Programme appraisal

The Programme Appraisal brings the investment needs for each wastewater system together into an investment needs programme for the Test and Itchen 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 Test and Itchen River Basin Catchment include

• Reducing the number of spills from the 62 storm overflows which together currently spill around 1000 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 Portswood, Harestock and Stockbridge
• Investigating the potential opportunity to designate the River Itchen at Riverside Park as an inland bathing water 
• Reducing nutrient discharges from the WTWs across the river basin to prevent deterioration of the Solent and River Itchen internationally designated Habitats sites
• Planning for potential significant development at Winchester, Romsey and the Mayflower Quarter in Southampton
• Improving the resilience of our networks and treatment works to prevent pollution incidents, particularly in Harestock Amport and Barton Stacey
• 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 Kings Worthy, Basset, Harefield and Townhill Park
• Reducing the risk to groundwater by reducing leakage from our sewers in the Barton Stacey, Andover, South Wonston, Kings Worthy and Easton areas.

 

Investment Needs for the river basin catchment

We progressed 12 wastewater systems through the ODA stage in the first cycle of the DWMP. These 12 wastewater systems serve a population of around 529,000 which is approximately 94% of customers in this river basin catchment.

We extrapolated the investment needs for these 12 systems to the other 18 systems in the Test and Itchen 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: Test and Itchen: Extrapolated Investment Needs and Risk Band Reduction

The programme appraisal for the Test and Itchen identified the following:

• The 12 wastewater systems serve a population of around 529,000 which is approximately 94% of customers in this river basin catchment.
• A total of 87 band reductions are required in 2020 across the 14 planning objectives for the 12 wastewater systems.
• By 2050, this will increase to 105 band reductions due to the impact of climate change, growth and creep.
• The options identified to date would cost around £437 million for the 12 systems and is expected to provide 21 Band reductions by 2050 (the options do not result in a band 0 for all risks).
• The Test and Itchen has 30 systems which require 129 band reductions in 2020 and 158 band reductions by 2050 in order to achieve band 0 across 14 planning objectives.
• Extrapolating the investment needs for all the systems in the Test and Itchen will cost around £1.27 billion for a population of 563,000. This illustrates the scales of investment needed to get to Band 0 by 2050.

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