Freeing the River Anton

The challenge

The River Anton is a rare chalk groundwater fed river running through Andover town centre. A range of factors – the impoundment from College Weir, extensive tree shading and sediment accumulation—had altered the natural character of this reach. What would have been a flowing chalk stream with clean gravels and diverse aquatic plant life had become slow moving and silted, with limited habitat value and restricted fish passage.

Southern Water needed to meet its Environment Agency Water Industry National Environment Programme requirement to improve river habitat while continuing to operate a nearby public water supply abstraction. Any solution also had to work within a constrained urban environment, manage flood risk and respond to the expectations of regulators, landowners and the local community.

Client

Southern Water Services Ltd

Project Status

Due for completion summer 2026

Scope

Habitat enhancement

Understanding the river system

We began by establishing a robust evidence base. Our teams carried out groundwater modelling and ecological surveys of macrophytes, macroinvertebrates and fish as well as a whole river walkover to understand the key hydromorphological pressures and their distribution to understand how abstraction and physical structures were influencing river condition. This work assessed both the degree of habitat degradation and the relative contribution of different pressures on the river.

We shared the findings through a series of project steering group meetings with regulators, supported by multi criteria and cost benefit analysis. This collaborative process ensured decisions were transparent, proportionate and grounded in data.

The investigation demonstrated that changes to abstraction alone would deliver only limited improvement. The dominant controls on river health were physical. The impounding effect of College Weir and heavy shading from a continuous canopy of mature trees were suppressing flow, encouraging silt deposition and preventing the growth of chalk stream flora. The weir also acted as a barrier to fish passage. Addressing these constraints became central to the project.

Developing the preferred option

We explored a range of options to remove the impounding effect of College Weir. Retaining the structure and lowering the crest was discounted due to its poor condition and the risk of instability once upstream water and riverbed levels were reduced. Constraints on one bank—including protected trees, utilities and landowner requirements—limited what could be achieved in situ.

Instead, we identified an opportunity to create a bypass channel on the opposite bank within a public park. This approach removes the impounding influence of the weir while retaining the historic structure in place, infilled and disconnected from the main flow. It improves fish passage, reduces safety risks associated with a deteriorating unfenced structure and brings the river further into the park, strengthening its role as a visible and valued natural asset. Early discussions with the local council’s countryside and parks team confirmed strong support for this approach.

Designing for people, nature and flood risk

Design development was informed by extensive surveys, including ecology, arboriculture, topography, archaeology, water framework assessment and construction design management. We shared initial habitat enhancement plans widely to support stakeholder engagement and refine the proposals.

Flood risk modelling was a critical part of the process. Historic floodplain modification in Andover means flood risk follows the river corridor through the town centre, and any river works must avoid increasing that risk. Our modelling demonstrated that removing constraints created by the weir, accumulated silt and channel infill would reduce flood risk by keeping flows within the riparian corridor and limiting routing through urban areas.

The final design focuses on restoring natural processes. Alongside removing the weir’s impounding effect, we introduced selective tree management to daylight the channel and support aquatic plant growth. Gravel and woody berms narrow the river to more natural proportions, diversify flow patterns and create a range of habitats within a previously over wide, modified channel.

Securing consent and delivering the scheme

As the project progressed to detailed design, we worked closely with planners, landowners and statutory bodies to secure the necessary consents. The requirement for a full planning application and Biodiversity Net Gain added complexity. This is particularly so for a linear river restoration scheme where compensating for the on-site loss of terrestrial (trees, grass) can be constrained since the gain of aquatic habitats is non-transferable to compensate, and the location in a public park can limit the land available to provide alternative compensation. However, our ecologists identified opportunities within the public park to suitably enhance terrestrial habitats while maintaining its open character for public use, and we coordinated long term management arrangements with the landowner.

Construction is being led by Southern Water’s appointed contractor, with WSP supporting delivery through site supervision, ecological clerk of works, land quality advice and archaeological oversight. We remain closely involved to resolve issues as they arise and to ensure the built scheme reflects the approved design.

Creating lasting value

The River Anton project shows how a multi disciplinary, evidence led approach can unlock multiple benefits. By restoring flow, reconnecting habitats and reducing flood risk, the scheme improves river health while supporting essential water supply infrastructure and enhancing a public space at the heart of Andover. It also contributes to the wider River Anton Improvement Strategy, helping to shape a healthier river corridor for years to come.

Water solutions

We are working closely with our clients to reshape resilience, by protecting water sources, optimising use, and designing systems that are resilient and ready for change. Together, we safeguard water for future generations. From restoring ecosystems and remediating groundwater to treating wastewater and delivering infrastructure, we create sustainable solutions that work with nature and bring long-term value.

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