigation to inform the design development.
• Undertaken topographic and ecological surveys.
• Refined the outline designs to include more detail (site plan, kiosk arrangement, defined required equipment) to produce the detailed designs.
• Met with stakeholders on site to discuss possible opportunities, constraints, and gather local knowledge.
• Drilled the river support borehole.
• Tested the yield and water quality of the river support borehole.

We have been monitoring the River Ivel’s headwaters since 2015 to understand any impacts of our local public water supply groundwater abstraction.

The monitoring and investigation work was included in our AMP6 Water Industry National Environment Programme (2015 to 2020) programme of works, with the aim of assessing the impact of groundwater abstraction against Water Framework Directive (WFD) requirements.

• The local groundwater abstractions have the potential to influence groundwater levels in the Ivel Springs area, and consequently under certain conditions the river baseflow.
• Groundwater quality is suitable for direct input into the River Ivel, to provide river support (this is also known as an augmentation scheme). A river support (augmentation) scheme is where groundwater is pumped from the chalk aquifer from a borehole and then piped into the river. This provides a support flow to the river when groundwater levels are below the riverbed and when the spring is not flowing naturally.
• The morphology (shape and structure) and the ecology of the River Ivel has been impacted by historic alterations of the channel. By narrowing the channel it will help to improve river velocity, keeping gravels clear and creating suitable habitat for fish and macroinvertebrates.
• A former sewage treatment works close to the springs, previously discharged treated effluent into the springs area, adding to the flow in the River Ivel. The site now pumps sewage to Letchworth for treatment, reducing the input of water in to the Ivel at Ivel Springs Nature Reserve.

Taking the above findings into account, we considered numerous different options that could help improve the resilience of the River Ivel at Ivel Springs Nature Reserve.

As the name Ivel Springs Nature Reserve suggests, springs found on site are the source of the River Ivel. Springs occur where the groundwater moves through cracks and tunnels in the chalk and flows out at the surface. The location of a spring depends on the features in the geology, the groundwater level, and the existing surface level. Springs often move up and down the landscape, depending on the level of the groundwater which naturally changes seasonally.

The flow from a spring at one location may increase following rainfall as more groundwater bursts out at the surface. It can also stop flowing completely during a lack of rain as the groundwater no longer meets the surface at this location.

Groundwater levels fluctuate seasonally, typically reaching the highest level in spring following rainfall over the autumn and winter period which recharges the aquifer. Groundwater levels typically reach the lowest level in late summer, as during the summer months when temperatures are higher evaporation and uptake of water by plants reduces the amount of rainfall that can soak into the ground and recharge the aquifer.

Groundwater abstraction for public water supply or irrigation can also impact on a spring’s flow due to the localised dip in groundwater levels.