Programme appraisal

The Programme Appraisal brings the investment needs for each wastewater system together into an investment needs programme for the Arun and Western Streams. 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 also look 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.

 

The investment needs in the Arun and Western Streams River Basin Catchment include

• Reducing the number of spills from the 90 storm overflows which together 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 Fittleworth, Loxwood, Chiddingfold, Northchapel and Billingshurst
• Investigating the potential impact of wastewater discharges on Good Ecological Status at the Aldingbourne Rife and the River Arun
• Planning for potential significant developments at Bersted, Horsham, the old Ford Airfield, Arundel, Southleigh, Southbourne, Tangmere, Bracklesham, Barnham and Littlehampton
• Considering the Manhood Peninsular (Sidlesham and Pagham systems) for a catchment approach to tackle multiple water related issues including climate change, sea level rise, flooding, water resources, water quality, new development, biodiversity and habitat loss
• Improving the resilience of our networks and treatment works to prevent pollution incidents, particularly in Bosham, Horsham, Barnham (Lidsey) and Siddlesham
• 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 Horsham, Littlehampton, Bognor Regis, Nutbourne and Emsworth.

 

Investment Needs for the river basin catchment

We progressed 10 wastewater systems through the ODA stage in the first cycle of the DWMP. These 10 wastewater systems serve a population of around 323 000 which is approximately 78% of customers in this river basin catchment.

We extrapolated the investment needs for these 10 systems to the other 49 systems in the Arun and Western Streams 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: Arun and Western Streams: Extrapolated Investment Needs and Risk Band Reduction

The programme appraisal for the Arun and Western Streams has identified the following:

• A total of 92 band reductions are required in 2020 to reduce the risks across the 14 planning objectives in the 10 wastewater systems
• By 2050, this requirement will increase to 107 band reductions due to the impact of climate change, growth and creep.
• The options identified to date would cost around £517 million for the 10 systems and is expected to provide 44 Band reductions in 2050 (the options do not result in a band zero for all risks).
• The Arun and Western Streams River Basin consists of 59 wastewater systems, which require 234 band reductions in 2020 and 276 band reductions by 2050 in order to achieve band 0 across 14 planning objectives.
• Extrapolating the investment needs for all the systems in the Arun and Western Streams will cost around £1.46 billion for a population of 412,000. This illustrates the scale of investment needed to get to Band 0 by 2050 for all 14 planning objectives.

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.