Low flow investigations (AMP3-AMP5)

Case Study



The Environment Agency’s AMP5 National Environment Programme (NEP) identified a large number of Severn Trent Water Ltd’s (STWL) abstractions that were potentially contributing to the failure of water bodies to meet Good status under the Water Framework Directive (WFD). The potential reductions in abstraction to meet the default flow targets would have had a significant impact on STWL’s supply demand balance.


ESI and consortium partners APEM and Hydro-Logic investigated these sources and through careful measurement of flows, water quality, ecology and the application of leading edge science, developed robust flow targets for the affected streams.


As a result, the final abstraction reductions in STWL’s Water Resources Management Plan were substantially lower than initially identified.



The Challenge


ESI-led Alliance awarded place on Severn Trent Water Framework for AMP6

STWL’s AMP NEP low flow programme included over 30 sites, with a total assessed flow deficit against WFD Environmental Flow Indicators of over 200 Ml/d. Investigating such a large number of sites was a major programme of work and also represented a significant risk to STWL, as the potential reductions could significantly affect its supply demand balance.


By appointing ESI and consortium partners APEM and Hydro-Logic, STWL were given direct access to the largest group of experienced aquatic scientists in the UK. STWL’s confidence in the consortium was due to a proven track record of delivering similar services in previous AMP cycles and the pro-active approach to project management proposed by ESI.


Our Approach


The team were able to build on their existing experience of the sources, aquifers and streams, to propose a focussed and coordinated programme of hydrometric, quality and ecological monitoring to reduce uncertainty in conditions at the sites. The work was led by experienced staff who provided continuity throughout the five year programme.
Using the data collected, together with the results of groundwater models, the team developed robust relationships between the effects of abstraction and aquatic ecology, which have subsequently been presented in peer reviewed journal papers. This high level scrutiny of the science gave the regulators confidence to accept the resultant revised flow targets.


The results of the assessments were presented in concise, well written, impact assessment reports. The reports considered the effects of abstraction in the light of other pressures in the catchment (often considerable) and, where appropriate, proposed specific flow targets and required abstraction reductions. Reports were reviewed in detail by the client and regulators and final versions signed off as part of the regulatory process. The large number of sites meant that the reporting programme had to be carefully managed and deadlines were strictly adhered to by all parties.


The Outcome


The final reports and proposed abstraction reductions formed the basis of the abstraction reductions built into STWL’s Water Resource Management and AMP6 submissions to OFWAT.


Where uncertainty remained as to the significance of abstraction effects on ecology (particularly due to the interacting effects of other pressures in the catchment), sites were carried forward for further investigation in AMP6.


The abstraction reductions built into STWL’s AMP6 business plan were less than 10% of the flow deficit initially identified by the Environment Agency. Given that a re-location of 1 Ml/d of abstraction is usually at £1-3M, the investment by STWL in collecting evidence of the effects of abstraction on aquatic ecosystems represented a significant economic benefit.