Options development and appraisal for Arun and Western Streams

We commenced the ODA process at the river basin catchment (RBC) scale (level 2 planning). This enabled us to look across all the wastewater systems in the river basin and consider generic options that could work at the catchment scale, as well as those specific to a wastewater system.

The generic options are grouped into those that help tackle the risks at ‘source’, those that help to improve the wastewater system, ‘the pathway’, and those that protect or mitigate the impacts on the receiving waterbodies, ‘the receptors’. This process helped to identify the types of options that could be used individually or in combination with other options to address the risks.

We held meetings with partner organisations to build upon the list of generic options relevant to each wastewater system. As a group we identified and proposed ‘unconstrained’ options to tackle the drivers and causes of risks identified during the Problem Characterisation stage of the DWMP. These unconstrained options were then progressed by us through the options development and appraisal.

The options appraisal involved evaluating each of the options in two stages, firstly to screen out unviable options to leave a set of ‘constrained’ options, and then a second stage to reduce the list further to leave only potentially ‘feasible’ options(see the Options Development and Appraisal technical summary for full details of this process).. The process for evaluating the benefits and how we have taken the environment into account is set out in our Strategic Environmental Assessment (SEA) Scoping Report and the SEA Progress Report.

Only feasible options with positive benefits proceeded to the costing stage and this resulted in the selection of the preferred options and confirmed whether each was ‘least cost’ or provided ‘best value’.

The feasible options column in the table below shows how we applied the process within each wastewater system. Beginning with the generic options through the appraisal stages, the table shows the point at which some options were rejected and why. If an option was not rejected, it was costed and became either the final best value or the least cost preferred option (see ODA technical summary for details of this process).

Our final preferred options are set out in the Investment Needs tables for each wastewater system. The accompanying maps show the location of the proposed options within the wastewater system.

Please check the DWMP glossary for any unexplained acronyms.

The options and investment needs are not committed funding but an identification of the needs for funding. We will include these options in our future business plans as part of the Ofwat periodic review of water company funding to secure the investment needed to implement these options.

Note: The areas highlighted for customer education in the investment needs maps are indicative areas of likely focus, as they were derived from historical incident data.