Guidance

Appendix C: Estimating benefits of preventing deterioration

Published 29 November 2022

Applies to England

Appendix C to Investment requirements for England’s river basin management plans.

This appendix provides more detail on how the benefits of preventing deterioration were calculated.

Estimating the benefits of taking action to prevent water bodies deteriorating from 1 status class to a lower status class, for example from good to moderate, moderate to poor and so forth, was done in 2 stages. First the water bodies at risk of deteriorating were identified. Then the monetary value of the benefits of preventing deterioration in those water bodies was estimated.

The number of water bodies at risk of deteriorating was estimated using 7 different risk assessments for different pressures on the water environment:

• abandoned mines
• changes in water flow and water level
• invasive non-native species
• physical modification
• agriculture and rural land management
• water industry waste water

The methods varied but used baseline national spatial data and applied future pressure risk assessments using geographical projections of climate impacts, population growth and land use changes.

Water bodies were assessed for the degree to which they are likely to be affected at 3 intervals – a 2021 baseline, 2030 and 2050. Where a water body was at high or very high risk from any pressure at a time interval, it was assumed that this will result in deterioration of a single status class, that is good to moderate, rather than good to poor or bad. It was also assumed that additional high or very high risk from pressures at a later time interval would not result in further deterioration of status class. For example, remaining at moderate rather than falling from good to moderate, then from moderate to poor as pressure continues. This is likely to underestimate the risk and therefore benefit of preventing deterioration as there are examples of water bodies deteriorating more than 1 status class over short time periods, like 2015 to 2019.

The monetary benefit of preventing deterioration was estimated using the National water environment benefits survey (NWEBS) data on people’s willingness to pay for improvements to the water environment, moving from 1 status class to the next higher status. Research has shown that people’s willingness to pay for environmental improvements is lower than their willingness to accept compensation for a loss of environmental quality. Generally, people need to be paid more to accept a loss than they would pay to receive an improvement of similar size. However, given a lack of more relevant information, the NWEBS values were used ‘in reverse’; assuming that the value of improving a water body from moderate to good status is the same as preventing the deterioration of that water body from good to moderate. This is likely to underestimate the benefits of preventing deterioration.

Annual values for benefits of preventing deterioration over each interval (2021 to 2030, 2031 to 2050, 2051 to 2058) were calculated using NWEBS values, then discounted to give present values. In practice, the number of water bodies in a deteriorated condition accumulated over time, as the assumption was made that once deteriorated, a water body was not going to improve or deteriorate further.

Average annual NWEBS values (updated to 2021 prices and population) were used for the change in the whole water body (that is, not the per kilometre values). This is considered appropriate for the scale of the assessment.