To date catchment nutrient balancing, a catchment management solution using flexible permitting to tackle diffuse pollution at source, has only been trialled by two water companies.
But in an effort to meet increasingly stringent nutrient permit limits on wastewater treatment works in PR24 many water companies are looking to adopt the approach to help the agriculture sector reduce its contribution. According to Environmental Agency data from 2022, 62% of river stretches failed their health tests due to agriculture and land management practices.
Wessex Water has just submitted the first-year results of a three-year trial of catchment nutrient balancing (CNB) at 23 of its water recycling centres (WRC) across two of its catchments. Here catchment partnerships and delivery manager Tim Stephens reveals how the trial has helped flesh out the approach to using flexible permitting to tackle nutrient pollution, which should help pave the way for greater adoption by the industry.
Pushing for change
Wessex has been working with the Environment Agency (EA) since 2015 to develop innovative permitting, resulting in both the development of CNB permits and catchment permits.
Its Bristol Avon catchment permit, which has been in place in various forms since AMP6, implements one overarching phosphorus (P) reduction target across a catchment. Wessex is able to divide this one target between its different WRC within the catchment, which allows the company to exploit the greater potential for reductions at some of its WRCs, leading to greater reductions overall.
This new approach delivered an additional 37.4 tonnes of P from the catchment, compared to the target of 25.2 tonnes in its first year, while the company saved £25.3 million in capital and operating costs compared to the conventional solution.
Now the company has moved a step further by introducing catchment nutrient balancing in its Tone and Parrett catchment, which flows into the Bristol channel through the Somerset levels, and the Dorset Stour catchment, which flows south into the English Channel.
These permits, which are issued to individual WRCs in the catchment, set out how much of each centre’s overall nutrient reduction target can be delivered through reductions to diffuse pollution at source. This is achieved by Wessex funding farmers to install measures across their farms to reduce run-off.
This P offsetting initiative aims to reduce the run-off from farmyards, tracks and fields by three tonnes per year by 2025 in the Tonne and Parrett catchment.
“The sorts of measures that we fund have multiple benefits, so as well as delivering a kilo of P reduction, depending on the measure there will be some carbon sequestration, a reduction in nitrate leaching, biodiversity improvement, and natural flood management,” says Stephens. “Natural flood management is the one that meshes most neatly with P reduction.”
While fellow water company United Utilities was the first to trial CNB at one of its wastewater treatment works, the scale at which Wessex has implemented flexible permitting has required a different approach, says Stephens.
The first difficult step was defining the exact catchment for each WRC within which Wessex could fund agricultural measures to reduce diffuse pollution, which took some time.
The next step was agreeing with the EA which measures would be allowed within each WRC’s operating techniques agreement (OTA), which is attached to the permit, to deliver the hybrid strategy.
Wessex started the process of finding the most effective measures to reduce run-off, and those most suitable to large-scale rollout, during a five-year pilot that is ran near Wootten Basset on the Brinkworth Brook tributary.
Despite this, Stephens says it still took the company “a year or two” to complete the process. “We’ve had to go through it measure by measure asking if it is acceptable, and if the answer is no then going back with a different approach.”
The Farming Rules for Water, which sets out which measures farmers should already be doing to meet regulations, and can therefore not be funded by water companies, is “quite subjective” says Stephens.
“They can be quite open to interpretation as to whether a particular measure, such as growing cover crops, is a regulatory requirement or not,” he says.
While the process has been challenging and time consuming for Wessex, Stephens says other water companies looking to set up OTAs on their own treatment works should find the process much less arduous.
“We’ve had really positive engagement with the EA and they’ve now formed an innovating permitting team because the resource requirement from them on this kind of thing is increasing.
Stephens says that the EA has received a lot of proposals for CNB schemes for PR24 and is in the process of producing some national guidance about what measures are acceptable.
