Thames Water has a plan to close two abstraction points on the Darent by 2035. This is potentially good news for safeguarding river flow. However, there is a get-out clause. The company needs to know for sure that closing the abstractions will deliver the expected environmental and ecological benefits.

At our AGM in November, Jamie Riches, groundwater resources specialist at Thames Water, described how the company is responding to the need for future water supplies and its monitoring programme to gain more understanding about the hydrology and ecology of the Darent.

Water supply into the future

A planning process is under way to secure future water resources. In the short term (2025-30) increased demand is set to be met by reducing household use and fixing leaks. The plan assumes there is no need for new resources but contingencies include new groundwater abstraction at Addington and delivery of the Horton Kirby Aquifer Storage and Recharge (ASR) scheme – described below.

From 2030 to 2045, additional water sources will be needed. Teddington direct river abstraction is slated for 2033 (although is subject to objections) and there will be licence trading with Affinity Water in the mid 2030s. From 2040, the strategic reservoir near Oxford will be delivered and in use. Longer term (beyond 2045), depending on the sustainability reductions triggered for environmental reasons, the Severn-Thames transfer many be required.

Closing abstraction on the Darent

Within the Water Resources Management Plan, there is an ‘environmental destination’ for the River Darent. It includes a plan to close two abstraction points by 2035 – one at Horton Kirby/Eynsford which currently delivers 6.8 Ml/d and the other at Lullingstone which delivers 4.49 Ml/d.

Westminster Mill at Horton KirbyJamie explained that if reductions are made in abstraction, there must be a clearly identifiable benefit. He described the Darent as a complicated river which had undergone considerable human intervention, and which is not a chalk river throughout its course. He added that it was not possible to unequivocally identify the benefit of reductions made in the Darent Action Plan because consistent ecological data is not available – partly due to reductions in Environment Agency funding and activities.

Jamie said, collectively, we can no longer rely on the Environment Agency to gather and provide this information. At the same time, it is essential such information is gathered to increase understanding of how these catchments work. Thames needs to know how flow will improve with the closure of these abstractions and what the associated ecological and environmental improvements will be.

The Darent Vulnerable Catchment monitoring plan

To gain this understanding, Thames Water has begun a monitoring programme led by its Vulnerable Catchments Team and delivered by partners including South East Rivers Trust. They intend to work closely with all interested parties. Invertebrate monitoring starts in November 2023 at 18 sites. Fish monitoring will be carried out at nine sites and spot flow gauging at up to 20 sites.

The aim, before the next period of investment, is to understand the effect of abstractions and how it is reflected in the river. Key influences are hydrological, ecological and anthropological. Understanding will come through collecting and collating data, walking the river course, and historical review. Jamie mentioned that over time, people have modified the river to suit their needs and that some of these changes have been a cause of low flow. For example, leats used to be lined with clay by landowners to prevent leakage but this typically no longer happens.

Data transparency

There was much interest from the audience over the public availability of the data. It was pointed out that some historic Environment Agency data is available on the Internet – see Darent and Cray Management Catchment.  Jamie said data gathered will be publicly available and his hope was for a central repository where all interested groups could share the data they had.

He was also asked whether increased water demand due to growth in local housing was included in the planning, particularly in light of EA objections to an application for 1,000 new homes in Cambridge. This was due to the lack of evidence that the new homes could be supplied sustainably with water. Jamie said there was strong governmental pressure on water companies to facilitate housing development by providing any upgrade to resources required.

What is the Horton Kirby ASR?

The Aquifer Storage and Recovery scheme has been under test at Horton Kirby for the past decade. Water is taken from the Bean wellfield, treated and stored in the aquifer at Horton Kirby. During periods of drought and very high demand, abstraction will switch so that water is used, rather than putting additional pressure on the local ecosystem. Key to the viability of the project is that the water pumped in should not mix with mineral rich water resources already present. Jamie said the ASR scheme would be delivering from 2028.