Programme appraisal

The Programme Appraisal brings the investment needs for each wastewater system together into an investment needs programme for the Ise of Wight Catchment. 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 for the Isle of Wight Catchment include

• Reducing the number of spills from the 103 storm overflows which together currently spill around 2400 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 Sandown, Ryde, Cowes, Fairlee, Dodnor and Roud
• Investigating the impact of wastewater discharges on the Solent and Dorset Coasts and Isle of Wight lagoon
• Investigation of land stability issues in vulnerable urbanised coastal landslide complexes, including Ventnor and the north coast and the potential impact on local infrastructure
• Improving the resilience of our networks and treatment works to prevent pollution incidents, particularly in Ryde, Cowes, Sandown and Newport
• 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 Cowes, Sandown, and Newport.

 

Investment Needs for the river basin catchment

We progressed only the Sandown wastewater system through the ODA stage in the first cycle of the DWMP. Sandown serves a population of around 131 000 which is approximately 90% of customers in the Isle of Wight catchment.

We extrapolated the investment needs for Sandown to the other 19 systems in the Isle of Wight 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: Isle of Wight: Extrapolated Investment Needs and Risk Band Reduction

The programme appraisal for the Isle of Wight identified the following:

• A total of 17 band reductions are required in 2020 to reduce the risks across the 14 planning objectives for Sandown – the one wastewater system on the island that was considered in the first cycle of DWMP.
• By 2050, this requirement will stay the same at 17 band reductions even taking climate change, growth and creep into account. Although the risks will increase, this is not visible where the risk is already in the highest risk band 2
• The options identified to date would cost around £288 million for Sandown and is expected to provide 8 Band reductions in 2050 (the options do not result in a band zero for all risks)
• On the Island, there are 20 wastewater systems which need 72 band reductions in 2020 and 78 by 2050 in order to achieve band 0 across all 14 planning objectives.
• Extrapolating the investment needs for all the systems in the Island will cost around £637 million for a population of 144,000. 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.