The Hydro-Logic® Aquator water modelling platform enabled Severn Trent Water to create comprehensive Environmental Assessment Reports that help the water company to manage water supply during drought conditions. 

SItuation

Severn Trent Water Ltd (STWL), a UK water utility, abstracts water from the Derwent Valley and Tittesworth Reservoirs, and the rivers Derwent, Leam and Avon, for the purpose of public water supply. These bodies of water are strategically important water sources, so STWL undertakes extensive planning to prepare for times of drought.

In periods of unusually low rainfall, where water resources become scarce, UK water companies can apply for Drought Permits (DP) or Drought Orders (DO), which allow abstraction licence conditions to be modified. Each potential DP site requires an Environmental Assessment Report (EAR), however.

These reports provide details of likely changes to the flow regime due to implementation of the DP, as well as giving an assessment of any potential impacts on river ecology and river users that might result from these changes.

Problem

The previous EARs at these sites had been completed between 2012 and 2014, but since then additional environmental surveys and monitoring activities were undertaken that need to be accounted for.

In addition, regulatory drought planning guidance and frameworks have been updated, including a requirement to consider the effects of drought events worse than historically observed.

Updated assessments were therefore required.

Solution

The Hydro International Data, Insight & Analysis team provided hydrological and water resources modelling as part of a framework consortium for STWL.

To address the EAR the team used a Hydro-Logic® Aquator model to represent the water resources zones and systems that make up the STWL water supply network. The model included all the various asset and license constraints on the system, along with representation of customer demands and system operational rules.

The model ran on a daily time step, allocating water resources to meet demand each day, using an algorithm that considered both resource availability and cost to represent real-life activity.

By running the Hydro-Logic® Aquator model, outputs representing river flows at all the key assessment points on the river were produced to generate comparative baseline and DP-impacted reservoir storage and flow time series for key assessment points on the river system. These underpinned the wider environmental assessments. The team also used the model outputs to consider the impact of drought powers on water availability for other river users with ‘protected rights’.

Prior to the assessment, the team tailored the model to allow rapid switching on or off of various drought permits or orders in the model for model simulations. To meet the needs of the new drought planning guidance, the team also needed to set up the model appropriately to accommodate stochastically (statistically) generated hydrological data to represent and test drought events more severe than historically experienced.

This allowed this type of output to be considered for the first time in the EAR process.

Outcome

The DP/DO impacted reservoir storage and river flows are key pathways for every environmental and ecological receptor in the EAR, including protected rights, which were also assessed by the team.

As such, the Hydro-Logic® Aquator-generated time series were vital to the environmental impact assessment of the DP/DOs on each of the river systems, providing STWL with comprehensive insight into water resources and enabling them to make better decisions on water supply and demand.

The EARs that the Hydro International consulting team produced will be available to inform applications for DP/DOs until they are due for renewal at the end of the next five-year planning cycle.