Programme appraisal

The Programme Appraisal stage of the DWMP follows the Options Development and Appraisal (ODA) process. The ODA process identified feasible and preferred options for investment in a number of our wastewater systems to reduce the current risks as well as the risks up to 2050. 

The Programme Appraisal stage brings all the investment needs identified during the ODA stage together into a programme for each river basin catchment. This means we have been able to see the range of investments needed to meet our planning objectives and address the risks identified in the DWMP for the short, medium and long-term. We have also been able to consider the priorities and timing for investment to achieve the outcomes we want for our customers and the environment. By considering the wider benefits, we can identify the best value and the most cost effective options. In some cases, a single solution, such as surface water separation, can address a range of Planning Objectives (POs).

We explored the option for investment for four wastewater systems in the Adur and Ouse River Basin Catchment during the first cycle of the DWMP.  A full list of these Investment needs for these four wastewater systems is below.

The list has been prioritised using the risk reduction score. The details of the method for prioritisation can be found in our Technical Summary on Programme Appraisal.

A summary of the investment needs for these systems is: 

  • Enhanced maintenance: Proactive jetting, Siltation Removal, Wastewater Pumping Station, Enhanced maintenance: Wastewater Treatment Works. 
  • Pipe rehabilitation programme:  CCTV surveys, sewer integrity checks and re-lining to reduce exfiltration within Groundwater Protection Zones. 
  • Attenuate excess flows in sewer network using, upsizing sewer, storage tanks and creating new sewers to reduce risk of flooding
  • Study:  Model improvements, including flow surveys for storm and dry weather flow, and model calibration. 
  • Review permit for the WTW with the EA, and deliver associated works to increase capacity of the works (WOEA, PORT, NEWE)

We extrapolated the costs for these four systems to the other 64 systems in the Adur and Ouse river basin catchment to understand the total investment needs. The process for extrapolation is set out in the Technical Summary on Programme Appraisal (insert link).

A graph to illustrate the extrapolation of investment needs across the whole river basin catchment is shown in figure 1.


Figure 1:  Adur & Ouse: Extrapolated Investment Needs and Risk Band Reduction


The programme appraisal for the Adur and Ouse identified the following:

  • The 4 wastewater systems serve a population of around 553 000 which is approximately 76% of customers in this river basin catchment
  • A total of 42 band reductions are required in 2020 to reduce the risks across the 14 planning objectives in the 4 wastewater systems.
  • By 2050, this requirement will increase to 46 band reductions due to the impacts of climate change, growth and creep.
  • The options identified to date would cost around £247 million for the 4 systems and is expected to provide 22 band reductions in 2050 (the options do not result in a band zero for all risks).
  • The Adur and Ouse River Basin consists of 68 wastewater systems which require 140 band reductions in 2020 and 168 band reductions by 2050 in order to achieve band zero across 14 planning objectives.
  • Extrapolating the risks across all the systems in the Adur and Ouse will cost around £2.9 billion for a population of 723,000. This illustrates the scale of investment needed to achieve Band 0 by 2050 across all 14 planning objectives.

You can view the list of the Investment Needs for the Adur and Ouse river basin catchment.

Close agent lightbox  Close box