Defining catchments and measuring P
Although agreeing which measures are acceptable is not a simple process, the biggest challenge to successfully delivering CNB schemes, like all nature-based solutions, is measuring the direct effect of measures such as fencing livestock out of watercourses on pollution levels.
Stephens says: “While you can have a high degree of certainty that if we install a particular treatment process it will reduce P concentrations to a certain amount, and that can be checked daily or weekly, you can’t monitor agricultural measures like that because we are delivering hundreds if not thousands of measures around the landscape.”
Wessex is therefore reliant on a modelled approach. The catchment science team has created methodologies for estimating P run-off and the company has a big monitoring programme in place to sense check the modelling. The process is made more difficult due to the variability of agriculture.
“No model is perfect. On average the model is fairly accurate but there is a range, in that if it is a really wet winter it tends to underestimate the levels, and in a dry winter it overestimates. It’s fairly accurate on an aggregate basis.”
To give the EA confidence in the approach, the CNB schemes are being run as a three-year trial until 2025, with the company having just submitted the first year’s annual compliance report. If the approach is not found to be delivering the necessary results then Wessex has until 2027 to carry out the asset upgrades at its WRC to meet the P targets.
Farmer engagement in the scheme has been really good, says Stephens, but the variety of measures the company can fund is one of the biggest constraints that means meeting the reduction targets for diffuse pollution will be a challenge.
“It’s quite a narrow range of measures that we are able to fund and there’s a question mark over how much we can deliver through this approach. There is a lot of interest internally about that.”
As well as only being able to offer a few options, Wessex is finding this space increasingly crowded as farmers can access funding through the Environmental Land Management scheme, the Sustainable Farming Incentive, Biodiversity Net Gain, and in 50% of Wessex’s catchment, nutrient neutrality.
“CNB is harder in a catchment where there is nutrient neutrality. For us in the Tone and Parrett catchment we are also competing against developers looking to fund farmers in P reduction.”
While more funding streams should not be a bad thing, Stephens says that some farmers are finding the situation too confusing and are choosing to sit and wait to see how the schemes develop. But competition is not the only issue with planning a CNB in a nutrient neutrality catchment.
Wessex Water’s plans for rolling out CNB are less ambitious than the company would have liked due to new guidance set out by the Department for Environment, Food & Rural Affairs (Defra), which applies to the nearly half of the company’s operating area covered by nutrient neutrality.
The department recently asked water companies to submit proposals to enable CNB, nature-based solutions and catchment permitting in nutrient neutrality areas, as it is looking to understand if these could be more beneficial options than focussing on technically achievable P reductions.
Ruth Barden, director of environmental solutions at Wessex Water, says: “Defra said to companies, if you were to use these at complete catchment scale, rather than just targeting sewage treatment works above 2,000 population equivalent, what would you do differently?
“How would you still deliver a load reduction rather than a technically achievable concentration reduction at each works? And what would that offer in terms of cost savings, carbon benefits, and wider biodiversity or natural capital benefits?”
Unfortunately, Barden says Wessex has a fundamental difference of opinion on how CNB works, as guidance issued by Defra states that water companies would still need to achieve in river targets.
“Our view on that is that’s not catchment permitting, that’s water body permitting. There isn’t much option to actually realise the benefits of a true catchment permit if you are limited to hitting a target in a water body, and your fair share target as well,” she adds.
Barden points out that if a company only has one discharge into that water body there’s no opportunity for catchment permitting as there is only one asset. Similarly, CNB requires multiple landowners and managers to be able to achieve the necessary reductions, and this is unlikely to be the situation at water body scale.
The proposals submitted by Wessex are therefore limited, and centre largely on catchment permitting rather than CNB.
“That’s been our fundamental difference on that and has meant that our proposals are more limited than we would have liked them to be. My understanding from talking to colleagues at other water companies is they have run into exactly the same problem; they would have wanted to have far more ambitious proposals that are truly catchment based but they can’t be,” Barden says.
This article first appeared in Utility Week‘s Digital Weekly edition. To read the issue in full, click here.