Catchment Management

The main aim of the CaBA chalk stream restoration strategy is to attempt to address – how to restore good ecological health to these unique rivers and the landscapes which support them.

Our initial aims for the River Beane catchment are:

• To improve water quality, hydrological regime, river morphology to achieve good ecological status as per WFD and enhance chalk stream habitats for people and wildlife.
• To restore water quality, and the physical habitat of the channel, banks and floodplain to support iconic chalk stream species and ecology.
• To increase the attractiveness of the stream and public access to the river, so that people can appreciate their local chalk stream.
• To monitor the ongoing status of the river.

The Catchment Based Approach (CaBA) is an inclusive, civil society-led initiative that works in partnership with Government, Local Authorities, Water Companies, businesses and more, to maximise the natural value of our environment. The project is one of twelve project under the chalk stream strategy (catchmentbasedapproach.org/learn/chalk-stream-strategy/).

Chalk streams in their natural condition are home to a profusion of life. Botanically they are the most biodiverse of all English rivers. For invertebrates, fish, birds and mammals, they offer a vast range of habitat niches. In Wessex they are a stronghold of our chalk-stream Atlantic salmon, now known to be genetically distinct. The upper ephemeral reaches, known as winterbournes, are global hotspots for a unique range of specialist plants and invertebrates.

But chalk streams are under immense pressure: they flow through one of the most urbanised, industrialised and farmed parts of the UK. Three chalk streams flow through London and there are many more in the chalk hills that surround the capital. Further afield, though many flow through more open countryside, that countryside is busily farmed, while villages or towns are sited somewhere along most chalk rivers. All these streams are impacted in one way or another by the activities of people. We depend on chalk streams for public water supply, and have leant heavily on the resources of the underground body of water that feeds these streams. And yet every litre of water we take out of the aquifers – and we take billions and billions of litres to irrigate our crops, or run our taps – is water lost to the natural environment. Lost, that is, until we put it back. Only by the time we return water to these rivers it is no longer in the state in which we found it and has bypassed long reaches of the stream. It has passed through our sewage systems, becoming rich in nutrients and other pollutants. We may treat it, we may even treat it to a very high standard in some places, but in many others we do not. Routinely, we put back into these wonderful ecosystems water which makes them eutrophic, so that oxygen is sucked away from the river life which depends on it. Even the water which we do not take out, which actually makes it to the underground aquifer or the stream, is unnaturally changed by human activities. Our heavily farmed landscape exerts a huge pressure on water quality, either because rain runs off the land and along roads, accumulating harmful chemicals and nutrients along the way, or because it seeps down into the ground carrying with it the chemical fertilisers which have been applied to the land. There is now so much nitrogen in our chalk aquifers that we do not know how long it will take – even if we stopped applying nitrogen as fertiliser – for the aquifers to become clean again. Finally, we have changed the rivers themselves, modifying them heavily over the centuries. We have used them for milling, for transport, to drive multiple agricultural and industrial revolutions. More recently, in the post-war decades, we made one of the most drastic and permanent changes of all: we dredged them. We took out the gravel river-bed – on which almost all chalk-stream life ultimately depends – and dumped it on the banks, all in an ultimately misguided attempt to drain the landscape.

To investigate and determine the source(s) and pathway(s) for nitrates that affect the quality of water abstracted at pumping stations.

To inform future investment plans for Affinity Water, both in terms of catchment management and treatment in AMP8 and beyond.

Identifying sources for investigation

Affinity Water undertakes routine catchment risk assessments for all its sources, this includes reviewing 'raw' water quality data which is sampled before any treatment. These regular reviews identify sources that may require a thorough investigation due to poor water quality or trends indicating deteriorating water quality. In the case of nitrate if the concentrations follow a seasonal trend this is likely to be a diffuse source and/or influenced by groundwater levels. However, if the nitrate concentrations follow a diurnal pattern or have sporadic spikes, then it is likely related to a point source.

Nitrate investigation methods

A desk study and field is carried out on investigated sources. This can range from identifying all land uses that may contribute towards nitrate in groundwater, as well as recent developments that may impact the source. Additionally any pollution incidents within the catchment are investigated, conceptual modelling of the abstractions groundwater catchment, where appropriate sampling rivers and drilling observation boreholes to monitor nitrate levels, engagement with local landowners and farmer surveys, remote sensing wet weather walkovers, historic cropping, waste water infrastructure mapping. These methods are all carried out to determine the source of potential pollutants sand the pathways to abstraction.

Abstraction nitrate modelling

In the most recent nitrate investigations, hydrogeological modelling by Stantec was used to determine the key inputs of nitrate, spatially map nitrate inputs, predict long term averages and ranges trends. Some examples of this are shown below. In addition, Stantec included modelled scenarios of potential future catchment management schemes and how reductions of nitrate concentrations could be made to reduce long term trends.

Outcomes of investigations

Overall the investigations allow Affinity Water to make an informed decision for future management of its sources, taking into account appraisal of catchment management schemes to reduce nitrate, cost of installing or upgrading treatment, and long term sustainability of the aquifer.

Has covered:

• Evaluating the potential for remote sensing to identify changes in land use and other activities which may present a pollution risk to water supplies.
• Establishing thresholds and criteria on which site investigations or additional data capture can be based.
• Undertaken a risk review of all SPZ1s Will continue with:
• Presenting data in a user-friendly dashboard for ongoing operational management of pollution around extraction sites.
• Integrating the completed system into the current risk assessment methodology

In summary, the key objective is to provide an early warning to the Catchment Management team that would trigger desktop and site investigations, enabling timely interventions which could prevent or mitigate contamination to the aquifer.

In response to this requirement, it has been demonstrated, through the initial scoping and proof of concept development phases the efficacy of remote sensing for identifying a range of sources of pollution through a series of pilot workflows and prototype analytics dashboard. These methods were subsequently applied across all SPZ1 sites, with additional detailed manual interpretation applied to a subset of priority sites. This provided AWL with an up-to-date risk review from satellite data across all SPZ1 sites.

The piloted analysis workflows need to be implemented within an operational software environment to provide ongoing, periodic monitoring across SPZ1 and SPZ2 sites. This data can be integrated into a user dashboard to aid in review of anomalous data and prioritise further inspection, including site visits. The proposed system will provide an integrated system for management of pollution sources within SPZs that allows a significant volume of imagery data to be automatically and frequently captured and analysed with up to a monthly frequency. A built-in prioritisation based on trigger thresholds will allow for consistent methods for identification of potential incidents and clear processes for triaging and managing response activities.