ESI Consulting Ltd

Low flow investigations: Severn Trent


Courtesy of ESI Consulting Ltd

Over the last eight years ESI has worked closely with Severn Trent Water on key low flow sites in the Midlands.  The work has spanned the AMP3 and AMP4 programmes in 18 catchments and reviewed a total of over 30 PWS abstraction boreholes.

The sites were initially flagged up for investigation as part of the National Environment Programme by the Environment Agency and included several SSSIs and a Habitats Directive site.  ESI’s scope was to work closely with STWL, the regulators and other specialists in order to determine whether these concerns were justified.

At several of the sites it was quickly apparent that there was a significant low flow problem and the site could progress to options appraisal.  However, on most of the sites, the extent and the significance of the problem could not be quantified at this stage and additional investigation was required. 

ESI drew up a scope of further investigations for each site and was then appointed with Hydro-Logic to carry out the works.  This involved detailed site surveys, 15 new observation boreholes and an extensive programme of groundwater level and spot flow gauging (80 sites) over a 3-5 year period at each site.

The data collected were regularly reviewed and annual reports presented to all stakeholders.  At the end of the monitoring period, ESI prepared impact assessment reports to summarise the improvement of understanding of the problem that had been achieved and to make an assessment of the significance of any impacts.

At this point, the close integration of ESI’s work with the findings of a parallel investigation commissioned by STWL into the ecology of the relevant streams by aquatic ecology specialists APEM, produced new insights into hydro-ecological relationships of these streams.  This has allowed ESI/APEM to pilot an innovative approach to setting of flow targets that is likely to prove to be an important technical breakthrough in this area during AMP5.

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