Programme appraisal

The Programme Appraisal brings the investment needs for each wastewater system together into an investment needs programme for the Adur and Ouse Catchment. Each investment need has an associated estimated cost to deliver the actions, and an indicative timetable based on when the risk occurs.

These investment needs provide indicative costs that allow us to understand the level of funding required to reduce the risks. The funding has not been secured at this stage. The DWMP informs the development of our 5 yearly Business Plan which is submitted to our economic regulator, Ofwat, to agree how we should invest the money received from our customer bills.

We assess the priorities for investment during the Programme Appraisal stage of the DWMP. We look across the river basin catchment to review the investments needed, the timing of these needs and how they combine to reduce the risks to our customers and the environment. We looked at the wider risk reduction that each option provides across all the planning objectives. Some actions, like separating rainwater from wastewater sewers, could reduce risks under several planning objectives such as storm overflows, external flooding, bathing water quality, shellfish water quality and good ecological status. The details of the method for prioritisation can be found in our Technical Summary on Programme Appraisal.

Our priorities for investment in the Adur and Ouse River Basin Catchment include

• Reducing the number of spills from the 112 storm overflows which currently spill around 2600 times per annum
• Separating or attenuating excess rainwater in the sewer networks to reduce the risks of flooding and frequency of storm overflow discharges, especially in Lewes, Ashington, Ditchling, Lindfield, Shoreham and Barcombe
• Planning for potential significant developments at Burgess Hill, Brighton Marina and West Grinstead
• Improving the resilience of our networks and treatment works to prevent pollution incidents, particularly in Lewes, Newhaven and Brighton (Portobello)
• Reducing the risk of sewer blockages by increasing sewer jetting and targeting customer campaigns to reduce the amount of FOG (fats, oils and grease) and unflushables in the sewer network around The Lanes in Brighton and Church Road, Portslade.
• Investigating the potential opportunity to designate the River Ouse at Barcombe Mills as an inland bathing water.

We progressed 4 wastewater systems through the ODA stage in the first cycle of the DWMP. These 4 wastewater systems serve a population of around 553 000 which is approximately 76% of customers in this river basin catchment.

We extrapolated the investment needs for these four systems to the other 64 systems in the Adur and Ouse river basin catchment. This provides an estimate of the total investment needs required to reduce the risks in all our wastewater systems in the catchment to Band 0 (not significant). This concept of “Band Reduction” and full details of the process for extrapolation is explained in the Technical Summary on Programme Appraisal.

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:

• 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 £554 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 0 across 14 planning objectives.
• Extrapolating the risks across all the systems in the Adur and Ouse will cost around £1.8 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.